A construction method for shield tunneling in shallow backfill area with close side penetration of bridge pile foundation

Abstract

The present invention specifically discloses a construction method for a shield tunneling bridge pile foundation in a shallow backfill area at a short distance, comprising the following steps: step 1: constructing an isolation pile between the bridge pile foundation and the tunnel structure; step 2: constructing a cap beam on the top of the isolation pile; step 3: grouting and reinforcing the backfill area; step 4: constructing a cover plate and backfilling with counter pressure; step 5: conducting a test section excavation to determine the overall excavation parameters of the shield tunneling process; step 6: controlling and monitoring the shield tunneling process; step 7: synchronous grouting and secondary reinforcement grouting during the shield tunneling process. The method of the present invention can safely and smoothly complete the construction of the pile foundation through the shallow backfill area, and will not cause significant impact on the existing pile foundation and its surrounding environment at a short distance.

Description

Technical Field

[0001] The invention relates to the technical field of subway shield tunnel construction, and in particular to a construction method for a shield tunnel to penetrate a bridge pile foundation at a short distance in a shallow backfill area. Background Art

[0002] Shield tunnel construction is a construction method of building tunnels underground. The shield is used as a machine to excavate underground soil, support soil and assemble tunnel linings. One ring is excavated and one ring is assembled, and the work is repeated until the entire tunnel is completed. Compared with the traditional drilling and blasting method, the shield method has the advantages of high degree of automation, strong adaptability to different geological conditions, little impact on urban residents and buildings, and is conducive to controlling surface subsidence in soft strata, and high safety.

[0003] The close side penetration of bridge pile foundation by shield in shallow backfill area is one of the major risk sources in the construction process. If the construction is not done properly, it may seriously affect the safety of the existing pile foundation and its surrounding environmental facilities. Summary of the invention

[0004] The purpose of the present invention is to provide a construction method for a bridge pile foundation with a shield machine in a shallow backfill area at a short distance, so as to solve the above-mentioned technical problems existing in the prior art.

[0005] In order to achieve the above object, the technical solution of the present invention is:

[0006] A construction method for a bridge pile foundation with a shield tunnel in a shallow backfill area at a short distance, comprising the following steps:

[0007] Step 1: Install isolation piles between the bridge pile foundation and the tunnel structure;

[0008] Step 2: construct a cap beam on the top of the isolation pile;

[0009] Step 3: Grouting reinforcement is performed on the backfill area. Grouting reinforcement of the backfill area is divided into surface grouting and surface curtain grouting, and sleeve valve pipe grouting technology is used for reinforcement;

[0010] Step 4: Cover plate construction and backfilling. After the grouting reinforcement construction is completed, cover plates are constructed between the crown beams and backfilled with sandbags to ensure that the soil thickness is ≥ 6m. The crown beams and cover plates connect the isolation piles into a whole to form a closed frame.

[0011] Step 5: Conduct excavation of the test section to determine the overall excavation parameters of the shield side penetration process;

[0012] The test section is the 100m range before the shield starts, and the shield excavation in the test section is completely controlled according to the side penetration of the target bridge pile foundation;

[0013] Step 6: Shield side tunneling process control and monitoring;

[0014] (1) The control measures for the shield side-crossing excavation process include shield excavation direction control, shield excavation process deviation correction control, and shield excavation process soil bin pressure balance control;

[0015] Shield tunneling direction control: The shield tunneling direction is controlled by using the shield thrust cylinder operated in sections;

[0016] Deviation correction control during shield tunneling: including rolling deviation correction, vertical deviation correction, and horizontal deviation correction;

[0017] Earth bunker pressure balance control during excavation: During excavation, the dynamic balance between earth bunker pressure and water and soil pressure on the working surface is always ensured. At the same time, the screw conveyor is used to carry out earth discharge operations corresponding to the shield advance amount. During excavation, the balance between the excavated soil volume and the discharged soil volume is always maintained to keep the front soil stable.

[0018] (2) Monitoring of the shield tunneling process includes strengthening the deformation monitoring of shallow soil layers and bridges, and continuously adjusting and optimizing tunneling parameters based on the monitoring data;

[0019] Step 7: Synchronous grouting and secondary reinforcement grouting during shield side tunneling;

[0020] During the side-penetration excavation process of the shield, synchronous grouting is carried out through the shield tail grouting pipe while excavating, and according to the monitoring results, secondary reinforcement grouting is carried out on the outer stratum of the segment through the segment lifting hole; the synchronous grouting adopts the dual control technology of grouting volume and grouting pressure, and the grouting volume is controlled at 120%~140% of the theoretical building gap. The grouting pressure should be greater than the water and soil pressure, and the grouting pressure is set to 0.2MPa~0.4Mpa; the grouting pressure of the secondary reinforcement grouting is 0.3~0.5Mpa, and the grouting volume is determined according to the monitored gap and the results of monitoring and measurement.

[0021] Furthermore, in step 2, the width of the crown beam is the same as the diameter of the isolation pile, which is 0.5m, and the height is 0.4m.

[0022] Furthermore, in step 3, the grouting material used for surface grouting is cement slurry, and the grouting material used for surface curtain grouting is cement-water glass slurry.

[0023] Further, in step 3, the grouting construction is divided into the following three steps:

[0024] (1) The outermost two rows of curtain grouting holes are constructed on both sides of the left and right lines of the tunnel and curtain grouting is carried out;

[0025] (2) Construct reinforcement grouting holes in a plum blossom pattern according to the designed spacing and perform preliminary filling and grouting;

[0026] (3) Complete the remaining reinforcement grouting holes according to the plum blossom-shaped arrangement and carry out reinforcement grouting.

[0027] Furthermore, in step 3, the sleeve valve tube adopts a PVC tube with an outer diameter of 48 mm and an inner diameter of 42 mm.

[0028] Furthermore, in step 4, the thickness of the cover plate is 0.2 m, and the grade of the cover plate concrete is C40.

[0029] Further, in step 5, the main construction tasks of the test section are as follows:

[0030] (1) The test section should accurately grasp the various shield construction parameters and summarize the impact of ground load on ground settlement;

[0031] (2) Run-in the various performances of the shield machine to provide a good technical and equipment guarantee for smooth passage through the backfill area;

[0032] (3) Understand the law of pressure changes in the excavation chamber during the crossing period, set the soil pressure in a timely and accurate manner, adjust the construction parameters in real time, and guide the construction; summarize the parameters such as the secondary grouting volume and grouting pressure in the tunnel, especially to prevent ground uplift while controlling settlement, and ensure driving safety;

[0033] (4) Control the shield axis and ground settlement. In particular, establish a settlement process curve for the test section and predict the settlement to guide subsequent construction;

[0034] (5) Strengthen ground monitoring in the test section, analyze and summarize the monitoring data of the test section, and understand the actual scope of ground subsidence caused by shield construction in the crossing section, so as to provide a realistic basis for subsequent monitoring and construction.

[0035] Furthermore, in step 7, the synchronous grouting uses cement mortar as the grouting material, the slurry consistency is 8-12 cm, the slurry stone rate is >95%, and the consolidated body strength is not less than 0.2 MPa in one day and not less than 2.5 MPa in 28 days.

[0036] Furthermore, in step 7, the secondary grouting uses cement-water glass double liquid slurry as the grouting material, the slurry consistency is 12.5-13.0 cm, the slurry stone rate is >97%, and the consolidated body strength is greater than 0.3 MPa in one day and greater than 4.5 MPa in 28 days.

[0037] Furthermore, in step 7, the secondary reinforcement grouting uses a KBY-50 / 70 grouting pump, and the grouting pipeline for the secondary reinforcement grouting is homemade, which can realize the functions of rapid connection and unloading and sealing to prevent leakage of grout, and is equipped with a grout stop valve.

[0038] The beneficial effects of the present invention are:

[0039] The present invention installs isolation piles between the bridge pile foundation and the tunnel structure, installs cap beams on the tops of the isolation piles, performs grouting reinforcement on the backfill area, and installs cover plates and counter-pressure backfill. The cap beams and the cover plates connect the isolation piles into a whole to form a closed frame. The test section excavation is carried out to determine the overall excavation parameters of the shield side penetration process, the shield side penetration excavation process is controlled and monitored, and the synchronous grouting of the shield tail and the secondary reinforcement grouting are strengthened. The pile foundation construction through the shallow backfill area can be completed safely and smoothly without causing obvious impact on the existing pile foundation and its surrounding environment in the close distance. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 The present invention discloses a bored cast-in-place pile construction process.

[0041] Figure 2 The present invention discloses a crown beam construction process. DETAILED DESCRIPTION

[0042] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0043] Technical Parameters

[0044] (1) Base layer: C20 concrete.

[0045] (2) The longitudinal and transverse force-bearing steel bars and distribution steel bars of concrete structural members should be hot-rolled steel bars of grade not less than HRB400;

[0046] (3) Steel bars: A-HPB300 and C-HRB400 steel bars are used, and the materials meet the requirements of the current national standards "Hot-rolled ribbed steel bars for reinforced concrete" and "Hot-rolled plain round steel bars for reinforced concrete" respectively.

[0047] (4) Steel structural components (such as steel sections, embedded steel plates, etc.): Q235 and Q345 steels should be used. The material of steel structural components should comply with the requirements of "Carbon Structural Steel" GB / T700 and "Low Alloy High Strength Structural Steel" GB / T1591, and have a factory certificate that complies with national standards.

[0048] (5) Welding rods: E43 welding rods are used for arc welding of Q235 steel plates and HPB300 steel bars, and E55 welding rods are used for arc welding of HRB400 steel bars. The chemical composition and mechanical properties of the weld metal should meet the requirements of "Welding rods for non-alloy steel and fine-grained steel" (GB / T5117-2012) and "Welding rods for heat-resistant steel" (GB / T5118-2012).

[0049] (6) Grouting: cement slurry (surface grouting), M10 cement mortar (simultaneous and secondary grouting), cement-water glass slurry (surface curtain grouting).

[0050] (7) The performance and quality of steel bars, steel plates, steel strands, steel sections, anchors, etc. must comply with the provisions of current national standards and industry standards, and should be accompanied by quality certificates or inspection reports for various performance indicators.

[0051] (8) The minimum net protective layer thickness of concrete under normal environmental conditions shall meet the minimum net protective layer thickness requirements. The steel bar protective layer thickness is the minimum allowable protective layer thickness. However, in order not to reduce the design effectiveness of the component, the protective layer thickness cannot be increased arbitrarily.

[0052] This embodiment is a side-through Qinggangxi Bridge pile foundation. The bridge is located in the backfill section. The horizontal distance between the tunnel side wall and the bridge pile is about 3.3m. The tunnel structure is located in the backfill, and the shallowest fill on the tunnel top is 3.2m.

[0053] Backfill section: Artificial fill is mainly plain fill. Plain fill is variegated, mainly clay soil with sandstone and mudstone (block) stone, the skeleton particle size is mainly 20-600mm, and locally greater than 1m, the content is generally 20-45%, in the thicker section, the block (crushed) stone content increases significantly, locally up to 50-60%, the particle size also increases, and there is a phenomenon of overhead, mainly loose to slightly dense, slightly wet. Among them: Right FCK2+928.942~Right FCK3+940 is located in the road construction area, with a thickness of 0.4~15.5m, which is formed by recent clearing and dumping, and the backfill time is about 1 to 5 months; Right FCK3+940~Right FCK4+184.682 The proposed line mainly runs along the main urban road, with a thickness of 8.3~35.1m, and the filling period along the line is generally 1 to 3 years.

[0054] The present invention discloses a method for constructing a bridge pile foundation by a shield machine in a shallow backfill area at a short distance, which mainly includes the following construction steps:

[0055] 1. Install isolation piles between the bridge pile foundation and the tunnel structure

[0056] φ500 isolation piles are set on both sides of the side-through bridge pile section tunnel, with 24 isolation piles on each side. In view of the low groundwater level in the rotary drilling area, the isolation piles are constructed by dry drilling and waterless concrete pouring.

[0057] Working status of rotary drilling: The power head drives the drill bit at the lower end of the drill rod during construction of the rotary drilling drill. The cutting edge at the lower end of the drill bit is used to cut and crush the soil layer. The cut soil is squeezed into the drill bucket. After it is full, the drill bucket is lifted out of the hole, the drilling rig chassis is rotated, and the drill bucket valve is opened to discharge the soil to the ground or directly unload it onto a car for transportation. This process is repeated until the bottom elevation of the hole is reached.

[0058] Bored pile construction process Figure 1 As shown: processing of working conditions → laying out and positioning → burying of guard piles → positioning of drilling rig → preliminary drilling → positioning of casing → placing casing → formal drilling → hole completion and cleaning → making of steel cage → placing of steel cage → placing of guide tube → pouring of concrete → leaving test blocks for pile body → keeping records of pile pouring → testing.

[0059] 2. Construct a cap beam on the top of the isolation pile

[0060] After the isolation pile construction is completed and passed the inspection, the crown beam is laid along the top of the isolation pile. The width of the crown beam is the same as the diameter of the isolation pile, which is 0.5m, and the height is 0.4m. The main reinforcement of the protection pile is anchored into the crown beam to connect the crown beam and the isolation pile into a whole, and the crown beams are connected with cover plates.

[0061] Crown beam construction process Figure 2 As shown: construction preparation → measurement and layout → trench excavation → removal of slag from isolation piles → pouring of cushion layer → reinforcement binding and hidden acceptance → formwork → concrete pouring → concrete curing.

[0062] 3. Grouting reinforcement of backfill area

[0063] Grouting reinforcement in backfill area is divided into surface grouting and surface curtain grouting. The grouting materials used are: ① cement slurry (surface grouting), ② cement-water glass slurry (surface curtain grouting).

[0064] (1) The sleeve valve pipe grouting technology is used for reinforcement. The horizontal range of the reinforcement range is 1.5m beyond the left and right structural edges of the tunnel, and the vertical range is 3m from the top of the tunnel to the weathered rock surface at the bottom of the tunnel. The left and right grouting holes are drilled using vertical hole grouting. The longitudinal spacing of the grouting holes in the left and right reinforcement range is 1.5m, and they are arranged in a plum blossom shape.

[0065] (2) Before grouting reinforcement is implemented, a field grouting test should be conducted. Different slurry ratios should be selected, starting from low pressure and large injection volume to final pressure and small injection volume. Through the test, the best grouting method and optimal grouting parameters should be sought with a small grouting volume. The slurry ratio, grouting pressure, diffusion radius and grouting effect should be fed back to the design to further guide the grouting design and ensure that the design is practical.

[0066] (3) Grouting construction is divided into the following three steps:

[0067] 1) Construct the outermost two rows of curtain grouting holes on both sides of the left and right lines and carry out curtain grouting.

[0068] 2) Construct reinforcement grouting holes in a plum blossom pattern with a spacing of 4.5m×4.5m, and carry out preliminary filling and grouting.

[0069] 3) Complete the remaining reinforcement grouting holes according to the plum blossom-shaped arrangement and carry out reinforcement grouting.

[0070] (4) As the artificial fill layer has a high rock content, is anisotropic and has a large discreteness, grouting should be carried out multiple times. The interval time should be determined based on the initial setting test results of the slurry and should not be greater than 4 hours.

[0071] (5) Sleeve valve pipe grouting mainly uses cement slurry, the water-cement ratio of cement slurry should be 0.6-0.8, the grouting pressure should be 0.8-1.0MPa, and cement-water glass slurry is used for sealing around the reinforcement ring. The grouting pressure should be 0.3-0.5MPa, but it can be appropriately increased to reach the through hole when punching the sleeve valve pipe. During grouting, the slurry concentration should be changed from dilute to concentrated step by step. Concentrated slurry can be directly injected in areas with high injection rate, and additives such as fly ash and water glass can also be added. When encountering overhead voids, M10 cement mortar can be used, and the grouting pressure should be appropriately increased, but should not be greater than 3.0MPa. The fluidity of cement mortar should be greater than 240mm, and the maximum particle size of fine sand should not be greater than 2mm.

[0072] (6) Ordinary Portland cement of PO 42.5 grade should be used, and water glass with a modulus of 2.2-3.4 and a concentration of 38-43Be' should be used.

[0073] (7) It is recommended that sleeve valve pipes use PVC pipes with an outer diameter of 48 mm and an inner diameter of 42 mm. The diameter of the grouting hole should be no less than 108 mm, and the depth of the grouting hole should be no less than 0.2 m into the medium-weathered rock surface. The curtain grouting hole should be no less than 1.5 m into the medium-weathered rock surface. The deviation of the grouting hole position should not be greater than 2 cm, the deviation of the grouting hole depth should not be greater than 10 cm, and the deviation of the verticality of the drill hole should not be greater than 1.5%.

[0074] (8) The diameter of the grouting hole is 108 mm. Effective grouting prevention measures, such as casing material, should be taken between the reinforced area and the non-reinforced area.

[0075] (9) Grouting is carried out in sections from bottom to top, and skip-hole grouting should be adopted, with the grouting sequence of first the periphery and then the middle. Based on the experience of similar stratum engineering, the effective diffusion radius of grouting is 0.6-0.8m, and the specific effective diffusion radius should be determined based on grouting tests. According to detailed survey data, the porosity of the fill is 10%-30%.

[0076] (10) Grouting reinforcement monitoring and measurement

[0077] Strengthen monitoring during the construction process. If ground cracks, accelerated settlement, etc. are found, construction should be stopped immediately and effective measures should be taken. Construction can only be continued after safety is confirmed by the on-site construction supervisor and reported to the owner and designers for confirmation.

[0078] 1) Before the grouting reinforcement construction, the construction unit should formulate a detailed construction monitoring plan based on the grouting plan. The construction monitoring during the grouting reinforcement mainly includes surface subsidence, settlement and deformation of the bridge substructure.

[0079] 2) During the grouting reinforcement construction, the monitoring points and control indicators for ground subsidence, bridge substructure settlement and deformation should be comprehensively considered in conjunction with shield tunneling construction monitoring.

[0080] 3) The monitoring frequency within the range of less than 20m before and after grouting construction shall be 1 to 2 times / day, and the monitoring frequency within the range of less than 50m before and after grouting construction shall be once / day.

[0081] The monitoring and measurement items and methods are shown in Table 1.

[0082] Table 1 Monitoring measurement items and methods

[0083]

[0084] 4. Cover plate construction and backfilling

[0085] After the grouting reinforcement construction is completed, a 0.2m thick cover plate is applied between the crown beams and sandbags are used for backfilling to ensure that the cover thickness is ≥6m. The crown beam and the cover plate connect the isolation piles into a whole to form a closed frame. Three 11.2m×6.5m cover plates are applied on the left and right lines, and each cover plate is applied on 8 isolation piles. The concrete grade of the cover plate is C40.

[0086] Construction process: Construction preparation → Measurement and layout → Trench excavation → Chiseling off the slag of the crown beam → Pouring the cushion layer → Binding the steel bars of the cover plate → Supporting the formwork → Pouring concrete → Removing the formwork → Backfilling with sandbags for counter pressure.

[0087] 5. Conduct excavation in the test section to determine the overall excavation parameters of the shield side penetration process

[0088] In order to ensure safe passage, a test section is set up. The test section is the 100m range before the shield tunneling. The shield tunneling in the test section is completely controlled according to the pile foundation of the target bridge to be tunneled. Based on the previous construction experience and construction parameters of the backfill area, this project conducts test section tunneling according to the stratum conditions during the tunneling process:

[0089] The main construction tasks of the test section are as follows:

[0090] (1) The test section should accurately grasp the various shield construction parameters and summarize the impact of ground load on ground settlement.

[0091] (2) Run-in the various performance features of the shield machine to provide good technical and equipment support for smooth passage through the backfill area.

[0092] (3) Understand the law of pressure changes in the excavation chamber during the crossing period, set the soil pressure in a timely and accurate manner, adjust the construction parameters in real time, and guide the construction; summarize the parameters such as the secondary grouting volume and grouting pressure in the tunnel, especially to prevent ground uplift while controlling settlement to ensure driving safety.

[0093] (4) Control the shield axis and ground settlement. In particular, establish a settlement process curve for the test section and make a prediction of the settlement to guide subsequent construction.

[0094] (5) Strengthen ground monitoring in the test section, analyze and summarize the monitoring data of the test section, and understand the actual scope of ground subsidence caused by shield construction in the crossing section, so as to provide a realistic basis for subsequent monitoring and construction.

[0095] 6. Preparation work before shield tunneling through bridge pile foundation

[0096] (1) Before the shield tunnels pass through, the ground on the left and right lines must be reinforced with isolation piles, cover plates, and surface grouting to fill the foundation and improve the stress on the stratum to ensure the shield tunnels can safely pass through the bridge pile foundation.

[0097] (2) An environmental survey should be completed on the existing roads and surrounding structures and pipelines, and the hydrological and geological conditions of the project should be further clarified. If any problems are found during the survey, they should be dealt with in advance.

[0098] (3) Pay attention to the selection of shield equipment system parameters, such as the cutter head opening rate (not less than 35%), increase the number of stirring rods, reasonable arrangement of cutters (no blind spots in cutting, clear height difference levels), etc., set reasonable bin pressure and excavation speed, ensure smooth soil discharge of the screw machine, and adopt shield construction auxiliary measures such as slag improvement, such as the use of foaming agents; equip the shield front shoulder with radial grouting holes. If necessary, inject special bentonite during the shield excavation process to timely fill the gap between the shield body and the soil caused by the shield machine excavation, thereby reducing the stratum loss during excavation.

[0099] (4) Before side crossing, the shield construction plan shall be coordinated with the road traffic management department and the municipal engineering department, and the vehicle speed limit shall be 45 km / h or large vehicles shall be detoured during the crossing process through road traffic signs and road traffic control.

[0100] (5) Strengthen the overall rigidity of the shield segment structure, strengthen the reinforced concrete segment reinforcement in the backfill section, use R1 type reinforcing lining rings, and increase the strength grade of the segment connection bolts to improve the bearing capacity of the new tunnel structure.

[0101] (6) Setting of normal section excavation parameters: Based on the relevant data obtained from the first 100 meters of trial excavation, various excavation parameters need to be set on the PC in the operation room before starting normal excavation. Under normal circumstances, this value does not need to be modified after setting. It can be modified in special circumstances. The control table of normal section excavation parameters is shown in Table 2:

[0102] Table 2 Normal section excavation parameter control table

[0103]

[0104] 7. Shield side tunneling process control and monitoring

[0105] (1) The control measures for the shield side-crossing excavation process include shield excavation direction control, shield excavation process deviation correction control, and shield excavation process soil bin pressure balance control;

[0106] 1) Shield tunneling direction control:

[0107] The shield machine's attitude monitoring can be carried out through China Railway Construction Heavy Industry's automatic guidance system and manual measurement review. The system is equipped with guidance, automatic positioning, excavation program software and display, which can dynamically display the deviation and trend of the shield machine's current excavation position and the tunnel design axis around the clock.

[0108] As the rear-sight reference point of the shield advancement guidance system needs to be moved forward, it must be accurately positioned through manual measurement. To ensure the accuracy and reliability of the advancement direction, manual measurement is performed every 30 meters for curved sections and every 50 meters for straight sections to verify the measurement data of the automatic guidance system and verify the position and posture of the shield to ensure the correctness of the shield excavation direction.

[0109] Using zoned operation of shield thrust cylinder to control shield tunneling direction

[0110] The shield machine to be used for this contract construction has 20 sets of thrust cylinders, divided into 4 zones: up, down, left and right. Each zone's cylinder can independently control the thrust oil pressure. The shield machine's attitude adjustment and control can be achieved by adjusting the pressure difference of each zone's thrust cylinders to achieve the adjustment and control of the shield machine's excavation direction.

[0111] When excavating in an uphill section, appropriately increase the thrust of the lower cylinder of the shield; 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.

[0112] Under uniform geological conditions, keep the thrust of all cylinders consistent; when excavating in the soil-rock boundary strata, the operation should be carried out according to the specific distribution of different strata in the section, following the principle of appropriately increasing the thrust of the propulsion cylinder on the hard stratum side and appropriately reducing the thrust of the cylinder on the soft stratum side.

[0113] 2) Deviation correction control during shield tunneling

[0114] In actual construction, due to geological mutations and other reasons, the shield's advancement direction may deviate from the design axis and reach the management warning value; when excavating in stable strata, the rolling resistance provided by the strata is small, which may cause shield rolling deviation; when excavating in the slope change section or sharp bend section of the line, it may cause large deviation. Therefore, the shield should be adjusted in time to correct the deviation.

[0115] ①Rolling correction

[0116] When the rolling exceeds the limit, the shield machine will automatically alarm. At this time, the shield cutter head should be reversed to correct the rolling deviation.

[0117] The allowable rolling deviation is ≤1.5°. When it exceeds 1.5°, the shield machine will alarm, prompting the operator to switch the cutter head rotation direction and reverse the deviation.

[0118] ②Vertical deviation correction

[0119] The main factor controlling the direction of the shield is the unilateral thrust of the jack. When the shield appears to pitch downward, the thrust of the lower jack can be increased. When the shield appears to pitch upward, the thrust of the upper jack can be increased to correct the deviation.

[0120] ③Horizontal deviation correction

[0121] The same principle as the vertical direction deviation correction, when it deviates to the left, the pushing pressure of the left jack should be increased, and when it deviates to the right, the pushing pressure of the right jack should be increased.

[0122] 3) Earth bunker pressure balance control during excavation process:

[0123] During the excavation process, the dynamic balance between the soil bin pressure and the water and soil pressure on the working surface is always ensured. At the same time, a screw conveyor is used to carry out earth discharge operations corresponding to the shield advancement volume. During the excavation process, the balance between the excavated soil volume and the discharged soil volume is always maintained to keep the front soil stable.

[0124] (2) Monitoring of the shield side-penetration excavation process includes strengthening the deformation monitoring of shallow soil layers and bridges, and continuously adjusting and optimizing the excavation parameters based on the monitoring data.

[0125] 8. Synchronous grouting and secondary reinforcement grouting during shield side penetration

[0126] During the shield side-penetration excavation process, synchronous grouting is carried out through the shield tail grouting pipe while excavation is in progress, and secondary reinforcement grouting is carried out on the outer strata of the segment through the segment lifting holes.

[0127] Synchronous grouting uses the shield's own grouting pump to inject at the shield tail, timely fill the annular gap between the segment and the stratum, control stratum deformation, stabilize the segment structure, control the excavation direction, and strengthen the tunnel structure's self-waterproofing ability. Synchronous grouting uses dual control technology of grouting volume and grouting pressure. The grouting volume is controlled at 120% to 140% of the theoretical building gap. The grouting pressure should be slightly greater than the water and soil pressure, and the grouting pressure is set to 0.2MPa to 0.4MPa. Synchronous grouting uses cement mortar as the grouting material, slurry consistency: 8 to 12cm; slurry stone rate: >95%; consolidated body strength: not less than 0.2MPa in one day (equivalent to the unconfined compressive strength of soft rock strata), and not less than 2.5MPa in 28 days (slightly greater than the natural compressive strength of strongly weathered rock).

[0128] After synchronous grouting, the annular voids behind the segments are filled, and the deformation and settlement of the strata in most sections are controlled. In some sections, there may be local unevenness, solidification shrinkage of the slurry, and dilution loss of the slurry during the solidification process of the synchronous slurry. In order to improve the waterproofness and density of the backing grouting layer and effectively fill the annular voids behind the segments, secondary reinforcement grouting is carried out according to the monitoring results. The secondary reinforcement grouting uses a KBY-50 / 70 grouting pump. The grouting pipeline for the secondary reinforcement grouting is self-made, which can realize the functions of rapid connection and unloading and sealing without leakage, and is equipped with a slurry stop valve. The grouting pressure of the secondary reinforcement grouting is selected to be 0.3~0.5MPa, and the grouting amount is determined according to the monitored voids and monitoring measurement results. The secondary grouting uses cement-water glass double liquid slurry as the grouting material, and the double liquid slurry slurry ratio table is shown in Table 3. The slurry performance indicators are shown in Table 4. The cement uses PO42.5 grade ordinary Portland cement.

[0129] Table 3 Dual-liquid slurry ratio table

[0130]

[0131] Table 4 Slurry performance index table

[0132]

[0133] The purposes of synchronous grouting and secondary reinforcement grouting are mainly the following three aspects: a. Fill the gap of shield tail building in time, support the rock mass around the segment and effectively control the surface settlement; b. The condensed slurry will serve as the first waterproof barrier of the shield construction tunnel and enhance the waterproof capacity of the tunnel; c. Provide early stability for the segment and integrate the segment with the surrounding rock mass to prevent the segment from floating up in water-rich areas, which is conducive to the control of the shield excavation direction and can ensure the ultimate stability of the shield tunnel.

[0134] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0135] The above is only an embodiment of the present invention. The common sense such as the known specific structure and characteristics in the scheme is not described in detail here. The ordinary technicians in the relevant field know all the common technical knowledge in the technical field of the invention before the application date or priority date, can obtain all the existing technologies in the field, and have the ability to apply the conventional experimental means before that date. The ordinary technicians in the relevant field can improve and implement this scheme in combination with their own abilities under the enlightenment given by this application. Some typical known structures or known methods should not become obstacles for ordinary technicians in the relevant field to implement this application. It should be pointed out that for those skilled in the art, without departing from the structure of the present invention, several deformations and improvements can be made, which should also be regarded as the protection scope of the present invention, which will not affect the effect of the implementation of the present invention and the practicality of the patent. The protection scope required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A construction method for a bridge pile foundation with a shield tunnel in a shallow backfill area at a short distance, characterized in that: The steps include: Step 1: Install isolation piles between the bridge pile foundation and the tunnel structure; Step 2: construct a cap beam on the top of the isolation pile; Step 3: Grouting reinforcement is performed on the backfill area. Grouting reinforcement of the backfill area is divided into surface grouting and surface curtain grouting, and sleeve valve pipe grouting technology is used for reinforcement; Step 4: Cover plate construction and backfilling. After the grouting reinforcement construction is completed, cover plates are constructed between the crown beams and backfilled with sandbags to ensure that the soil thickness is ≥ 6m. The crown beams and cover plates connect the isolation piles into a whole to form a closed frame. Step 5: Conduct excavation of the test section to determine the overall excavation parameters of the shield side penetration process; The test section is the 100m range before the shield starts, and the shield excavation in the test section is completely controlled according to the side penetration of the target bridge pile foundation; Step 6: Shield side tunneling process control and monitoring; (1) The control measures for the shield side-crossing excavation process include shield excavation direction control, shield excavation process deviation correction control, and shield excavation process soil bin pressure balance control; Shield tunneling direction control: The shield tunneling direction is controlled by using the shield thrust cylinder operated in sections; Deviation correction control during shield tunneling: including rolling deviation correction, vertical deviation correction, and horizontal deviation correction; Earth bunker pressure balance control during excavation: During excavation, the dynamic balance between earth bunker pressure and water and soil pressure on the working surface is always ensured. At the same time, the screw conveyor is used to carry out earth discharge operations corresponding to the shield advance amount. During excavation, the balance between the excavated soil volume and the discharged soil volume is always maintained to keep the front soil stable. (2) Monitoring of the shield tunneling process includes strengthening the deformation monitoring of shallow soil layers and bridges, and continuously adjusting and optimizing tunneling parameters based on the monitoring data; Step 7: Synchronous grouting and secondary reinforcement grouting during shield side tunneling; During the side-penetration excavation process of the shield, synchronous grouting is carried out through the shield tail grouting pipe while excavating, and according to the monitoring results, secondary reinforcement grouting is carried out on the outer stratum of the segment through the segment lifting hole; the synchronous grouting adopts the dual control technology of grouting volume and grouting pressure, and the grouting volume is controlled at 120%~140% of the theoretical building gap. The grouting pressure should be greater than the water and soil pressure, and the grouting pressure is set to 0.2MPa~0.4Mpa; the grouting pressure of the secondary reinforcement grouting is 0.3~0.5Mpa, and the grouting volume is determined according to the monitored gap and the results of monitoring and measurement.

2. The method for constructing a bridge pile foundation with a shield tunnel in a shallow backfill area at a close distance according to claim 1, characterized in that: In step 2, the width of the crown beam is the same as the diameter of the isolation pile, which is 0.5m, and the height is 0.4m.

3. The method for constructing a bridge pile foundation with a shield tunnel in a shallow backfill area at a short distance according to claim 1, characterized in that: In step 3, the grouting material used for surface grouting is cement slurry, and the grouting material used for surface curtain grouting is cement-water glass slurry.

4. The method for constructing a bridge pile foundation with a shield tunnel in a shallow backfill area at a close distance according to claim 1, characterized in that: In step 3, the grouting construction is divided into the following three steps: (1) The outermost two rows of curtain grouting holes are constructed on both sides of the left and right lines of the tunnel and curtain grouting is carried out; (2) Construct reinforcement grouting holes in a plum blossom pattern according to the designed spacing and perform preliminary grouting; (3) Complete the remaining reinforcement grouting holes according to the plum blossom-shaped arrangement and carry out reinforcement grouting.

5. The method for constructing a bridge pile foundation with a shield tunnel in a shallow backfill area at a short distance according to claim 1, characterized in that: In step 3, the sleeve valve tube adopts a PVC tube with an outer diameter of 48 mm and an inner diameter of 42 mm.

6. The method for constructing a bridge pile foundation with a shield tunnel in a shallow backfill area at a short distance according to claim 1, characterized in that: In step 4, the thickness of the cover plate is 0.2 m, and the grade of the cover plate concrete is C40.

7. The method for constructing a bridge pile foundation with a shield tunnel in a shallow backfill area at a short distance according to claim 1, characterized in that: In step 5, the main construction tasks of the test section are as follows: (1) The test section should accurately grasp the various shield construction parameters and summarize the impact of ground load on ground settlement; (2) Run-in the various performances of the shield machine to provide a good technical and equipment guarantee for smooth passage through the backfill area; (3) Understand the law of pressure changes in the excavation chamber during the crossing period, set the soil pressure in a timely and accurate manner, adjust the construction parameters in real time, and guide the construction; summarize the parameters such as the secondary grouting volume and grouting pressure in the tunnel, especially to prevent ground uplift while controlling settlement, and ensure driving safety; (4) Control the shield axis and ground settlement. In particular, establish a settlement process curve for the test section and predict the settlement to guide subsequent construction; (5) Strengthen ground monitoring in the test section, analyze and summarize the monitoring data of the test section, and understand the actual scope of ground subsidence caused by shield construction in the crossing section, so as to provide a realistic basis for subsequent monitoring and construction.

8. The method for constructing a bridge pile foundation with a shield tunnel in a shallow backfill area at a short distance according to claim 1, characterized in that: In step 7, the synchronous grouting uses cement mortar as the grouting material, the slurry consistency is 8-12 cm, the slurry stone rate is >95%, and the consolidated body strength is not less than 0.2 MPa in one day and not less than 2.5 MPa in 28 days.

9. The method for constructing a bridge pile foundation with a shield tunnel in a shallow backfill area at a short distance according to claim 1, characterized in that: In step 7, the secondary grouting uses cement-water glass double liquid slurry as the grouting material, the slurry consistency is 12.5-13.0 cm, the slurry stone rate is >97%, and the consolidated body strength is greater than 0.3 MPa in one day and greater than 4.5 MPa in 28 days.

10. The method for constructing a bridge pile foundation with a shield tunnel in a shallow backfill area at a short distance according to claim 1, characterized in that: In step 7, the secondary reinforcement grouting uses a KBY-50 / 70 grouting pump. The grouting pipeline for the secondary reinforcement grouting is homemade, can achieve the functions of rapid connection and unloading and sealing to prevent leakage, and is equipped with a grout stop valve.

Images