A method for improving and grouting slag in shield construction of sandy gravel strata tunnel

Abstract

The invention discloses a shield construction method for a sand-pebble stratum tunnel, comprising the following steps: reinforcing an end portal and installing a starting bracket; installing a reaction frame support system; installing the shield in slag, extending a portal steel ring and a seal, optimizing shield excavation parameters, measuring and adjusting the shield, etc., thereby ensuring that the shield construction is safe, smooth and fast, and achieving an ideal working condition when the shield is excavating in the sand-pebble stratum.

Description

Technical Field

[0001] The invention relates to the field of tunnel construction, and in particular to a shield construction method for a sand and gravel stratum tunnel. Background Art

[0002] During tunnel shield construction, since water-rich and sandy strata will affect the progress and safety of construction, improving excavation parameters and optimizing steps and structures are an indispensable and important technical means to ensure safe, smooth and rapid shield construction. The existing technology has poor construction effect in the sandy and gravel-rich strata of the present invention, which greatly affects the progress and safety of construction. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a shield construction method for a sand and gravel stratum tunnel, which overcomes the problems of construction progress, quality and safety of the above-mentioned prior art.

[0004] The technical problem to be solved by the present invention is achieved through the following technical solutions:

[0005] A shield construction method for a sand and gravel stratum tunnel comprises the following steps:

[0006] Step 1: During the initial construction phase of the shield tunnel, the end portal is reinforced at the beginning of the tunnel entrance and exit, and the end portal reinforcement includes grouting reinforcement in the pipe shed, grouting reinforcement of the sleeve valve pipe on the ground, and / or plain concrete pile reinforcement;

[0007] The reinforcement of the large pipe shed for the tunnel portal includes: the opening position of the upper pipe shed is arranged along the outside of the steel pipe ring of the tunnel portal, the steel pipe ring has an insertion angle of 1-2° to the outside of the center of the tunnel portal, and the working platform is arranged below the pipe shed; the steel ring pipe adopts a seamless grouting steel flower pipe, the two sections of the grouting steel flower pipe of the pipe shed are connected by a connecting sleeve steel pipe thread, and the joints of two adjacent steel flower pipes are staggered and sleeved; the grouting holes are arranged on the steel flower pipe, and the holes are arranged in a plum blossom shape;

[0008] The ground sleeve valve pipe reinforcement includes: reinforcing the ground sleeve valve pipe at the entrance and exit of the tunnel, the reinforcement range is outside the shield outline, above the arch and the bottom of the tunnel, and the sleeve valve pipe adopts a plum blossom arrangement;

[0009] The plain concrete piles are reinforced with double rows of plain concrete piles;

[0010] Step 2, installing the originating bracket on the originating base;

[0011] Step 3: Install the reaction frame support system, which includes a reaction frame, mutually welded bottom straight support beams, side wall straight support columns, and oblique supports. The oblique supports are at an angle of 45° to the ground. One end of the oblique support is welded to the reaction frame side wall straight support column, and the other end is welded and fixed to a steel plate pre-buried in the ground; the reaction frame is welded to the station middle plate through steel sections;

[0012] When the reaction frame is fixedly installed with the starting base, the included angle between the vertical direction of the horizontal axis of the starting base and the reaction frame is less than ±2‰, the vertical trend deviation of the shield attitude from the design axis is less than 2‰, and the horizontal trend deviation is less than ±3‰; and the elevation and center of the negative ring segment and the center deviation of the shield shell on the starting reaction frame are less than ±5mm;

[0013] Step four, installation of the portal extension steel ring: including fixed connection of a pre-buried steel ring plate to the inner lining wall of the tunnel retaining structure; the pre-buried steel ring plate is fixedly connected to the portal extension steel ring by bolts; the other end of the portal extension steel ring is fixedly connected to the folding pressure plate by bolts; an annular sealing rubber plate and a clamping ring plate are provided in sequence between the portal extension steel ring and the folding pressure plate. The inner lining wall is a reinforced wall within the tunnel ring above the tunnel; the tunnel ring is located above the pipe segments installed during the construction of the tunnel shield machine. The clamping ring plate is an arc-shaped clamping ring plate; the folding pressure plate is a fan-shaped folding pressure plate composed of parts 1 and 2, and parts 1 and 2 are hinged or axially connected; the retaining piles within the shield tunnel range around the portal extension steel ring are made of glass fiber reinforcement;

[0014] Step five, assembling the negative ring segment: the negative ring segment is connected with the reaction frame reference ring by bolts. After the segment is assembled using the entire ring of the segment, the negative ring segment is pushed out of the shield tail by a thrust jack and fastened to the reaction frame reference ring. A triangular support frame, I-beam and wooden wedge are used to stabilize the negative ring segment and tighten the segment ring on the starting bracket.

[0015] Preferably, the method further comprises the following steps:

[0016] Step 6, shield tunneling construction: The geology of the starting section of the shield tunneling interval is mainly medium-dense pebble strata, and the starting parameters of shield tunneling are: 10-meter section of the starting section: soil pressure 0.3-0.4 bar, tunneling speed 30-50 mm / min, torque 1500-2100 KN·m, thrust <800t, cutter head speed 0.9 r / min or more, improvement method and injection amount foam 110L / ring, slag discharge 58-63 cubic meters / ring, synchronous grouting amount 5-6 cubic meters / ring, synchronous grouting pressure 0.2-0.4 bar;

[0017] Trial excavation of 90 meters section: soil pressure above 0.6 bar, excavation speed 40-60 mm / min, torque 1800-2300 KN·m, thrust 1000-1500 t, cutter head speed above 1.5 r / min, improved method and injection amount of foam 110L / ring, slag discharge 58-63 cubic meters / ring, synchronous grouting amount 5-6 cubic meters / ring, synchronous grouting pressure 0.2-0.4 bar.

[0018] Preferably, the method further comprises the following steps:

[0019] Step seven, slag improvement: add a mixed mud of a foaming agent and sodium bentonite, and mix it with the soil slag, the mixed mud comprises foam, bentonite and water, the weight parts of the components are 8-12 water, 0.5-1.5 bentonite, 0.1-0.3 foam, the slump of the prepared mud is within 20cm, such as 5-20cm; the viscosity of the foaming agent is 0.003-0.2Pa·s, and the pH value is 7.3-8.

[0020] The foaming agent used in the present invention is a shield machine foaming agent on the market, which utilizes the lubricating effect of fine foam to make the excavated soil flow plastically and reduce permeability, and is particularly suitable for sandy gravel soil layers, fully weathered soil layers, and mixed soil layers.

[0021] Preferably, the method further comprises the following steps:

[0022] Step 8: When the shield tail passes through the tunnel seal, synchronous grouting or secondary supplementary grouting is performed. The actual grouting volume is 5-7m 3 / ring;

[0023] The synchronous grouting includes: grouting cement mortar synchronously through the grouting holes on the pipe segment, grouting gel time: 6-8h; consolidation body strength: not less than 0.5Mpa in one day, not less than 2MPa in 3 days, and compressive strength not less than 5MPa in 28 days; slurry shrinkage value: consolidation shrinkage rate is less than 5%; slurry consistency: 8-12cm; slurry specific gravity: 1.7-2.0g / cm3; slurry stability: decantation rate is less than 5%; the synchronous grouting slurry is cement mortar, which is made of the following weight parts: cement 200-240, fly ash 360-400, bentonite 80-120, sand 700-860, water 400-500; the synchronous grouting pressure value is: 0.25-0.4MPa;

[0024] The secondary supplementary grouting uses cement slurry, including a two-liquid slurry mixture of cement and water glass, or a single-liquid slurry mixed with water and cement; the weight ratio of the cement slurry is 1:1, the slurry density is 1.44 (g / cm3), the setting time is 20 to 48 seconds, and the secondary grouting pressure is 0.3 to 0.5 MPa.

[0025] The grouting completion standard is controlled by grouting pressure and grouting volume. The grouting volume per ring shall not be less than 6m 3 The slump of the mixed mud configured as described above is less than 20 cm, such as 5-20 cm.

[0026] Preferably, the method further comprises the following steps:

[0027] Step 9: Segment assembly:

[0028] Prefabricated segments are used for lining, segments are assembled with staggered joints, and segment joints are waterproofed with rubber waterstop strips; three sealing brushes are installed at the tail of the shield machine, and sealing grease is added to the sealing brushes at the same time;

[0029] First assemble the bottom segment, then install it crosswise from bottom to top, and finally assemble the locking block. During the assembly, each ring of segments should be evenly distributed and the height difference of the ring surface should be strictly controlled. After the jack is tightened, the segment connection bolts can be installed.

[0030] Preferably, the method further comprises the following steps:

[0031] Step 10: Initial measurement of shield machine posture;

[0032] Step 11: Shield machine excavation measurement, segment position measurement, shield attitude measurement, lining ring segment measurement, ground near-well wire measurement, ground near-well elevation measurement, directional measurement, shield machine guide rail positioning measurement, receiving frame positioning measurement, and embedded steel ring portal center measurement;

[0033] Step 12: Shield machine attitude arrival measurement: including measurement of horizontal yaw, pitch, and torsion.

[0034] Preferably, the method further comprises the following steps:

[0035] Step 13: Shield machine arrives at receiving construction: positioning of shield machine and verification and measurement of receiving tunnel door position, stratum reinforcement, tunnel door treatment, installation of tunnel door ring sealing equipment, and installation of receiving base;

[0036] The positioning of the shield machine and the re-measurement of the receiving portal position before the arrival of the shield machine: one is the deviation between the central axis of the shield machine when it penetrates and the design axis of the tunnel, and the other is the deviation adjustment of the receiving portal position.

[0037] 8. The sand-pebble stratum tunnel shield construction method according to claim 1 or 2, further comprising the following steps:

[0038] Step 14: When the shield machine reaches the last 10m section of excavation, determine the reasonable excavation parameters. When receiving, follow the low speed, small thrust, reasonable soil bin pressure and timely and full synchronous grouting volume to ensure reasonable construction parameters such as soil bin pressure, timely synchronous grouting, and uniform and continuous operation mode to receive the shield machine. The construction parameters of the receiving section are as follows: (1) soil bin pressure: 0.3-0.4Mpa; (2) excavation speed is not more than 10mm / min; (3) shield machine thrust is controlled between 600 and 1000t; (4) cutter head torque: not more than 2000KN*M; (5) synchronous grouting volume: 5-7 cubic meters;

[0039] Preferably, the method further comprises the following steps:

[0040] Step 15, assembly of the last few rings of segments:

[0041] 1. Install the tensioning device and connect the last 20 rings of segments one by one; first assemble the special steel plate at the longitudinal hand hole and tighten it with the segment bolts, then weld the angle steel to the steel plate after assembling each ring of segments;

[0042] 2. Reasonable segment assembly points to avoid rigid dragging of segments by the shield tail. The segment assembly points should comprehensively consider the linear requirements and the shield tail clearance. When the two cannot be met at the same time, the shield tail clearance should be given priority to ensure the quality of the tunnel lining;

[0043] 3. When the tail machine enters the soil reinforcement area at the end, the slurry is changed to quick-hardening slurry. When the tail machine pushes out the sealing ring at the opening, the position of the fan-shaped pressure plate at the opening is quickly adjusted to ensure the temporary plugging effect of the opening.

[0044] 4. When the shield shell of the front body of the shield machine is pushed out of the tunnel gate, the folding plate is adjusted by the wire rope on the clamp ring of the plate to press the rubber sheet as tightly as possible to prevent the leakage of mud and slurry from the tunnel gate; when the segment is dragged out of the shield tail, the wire rope is tightened again so that the plate can press the rubber sheet tightly, so that the sheet can play a sealing role all the time, so that the segment is tightened and the tunnel gate seal is tightened;

[0045] 5. Complete the bolt tightening and re-tightening steps of the last 20 rings of segments, and use channel steel to tighten the last 20 rings of segments along the longitudinal direction of the tunnel to connect the last 20 rings of segments into a whole to prevent the segments from loosening and affecting the sealing and waterproofing effect;

[0046] 6. Shield machine arrives at the construction site: When the cutter head of the shield machine is 0.5m away from the tunnel face, the debris in the soil bin is emptied, and the segments installed after the shield machine is through are ensured to be grouting full and dense, and are tightened in time to prevent the segments from sinking, shifting and leaking.

[0047] Preferably, the method further comprises the following steps:

[0048] Step 16, abnormal situation treatment steps for delayed settlement:

[0049] (1) Calculate the theoretical excavation volume of each ring in advance. During excavation, count the actual excavation volume by ring and compare it with the theoretical value;

[0050] (2) When the ground excavation volume exceeds the theoretical value by 5%, analyze the monitoring data inside and outside the tunnel, and judge the changes in the surrounding rock and invert the characteristics of the formation by analyzing the soil samples. If it is inferred that it is indeed over-excavation, adjust the excavation speed of the screw conveyor and increase the content of the soil in the soil bin. In order to protect the upper buildings or pipelines, full-bin excavation or air-pressured non-full-bin excavation is required when necessary.

[0051] (3) Based on the statistical over-excavation position and over-excavation amount, the over-excavation amount shall be replenished in time through shield tail grouting. If necessary, secondary grouting or double liquid grouting shall be carried out at the over-excavation location. The grouting pressure at the shield tail grouting hole shall be greater than the water and soil pressure at the tunnel burial depth;

[0052] (4) Two grouting systems are used: synchronous grouting and secondary grouting system to ensure that the grouting volume meets the requirements;

[0053] (5) According to theoretical calculation, the construction gap volume between the segment and the surrounding rock is 4.05m 3 The grouting volume in the pebble soil layer is controlled at more than 150-200%, that is, the grouting volume per ring is 6-8m 3 The synchronous grouting volume of mudstone formation shall not be less than 5m 3 ;

[0054] (6) The grouting volume should also be controlled in combination with the grouting pressure. The grouting pressure should be controlled between 2.5 and 4 bar. If the pressure increases significantly, the grouting should be temporarily stopped to prevent the grouting pressure from penetrating the formation or damaging the pipe segment.

[0055] (7) Information-based construction should be adopted, on-site monitoring should be strengthened to understand the deformation laws of the surrounding rock and soil, and corresponding engineering measures should be taken in a timely manner.

[0056] The mechanism of action of the slurry and foam mixture of the present invention is mainly manifested in the following aspects:

[0057] ① By injecting mud and foam, a mud film is formed in front of the cutterhead, which builds up soil pressure and provides horizontal thrust for the soil structure, which is conducive to the formation of an arch structure.

[0058] ② Mud and foam enhance the strength and rigidity of the excavation surface soil, improve the vertical resistance of the excavation surface soil, support the excavation surface soil, and reduce the possibility of instability of the excavation surface soil.

[0059] The particles in the sand and gravel formation are loose and have no cohesion. The force transmission between the particles is point-to-point. After adding mud to the excavation surface soil, the mud surrounds the particles and forms a mud film, which increases the cohesion between the particles, diffuses the force transmission between the particles, and improves the stress condition of the soil. In addition, the volume of the foam is very small, and the diffusion of the mud of the foam is enhanced after mixing. It can quickly penetrate into the soil layer under the stirring of the cutter head, wrap the sand and gravel particles, reduce the density of the soil, and improve the plastic flow of the soil.

[0060] ③Use the excellent lubrication performance of foam to improve the granular structure of soil. At the same time, the bubbles adsorbed between the particles can reduce the direct friction between the soil particles and the cutter system. Reduce the permeability of the soil. Because of its small specific gravity and light mixing load, it is easy to mix the soil evenly, so as to balance the soil pressure on the excavation surface and discharge the soil continuously and smoothly. At the same time, the foam is compressible, which also has a positive effect on the stability of soil pressure.

[0061] The technical solution of the present invention has the following technical effects compared with the prior art:

[0062] The invention discloses a shield construction method for a tunnel in a sandy and gravel stratum, which ensures safe, smooth and rapid shield construction and achieves an ideal working condition when the shield is excavated in a sandy and gravel stratum through the steps of reinforcing an end portal and installing a starting bracket; installing a reaction frame support system; installing the shield in slag, installing a portal extension steel ring and a seal, optimizing shield excavation parameters, and measuring and adjusting the same. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Figure 1-1 Schematic diagram of the grouting structure of the large pipe shed of the present invention

[0064] Figure 1-2 This is a schematic diagram of the expanded structure of the steel ring pipe of the large pipe shed of the present invention.

[0065] Figure 1-3 This is a schematic diagram of the steel ring pipe socket structure of the large pipe rack of the present invention.

[0066] Figure 2 This is the plane layout diagram of the ground sleeve valve pipe of the present invention

[0067] Figure 3-1 Schematic diagram of the starting bracket of the present invention

[0068] Figure 3-2 Schematic diagram of the mounting structure of the starting bracket of the present invention

[0069] Figure 4-1 Schematic diagram of the reaction frame structure of the present invention

[0070] Figure 4-2 Schematic diagram of the longitudinal structure of the reaction frame of the present invention

[0071] Figure 5-1 This is the installation structure diagram of the folding sealing pressure plate of the present invention

[0072] Figure 5-2 This is the principle diagram of the sealing of the initial opening of the present invention

[0073] Figure 6 This is the reinforcement diagram of the negative ring segment of the present invention

[0074] Figure 7-1 This is a schematic diagram of the 10-6 shield machine posture measurement of the present invention

[0075] Figure 7-2 For the present invention Figure 7-1 Schematic diagram of 3D coordinate enlargement

[0076] Figure 8 This is the thrust calculation diagram of the shield machine of the present invention.

[0077] In the figure: 1-pipe shed, 2-orifice, 3-steel pipe ring, 4-working platform, 5-tunnel, 6-connecting sleeve steel pipe, 7-sleeve valve pipe, 8-starting bracket, 9-reaction frame, 10-crossbeam, 11-column, 12-inclined support, 13-starting base, 14-negative ring segment, 15-portal extension steel ring sealing structure, 1510-enclosing structure, 151-lining wall, 152-steel ring plate, 153-bolt, 154-annular sealing rubber plate, 155-pressing ring plate, 156-folding pressure plate, 1561-item 1, 1562-item 2, 157-portal extension steel ring, 14-segment, 16-triangular support frame, 17-I-beam, 18-wooden wedge, 19-shield machine. DETAILED DESCRIPTION

[0078] As shown in the figure, a shield construction method for a tunnel in a gravel stratum is provided according to the present invention. The numbers and structure names involved in the embodiment diagram are respectively as follows: 1-pipe shed, 2-orifice, 3-steel pipe ring, 4-working platform, 5-tunnel, 6-connecting sleeve steel pipe, 7-sleeve valve pipe, 8-starting bracket, 9-reaction frame, 10-crossbeam, 11-column, 12-inclined support, 13-starting base, 14-negative ring segment, 15-portal extension steel ring sealing structure, 1510-enclosing structure, 151-lining wall, 152-steel ring plate, 153-bolt, 154-annular sealing rubber plate, 155-pressing ring plate, 156-folding pressure plate, 1561-piece 1, 1562-piece 2, 157-portal extension steel ring, 14-segment, 16-triangular support frame, 17-I-beam, 18-wooden wedge, 19-shield machine.

[0079] The construction sections of this embodiment are respectively Sase Road, Zhonghe Station, the shield section between Jinshi Road Station and Sase Road Station, the shield section between Sase Road Station and Zhonghe Station, and the shield section of Longdengshan entry and exit line. The large and small mileage ends of Sase Road Station are both shield starting shafts, and the Longdengshan Depot is the small mileage shield starting shaft. Shield section between Jinshi Road Station and Sase Road Station: The strata traversed by the shield are mainly moderately weathered mudstone, and some sections are sandy and gravel strata. Shield section between Sase Road Station and Zhonghe Station: The strata traversed by the shield are basically mudstone strata, and some sections are sandy and gravel strata. Shield section of Longdengshan entry and exit line: The strata traversed by the shield are basically mudstone strata, and some sections are sandy and gravel strata.

[0080] 1. Project Overview

[0081] The shield tunnel section consists of two stations and three sections, namely Sanse Road, Zhonghe Station, Jinshi Road Station-Sanse Road Station Shield Tunnel Section, Sanse Road Station-Zhonghe Station Shield Tunnel Section, and Longdengshan Entrance and Exit Section Shield Tunnel Section. The total length of the left-line shield tunnel section is 6128m, and the total length of the right-line shield tunnel section is 6057m. It is planned to use 6 Tiejian Heavy Industry shield machines. The large and small mileage ends of Sanse Road Station are both shield starting shafts, and the Longdengshan Depot is the small mileage shield starting shaft.

[0082] In the shield tunnel section between Jinshi Road Station and Sase Road Station, the strata traversed by TBM 19 are mainly moderately weathered mudstone, and some sections are sandy and gravel strata.

[0083] The shield tunnel section between Sanse Road Station and Zhonghe Station is basically a mudstone formation, and some sections are gravel formations. The shield tunnel section of the Longdengshan entry and exit line is basically a mudstone formation, and some sections are gravel formations. The current site status is a municipal road with heavy traffic.

[0084] The groundwater is mainly pore water in the Quaternary sand and pebble soil layers. The pebble soil layer on the site is thick and distributed in layers, with thin layers of sand in some places. There is a large amount of pore water in between, with a large amount of water and a high water level. Atmospheric precipitation and regional surface water are its main sources of replenishment. The pore water in the pebble soil layer forms a continuous free water surface.

[0085] The strata that the shield machine of this section passes through are mainly mudstone, among which the shield section of Longdengshan entrance and exit section, Zhonghe Station ~ Sanse Road Station section are mainly mudstone, Sanse Road Station ~ Jinshi Road Station section is mainly pebbles in the upper part and mudstone in the lower part, and some sections are full-section mudstone. The geological conditions of the site where the shield machine is hoisted out at the right end of the Jinshi Road Station are as follows from top to bottom: miscellaneous fill, loose pebbles, slightly dense pebbles, medium dense pebbles, dense pebbles, strongly weathered mudstone, and medium weathered mudstone.

[0086] 2. Summary of risk sources: negative ring removal, gantry crane installation and removal, shield hoisting, shield start, excavation, opening and cutting tool change, interval precipitation

[0087] 3. Parameters and performance of the shield machine used in this section

[0088] A total of 6 shield machines were used for construction in this section, which were ZTE6250 earth pressure balance shield machines produced by China Railway Construction Heavy Industry, suitable for pebble, pebble soil, mudstone and sandstone geological layers.

[0089] 4. Shield construction starts

[0090] The overall process of shield construction

[0091] First, before the shield arrives at the site, the end soil is reinforced and the starting base is in place; secondly, the shield trailer is assembled and hoisted into the station; the shield main machine is assembled and connected to the main machine and the rear trailer, and then the reaction frame is installed to complete the debugging of the shield machine, and the vertical transportation system, horizontal transportation system, and slurry system are installed and debugged. During the above work, cross-operation can be carried out to complete the extension steel ring and sealing of the tunnel door, and finally the reaction support is completed and the negative ring segment is assembled to form the starting state of the shield, and the shield excavation begins.

[0092] 4.1 End reinforcement

[0093] The shield machine in this section needs to enter and exit the tunnel 12 times in total. When the shield machine enters and exits the tunnel 5, the working face will be in an open state, and this open state will last for a long time. If not handled properly, groundwater, quicksand, mud, etc. will enter the working well, and in severe cases, it will cause the tunnel gate to collapse. Therefore, the end reinforcement work is extremely important in shield construction. For specific end reinforcement measures, please see Table 1 End Reinforcement Measures Table below.

[0094] Table 1 End reinforcement measures

[0095]

[0096] Note: In the table, (a) indicates the use of “large pipe shed + inside the pipe shed” grouting reinforcement, (b) indicates the use of “sleeve valve pipe” grouting reinforcement, and (c) indicates the use of “plain concrete piles” reinforcement.

[0097] 1. Reinforcement of the large pipe shed at the tunnel entrance Figure 1-1 , Figure 1-2 , Figure 1-3 shown.

[0098] 1. The layout of the large pipe shed is as shown in the figure. The position of the opening 2 of the pipe shed 1 is arranged 250mm outside the steel ring 3 of the tunnel, the center spacing of the steel pipe ring is 335mm, and the external insertion angle is about 1-2°. Drilling and grouting construction of 23 large pipe sheds are carried out.

[0099] 2. The steel pipe is seamless steel pipe. A single pipe shed is installed in sections. The two sections are connected by threads. The length of the threaded section is greater than 150mm. The joints of two adjacent steel pipes 6 should be staggered by a distance of not less than 1.0m. Grouting holes are drilled on the grouting steel pipe in a plum blossom shape. The orifice section at the tail of the steel pipe is not drilled and serves as a grouting stop section.

[0100] 2. Ground sleeve valve pipe reinforcement, such as Figure 2 shown.

[0101] According to the design requirements, the ground is reinforced at the entrance and exit of the tunnel. The reinforcement method is 7 ground sleeve valve pipes. The reinforcement range is 3m outside the shield outline, 3m above the arch, and 1.5m from the tunnel bottom. The sleeve valve pipes are arranged in a plum blossom shape.

[0102] 3. Double-row plain concrete pile reinforcement construction

[0103] The shield tunnel end reinforcement method uses double-row plain concrete piles. The pile position deviation should not be greater than 50mm, the verticality deviation of the pile body should not be greater than 0.5%, and the pile diameter deviation should not be greater than 50mm. Before concrete pouring, remove the sediment at the bottom of the hole, and the sediment at the bottom of the pile should not be greater than 100mm.

[0104] 4.2 The originating base 13, such as Figure 3-1 , Figure 3-2 shown.

[0105] The starting bracket 8 is a steel structure, which mainly bears the gravity of the shield machine and the friction and torsion force generated by the shield machine during advancement. The structural design takes into account the convenience of shield forward construction and structural stress to meet the need for the shield to move the main machine forward during assembly.

[0106] The total weight of the shield machine mainframe is nearly 317.5 tons, and the starting bracket must have sufficient strength, rigidity and stability. The starting bracket is the support and positioning bracket of the shield machine in the starting shaft. First, the center line of the starting bracket is determined according to the design axis line of the tunnel here, and the installation position of the bracket is indicated by measuring and laying out. In order to prevent the shield from bowing when starting, the starting bracket is raised 20mm for installation, and the bracket is installed with steel and steel plates for padding and leveling; after the bracket is installed in place, the bracket is supported by steel at the bottom of the well and the surrounding well walls. After welding and positioning, the shield body is assembled on the bracket.

[0107] 4.3 Reaction frame and support system, such as Figure 4-1 , Figure 4-2 shown.

[0108] 1. Determination of the position of the reaction frame

[0109] After the shield mainframe is assembled, the reaction frame 9 is installed. The reaction frame is a steel structure used to provide reverse thrust when the shield starts. The thickness of the station main structure is 800mm, the number of negative ring segments is 7, and the distance between the bracket and the tunnel door is 1m, so the front center mileage of the reaction frame is determined as:

[0110] D = D tunnel gate - L tunnel gate steel ring length - 1m - L pipe × NL (shield tunneling direction is from large mileage to small mileage)

[0111] Among them: D tunnel gate --- tunnel gate mileage

[0112] L hole - length of the steel ring of the hole

[0113] L tube---segment length

[0114] N ---Number of negative ring segments

[0115] L steel ---------------- ...

[0116] 2. Types and installation of reaction frames in this section

[0117] When installing the reaction frame, first measure the center line of the starting mileage section at the reaction frame position and mark it on the side wall of the starting shaft to locate the center of the reaction frame. The center of the reaction frame rises simultaneously with the rise of the starting bracket. The key to positioning is that the positioning plane of the reaction frame close to the negative ring segment is perpendicular to the tunnel axis at this point. The gap between the reaction frame and the station structure connection should be padded to ensure that the reaction frame foot plate has sufficient compressive strength.

[0118] The crossbeam 10 and column 11 at the bottom of the reaction frame are supported at the rear with straight supports. After the position is determined, they are welded to the steel plates pre-buried during the construction of the station. The reaction frame diagonal support 12 is at a 45-degree angle to the ground, one end is welded to the reaction frame, and the other end is welded and fixed to the steel plate pre-buried in the ground. The diagonal support is supported by 900*600mm steel. The reaction frame is connected to the center plate of the station with 4 steel sections to ensure that the overall force of the reaction frame meets the departure requirements.

[0119] Since the reaction frame and the starting base provide the initial thrust and initial spatial posture when the shield starts, when installing the reaction frame and the starting base, the left and right deviation of the reaction frame is controlled within ±10mm, the elevation deviation is controlled within ±5mm, and the up and down deviation is controlled within ±10mm. The angle between the vertical direction of the horizontal axis of the starting base and the reaction frame is <±2‰, the vertical trend deviation of the shield posture and the design axis is <2‰, and the horizontal trend deviation is <±3‰. When installing the reaction frame and the starting frame, it is necessary to ensure that the elevation and center of the negative ring segment and the center deviation of the shield machine shell on the starting frame are less than ±5mm. This ensures the smooth installation of the negative ring segment.

[0120] When positioning the starting bracket and reaction frame, the surveying team will conduct centerline and elevation positioning of the starting bracket and reaction frame on site.

[0121] 3. Force analysis of reaction frame

[0122] The reaction frame 9 is a portal frame. It includes columns, two crossbeams at the top and bottom, and is designed according to the connection form and load transfer path. L1 and L2 are horizontal crossbeams that are in direct contact with part of the steel negative ring. H1 and H2 are columns, the bottom is fixedly connected to the embedded steel plate of the well bottom plate, and the middle is fixedly connected to the crossbeam, diagonal beam, and horizontal support. Z1~Z8 are horizontal supports, one end of which is fixedly connected to the reaction frame and the other end is fixedly connected to the embedded steel plate of the well wall.

[0123] Analysis of load transfer path: horizontal thrust F of shield machine -> negative ring segment -> steel negative ring -> reaction frame -> horizontal support and supports of shaft bottom and shaft wall.

[0124] The reaction frame is connected to the side wall with 900*600 steel. The reaction frame support is designed according to the load of 2000t. The load calculation is as follows:

[0125] The reaction frame support uses 6 900×600×20×20 steel supports and 5 600×600×20×20 steel straight supports. 3 400×250×20×20 steel supports are supported on the middle plate structure of the starting shaft to reinforce the reaction frame. On the left side facing the tunnel direction, there are 2 900×600×20×20 steel inclined supports at a 45° angle to the ground. One end is welded to the embedded steel plate of the bottom plate, and the other end is connected to the reaction frame with bolts. The remaining 5 600×600×20×20 steel supports are directly welded to the embedded steel plate of the starting shaft station.

[0126] The actual normal thrust of initial excavation generally does not exceed 1000T, and the additional steel ring plays a role in balancing stress. Considering the uneven force and safety factor, the total thrust is calculated as 2000T, and the four concentrated forces P are evenly distributed and calculated as 2000T, and the concentrated force points are evenly distributed to get 500T. Considering the support form and number of the reaction frame, the three supports on both sides of the reaction frame each bear a thrust of 700T, the three supports on the top bear a thrust of 300T, and the three supports in the middle below bear a thrust of 300T.

[0127] 1) Calculation of left side oblique support: There are 2 900×600×20×20 steel supports on the left side. The average force on each steel is 700 / 2=350T. The cross-sectional area of ​​900×600×20×20 H-shaped steel is 23200mm2. The oblique support and the reaction frame form a 45° angle for support. Therefore, the stress of the H-shaped steel is (350T / 23200mm2) / cos45°=215.5N / mm2. The design strength of the steel is 235N / mm2. Therefore, the oblique support can meet the starting requirements of the shield, that is, the reaction frame is stable.

[0128] 2) Calculation of right side support: There are 3 600×600×20×20 steel supports on the right side, and the average force on each steel is 700 / 3=233.3T. The cross-sectional area of ​​600×600×20×20 steel is 23200mm2. The support and the reaction frame are directly supported on the concrete structure of the middle wind shaft at right angles, and a 20mm thick steel plate is placed at the connection between the structure and the support. Therefore, the stress of the steel is 233.3T / 23200mm2=100.6N / mm2, and the design strength of the steel is 235N / mm2. Therefore, the support can meet the requirements for the start of the shield, that is, the reaction frame is stable.

[0129] 3) Calculation of the three supports in the middle of the upper side: There are three 400×250×20×20 steel supports on the upper side. The average force of each H-shaped steel is 300 / 3=100T. The cross-sectional area of ​​the 400×250×20×120 steel is 13050mm2. The support and the reaction frame are directly supported on the middle plate concrete structure at right angles. The connection between the structure and the support is padded with a 20mm thick steel plate. Therefore, the stress of the steel is 100T / 13050mm2=76.6N / mm2, and the design strength of the steel is 235N / mm2. Therefore, the oblique support can meet the requirements for the start of the shield, that is, the reaction frame is stable.

[0130] 4) Calculation of the three supports on the lower side: There are two 600×600×20×20 steel supports in the middle of the lower side. The average force on each steel is 300 / 2=150T. The cross-sectional area of ​​the 600×600×20×20 steel is 23200mm2. The support and the reaction frame are directly supported on the concrete structure of the middle wind shaft at right angles. A 20mm thick steel plate is placed at the connection between the structure and the support. Therefore, the stress of the steel is 150T / 23200mm2=64.7N / mm2, and the design strength of the steel is 235N / mm2. Therefore, the support can meet the requirements for the start of the shield, that is, the reaction frame is stable.

[0131] 4.4 Track laying

[0132] 1. Track laying for the supporting trolley after the starting wellhead

[0133] After the shield machine's rear supporting trolley is hoisted down the well, it is towed to the designated location in sequence by an electric locomotive for connection and assembly. Before the shield is lowered into the well and after the negative ring is removed, track laying is required at the starting wellhead.

[0134] 2. Track layout in stations and tunnels

[0135] Channel steel is used as sleeper, and the axial spacing is arranged

[0136] 4.5 Installation of the extended steel ring of the tunnel gate, such as Figure 5-1 , Figure 5-2 shown.

[0137] The retaining piles within the shield tunnel of this section are all made of glass fiber reinforcement. In order to reduce the risk of entering the tunnel and avoid the adverse effects of face collapse during construction, our department adopts the tunnel gate extension steel ring construction technology, which can reduce the risk of face exposure and avoid the face being exposed for too long and causing instability and collapse. By using the extension steel ring technology, the shield start progress can be effectively improved. Compared with the shield start pile drilling, the efficiency can be advanced by 3 days.

[0138] 4.6 Installation of the hole sealing structure 15

[0139] 1. Installation of the tunnel door extension steel ring sealing structure (15): Figure 5-1 , Figure 5-2 shown.

[0140] When the shield machine starts, in order to prevent the water in the tunnel and the backfill grouting from flowing out along the shield machine shell toward the tunnel entrance, an annular sealing rubber plate water-stopping device is installed around the shield machine entrance tunnel ring on the inner lining wall. It includes a pre-buried steel ring plate (152) fixedly connected to the inner lining wall (151) of the tunnel enclosure structure (1510); the pre-buried steel ring plate is fixedly connected to the tunnel door extension steel ring (157) through bolts (153); the other end of the tunnel door extension steel ring is fixedly connected to the folding plate (156) through bolts (153); an annular sealing rubber plate (154) and a clamping ring plate (155) are arranged in sequence between the tunnel door extension steel ring and the folding plate (156). The inner lining wall is a reinforced wall in the tunnel ring above the tunnel; the tunnel ring is located above the pipe segment (14) installed before the construction of the tunnel shield machine. The clamping ring plate (155) is an arc-shaped clamping ring plate; the folding plate is a fan-shaped folding plate composed of a piece 1 (1561) and a piece 2 (1562), and the pieces 1 and 2 are hinged or axially connected; the retaining piles within the shield tunnel range around the portal extension steel ring are made of glass fiber reinforcement.

[0141] 2. When the shield machine excavates in the thrust direction, the hinged fan-shaped pressure plate is driven by the shield machine to rotate clockwise and support the sealing rubber plate, which is sealed at the outer diameter of the shield body to stop water from flowing into the starting well. When the shield body passes through the tunnel door sealing device, the rubber curtain shrinks and presses the fan-shaped pressure plate to prevent water from flowing into the starting well along the outer diameter of the segment, and also prevents the synchronous grouting slurry from overflowing. After removing the negative ring segment and cleaning the tunnel opening sealing structure, install the sealing device to the tunnel door in the same way to seal and stop the water when the shield machine arrives at the station.

[0142] 4.7 Grease the shield tail

[0143] Before the shield starts, fill the brush chamber at the tail of the shield with grease.

[0144] 4.8 Negative ring segment assembly, such as Figure 6 shown.

[0145] 1. Negative ring segment installation

[0146] 1) After the shield machine is debugged, the negative 7 ring segments 14 are assembled and the shield machine is put into trial operation. The negative ring segments are all standard rings and are assembled with through seams.

[0147] 2) Since the outer diameter of the negative ring segment is in an unconstrained state, there are relatively few connecting bolts between the ring and the segment. In order to ensure the stability of each ring segment, the shield machine is moved backward after the shield assembly is completed so that the shield tail is close to the reaction frame reference ring.

[0148] 3) The key point of the assembly of the negative ring segments is that the negative 6 ring segments are connected to the reaction frame reference ring with special bolts. After the segments are assembled in the shield tail by the segment assembly machine, the negative 7 ring segments are pushed out of the shield tail by the thrust jack and are tightly connected to the reaction frame reference ring. The installation of other negative ring segments is the same as the normal tunneling segment assembly.

[0149] 4) In order to ensure the stability of the negative ring segment installation and bear the thrust during excavation, in addition to using triangular support frames and wooden wedges to stabilize the negative ring segment, each ring segment also uses wire ropes, wire rope clips and power engineering tightening tools to assemble them into tight negative ring segment ropes along the ring direction. The two ends of the ropes are hooked on the starting bracket to tighten the segment ring. While installing the negative ring segment, the shield machine is tested and prepared for excavation.

[0150] 5) The negative 7 ring segments are connected to the reaction frame reference ring by special bolts. After the negative 7 ring segments are assembled in the shield tail by the shield machine's segment assembly machine, the negative 7 ring segments are pushed out of the shield tail by the shield machine jack and firmly connected to the reference ring. The installation of other negative ring segments is the same as the assembly of the whole tunnel excavation segments.

[0151] 6) When the negative ring segments continue to be assembled, the negative ring segments in the shield tail will be gradually moved out. In addition to using wooden wedges to support the segments on the starting bracket, after each ring of segments is pushed out of the shield tail, wooden wedges 18 are used to support the longitudinal I-beams 17 of the supporting tripod 16 outside the segments and the starting platform track in time to evenly transfer the segment pressure to the tripod and bracket. Two wooden wedges are added to each ring of segments. In order to ensure the stability of the installation of the negative ring segments and bear the thrust during excavation, in addition to using a triangular support frame to stabilize the negative ring segments, each ring of segments also uses a wire rope and a wire rope clip tightening tool to assemble a tight negative ring segment rope. The two ends of the rope are hooked on the starting bracket to tighten the segment ring. As shown in the figure below.

[0152] 2. Dismantling of negative ring segments

[0153] 1. Negative ring removal conditions

[0154] The stress condition for negative ring removal is that the friction resistance of the assembled tunnel segments is greater than the actual thrust of the shield.

[0155] F=μ×π×L×D×P

[0156] Where μ is the friction coefficient between soil and segment, which is taken as 0.3

[0157] D——segment diameter (m), 6m

[0158] L——Assembled tunnel length (m)

[0159] P——Average soil pressure acting on the back of the segment (Kpa), take 100Kpa

[0160] The maximum thrust of the shield is calculated as the rated thrust of 42575KN. The negative ring can be removed at 75m. However, considering the relevant factors such as the strength of the synchronous grouting slurry reaching 2.0Mpa, the reaction frame and negative ring segments are removed when the shield excavation advances about 100 meters.

[0161] 2. Removal steps

[0162] A. Removal of the pressure relief ring

[0163] B. Negative ring segment removal

[0164] C. Removal of reaction frame

[0165] D. Then remove the starting base.

[0166] 5. Shield tunneling construction

[0167] 5.1 Shield machine excavation process and parameter setting

[0168] According to the geological conditions in the bidding section, the shield tunneling adopts the earth pressure balance mode, which can effectively ensure the stability of the soil, surface buildings and construction safety. The shield construction parameters are selected within the range in the table and are continuously optimized and adjusted during construction.

[0169] The best parameters obtained from the 100m trial excavation were used in the normal advancement stage. By strengthening construction monitoring, the construction process was continuously improved to control ground settlement. The shield excavation parameters in composite strata are shown in Table 2 below.

[0170] Table 2 Parameters of shield tunneling in composite strata

[0171]

[0172] Part of the Jin~San section of this bidding section is in composite strata, and there is pebble intrusion in the upper part. In the actual construction process, synchronous grouting and secondary grouting are strengthened. If there is over-squareness, ground drilling and grouting are carried out as soon as possible. At the same time, the excavation parameters are adjusted in time according to the actual parameters of the shield excavation in the composite stratum.

[0173] 1) Preparation for the knife tip hitting the wall

[0174] ①Adjust the pressure plate and slowly pressurize the soil bin.

[0175] ②The cutter disc starts to rotate and advance at 0.9-1r / min. The advancement speed is controlled below the specified range and the total thrust is controlled below 800T. It is gradually adjusted according to the on-site conditions.

[0176] 2) Start of formal excavation mode

[0177] ① Strictly calculate the soil bin pressure according to the water and soil calculation. For specific calculations, please refer to the above calculation process.

[0178] ② Strictly control the occurrence of over-excavation and under-excavation of the shield machine.

[0179] The excavation volume must be strictly controlled during the excavation process, and timely adjustments must be made if over-excavation or under-excavation is found.

[0180] During the excavation process, the excavation speed and soil bin pressure should be recorded at all times, and the surface of the excavation section should be monitored in real time. When a sudden change in excavation is found, analysis should be carried out immediately. After finding out the cause, the relevant parameters should be adjusted in time to ensure the stability of the excavation surface.

[0181] 3) Issues that should be paid attention to when starting to explore

[0182] ① In order to control the propulsion axis and protect the cutterhead, the propulsion speed should not be too fast. The shield should move forward slowly and steadily, and the propulsion speed should be controlled at 5-10mm / min.

[0183] ② During the first ring of excavation, the excavation speed should be kept constant as much as possible to reduce fluctuations to ensure stable soil bin pressure and smooth excavation.

[0184] ③ When the shield machine is started, the shield machine driver must check whether the jack is fully supported, and the speed should not be too fast before starting and ending the advancement. At the beginning of each ring of excavation, the excavation speed should be gradually increased to prevent the starting speed from being too high.

[0185] ④ The advancement speed must meet the requirements of the grouting volume for each ring of excavation to ensure that the synchronous grouting system is always in good working condition.

[0186] ⑤ When adjusting the excavation speed, the excavation surface should be kept stable.

[0187] ⑥ Except in special circumstances, it is strictly forbidden for the shield machine to retreat during excavation.

[0188] 4) The main parameter adjustment and optimization measures are as follows:

[0189] ① Use a composite cutter disc with a hob as the main tool to cut the sand and gravel layer, and propel it at a low speed and high torque.

[0190] ② Appropriately increase the excavation soil pressure (the soil bin pressure is set to 1.2 to 1.3 times the theoretical value) to prevent water gushing, and continuously adjust and optimize during excavation.

[0191] ③ The soil bin pressure is established by setting the excavation speed and adjusting the soil discharge volume or setting the soil discharge volume and adjusting the excavation speed. The balance between the amount of cut soil and the amount of soil discharge should be maintained to ensure a stable and balanced pressure in the soil bin.

[0192] ④ The tunneling speed of the shield machine is mainly controlled by adjusting the shield thrust and speed (torque), and the amount of soil discharge is mainly adjusted by adjusting the speed of the screw conveyor. In actual tunneling construction, dynamic adjustment and optimization should be made according to geological conditions, the state of the discharged soil, and the various working state parameters of the shield machine.

[0193] ⑤During excavation, measures to improve the soil should be taken to increase the fluidity and water-stopping properties of the soil, and the embolism and excavation of the screw conveyor should be closely observed to adjust the dosage of additives.

[0194] ⑥ The propulsion speed is controlled at 40-60 mm / min and adjusted according to the monitoring results and soil discharge conditions. The screw machine speed matches the propulsion speed according to the set soil pressure.

[0195] The starting section of the shield machine is the construction section of about 10m from the shield cutter head entering the soil to the shield body entering the soil. Before construction, various parameters of the shield machine excavation process must be set first. After the trial excavation section of 100 meters, the parameters are adjusted within an appropriate range according to the use effect of various parameters and changes in geological conditions. The parameters that need to be set mainly include soil pressure, thrust, cutter head torque, propulsion speed and cutter head speed, excavation volume, synchronous grouting pressure, additive usage, etc. The geology of the starting section of the shield section of this project is mainly medium-dense pebble strata, and the starting parameter values ​​are shown in Table 3 below.

[0196] Table 2 Excavation parameters of the initial trial excavation section

[0197]

[0198] Excavation soil pressure setting

[0199] When excavating, soil bin pressure should be gradually built up to control surface settlement.

[0200] 1. Theoretical calculation of soil bin pressure; P = P1 + P2 + P3 = γw·h + K0·[(γ-γw)·h + γ·(Hh)]+15

[0201] P: soil bin pressure (kPa); P1: groundwater pressure (kPa);

[0202] P2: static soil pressure (kPa); P3: preparation pressure (take 15KPa);

[0203] γw: dissolved weight of water (kN / m3); h: tunnel depth below groundwater level (calculated to the center of the tunnel) (m);

[0204] K0: Lateral earth pressure coefficient, which is 0.34 for this construction (provided by geological survey report);

[0205] γ: Soil soluble weight (23kN / m3);

[0206] H: Tunnel burial depth (measured to the tunnel center) (m).

[0207] 2. Actual setting value of soil bin pressure

[0208] During the initial excavation stage of the shield machine, the actual setting value of the soil bin pressure should not be too high due to the limitations of factors such as the tail shield seal and the tunnel portal seal.

[0209] ① Setting of soil bin pressure in reinforcement area

[0210] The starting end is reinforced with ground sleeve valve pipes and enlarged pipe sheds. The planned soil bin pressure value for excavation in this area is 60~80Kpa.

[0211] ② Setting of soil bin pressure outside the reinforcement area

[0212] When the shield machine exits the reinforcement area, the earth bin pressure setting value is gradually increased to the theoretical calculated value (80-100Kpa) while ensuring the safety of the tail shield seal and the tunnel portal seal, and is adjusted based on ground monitoring conditions.

[0213] ③ Setting of soil bin pressure after leaving the reinforcement area

[0214] According to the ground monitoring situation and the theoretical calculated value of the soil bin pressure, the soil bin pressure setting value is adjusted within a small range. The theoretical value is 100~130Kpa.

[0215] 4. Shield construction thrust. The initial thrust of the shield mainly considers the front soil pressure P1, the friction resistance of the main machine and the rear supporting trailer P2, P3: Figure 8 shown.

[0216] Pressure on the shield machine:

[0217] Pe=γh+P0

[0218] P01=Pe+G / DL

[0219] P1=Pe×λ

[0220] P2=(P+γ.D)λ

[0221] Where: λ is the horizontal side pressure coefficient, λ=0.47

[0222] h is the thickness of the overlying soil, h = 12.8m

[0223] γ is the soil bulk density, γ = 1.94t / m3

[0224] G is the weight of the shield machine, G = 317.5t

[0225] D is the outer diameter of the shield machine, D = 6.25m; L is the length of the shield machine, L = 9m; P0 is the load on the ground, P0 = 2t / m2; P01 is the uniform pressure at the bottom of the shield machine; P1 is the lateral water and soil pressure at the top of the shield machine; P2 is the lateral water and soil pressure at the bottom of the shield machine; Pe = 1.94 × 12.8 + 2 = 26.83t / m2

[0226] P01=26.83+340 / (6.25×9)=32.474t / m2 P1=26.83×0.47=14.89t / m2

[0227] P2=(26.83+1.94×6.25)×0.47=18.3t / m2

[0228] The thrust of the shield machine is mainly composed of the following five parts:

[0229] F=F1+F2+F3+F4+F5

[0230] Where: F1 is the friction between the shield shell and the soil; F2 is the thrust caused by the horizontal thrust on the cutterhead

[0231] F3 is the thrust required for cutting soil; F4 is the friction between the shield tail and the segment

[0232] F5 is the resistance of the rear trolley

[0233]

[0234] Where: μ: friction coefficient between soil and steel, μ=0.3

[0235]

[0236] F2=π / 4(D 2 P d )

[0237] Where: P d is the horizontal earth pressure,

[0238]

[0239] P d =0.47×1.94×15.93=14.52t / m 2

[0240] F2=π / 4(6.28 2 ×14.52)=445.48t

[0241] F3=π / 4(D 2 C)

[0242] Where: C is the cohesive force of soil, C = 4.5t / m2

[0243]

[0244] F4=W c μ c

[0245] Where: WC, μC are the weights of two rings of segments (the calculation assumes that the weight of two rings of segments acts on the shield tail. When the segment density is 2.5t / m3 and the segment width is 1.5m, the weight of each ring of segments is 24.12t). The weight of two rings of segments is 48.24t. μC=0.3

[0246] F4=48.24×0.3=14.47t

[0247] F5=Gh ·sinθ+μ g G h cosθ

[0248] Where: Gh is the weight of the shield tail trolley, Gh≈160t;

[0249] θ is the slope, tgθ=0.025

[0250] μg is rolling friction, μg = 0.05

[0251] F5≈160×0.025+0.05×160×1=12.00t

[0252] Total thrust of shield machine: F = 1225.26 + 445.48 + 138.06 + 14.47 + 12.00 = 1835.27t

[0253] The initial thrust of the shield is mainly determined by the following factors: the friction resistance or adhesion resistance between the outer periphery of the shield (the outer layer of the shield shell) and the soil, the front resistance of the shield, the friction resistance between the segments and the shield tail brushes, and the friction resistance between the shield and the starting base track.

[0254] To ensure construction safety, the total thrust of the shield jack is controlled with 1200t as the target value. The total thrust of the shield jack for the initial trial excavation is controlled within 400-800t, and corresponding adjustments are made according to specific circumstances.

[0255] 5. Setting of the thrust speed of the shield jack and the cutterhead speed

[0256] The propulsion speed of the shield jack and the cutterhead speed are closely related to the performance of the shield machine, and are also affected by engineering geological and hydrogeological conditions. At the beginning, the parameter setting must first be based on the theoretical calculation value. In the trial excavation stage after the initial completion, various parameters can be compared, and the relationship between the propulsion speed and thrust, the cutterhead speed and torque can be adjusted to determine the range of propulsion speed and speed.

[0257] In this starting section, the strata within the tunnel body are mainly dense gravel layers. Since it is in the initial excavation stage, the advancement speed is initially set to 5-20 mm / min, and the initial cutterhead speed should be less than 1.0 r / min.

[0258] 5.2 Posture adjustment and correction principles

[0259] 1. Shield tunneling direction control

[0260] 1. The shield machine is equipped with an automatic total station:

[0261] The total station can reflect the current position and theoretical position of the shield machine in real time and provide adjustment instructions. It can dynamically display the deviation and trend between the current position of the shield machine and the tunnel design axis in the shield machine main control room around the clock. Based on this, the shield machine excavation direction is adjusted to keep it within the allowable deviation range.

[0262] 2. Operate the shield machine's thrust cylinder in sections to control the shield machine's excavation direction:

[0263] The thrust cylinders are divided into four groups: up, down, left and right. Each group of cylinders has a thrust cylinder with stroke measurement and thrust calculation. The thrust force of each group of cylinders is adjusted as needed to control the excavation direction.

[0264] When excavating in an uphill section, appropriately increase the thrust of the lower cylinder of the shield machine; when excavating in a downhill section, appropriately increase the thrust of the upper cylinder; when excavating in a left-turn curve section, appropriately increase the thrust of the right cylinder; when excavating in a right-turn curve, appropriately increase the thrust of the left cylinder; when excavating in a straight and flat slope section, try to keep the thrust of all cylinders consistent.

[0265] 2. Shield Tunneling Attitude Adjustment and Correction

[0266] In actual construction, the advancement direction of the shield machine may deviate from the design axis and exceed the management warning value due to reasons such as incorrect segment selection and operating errors by the shield machine driver; when excavating in stable strata, the shield body may roll due to the small rolling resistance provided by the strata; during excavation in slope-changing sections or sharp bends of the line, large deviations may occur. At this time, it is necessary to adjust the shield machine posture and correct the deviation in time.

[0267] 1. Refer to the above method to operate the thrust cylinder in sections to adjust the shield machine's posture, correct deviations, and adjust the shield machine's direction control to within the required range.

[0268] 2. In sharp bends and slope change sections, if necessary, the shield machine's over-excavation cutter can be used to carry out local over-excavation and enter the curved section in advance within the allowable deviation range of the axis to correct the deviation.

[0269] 3. When the rolling exceeds the limit, the shield cutter head should be reversed in time to correct the rolling deviation.

[0270] 5.3 Landfill improvement

[0271] 1. The role of soil improvement

[0272] When shield construction is carried out in water-rich and sandy strata, soil improvement is an indispensable and important technical means to ensure the safety, smoothness and speed of shield construction. It has the following functions:

[0273] (1) Ensure that the slag and the added medium are fully mixed to form impermeable and plastic slag, thereby establishing a good earth pressure balance mechanism. Only when the slag improvement effect is good can the surface settlement control during the excavation process be fundamentally guaranteed, while ensuring the scheduled construction progress;

[0274] (2) Make the soil plastic and have low water permeability, thus forming a better earth pressure balance effect to stabilize the excavation surface and control surface settlement;

[0275] (3) Control groundwater loss and prevent or reduce the gushing phenomenon when the screw conveyor discharges soil;

[0276] (4) Improve the flow plasticity of the slag, so that the cut slag can enter the soil bin smoothly and quickly, and facilitate the smooth discharge of the screw conveyor;

[0277] (5) Improve the fluidity of the slag and reduce its internal friction angle, effectively reduce the torque of the cutter head, reduce the wear on the cutter and screw conveyor, reduce the friction and heat generated during excavation and cutting, and improve the excavation efficiency.

[0278] 2. Methods of improving soil

[0279] Muck improvement is to inject additives into the cutter head, soil bin, or screw conveyor through the special device equipped with the shield machine, and mix the additives with the soil slag by rotating the cutter head, stirring the soil bin stirring device, or rotating the screw conveyor. The main purpose is to make the slag cut by the shield machine have good fluidity, suitable consistency, low permeability and small friction resistance, so as to achieve ideal working conditions when excavating under different geological conditions. The main additives are foam, bentonite and polymer.

[0280] (1) Determination, ratio and dosage of improver

[0281] Table 4 Performance index of various improvers

[0282]

[0283] According to construction experience, this project plans to add a foaming agent to the bentonite slurry, which has a much better effect than any other improvement: significantly reducing the oil pressure of the cutterhead and screw conveyor and the thrust of the shield, reducing the torque of the cutterhead, reducing the wear of the shield equipment on the sand and gravel strata, and increasing the excavation speed and the service life of the equipment.

[0284] The bentonite slurry mix ratio is water: bentonite: admixture = 10:1:0.2. The bentonite is high-quality sodium-based bentonite, and the admixture is a mixture of alkali, CMC and superfluidizer DAV. Special admixtures for shield machines can be purchased from the market, and the slump of the slurry is controlled within 20cm.

[0285] Foam: 95% compressed air and 5% foam solution; the composition of the foam solution is 3% foam additive and 97% water. The viscosity of the foam agent used in this project is not less than 0.1Pa·s.

[0286] (2) Mechanism of action of mud and foam mixture

[0287] The action mechanism of the mud and foam mixture is mainly manifested in the following aspects:

[0288] ① By injecting mud and foam, a mud film is formed in front of the cutterhead, which builds up soil pressure and provides horizontal thrust for the soil structure, which is conducive to the formation of an arch structure.

[0289] ② Mud and foam enhance the strength and rigidity of the excavation surface soil, improve the vertical resistance of the excavation surface soil, support the excavation surface soil, and reduce the possibility of instability of the excavation surface soil.

[0290] The particles of the sand and gravel formation are loose and have no cohesion. The force transmission between the particles is point-to-point. After adding mud to the excavation surface soil, the mud surrounds the particles and forms a mud film, which increases the cohesion between the particles, diffuses the force transmission between the particles, and improves the force condition of the soil, as shown in the figure. In addition, the volume of the foam is very small, and the diffusion of the mud of the foam is enhanced after mixing. It can quickly penetrate into the soil layer under the stirring of the cutter head, wrap the sand and gravel particles, reduce the density of the soil, and improve the plastic flow of the soil.

[0291] ③Use the excellent lubrication performance of foam to improve the granular structure of soil. At the same time, the bubbles adsorbed between the particles can reduce the direct friction between the soil particles and the cutter system. Reduce the permeability of the soil. Because of its small specific gravity and light mixing load, it is easy to mix the soil evenly, so as to balance the soil pressure on the excavation surface and discharge the soil continuously and smoothly. At the same time, the foam is compressible, which also has a positive effect on the stability of soil pressure.

[0292] (3) Main technical measures for soil improvement

[0293] Considering that the excavation in this section in the water-rich and sandy strata is mainly to reduce the wear of the cutter, reduce the torque of the cutter head, and the wear of the screw conveyor to prevent gushing, the method of injecting bentonite and foam mixture in front of the cutter head, in the soil compartment and in the screw conveyor is adopted to improve the slag. And increase the injection amount in the screw conveyor to facilitate the formation of soil plug effect of the screw conveyor to prevent gushing. In the process, the proportion of bentonite and foam is adjusted in time according to the improvement effect.

[0294] 5.4 Setting of excavation volume

[0295] The outer diameter of the pipe segments used in this project is 6000mm and the ring width is 1500mm.

[0296] V = πL(d / 2)2 (d - cutter head diameter; L - segment ring width)

[0297] The diameter of the cutter disc is 6280 mm, and the excavation volume per ring is 46.59 cubic meters;

[0298] According to the construction experience of similar strata in Chengdu, the excavation volume of each ring of mudstone strata is controlled at 56m 3 , the pebble layer is controlled at 60m 3 The weight is considered to be improved by bentonite and foamed slag on the cutter head. The density of compacted pebble soil is 2.3g / cm3, and the excavated weight is controlled by G=46.59*2.3+10=117.2T. The construction process adopts volume (18 cubic meters per slag bucket) and quality dual control (the gantry crane has its own weighing system). During the excavation process, the excavated amount of each ring must be strictly controlled and recorded.

[0299] In accordance with the subway company's shield construction management methods and combined with the on-site construction conditions, a slag output management method is formulated. When the slag output of a single ring exceeds 3 cubic meters and the triple ring exceeds 5 cubic meters, the machine is immediately shut down and reported to the supervisor and the owner, and corresponding treatment measures are formulated. Construction can only be continued after discussion and acceptance at a meeting.

[0300] 5.5 Synchronous grouting and secondary grouting behind the wall

[0301] After the cutterhead enters the original soil layer, single-liquid slurry can be used for synchronous grouting. The selection of single-liquid slurry is closely related to the quality of the tunnel. It is required to provide practical data based on the test during the initial selection to meet the design standards. It is required to do a lot of screening tests in the early stage, and strictly control the large sample test and grouting outlet pressure, Pout = Pcut + P coefficient (0.06~0.1MPa).

[0302] In order to ensure the effectiveness of single-liquid grouting and ensure that the segments are not deformed or damaged due to external pressure, the grouting pressure must be strictly controlled. The grouting pressure should be greater than the soil bin pressure by 0.6 to 1.0 bar, but must be less than the shield tail grease tank pressure.

[0303] Selection of synchronous grouting implementation time and slurry properties

[0304] According to the formula calculation and relevant technical requirements, the grouting volume should be about 1.5 to 2 times of the theoretical volume of the annular gap. This project takes 1.7, and the grouting volume Q = 6m3. In order to ensure that the tunneling can be fully injected according to the above requirements, the dual means of automatic synchronous grouting and manual segment wall grouting are adopted.

[0305] The synchronous grouting system has a certain reasonable use range, and has certain limitations in some sensitive areas, such as in strata with large permeability coefficients. Since the shield advances relatively fast in this stratum, and the automatic grouting outlets are all distributed in the upper part, it is difficult to form a separate solid body after the slurry is injected, especially in the middle and lower parts, forming a local injection blind spot. For the grouting system, a set of artificial segment wall grouting equipment is also configured. In the grouting management, a combination of automatic and manual grouting is adopted, and the artificial segment wall grouting system is used to fill certain geologically sensitive areas of the automatic grouting equipment.

[0306] When the shield tail passes through the tunnel seal, synchronous grouting begins. The grouting liquid is cement mortar, and the main indicators of grouting are:

[0307] ① Gelation time: 6-8h according to geological conditions.

[0308] ② Consolidation body strength: not less than 0.5Mpa in one day and not less than 2Mpa in 28 days.

[0309] ③Slurry shrinkage value: greater than 95%, that is, the consolidation shrinkage rate is less than 5%.

[0310] ④Slurry consistency: 8-12cm.

[0311] ⑤ Slurry specific gravity: required to be controlled at 1.7~2.0g / cm3.

[0312] ⑥ Slurry stability: decantation rate is less than 5%.

[0313] 1. Methods and materials

[0314] The grouting behind the wall adopts two methods: synchronous grouting and secondary supplementary grouting. The synchronous grouting is injected simultaneously with the excavation through the synchronous grouting system, and the secondary supplementary grouting is carried out through the grouting holes of the pipe segment behind the shield tail using the supplementary grouting system.

[0315] The grout for synchronous grouting is cement mortar, and the proportion is shown in the table. Secondary supplementary grouting mainly uses cement mortar. In areas where tunnel excavation has a greater impact on surface buildings or pipelines, in order to reduce ground settlement, quick-setting grouts such as cement-water glass double liquid grout can be selected. The proportion of cement single liquid grout is generally 1:1 water-cement ratio. The proportion of cement-water glass double liquid grout is shown in Tables 5 and 6 below.

[0316] Table 5 Synchronous grouting material ratio table

[0317]

[0318] Table 6 Slurry ratio and main properties of slurry

[0319] Group Water-cement ratio Liquid A: Liquid B (volume ratio) Slurry density (g / cm3) Coagulation time (seconds) 1 1∶1 1∶1 1.44 20～48

[0320] Initial setting time of slurry: 6-8 hours. According to the formation conditions and excavation speed, the setting time can be adjusted by adding accelerators and changing the proportion through field tests. Consolidation strength: 24h compressive strength is not less than 0.5MPa, 3d is not less than 2MPa, and 28d compressive strength is not less than 5MPa. Slurry stone rate: >95%, that is, consolidation shrinkage rate <5%; Slurry consistency: 8-12cm / m; Slurry stability: decantation rate (ratio of floating water volume to total volume after static sedimentation) is less than 5%.

[0321] 2. Technical parameters

[0322] ① Grouting pressure

[0323] During synchronous grouting, the slurry pressure in the stratum is required to be greater than the sum of the static water pressure and the soil pressure at that point, so as to fill as much as possible without causing splitting. If the grouting pressure is too high, the soil layer around the pipe segment will be disturbed by the slurry, causing the subsequent stratum settlement and the settlement of the tunnel itself, and easily causing slurry leakage; while if the grouting pressure is too low, the slurry filling speed is too slow, the filling is insufficient, and the surface deformation will increase.

[0324] The synchronous grouting pressure is 0.25~0.4MPa, and the secondary grouting pressure is controlled at 0.3~0.5MPa.

[0325] ② Grouting volume

[0326] Theoretically, the synchronous grouting volume is to fill the gap in the shield tail building, but at the same time, factors such as the distortion during the shield advancement process, slurry penetration (related to geological conditions) and consolidation shrinkage of the grouting material should be considered. The grouting volume can be calculated using the following formula:

[0327] Q=Vλ

[0328] In the formula: Q—grouting volume (m3) λ—grouting rate (1.5~2) V—shield tail building gap (m3)

[0329] V=π(D2-d2)L / 4

[0330] Where: D—diameter of soil cut by shield machine d—outer diameter of segment (6m) L—width of segment (1.5m)

[0331] When the cutter head diameter is 6280mm: V = π (6.292-6.02) × 1.5 ÷ 4 = 4.2m3

[0332] According to experience, the grouting volume is generally 1.5 to 1.8 times the theoretical grouting volume, and should be adjusted through ground deformation observation. The actual grouting volume is 5 to 7 m3 / ring.

[0333] The amount of secondary reinforcement slurry is controlled by grouting pressure according to the geological and grouting records, analysis of grouting effect, and monitoring conditions. The grouting end standard is controlled by grouting pressure and grouting amount. Under normal circumstances, the grouting amount per ring should not be less than 6m3.

[0334] The following exceptions apply:

[0335] a. In sandy formations, when the grouting pressure is very small and the grouting volume is large, increase the grouting volume until the grouting pressure reaches the lower limit of the grouting pressure;

[0336] b. When the shield machine is located in a curved section, consider over-excavation and increase the grouting volume appropriately;

[0337] c. For clay layers with poor self-stabilization ability, when the grouting volume is small and the grouting pressure is high, it may be due to the collapse of the rock and soil around the shield, which affects the flow of the slurry. When the grouting pressure reaches the upper limit of the grouting pressure, stop grouting and then carry out secondary reinforcement grouting.

[0338] ③ Grouting speed

[0339] The synchronous grouting speed should match the excavation speed, and the average grouting speed should be determined by the amount of grouting completed in one ring within the time it takes for the shield to complete a 1.5m excavation, so as to achieve uniform grouting.

[0340] ④ Grouting sequence

[0341] Synchronous grouting is injected through the reserved grouting holes of the segments while the shield machine is advancing. A pressure sensor is set at the outlet of each grouting hole to detect and control the grouting pressure and grouting volume of each grouting hole, thereby achieving symmetrical and uniform injection behind the segments. In order to prevent the uneven force on the segments caused by grouting, resulting in bias pressure and dislocation of the segments, causing misalignment and slope damage, it is very important to inject symmetrically and evenly during synchronous grouting. Reinforcement grouting should be injected first on the side where there may be a large gap.

[0342] 3. After the shield tail passes through the tunnel seal, backfill and grouting are carried out

[0343] When the shield tail passes through the tunnel seal, the tunnel opening is immediately grouted, and the reserved grouting valve on the extended steel ring is used for supplementary grouting. At the same time, the secondary grouting in front of the 0 ring segment is strengthened, and the grouting adopts cement-water glass double liquid grout. . The ground settlement at the origin of the structure is too large.

[0344] 5.6 Segment Assembly

[0345] Prefabricated segment lining is used in this project. The outer diameter of the segment is 6000mm, the inner diameter is 5400mm, the length of each segment ring is 1500mm, the segments are assembled with "3A+2B+1C (wedge block)" staggered seams, and the segment joints are waterproofed with rubber waterstop strips.

[0346] ① Segment selection

[0347] a The travel difference between shield jack and articulated jack

[0348] The general principle of segment assembly is that the structural direction of the assembled segment and the shield tail should be kept consistent as much as possible. For an articulated shield, the stroke difference of the jack after segment assembly is preferably the stroke difference of the articulated jack.

[0349] b. The gap between the outer surface of the segment and the inner surface of the shield before and after segment assembly

[0350] There are three sealing brushes at the tail of the shield machine to ensure that no water or soil will enter the tunnel during the construction process. While the shield machine is excavating, grease will be added to the sealing brushes to ensure the sealing performance of the shield machine. A protective block is provided at the front end of the sealing brush to protect the sealing brush from damage. If the gap at the tail of the shield is too small, when the segment falls out of the tail of the shield, it will cause a large deformation, affecting the quality of the formed tunnel; at the same time, a too small gap at the tail of the shield will directly damage the sealing brush of the shield machine.

[0351] ②Segment cleaning

[0352] After the segment model is determined, the surface of the segment to be hoisted should be cleaned. When cleaning, special attention should be paid to wiping the surface of the rubber sealing pad around the segment to ensure the waterproof quality after the segment is assembled. In addition, during the assembly process, the garbage at the shield tail assembly area should be removed at any time.

[0353] ③ Segment transportation

[0354] Vertical transportation: The gantry crane transports the pipe segments from the ground to the end well of the shield construction and places them on the pipe segment transport flatbed truck. Horizontal transportation in the well: The battery car transports the pipe segments to the rear supporting equipment of the shield.

[0355] Transportation within the supporting facilities: Before transportation, the segment lifting points must be firmly connected to the segment crane, and then the segment crane will transport the segments to the segment assembly area.

[0356] ④ Segment assembly

[0357] The assembly should be carried out in the order determined by the segment assembly plan. Generally, the bottom segment is assembled first, then the left and right cross-installation is carried out from bottom to top, and finally the locking block is assembled. During the assembly, each ring of segments should be evenly distributed and the height difference of the ring surface should be strictly controlled. Before assembling the segments, mark the position of the bolt holes of each segment to facilitate the positioning of the segments. When assembling the segments, the jack cylinder in the area of ​​the segments to be assembled should be retracted first to meet the space requirements for the segments to be in place. During the initial positioning of the segments, the movement of the segment assembly machine should be smoothly controlled to avoid friction and collision between the segments to be assembled and the adjacent segments, which may cause damage to the segments or rubber gaskets. After the segments are initially in place, the height difference of the adjacent ring surfaces of the adjacent segments is measured by feeler gauges and rulers, and the segments are fine-tuned according to the measured values. When the height difference of the adjacent ring surfaces of the segments meets the requirements, the jacks are brought close in time to prevent the segments from shifting. After the jacks are tightened, the segment connection bolts are installed. After the assembly of the previous pipe segment is completed, repeat the previous step and continue to assemble other pipe segments.

[0358] In order to ensure the quality and progress of segment assembly, the segment assembly must be carried out strictly in accordance with the following requirements:

[0359] a. In order to speed up the assembly construction, it is necessary to ensure that the pipe segments enter the assembly area 10 minutes before the excavation construction is completed so as to prepare for the next step of construction; in addition, in order to ensure that the pipe segments are not contaminated by soil during the excavation process, it is not advisable to prepare the pipe segments in advance.

[0360] b. At the same time, attention must be paid to the correct positioning of the segments, especially the positioning of the first segment, which will affect the assembly quality of the entire ring of segments and its relative position with the shield, so try to achieve symmetry.

[0361] c. When assembling the pipe segments, the flatness of the ring surface and the ovality of the assembly ring must be strictly controlled.

[0362] d. After each segment is assembled, the jack should be moved close in time to prevent the shield from retreating and the segment from shifting. After each ring of lining is assembled, the longitudinal and circumferential bolts connecting the lining should be tightened in time. When tightening, pay attention to check whether the bolt hole sealing rings have been fully penetrated and no omissions should be made. After the lining is out of the shield tail, the longitudinal and circumferential bolts should be tightened again. Before entering the next ring of segment assembly, the segment connection bolts of the tunnel within the adjacent 3 rings that have been assembled should be fully inspected and tightened.

[0363] e. The waterproof sealing gasket of the capping block should be lubricated before assembly to reduce the friction between the sealing gaskets during insertion. If necessary, nylon rope or canvas lining should be set to limit the extension of the rubber strip during insertion.

[0364] f If the position of the segments needs to be adjusted during the segment assembly process, the adjustment cannot be made when the segments are under axial force to prevent damage to the waterproof rubber strips.

[0365] 5.7 Inter-area transport organization

[0366] This project uses 18-cubic-meter ballast trucks for excavation. The diameter of the shield machine cutting disc is 6.28m, and the support segment is 1.5m wide. The volume of ballast soil for each excavation ring is calculated. According to engineering experience and the geological conditions of Chengdu Line 6, the loose coefficient of ballast soil is selected as 1.3. According to the construction requirements of Chengdu Metro, the excavation volume of each ring of mudstone strata is controlled at 56m 3 18*4=72>56m 3 , meet the excavation requirements. 5.8 Matters needing attention in normal shield tunneling construction

[0367] After completing 100m of excavation in the starting section, the shield machine made necessary adjustments to the starting posture. The adjustment work included: removing the negative ring segments, the starting base and the reaction frame; laying double-track tracks at the station end; installing ventilation facilities; and extending and connecting various other pipelines.

[0368] 1) The shield machine is advanced by the operator in the central control room. When the construction starts, open the excavation gate, turn on the belt conveyor, screw conveyor and large cutter head in turn, push the jack, adjust the oil pressure of each jack, and then the large cutter head cuts the soil and the shield machine moves forward. The shield machine automatically controls the excavation speed or excavation speed according to the set positive soil pressure. The shield machine's stroke, the jack pressure in the four areas of up, down, left and right, the screw conveyor speed, the shield machine torsion, pitch and other parameters will be displayed on the display screen. The shield machine driver will record the parameters in time, and refer to the instrument display and other manual measurements and construction experience to adjust the shield machine posture and various construction parameters, so that the shield machine always advances along the designed axis.

[0369] 2) The shield should be advanced according to the parameters set by the shift instructions, and the excavation and grouting should be carried out simultaneously. During the shield construction, according to the different soil types, cover thickness, and ground buildings, the balance pressure value should be adjusted in time in coordination with the monitoring information analysis. At the same time, according to the monitoring data of the advancement speed, excavation volume, and stratum deformation, the grouting volume should be adjusted in time to control the axis and stratum deformation within the allowable range, and the maximum deformation after surface construction should be within +10mm to -30mm.

[0370] 3) During the shield tunneling process, the advancement slope should be kept relatively balanced. Strictly control the advancement mileage, check the construction measurement results with the calculated three-dimensional coordinates in a timely manner, and make timely adjustments. Small deviations that appear initially should be corrected in a timely manner, and the shield machine should be prevented from "snake" shape as much as possible. The amount of correction each time should be controlled. The amount of correction of the shield machine at one time should not be too large to reduce the disturbance to the stratum and create good conditions for the assembly of the segments.

[0371] 4) The shield tunneling of this project is basically in gravel soil and mudstone strata. Additives need to be injected into the cutterhead, soil compartment or screw conveyor to ensure that the excavated soil has a good flow plastic state, low permeability and low internal friction angle.

[0372] 5) To prevent groundwater and synchronous grouting slurry from entering the tunnel from the shield tail during shield excavation, shield tail grease must be injected at the shield tail wire brush position to ensure that the gap between the shield tail and the pipe segment is filled with shield tail grease during construction to achieve the shield's sealing function. During construction, centralized lubrication grease injection must be carried out from time to time to maintain the normal operation of all parts of the shield machine.

[0373] 6) Settlement control measures during excavation: A. After the ground settlement observation points along the line are established, initial data should be obtained before excavation begins, and all monitoring points should be clearly marked on the 1:500 line plan; B. During the trial excavation of the shield machine, denser settlement monitoring points will be set to obtain the relationship between the shield machine excavation parameters and the ground settlement; C. During the excavation process, measurements should be taken at least once a day in the morning and evening within the range of 20m in front of and 30m behind the shield machine head, and once a week outside the range until it stabilizes; D. During the shield machine excavation, jacks and thrusts should be appropriately selected, the soil bin pressure should be determined according to the ground settlement observation results, the excavation direction should be adjusted at any time, and serpentine and over-excavation should be minimized; E. Backfill grouting should be carried out in a timely manner during the excavation process, and appropriate grouting pressure and grouting volume should be maintained, and secondary grouting should be carried out in a timely manner.

[0374] 7) Construction personnel should make construction records item by item, link by link and day by day, recording contents: shield tunneling posture, segment assembly, synchronous grouting, tunnel water leakage, etc., and submit a copy of the record to the supervising engineer in time.

[0375] 8) Common problems and solutions:

[0376] (1) In order to protect the tool and reduce tool wear, the cutter torque must be controlled within a certain allowable range. The main control methods are: reducing the thrust, which will also reduce the excavation speed; adding soil conditioners to the excavation face and soil bin.

[0377] (2) If the screw conveyor is stuck (i.e. the torque exceeds the limit) and cannot discharge the mucking normally, you can repeatedly extend and retract the screw and rotate it forward and reverse at the same time. For example, you can rotate it forward at a low speed and extend and retract the screw at the same time. If it exceeds the limit, you can reverse the rotation and extend and retract the screw at the same time. Repeat this process and you can basically get out of trouble.

[0378] (3) If the cutter disc gets stuck when starting, partially retract the thrust jack to reduce the soil pressure and cutter penetration, and then the cutter disc can be rotated.

[0379] (4) If the pulling force of the articulated jack is large, it means that the hole expansion ability of the cutter disc is poor. In this case, check whether the edge of the cutter disc is excessively worn and should be replaced.

[0380] 5.9 Opening and changing the knife

[0381] This bidding section plans to use the connecting channel location as a tool-changing point, and the ground reinforcement at the connecting channel location will be completed before shield construction.

[0382] 5.10 Control Measurement

[0383] Before shield construction, the ground control network is brought underground to measure the shield machine's posture and complete the adjustment of the shield machine's starting and arrival postures; during excavation, the coordinates of the tunnel design axis are input into the shield machine's built-in automatic guidance system, and the shield machine performs uninterrupted shield posture measurements through the guidance system, and the results are displayed on the guidance interface of the operating room; in special cases, manual re-measurement is used to correct the guidance system data to complete the measurement work during the shield construction process.

[0384] 1. Monitoring and measurement items and standards

[0385] Table 7 Metro shield construction monitoring measurement value control standards

[0386]

[0387]

[0388] 2. Data processing method

[0389] Building settlement, underground pipeline settlement and differential settlement, and road surface settlement monitoring all adopt geometric leveling methods, use Tianbao Dini03 electronic level for observation, and use electronic recording of field observation data.

[0390] After the elevation reference point is selected, it must be remeasured at least 3 times to confirm that the elevation reference point is in a stable state before it can be used.

[0391] 1) Data adjustment calculation

[0392] After the observation is completed, the original observation record file is formed. After the inspection is qualified, the special leveling network adjustment software is used for strict adjustment to obtain the elevation value of each point. The adjustment calculation requirements are as follows:

[0393] 1) Because a stable reference point is used as the starting point, and the independent closure error and the mutual conformity error with more than two reference points are checked;

[0394] 2) Use professional adjustment software to perform calculations according to rigorous adjustment methods;

[0395] 3) After adjustment, the data position should be accurate to 0.1mm.

[0396] The settlement amount of each stage, deformation rate of each stage, accumulated settlement amount and other data are calculated through the elevation values ​​of the deformation observation points at each stage.

[0397] 2) Deformation data analysis

[0398] The principles of monitoring point stability analysis are as follows:

[0399] 1) The stability analysis of the monitoring point is based on a stable reference point;

[0400] 2) The change of the monitoring point in two adjacent periods is determined by comparing the maximum deformation and the maximum measurement error (taking twice the mean error) in the two adjacent periods. When the deformation is less than the maximum error, it can be considered that the monitoring point has not changed or has not changed significantly in the period;

[0401] 3) For the results of multiple-period deformation observations, when the deformation in adjacent periods is small but multiple periods show an obvious trend of change, it should be regarded as a change.

[0402] The deformation law prediction of the monitoring point can be given through mathematical calculation methods such as regression analysis, and compared with simulation calculations such as geological conditions, structural design form, and construction sequence.

[0403] The early warning judgment of the monitoring point is given by comparing the dual control indicators of deformation rate and cumulative deformation with the early warning, alarm and control indicators.

[0404] 3. Measurement method

[0405] (1) Segment lining crown settlement

[0406] 1) Monitoring point layout

[0407] The measuring points are arranged at fixed positions on the top and bottom of the lining ring and are marked with paint. For each section tunnel constructed by shield construction, a main measuring section is set every 50m, and sections are arranged at the starting and interface positions of the shield.

[0408] 2) Monitoring methods, data collection and analysis

[0409] Measurement method: Ordinary leveling method is used. The encrypted leveling base point on the tunnel lining ring is used as the initial elevation. During observation, the sight line of a measuring station should not exceed 50 meters. If it exceeds, the backsight point reading should be reread for verification. When taking the initial value measurement, the values ​​measured three times in a row must be basically consistent before it can be determined as the initial reading. Otherwise, the measurement should be continued until the requirements are met.

[0410] Data collection and analysis: When conditions permit, improve the observation accuracy as much as possible, and then adjust according to the measuring station to obtain the elevation of each point. Before construction, the initial elevation H0 of the uplift observation point is measured by leveling from the base point, and the elevation measured during the construction process is Hn. Then the height difference △H=Hn-H0 is the settlement value.

[0411] (2) Segment lining clearance convergence

[0412] 1) Monitoring point layout

[0413] The monitoring points are buried in the structural section, which is the same as the section of the segment lining vault settlement. For each interval tunnel of shield construction, a main measuring section is set up every 50m, and sections are arranged at the starting and interface positions of the shield.

[0414] 2) Measurement point embedding method and instrument

[0415] Select 22mm diameter threaded steel bars, bury them on both sides of the structural section, and expose them for 5cm. Weld an elliptical steel ring on the exposed threaded steel head, mark them with red paint and set up protective devices. SL type convergence meter is used for clearance convergence monitoring.

[0416] (3) Settlement of underground pipelines

[0417] 1) Monitoring point layout

[0418] 1. In principle, underground pipeline monitoring points are mainly arranged on gas pipelines, water pipelines, sewage pipelines, and large rainwater pipes. The relative position relationship between the underground pipelines and the caverns should be considered when arranging the measuring points.

[0419] 2. The measuring points should be arranged at the joints of the pipeline or at the locations that are sensitive to displacement changes;

[0420] 3. According to the requirements of the design drawings, pipelines with special requirements shall be arranged with pipeline top measurement points, and those without special requirements shall be arranged at the corresponding surface above the pipeline.

[0421] 2) Monitoring methods, data collection and analysis

[0422] The observation method adopts the precision leveling method. The initial elevation is obtained by joint measurement of the base point and the nearby leveling points. During observation, the tolerances should be strictly controlled. The height difference of each measuring point should not exceed 0.3mm. For observation points that are not on the leveling route, there should not be more than 2 at a measuring station. If exceeded, the backsight point reading should be reread for verification. For the first observation, the measuring point should be measured twice in succession. The difference between the two elevations should be less than ±0.5mm, and the average value should be taken as the initial value.

[0423] (4) Surface subsidence monitoring

[0424] The project focuses on monitoring the adjacent roads and ground surfaces within a range of 2 times the buried depth of the interval structure.

[0425] 1) Monitoring point layout

[0426] Incorporate road and surface settlement monitoring points into the monitoring and control network to form attached lines, etc.

[0427] For this project, a row of monitoring points is set up 150m along the shield advancement axis, with a spacing of 30m between monitoring points. A transverse section is set in the direction perpendicular to the axis, with 11 monitoring points arranged in each section, with a row spacing of 30m. The average tunnel burial depth is 15m, and the monitoring points are encrypted within 100m of the shield starting and receiving areas.

[0428] In order to protect the measuring points from rolling, the road and settlement measuring point signs are in the form of pit measuring points, which are buried by manual excavation or drilling. The hole diameter of the surface measuring point shall not be less than 150mm. The road and surface settlement monitoring measuring points should be buried flat to prevent the unevenness from affecting the passage of people and vehicles. At the same time, the measuring points should be buried firmly and clearly marked for easy storage.

[0429] 2) Monitoring methods, data collection and analysis

[0430] If conditions permit, lay out the wire network as much as possible to improve the observation accuracy through adjustment, and then adjust according to the measuring station to obtain the elevation of each point. Before construction, the initial elevation H0 of the settlement observation point is measured by leveling from the base point, and the elevation measured during the construction process is Hn. Then the height difference △H=Hn-H0 is the cumulative settlement value.

[0431] (5) Installation measurement of shield machine starting bracket and reaction frame

[0432] Before installing the starting bracket of the shield machine, the underground control points are used to accurately calibrate the design center line of the tunnel and the center line of the shield bracket support rail on the ground. The underground elevation control points are used to lay out the design elevations of the guide rails at the shield head and shield tail, and the inclination angles of the shield machine and reaction frame are determined as the basis for the installation and adjustment of the shield bracket and reaction frame.

[0433] (6) Measurement at the initial excavation stage

[0434] The initial measurement of the shield machine's attitude includes measuring horizontal yaw, pitch, and torsion. The horizontal yaw and pitch of the shield machine are used to determine whether the shield machine is moving along the tunnel design centerline during the subsequent excavation process, and the torsion is used to determine whether the shield machine is twisted within the allowable range.

[0435] 1) Shield machine guide rail positioning measurement

[0436] The difference between the center line of the shield machine guide rail and the designed tunnel center line should be less than 3mm, the difference between the front and rear elevations of the guide rail and the designed elevation should be less than 3mm, and the bottom of the guide rail should be solid and flat.

[0437] 2) Reaction frame positioning measurement

[0438] The reaction frame positioning measurement includes the reaction frame's height, pitch, yaw, etc., and whether the bottom of the reaction frame is solid and flat. The stability of the reaction frame directly affects whether the shield machine can proceed normally in the designed direction when it starts excavating.

[0439] 3. Initial measurement of shield machine posture, such as Figure 7-1 , Figure 7-2 shown.

[0440] The initial measurement of the shield machine's posture includes measuring horizontal yaw, pitch, and torsion.

[0441] The shield machine is a three-dimensional body that is approximately cylindrical. Observation points are selected at appropriate positions inside the shield machine shell. In Figure 4-7, point O is the center point of the shield machine cutterhead, and points A and B are two selected points below the root of the screw machine at the hinge between the front body and the middle body of the shield machine. Points C and D are two points on the lower side of the middle section of the screw machine, and point E is the center coordinate of the front section of the shield machine middle body. A, B, C, and D. There are measuring reflective lenses on all four points. In the two tetrahedrons formed by the five points A, B, C, D, and O, after measuring the three-dimensional coordinates (xi, yi, zi) of each corner point, the relative position relationship between the four points of each tetrahedron and the length L of the six sides are calculated as the initial value for subsequent calculations. In the subsequent excavation process, Li will be an unchanging constant (assuming that the forebody does not deform during the shield machine excavation process). By measuring the three-dimensional coordinates of the four points A, B, C, and D, the three-dimensional coordinates of the point O can be calculated using (x, y, z) and L.

[0442] Using the same principle, the five points A, B, C, D, and E can also form two tetrahedrons, and the three-dimensional coordinates of point E can also be obtained accordingly. The horizontal yaw and vertical yaw of the center of the shield machine cutter head can be calculated from the three-dimensional coordinates of points E and O and the twist angle of the shield machine, and the torsion angle of the shield machine can be determined from the three-dimensional coordinates of points A, B, C, and D, thereby achieving the purpose of detecting the shield machine.

[0443] (7) Shield tunneling measurement

[0444] 1) Composition of the guidance system

[0445] The guidance system is mainly composed of a laser total station purchased from the market, an ELS laser system, a personal computer, a modem, a power supply, a PLC, an inclinometer, software and other parts.

[0446] 2) Measurement method

[0447] 1. Establish shield control points

[0448] In the shield manufacturing plant, control points are built at immovable positions of the shield to facilitate frequent inspections in the future.

[0449] 2. Measurement steps

[0450] ① After the shield is installed on site, measure the coordinates of the shield control points in the engineering coordinate system;

[0451] ② The rotation angle and slope of the shield are measured by the inclinometer in the ELS;

[0452] ③ Input the basic dimensions and measurement data of the shield into the DDJ-2S system, set the laser total station on the measuring table, start the DDJ-2S system, and the system will automatically collect data every 30 seconds.

[0453] Through software operation, the real-time posture of the shield can be easily obtained; a calculator can also be used to utilize three-dimensional coordinate conversion to reversely calculate the three-dimensional coordinates of the shield cutout and shield tail, and compare them with the tunnel design axis to calculate the shield deviation, so that the shield operator can promptly correct the propulsion parameters and optimize the shield propulsion axis.

[0454] 3. Measurement of segment position

[0455] After the advancement is completed, the gap value between the segment and the shield tail is input. The elongation value of the jack and the state of the shield articulation can be obtained through PLC, and the offset between the segment and the design axis can be calculated. Using software such as NRG and Tastring, the three-dimensional coordinates of the center of the circle and the corresponding tunnel design coordinates can be calculated based on the three-dimensional coordinates of the formed segment measured, and finally the deviation value can be calculated. The report can not only show the roundness of the segment and the advance amount of the segment, but also more specifically and realistically evaluate the loop quality of the segment.

[0456] Shield Tunneling Attitude Measurement

[0457] When measuring the real-time posture of the shield machine, a characteristic point and a characteristic axis are measured, and the center of the cut is selected as the characteristic point and the longitudinal axis is selected as the characteristic axis. The azimuth of the longitudinal axis of the control wire is used in tunnel construction. The difference between this azimuth and the azimuth of the shield itself is the azimuth correction value, and the shield excavation direction is corrected by this.

[0458] 5. Lining ring measurement

[0459] The measurement of lining ring segments includes measuring the ring center deviation, ring ovality and ring posture of the lining ring. The lining ring segments are measured once for no less than 3 to 5 rings (each ring is 1.5m), and each ring is measured during the measurement, and the front end face of the ring to be measured is measured. When measuring adjacent lining rings, 5 ring segments are overlapped and measured. The allowable error of the ring segment plane and elevation measurement is ±15mm. After the shield measurement data is sorted out, it shall be reported to the shield operator in a timely manner.

[0460] (8) Measurement at the excavation stage

[0461] 1) Contact measurement

[0462] 1. Ground near-well wire measurement

[0463] From the ground control point, use the near-well wire to measure the coordinates and azimuth to the receiving well. The ground near-well wire should be attached to the precision wire point, and the near-well point should be in sight with the precision wire point to make the orientation most favorable. In addition to setting fixed marks at the near-well point, temporary marks can be set at other ground approaching wire points. The total length of the ground near-well wire cannot exceed 350m, and the number of wire sides should not exceed 5. The near-well wire point should be measured according to the technical requirements of the precision wire network measurement, and the shortest side length should not be less than 50m. The point error of the near-well point is within ±10mm.

[0464] 2. Surface elevation measurement near the well

[0465] The elevation of the near-well point should be directly measured using the second-class leveling point, and a closed leveling line should be formed. No less than two elevation points should be buried to facilitate verification.

[0466] 3. Directional Measurement

[0467] In the receiving well, the ground coordinates and directions are transmitted to the well through the connection triangle orientation measurement, and the position of the receiving frame is determined in combination with the central axis of the tunnel.

[0468] 2) Shield machine guide rail positioning measurement

[0469] The difference between the center line of the shield machine guide rail and the designed tunnel center line should be less than 3mm, the difference between the front and rear elevations of the guide rail and the designed elevation should be less than 3mm, and the bottom of the guide rail should be solid and flat.

[0470] 3) Receiving frame positioning measurement

[0471] The receiving frame positioning measurement includes the height, pitch, yaw, etc. of the receiving frame, and whether the bottom of the receiving frame is solid and flat. The stability of the receiving frame directly affects whether the shield machine can receive the shield machine normally and smoothly.

[0472] 4) Center measurement of embedded steel ring portal

[0473] The center of the embedded steel ring is measured at the point approved by the third-party monitoring agency in the receiving shaft, and the vehicle result is reviewed by the third-party monitoring agency to determine the deviation between the center of the embedded steel ring and the design axis, so as to adjust the final exit posture of the shield machine and ensure the smooth exit and reception of the shield machine.

[0474] 5) Shield machine attitude arrival measurement

[0475] The shield machine attitude arrival measurement includes the measurement of horizontal yaw, pitch and torsion.

[0476] Before arriving, use the underground control point to manually re-measure the shield posture, and promptly compare the manually re-measured data with the data recorded by the automatic guidance system. When the difference is large, use the total station to check the coordinates of the laser station and the rear-view prism point, and modify the setting parameters in the automatic measurement system to ensure the correct shield posture during excavation. Manual re-measurement of the shield posture is performed every 5-10 rings. When the excavation reaches 100m, a re-measurement of the underground wire including the connection measurement is performed.

[0477] For the shield posture of the last fifty rings, the actual shield excavation axis, the design axis and the center of the tunnel should be comprehensively adjusted. If the center of the tunnel meets the design and specification requirements, the excavation will be controlled according to the actual center line of the tunnel. If correction is required, the principle of small correction must be followed, and each ring shall not exceed 4mm.

[0478] 6 Shield acceptance construction

[0479] 6.1 Shield machine arrival construction process

[0480] The shield machine arrival receiving construction refers to the entire construction process from 50m before the shield machine arrives at the next station receiving well to the shield machine passing through the interval tunnel and entering the station or being lifted out of the well and pushed onto the shield receiving base. Its work content includes: shield machine positioning and receiving tunnel door position verification measurement, stratum reinforcement, tunnel door treatment, installation of tunnel door ring sealing equipment, installation of receiving base, etc.

[0481] 6.2. Preparation before the arrival of the shield machine

[0482] 1. Shield machine positioning and receiving tunnel door position verification measurement

[0483] When the shield machine is advanced to the shield reaching range, the position of the shield machine is accurately measured to clarify the relationship between the central axis of the formed tunnel and the central axis of the tunnel design. At the same time, the position of the receiving portal is rechecked and measured to determine the penetration posture of the shield machine and the excavation correction plan. When considering the penetration posture of the shield machine, pay attention to two points: one is the deviation between the central axis of the shield machine when it penetrates and the tunnel design axis, and the other is the deviation of the receiving portal position. Take these factors into consideration and make appropriate adjustments based on the central axis of the tunnel design. Correction should be completed step by step, and the correction amount of each ring should not be too large.

[0484] 2. Soil reinforcement and reinforcement effect detection of the receiving tunnel section

[0485] For details, please refer to the previous content of "Shield Tunnel Entry and Exit Tunnel End Reinforcement". The reinforcement effect shall be checked one month before arrival, and the reinforcement effect shall be tested by core sampling. If the effect is not ideal, additional reinforcement measures shall be taken to meet the shield tunneling requirements at the station.

[0486] 3. Installation of door seal

[0487] In order to prevent the debris pushed out by the shield machine when entering the tunnel from damaging the curtain rubber sheet, the tunnel gate waterproofing device is installed after the tunnel gate is broken for the first time and the debris is completely cleaned up.

[0488] 4. Installation of receiving base

[0489] The central axis of the receiving base should be consistent with the tunnel design axis, and the shield machine exit posture should also be taken into account. In addition to adapting to the line conditions, the track surface elevation of the receiving base should be appropriately lowered by 20mm to allow the shield machine to smoothly get on the base. In order to ensure that there is enough reaction force for assembling the segments after the shield cutterhead is penetrated, the receiving base is installed in the direction of the shield entering the tunnel + a certain slope. Special attention should be paid to the reinforcement of the receiving base, especially the longitudinal reinforcement, to ensure that the shield machine can smoothly reach the receiving base.

[0490] 6.3. Shield machine arrives for construction

[0491] 1. Advance according to the through-state of the shield machine and the excavation correction plan. The correction should be completed step by step, and the correction amount for each link should not be too large.

[0492] 2. In addition to achieving the purpose of deviation correction, the excavation of the shield arrival section should also pay special attention to the excavation control of the last 10m section, because the disturbance of the stratum by the shield excavation in the last 10m near the tunnel gate is extremely obvious. Therefore, reasonable excavation parameters should be determined according to the geological conditions of the arrival section. When receiving, follow low speed, small thrust, reasonable soil bin pressure and timely and full synchronous grouting volume. Ensure the overall safety of shield reception. When the shield machine reaches the station retaining pile, the soil bin pressure will slowly decrease, and the soil pressure on the face will be difficult to establish, which can easily cause surface collapse and then cause ground pipeline ruptures. Therefore, reasonable construction parameters such as soil bin pressure, timely synchronous grouting, and uniform and continuous operation methods should be ensured to receive the shield.

[0493] The construction parameters of the receiving section are proposed as follows:

[0494] (1) Soil bin pressure: 0.3~0.4Mpa;

[0495] (2) The excavation speed shall not exceed 10 mm / min;

[0496] (3) The thrust of the shield machine is controlled between 600 and 1000 tons;

[0497] (4) Cutter torque: not more than 2000KN*M;

[0498] (5) Synchronous grouting volume: 5-7 cubic meters;

[0499] 3. After the shield machine enters the arrival section, strengthen surface settlement monitoring and provide timely feedback to guide excavation.

[0500] 4. When the cutterhead of the shield machine is less than 10m away from the through-hole mileage, during the excavation process, a dedicated person shall be responsible for observing the changes in the exit of the tunnel, always keeping in touch with the shield machine driver, and adjusting the excavation parameters in a timely manner.

[0501] 5. After the assembled pipe segments enter the reinforcement range, secondary grouting is carried out and the slurry is changed to quick-hardening slurry to block the mud and water outside the reinforcement area in advance.

[0502] 6. Assembly of the last few rings of segments

[0503] When the shield machine reaches the excavation stage, the thrust of the shield decreases. When the tunnel is penetrated, there is no reverse thrust in front of the shield, which will cause the annular joints between the segments to be loose and cause water leakage. Therefore, effective measures must be taken to ensure the assembly quality of the final segments. The details are as follows:

[0504] A: Install the tensioning device and connect the last 20 rings of segments one by one. First, assemble the special steel plate at the longitudinal hand hole and tighten it with the segment bolts. Then, weld the angle steel to the steel plate after assembling each ring of segments. As shown in the figure.

[0505] B: Reasonable segment assembly points to avoid rigid dragging of segments by the shield tail. The segment assembly points should comprehensively consider the linear requirements and the shield tail clearance. When the two cannot be met at the same time, the shield tail clearance should be given priority to ensure the quality of the tunnel lining.

[0506] C: When the tail machine enters the soil reinforcement area at the end, the slurry is changed to quick-hardening slurry. When the tail machine pushes out the sealing ring at the opening, the position of the fan-shaped pressure plate at the opening is quickly adjusted to ensure the temporary sealing effect of the opening.

[0507] (7) When the shield shell of the front body of the shield machine is pushed out of the tunnel, the folding plate is adjusted by the wire rope on the clamp ring to press the rubber curtain as tightly as possible to prevent the leakage of mud and slurry from the tunnel. When the segment is dragged out of the shield tail, the wire rope is tightened again so that the plate can press the rubber curtain tightly, allowing the curtain to continue to play a sealing role.

[0508] (8) Since the thrust of the shield machine is relatively small when it arrives at the station, the connection between the segments near the tunnel gate is not tight enough, so the bolts of the last 20 segments are tightened and re-tightened. Channel steel is used to tighten the last 20 segments along the longitudinal direction of the tunnel to connect the last 20 segments into a whole to prevent the segments from loosening and affecting the sealing and waterproofing effect.

[0509] 6.4. Precautions for the arrival of shield machine for construction

[0510] (1) Before the arrival of the shield machine, check the reinforcement quality of the soil at the end to ensure that the reinforcement quality meets the design requirements.

[0511] (2) Before arriving, prepare emergency supplies and tools such as sandbags, water pumps, water pipes, square timber, and pneumatic cannons inside the cave entrance.

[0512] (3) Prepare communication tools inside and outside the cave and lighting equipment inside the cave.

[0513] (4) Increase the frequency of surface subsidence monitoring and provide timely feedback on monitoring results to guide construction.

[0514] (5) Apply grease to the inside of the rubber curtain to prevent the blade from scratching the curtain and affecting the sealing effect.

[0515] (6) When the shield machine cutterhead is 0.5 m away from the tunnel portal face, the debris in the soil bin should be emptied as much as possible to reduce the pressure on the tunnel portal and end wall to ensure the safety of the tunnel portal concrete excavation construction.

[0516] (7) The several rings of segments installed after the shield has penetrated must be grout-filled and dense, and must be tightened in time to prevent the segments from sinking, shifting, and leaking.

[0517] 7. Abnormal situation handling measures and emergency rescue measures

[0518] 1. Emergency measures for sand and water gushing during initial excavation

[0519] 1. Analysis of risk factors: Due to the abundant groundwater at the start of this excavation, if the initial tunnel gate reinforcement and end dewatering are not in place, sand and water gushing accidents may easily occur during the initial excavation of the shield.

[0520] 2. Disposal measures: Apply butter to the cutter head and sealing device before starting to prevent the cutter head on the cutter disc from damaging the hole sealing device. After the shield tail has completely entered the extension ring, immediately seal the hole ring. First, open the shield tail grease system to inject sufficient shield tail grease into the shield tail, and then pressurize the double liquid slurry into the hole ring through the reserved grouting hole of the pipe segment to seal it.

[0521] 2. Emergency measures for deformation of reaction frame and displacement of starting bracket

[0522] 1. Analysis of risk factors: The shield machine itself is too heavy during the forward movement, and the thrust of the jack to push back the starting bracket is too large. If the reaction frame and the starting bracket are not fixed in place, the reaction frame and the starting bracket will be deformed and shifted, affecting the starting of the shield machine.

[0523] 2. Preventive measures: Strictly check the reinforcement of the reaction frame and the starting bracket before starting to prevent deformation of the reaction frame and displacement of the starting bracket during the starting process. Use a total station to monitor the displacement of the reaction frame and the starting bracket in real time.

[0524] 3. Disposal measures:

[0525] 1) Support and reinforce the deformed position;

[0526] 2) After the starting bracket is pushed back to the starting position with a jack, measure whether the shield machine posture is good. When the shield machine posture verifies the starting standard, the bracket is reinforced.

[0527] 3. Emergency measures for steel ring plate falling off

[0528] 1. Analysis of risk factors:

[0529] 1) When the shield machine was started, the shield body was close to the rubber curtain. During the advancement process, the excessive friction resistance caused the steel ring plate of the tunnel portal to fall off easily; 2) The steel ring plate of the tunnel portal was not properly reinforced during the main construction of the station.

[0530] 2. Preventive measures:

[0531] 1) During the construction of the main structure, the fixation of the steel ring plate must be strictly checked, and the pouring of the portal concrete can only be carried out after the fixation is qualified;

[0532] 2) Check the fixing of the steel ring plate before starting the shield tunnel to ensure that the steel ring plate is stable and firm.

[0533] 3. Disposal measures: If the steel ring plate is found to fall off during the initial excavation process, stop excavation immediately, quickly drive a Φ20 25cm long expansion bolt and a steel plate into the falling position to secure the original steel ring plate, and continue excavation after ensuring stability.

[0534] 4. Emergency measures for rubber cord damage and leakage

[0535] 1. Analysis of risk factors:

[0536] 1) When the shield machine starts to move, the rubber curtain is squeezed by the shield machine and damaged;

[0537] 2) Due to improper operation at the start of the shield, the cutter head rotates and the rubber curtain is damaged;

[0538] 3) When the shield machine is excavating, the grouting pressure is too high, and the rubber curtain and the pipe segment are not squeezed tightly, causing leakage.

[0539] 2. Disposal measures:

[0540] 1) When the rubber cord is damaged, squeeze it with other thick rubber and then fix it with steel plate expansion bolts;

[0541] 2) When the rubber curtain leaks, use steel plates and expansion bolts to squeeze and fix it;

[0542] 3) After the shield tail has completely entered the two rings of soil, double liquid grouting is carried out to seal the tunnel entrance to prevent water leakage and grout leakage.

[0543] V. Measures for dealing with ground subsidence

[0544] Contact the monitoring unit to coordinate matters such as intensified monitoring, and promptly report the monitoring situation to the project department. When ground subsidence occurs, immediately organize parameter consultations to clarify the cause of the subsidence, and promptly report to the property owner. Both parties coordinate the next emergency matters and arrange ground grouting and secondary grouting in the tunnel.

[0545] 6. Anti-caking

[0546] Do a good job in improving the excavation soil during the excavation process, appropriately reduce the excavation speed, and avoid the risk of cutterhead cake formation.

[0547] 7. Delayed Settlement

[0548] The strata of the Jin-San-Zhonghe Longdengshan access line section are mainly mudstone strata, and the ground along the line is Zhongbai Avenue. After entering Zhonghe Town, the ground traffic volume is large and the traffic is dense, which has high requirements for road settlement shield construction, and it passes through buildings (structures) and pipelines. In view of the above characteristics, the following shield measures are considered in shield construction:

[0549] (1) Taking into account the looseness coefficient of each stratum and groundwater and other factors, the theoretical excavation volume of each ring is calculated in advance. During excavation, a dedicated person is assigned to calculate the actual excavation volume by ring and compare it with the theoretical value.

[0550] (2) When the ground excavation volume exceeds the theoretical value by 5%, the monitoring data outside and inside the tunnel should be analyzed, and the surrounding rock changes and stratum characteristics should be inverted by analyzing the soil samples. If it is inferred that it is indeed over-excavation, the excavation speed of the screw conveyor should be adjusted to increase the content of the soil in the soil bin. In order to protect the upper buildings or pipelines, full bin excavation or air pressure non-full bin excavation should be required when necessary.

[0551] (3) Based on the statistical over-excavation position and over-excavation amount, the over-excavation amount shall be replenished in time through shield tail grouting. If necessary, secondary grouting or double liquid grouting shall be carried out at the over-excavation location. The grouting pressure at the shield tail grouting hole shall be greater than the water and soil pressure at the tunnel burial depth.

[0552] (4) Use two grouting systems (simultaneous grouting and secondary grouting system) to ensure that the grouting volume meets the requirements.

[0553] (5) According to theoretical calculations, the construction gap volume between the pipe segment and the surrounding rock is 4.05m3 ring (1.5m). Based on previous construction experience, to achieve a better filling effect, the grouting volume in the pebble soil layer should be controlled at more than 150-200%, that is, 6-8m3 per ring. The synchronous grouting volume in the mudstone formation should not be less than 5m 3 .

[0554] (6) The grouting volume should also be controlled in combination with the grouting pressure. The grouting pressure is generally controlled between 2.5 and 4 bar. If the pressure increases significantly, the grouting should be temporarily stopped to prevent the grouting pressure from penetrating the formation or damaging the pipe segment.

[0555] (7) Information-based construction should be adopted, on-site monitoring should be strengthened to understand the deformation laws of the surrounding rock and soil, and corresponding engineering measures should be taken in a timely manner.

Claims

1. A shield construction method for a sand and gravel stratum tunnel, comprising the following steps: Step 1: During the initial construction phase of the shield tunnel, the end portal is reinforced at the beginning of the tunnel (5) entering and exiting the tunnel. The end portal reinforcement includes grouting reinforcement in the pipe shed, grouting reinforcement of the sleeve valve pipe on the ground, and / or plain concrete pile reinforcement; The grouting reinforcement in the pipe shed includes: arranging the opening (2) of the upper pipe shed (1) along the outside of the steel pipe ring (3) of the tunnel portal, the steel pipe ring has an insertion angle of 1-2° to the outside of the center of the tunnel portal, and the working platform (4) is arranged below the pipe shed (1); the steel pipe ring (3) adopts a seamless grouting steel flower pipe, and the two sections of the grouting steel flower pipe of the pipe shed are connected by a connecting sleeve steel pipe (6) threadedly, and the joints of two adjacent steel flower pipes are staggered and sleeved; Grouting holes (2) are provided on the steel flower tube, and the holes are arranged in a plum blossom shape; The ground sleeve valve pipe reinforcement includes: reinforcing the ground sleeve valve pipe (7) at the entrance and exit of the tunnel (5), the reinforcement range is outside the shield outline, above the arch and the tunnel bottom, and the sleeve valve pipe is arranged in a plum blossom shape; The plain concrete piles are reinforced with double rows of plain concrete piles; Step 2, installing the starting bracket (8) on the starting base (13); Step 3, installing a reaction frame support system, the support system comprising a reaction frame (9), mutually welded bottom straight support beams (10), side wall straight support columns (11), and an inclined support (12), wherein the inclined support (12) forms an angle of 45° with the ground, one end of the inclined support is welded to the reaction frame side wall straight support column (11), and the other end is welded and fixed to a steel plate pre-buried in the ground; the reaction frame is welded to the station middle plate by section steel; When the reaction frame is fixedly installed on the starting base (13), the included angle between the vertical direction of the horizontal axis of the starting base and the reaction frame is less than ±2‰, the vertical trend deviation of the shield posture and the design axis is less than 2‰, and the horizontal trend deviation is less than ±3‰; Step 4: Installing the tunnel portal extension steel ring sealing structure (15): comprising: fixing a pre-buried steel ring plate (152) on the inner lining wall (151) of the tunnel enclosure structure (1510); fixing the pre-buried steel ring plate with the tunnel portal extension steel ring (157) by bolts (153); fixing the other end of the tunnel portal extension steel ring with a folding plate (156) by bolts (153); and providing an annular sealing rubber between the tunnel portal extension steel ring and the folding plate (156) in sequence. plate (154), a clamping ring plate (155); the inner lining wall is a reinforced wall in the hole circle above the tunnel; the hole circle is located above the pipe segment (14) installed before the tunnel shield machine is constructed; the clamping ring plate (155) is an arc-shaped clamping ring plate; the folding plate is a fan-shaped folding plate composed of a piece 1 (1561) and a piece 2 (1562), and the pieces 1 and 2 are hinged or axially connected; the retaining piles within the shield tunnel around the extended steel ring of the tunnel portal are made of glass fiber reinforcement; Step 5, assembling the negative ring segment (14): the negative ring segment is connected to the reference ring of the reaction frame (9) by bolts. After the negative ring segment is assembled using the whole ring of the segment, the negative ring segment is pushed out of the shield tail by a thrust jack and fastened to the reference ring of the reaction frame (9). A triangular support frame (16), an I-beam (17), and a wooden wedge (18) are used to stabilize the negative ring segment on the starting bracket (8) and tighten the segment ring. The deviation between the elevation and the center of the negative ring segment (14) and the center of the shield shell of the shield machine on the starting reaction frame is less than ±5 mm.

2. The sand and gravel stratum tunnel shield construction method according to claim 1 further comprises the following steps: Step 6: Shield tunneling construction: The geology of the starting section of the shield tunneling section is mainly medium-dense pebble strata, and the starting parameter values ​​of the shield tunneling are: 10-meter section of the starting section: soil pressure 0.3-0.4 bar, excavation speed 30-50 mm / min, torque 1500-2100 KN·m, thrust <800 t, cutter head speed 0.9 r / min or more, improved method and injection volume foam 110 L / ring, slag discharge 58-63 cubic meters / ring, synchronous grouting volume 5-6 cubic meters / ring, synchronous grouting pressure 0.2-0.4 bar; Trial excavation of 90 meters section: soil pressure above 0.6 bar, excavation speed 40-60 mm / min, torque 1800-2300 KN·m, thrust 1000-1500 t, cutter head speed above 1.5 r / min, improved method and injection amount of foam 110L / ring, slag discharge 58-63 cubic meters / ring, synchronous grouting amount 5-6 cubic meters / ring, synchronous grouting pressure 0.2-0.4 bar.

3. The method for constructing a tunnel in sand and gravel stratum according to claim 1 or 2, further comprising the following steps: Step seven, slag improvement: add a mixed mud of a foaming agent and sodium bentonite and mix it with the soil slag, the mixed mud comprising foam, bentonite and water, the weight parts of which are 8-12 parts water, 0.5-1.5 parts bentonite and 0.1-0.3 parts foam, and the slump of the prepared mud is within 20 cm; the viscosity of the foaming agent is 0.003-0.2 Pa·s, and the pH value is 7.3-8.

4. The method for constructing a tunnel in sand and gravel strata according to claim 1 or 2, further comprising the following steps: Step 8: When the shield tail passes through the tunnel seal, synchronous grouting or secondary supplementary grouting is performed. The actual grouting volume is 5-7m3 / ring. The synchronous grouting comprises: grouting cement mortar synchronously through the grouting holes on the pipe segment (14), the grouting gel time is 6-8h; the strength of the consolidated body is not less than 0.5Mpa in one day, not less than 2MPa in three days, and the compressive strength is not less than 5MPa in 28 days; the slurry shrinkage value is: the consolidation shrinkage rate is less than 5%; the slurry consistency is 8-12cm; the slurry specific gravity is 1.7-2.0g / cm3; the slurry stability is: the decantation rate is less than 5%; the synchronous grouting slurry is cement mortar, which is made of the following components by weight: cement 200-240, fly ash 360-400, bentonite 80-120, sand 700-860, water 400-500; the synchronous grouting pressure is 0.25-0.4MPa; The secondary supplementary grouting uses cement slurry, including a two-liquid slurry mixture of cement and water glass, or a single-liquid slurry mixed with water and cement; the weight ratio of the cement slurry is 1:1, the slurry density is 1.44 (g / cm3), the setting time is 20 to 48 seconds, and the secondary grouting pressure is 0.3 to 0.5 MPa.

5. The sand and gravel stratum tunnel shield construction method according to claim 1 or 2, further comprising the following steps: Step 9: Segment assembly: Prefabricated segments are used for lining, segments are assembled with staggered joints, and segment joints are waterproofed with rubber waterstop strips; three sealing brushes are installed at the tail of the shield machine, and sealing grease is added to the sealing brushes at the same time; First assemble the bottom segments, then install them crosswise from bottom to top, and finally assemble the locking blocks; during assembly, each ring of segments is evenly distributed and the height difference of the ring surface is strictly controlled; after tightening with the jack, install the segment connecting bolts.

6. The sand-pebble stratum tunnel shield construction method according to claim 1 or 2, further comprising the following steps: Step 10, initial measurement of the posture of the shield machine (19); Step 11: Shield machine excavation measurement, segment position measurement, shield attitude measurement, lining ring segment measurement, ground near-well wire measurement, ground near-well elevation measurement, directional measurement, shield machine guide rail positioning measurement, receiving frame positioning measurement, and embedded steel ring portal center measurement; Step 12: Shield machine attitude arrival measurement: including measurement of horizontal yaw, pitch, and torsion.

7. The sand and gravel stratum tunnel shield construction method according to claim 1 or 2, further comprising the following steps: Step 13: Shield machine arrives at receiving construction: positioning of shield machine and verification and measurement of receiving tunnel door position, stratum reinforcement, tunnel door treatment, installation of tunnel door ring sealing equipment, and installation of receiving base; The positioning of the shield machine and the re-measurement of the receiving portal position before the arrival of the shield machine: one is the deviation between the central axis of the shield machine when it penetrates and the design axis of the tunnel, and the other is the deviation adjustment of the receiving portal position.

8. The sand-pebble stratum tunnel shield construction method according to claim 1 or 2, further comprising the following steps: Step 14: When the shield machine reaches the last 10m section of excavation, determine the reasonable excavation parameters. When receiving the tunnel, follow the low speed, small thrust, reasonable soil bin pressure and timely and full synchronous grouting volume to ensure reasonable construction parameters such as soil bin pressure, timely synchronous grouting, and a uniform and continuous operation method to receive the shield machine. The construction parameters of the receiving section are as follows: (1) Soil bin pressure: 0.3~0.4Mpa; (2) Excavation speed not exceeding 10mm / min; (3) Shield machine thrust is controlled between 600 and 1000t; (4) Cutter head torque: not exceeding 2000KN*M; (5) Synchronous grouting volume: 5~7 cubic meters.

9. The sand-pebble stratum tunnel shield construction method according to claim 1 or 2, further comprising the following steps: Step 15, assembly of the last few rings of segments:

1. Use the tensioning device to connect the last 20 rings of segments one by one. First, assemble the special steel plate at the longitudinal hand hole and tighten it with the segment bolts. Then, weld the angle steel to the steel plate after assembling each ring of segments.

2. Reasonable segment assembly points to avoid rigid dragging of segments by the shield tail; the segment assembly points should comprehensively consider the linear requirements and the shield tail gap. When the two cannot be met at the same time, the shield tail gap should be given priority to ensure the quality of the tunnel lining; 3. When the tail machine enters the soil reinforcement area at the end, the slurry is changed to quick-hardening slurry. When the tail machine pushes out the sealing ring at the opening, the position of the fan-shaped pressure plate at the opening is quickly adjusted to ensure the temporary plugging effect of the opening.

4. When the shield shell of the front body of the shield machine is pushed out of the tunnel gate, the folding plate is adjusted by the wire rope on the clamp ring of the plate to press the rubber sheet as tightly as possible to prevent the leakage of mud and slurry from the tunnel gate; when the segment is dragged out of the shield tail, the wire rope is tightened again so that the plate can press the rubber sheet tightly, so that the sheet can play a sealing role all the time, so that the segment is tightened and the tunnel gate seal is tightened; 5. Complete the bolt tightening and re-tightening steps of the last 20 rings of segments, and use channel steel to tighten the last 20 rings of segments along the longitudinal direction of the tunnel to connect the last 20 rings of segments into a whole to prevent the segments from loosening and affecting the sealing and waterproofing effect; 6. Shield machine arrives at the construction site: When the cutter head of the shield machine is 0.5m away from the tunnel face, the debris in the soil bin is emptied, and the segments installed after the shield machine is through are ensured to be grouting full and dense, and are tightened in time to prevent the segments from sinking, shifting and leaking.

10. The sand-pebble stratum tunnel shield construction method according to claim 1 or 2, further comprising the following steps: Step 16, abnormal situation treatment steps for delayed settlement: (1) Calculate the theoretical excavation volume of each ring in advance. During excavation, count the actual excavation volume of each ring and compare it with the theoretical value; (2) When the ground excavation volume exceeds the theoretical value by 5%, analyze the monitoring data outside and inside the tunnel, and through the analysis of soil samples, judge the changes in the surrounding rock and invert the characteristics of the stratum. If it is inferred that it is indeed over-excavation, adjust the excavation speed of the screw conveyor to increase the content of the soil in the soil bin; in order to protect the upper buildings or pipelines, it is necessary to excavate with a full bin or with air pressure and not full bin; (3) Based on the statistical over-excavation position and over-excavation amount, the over-excavation amount shall be replenished in time through shield tail grouting. If necessary, secondary grouting or double-liquid grouting shall be carried out at the over-excavation location; the grouting pressure at the shield tail grouting hole shall be greater than the water and soil pressure at the tunnel burial depth; (4) Two grouting systems are used: synchronous grouting and secondary grouting system to ensure that the grouting volume meets the requirements; (5) According to theoretical calculation, the construction gap volume between the segment and the surrounding rock is 4.05m 3 The grouting volume in the pebble soil layer is controlled at more than 150-200%, that is, the grouting volume per ring is 6-8m 3 ; The synchronous grouting volume of mudstone formation is not less than 5m 3 ; (6) The grouting volume should also be controlled in combination with the grouting pressure. The grouting pressure should be controlled between 2.5 and 4 bar. If the pressure increases significantly, the grouting should be temporarily stopped to prevent the grouting pressure from penetrating the formation or damaging the pipe segment. (7) Information-based construction should be adopted, on-site monitoring should be strengthened to understand the deformation laws of the surrounding rock and soil, and corresponding engineering measures should be taken in a timely manner.

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