Shield construction process for metro tunnel with silty clay layer

Abstract

The invention discloses a silty clay layer subway tunnel shield construction process which comprises the following steps: before shield construction, reinforcing the ends of a starting well and a receiving well by adopting in-hole grouting, and chiseling away a tunnel portal; a starting base is installed; mounting and laying a matched traveling track and a battery car traveling track after shield tunneling in the station; assembling in a matching manner, assembling a main machine of the shield tunneling machine, and carrying out no-load debugging; before the counter-force frame is installed, whether the center line of the counter-force frame, the center line of a bracket and the center line of a tunnel coincide or not is checked; mounting a portal sealing device; mounting the negative ring duct piece until the reaction frame is stressed; shield launching and in-time trial tunneling are carried out; and normally tunneling the shield. According to the method, a proper soil layer can be selected for use according to the characteristics of geological conditions and soil environment, and corresponding engineering measures and technical means are adopted to cope with challenges brought by the silty clay layer, so that the safety and stability of engineering construction are guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of subway construction, and more specifically to a subway tunnel shield construction process in a silty clay layer. Background Art

[0002] Silty clay is clay with a plasticity index between 10 and 17, or clay with a clay content of 30% to 50% and a silt group content greater than the sand group content.

[0003] When constructing subway in silty clay layer, the arch stratum at the starting end of shield machine is mainly artificial fill, loess-like silt, loess-like silty clay, clay silt, and the tunnel body stratum is mainly silty clay, with a small amount of seepage in the soil layer. The starting and arrival of shield machine involve the entry and exit of shield machine, which may cause accidents such as water gushing. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a shield construction process for a subway tunnel in a silty clay layer to ensure the safety and stability of the engineering construction.

[0005] In order to solve the above technical problems, the technical solutions adopted by the present invention are as follows.

[0006] The shield construction process of subway tunnel in silty clay layer includes the following steps:

[0007] S1. Before shield construction, the starting shaft and receiving shaft ends are reinforced by grouting in the tunnel, and the tunnel door is chiseled out;

[0008] S2. Install the starting base: According to the height, width and length requirements of the starting base, combined with the outer diameter of the shield and the center of the starting hole and the elevation requirements of the tunnel bottom, adjustments are made based on the deviations obtained from actual measurements to determine the spatial position of the starting base in the shield shaft. At the same time, according to the determined position, a steel structure supporting starting frame is made in the clearance from the bottom of the base to the bottom plate to install the starting base;

[0009] S3. Install and lay the supporting running tracks for shield tunneling and battery car running tracks in the station;

[0010] S4. Post-assembly and shield machine assembly and no-load commissioning;

[0011] S5. Install the reaction frame in the station and support and reinforce the reaction frame: Before installing the reaction frame, check whether the center line of the reaction frame, the center line of the bracket, and the center line of the tunnel coincide;

[0012] S6. Install the door sealing device;

[0013] S7. Install the negative ring segment to the reaction frame to bear the force;

[0014] S8. Start the shield tunneling test in time;

[0015] S9. Shield tunneling is proceeding normally.

[0016] To further optimize the technical solution, in step S1, after the initial bottom end is reinforced, core sampling is performed in the reinforced area and 9 horizontal exploration holes are evenly arranged in a "M" shape at the tunnel entrance to detect the reinforcement effect.

[0017] To further optimize the technical solution, in step S1, the chiseling of the tunnel portal is divided into three stages: the first chiseling of the tunnel portal is carried out manually, and the chiseling is carried out in the order of top first and then bottom, and middle first and then both sides; the second chiseling of the tunnel portal is carried out to remove the remaining concrete, and no less than 5 steel bars are retained on the inside. After the chiseling is completed, the concrete surface around the tunnel portal is trimmed with a pneumatic pick to make the area around the tunnel portal round and smooth; the third chiseling of the tunnel portal is carried out to remove the remaining reinforced concrete on the periphery, and the steel bars around the tunnel portal are trimmed and cut to be round and smooth, thereby shortening the time when the tunnel portal soil is unsupported.

[0018] To further optimize the technical solution, in step S3, the rails are connected by rail clamps, hot-rolled channel steels are used as steel sleepers under the rails, and standard fasteners are used to fix the rails and the steel sleepers.

[0019] To further optimize the technical solution, in step S6, the construction of the portal sealing device is carried out in two steps. The first step is to bury the starting portal steel ring during the construction of the station structure. During the burying process, the embedded parts must be connected to the station structure steel bars; the second step is to clean the slag at the tunnel entrance before the shield is officially started, clean the threaded holes of the circular ring plate with steel wire before installation, and apply grease, and then complete the installation of the portal sealing device.

[0020] To further optimize the technical solution, in step S7, the installation of the negative ring segment includes the following steps:

[0021] S701. Determine the number of negative ring segments;

[0022] S702. Install the negative ring segment support system;

[0023] S703. Assemble negative ring segments;

[0024] The assembly method of the negative ring segment is:

[0025] S7031. According to the segment installation sequence, retract the jacks at the locations where the segments are to be installed to leave space for segment assembly;

[0026] S7032. To ensure the shield tail gap, it is placed in the range of the inverted arch, and steel bars with a thickness not less than the shield tail gap are installed in the shield shell to ensure the position of the segment in the shield shell. It can be removed after the second ring is assembled;

[0027] S7033. The segment installation is operated by remote control. The installation head must be adjusted relative to the segment, and then the segment is lifted for installation;

[0028] S7034. Rotate the segments to their final correct positions and take temporary fixing measures for the segments in the shield shell;

[0029] S7035. Put on the bolts, tighten the nuts, and only install the ring bolts;

[0030] S7036. Assemble the A-type segment, B-type segment, and K-type segment in sequence; when installing the A1 segment and A2 segment, take temporary fixing measures inside the shield to prevent the segment from sagging;

[0031] S7037. After the last negative ring is formed, use the jack to push the ring backward as a whole. The extension speed of the jack should not be too fast.

[0032] S7038. The segment conveyor continues to convey the last negative ring segment to the installation position and repeats the above steps to assemble into a complete ring and connect it with the last negative ring with longitudinal bolts;

[0033] S7039. When the last negative ring is separated from the shield, a wooden wedge is driven into the gap between the guide rail of the starting bracket and the outer diameter of the negative ring to support the negative ring; and a steel wire rope plus a turnbuckle bolt or a guide chain is used to tighten the back of the negative ring segment to increase the rigidity of the negative ring segment;

[0034] S70310. After the front half of the negative ring is assembled, the shield machine cutterhead cuts into the soil, and the subsequent assembly of the negative ring is consistent with the assembly of the initial excavation section segments.

[0035] To further optimize the technical solution, in step S8, the construction method of starting and trial excavation includes the following steps:

[0036] S801. Calculation of main parameters, including soil pressure and thrust;

[0037] S802. Conduct trial excavation of 100 rings for summary and acceptance;

[0038] S803. Control, adjustment and deviation correction of excavation posture;

[0039] S804. Start synchronous grouting after the shield tail passes the seal.

[0040] To further optimize the technical solution, in step S9, the shield tunneling direction is controlled and the shield tunneling posture is adjusted and corrected during the shield tunneling process.

[0041] Due to the adoption of the above technical scheme, the technical progress achieved by the present invention is as follows.

[0042] The shield construction process for subway tunnels in silty clay layers provided by the present invention can select a suitable soil layer for use according to the geological conditions and characteristics of the soil environment, and take corresponding engineering measures and technical means to cope with the challenges brought by the silty clay layer, thereby ensuring the safety and stability of the engineering construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 is a process flow chart of the present invention;

[0044] Figure 2 It is a schematic diagram of soil displacement trend under the active limit equilibrium state of the present invention;

[0045] Figure 3 It is a schematic diagram of soil displacement trend under the passive limit equilibrium state of the present invention. DETAILED DESCRIPTION

[0046] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0047] Shield construction technology for subway tunnels in silty clay layers, combined with Figure 1 As shown, it includes the following steps:

[0048] S1. Before shield construction, the starting shaft and the receiving shaft ends are reinforced by grouting in the tunnel, and the tunnel entrance is chiseled out.

[0049] Nine horizontal exploration holes are evenly arranged in a "M" shape at the tunnel entrance to test the reinforcement effect.

[0050] Before the tunnel portal is chiseled out, core samples are taken from the tunnel portal reinforcement soil for inspection. After passing the inspection, the steel bars within the passage range of the shield machine are cut off to allow the shield machine to smoothly enter the end soil.

[0051] The chiseling of the tunnel portal is divided into three stages: the first chiseling of the tunnel portal is done manually, in the order of top to bottom, middle to sides; the second chiseling of the tunnel portal is done to remove the remaining concrete, leaving no less than 5 steel bars on the inside. After the chiseling is completed, the concrete surface around the tunnel portal is trimmed with a pneumatic pick to make the area around the tunnel portal smooth; the third chiseling of the tunnel portal is done to remove the remaining reinforced concrete on the periphery, and the steel bars around the tunnel portal are trimmed and cut to make it smooth, so as to shorten the time when the tunnel portal soil is unsupported.

[0052] S2. Install the starting base.

[0053] According to the height, width and length requirements of the starting base, combined with the outer diameter of the shield and the requirements for the center of the starting tunnel and the tunnel bottom elevation, adjustments are made based on the deviations obtained from actual measurements to determine the spatial position of the starting base in the shield shaft. At the same time, based on the determined position, a steel structure supporting starting frame is made in the clearance from the bottom of the base to the bottom plate to install the starting base.

[0054] S3. Install and lay the supporting running tracks for shield tunneling and battery car running tracks in the station.

[0055] The rails are connected with track clamps, hot-rolled channel steel is used as steel sleepers under the rails, and standard fasteners are used to fix the rails and steel sleepers.

[0056] S4. Post-assembly and shield machine assembly and no-load commissioning;

[0057] S5. Install reaction frames and supports in the station.

[0058] Before installing the reaction frame, check whether the center lines of the reaction frame, the bracket and the tunnel are aligned. After the reaction frame is hoisted, check the verticality in both directions immediately to control the verticality within 2‰ and 10mm. Temporarily reinforce the reaction frame in time.

[0059] Afterwards, top bracing is carried out behind the columns on both sides of the reaction frame. Two 500mm diameter steel pipes are used as horizontal braces on the side close to the structural wall, and two 500mm diameter steel pipes are used as diagonal braces for reinforcement on the side away from the structural wall. Double-legged 36 I-beams are used to weld top braces behind the bottom and top beams of the reaction frame, with 4 braces set on each layer.

[0060] During the installation process, the reaction frame is precisely positioned with the cooperation of the measurement team to keep it perpendicular to the central axis of the shield machine. During installation, 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 platform and the reaction frame is <±2%, the vertical deviation of the shield machine posture and the design axis is <±2%, and the horizontal trend deviation is <±3%. In order to ensure the lateral stability of the reaction frame during the shield advancement, the reaction frame is fixed horizontally with steel.

[0061] S6. Install the tunnel door sealing device.

[0062] The purpose of sealing the tunnel portal is to prevent water and soil loss at the tunnel portal caused by the start of the shield tunneling and to ensure the grouting effect.

[0063] The construction of the tunnel opening sealing device is carried out in two steps. The first step is to bury the steel ring of the starting tunnel gate during the construction of the station structure. Special attention should be paid to the fact that the embedded parts must be connected to the steel bars of the station structure during the burying process. The second step is to clean the slag at the tunnel opening before the shield is officially started. Before installation, clean the threaded holes of the circular ring plate with steel wire, apply grease, and then complete the installation of the tunnel opening sealing device.

[0064] S7. Install the negative ring segment to the reaction frame to bear the force.

[0065] Before assembling the negative ring, the shield tail wire brush should be filled with shield tail sealing grease. The shield tail grease can stop water and prevent the backflow of synchronous grouting slurry. In addition, the shield tail grease can also reduce the wear of the wire brush. Therefore, when assembling the first ring of segments, the shield tail sealing grease must be filled, and before assembling the segments, the wire brushes must be separated and the stainless steel mesh in the middle of the wire brush and the wire brush must be fully filled.

[0066] The installation of the negative ring segment includes the following steps:

[0067] S701. Determine the number of negative ring segments.

[0068] The minimum number of negative ring segments N at the start of installation in the well is calculated using the following formula:

[0069] N=(DKF-DK1S+LTBM) / WS(ring)

[0070] in:

[0071] DKF: the mileage of the cave enclosure structure after the first chiseling is completed;

[0072] DK1S: starting mileage of the zeroth ring segment;

[0073] LTBM: length of the tunnel boring machine design;

[0074] WS: Segment ring width.

[0075] S702. Install the negative ring segment support system.

[0076] The negative ring segment support system adopts a steel structure reaction frame. The negative ring segment is assembled in a straight line with staggered joints. The principle of keeping the end face of the segment parallel to the ring surface of the reaction frame is followed during assembly. When installing the reaction frame, the mileage must be strictly controlled. The supports of the two columns of the reaction frame are connected by pre-buried steel plate bolts to control their surface elevation, and the reaction frame mileage control line is popped up on the support. The verticality of the two columns is bidirectionally corrected with a theodolite.

[0077] S703. Assemble negative ring segments.

[0078] When the shield machine starts, it is necessary to assemble the negative ring between the reaction frame and the tunnel opening. The negative ring segments are assembled with staggered seams, and the centerline slope of the negative ring is consistent with the design slope of the starting section.

[0079] The assembly method of the negative ring segment is:

[0080] S7031. According to the segment installation sequence, retract the jacks at the locations where the segments are to be installed to leave space for segment assembly;

[0081] S7032. To ensure the shield tail gap, it is placed in the range of the inverted arch, and steel bars with a thickness not less than the shield tail gap are installed in the shield shell to ensure the position of the segment in the shield shell. It can be removed after the second ring is assembled;

[0082] S7033. The segment installation is operated by remote control. The installation head must be adjusted relative to the segment (by adjusting the six degrees of freedom on the installation head), and then the segment is lifted for installation;

[0083] S7034. Rotate the segments to their final correct positions and take temporary fixing measures for the segments in the shield shell;

[0084] S7035. Put on the bolts and tighten the nuts (only install the annular bolts);

[0085] S7036. Assemble the A-type segment, B-type segment, and K-type segment in sequence; when installing the A1 segment and A2 segment, take temporary fixing measures inside the shield to prevent the segment from sagging;

[0086] S7037. After the last negative ring is formed, use the jack to push the ring backward as a whole. The extension speed of the jack should not be too fast.

[0087] S7038. The segment conveyor continues to convey the last negative ring segment to the installation position and repeats the above steps to assemble into a complete ring and connect it with the last negative ring with longitudinal bolts;

[0088] S7039. When the last negative ring is separated from the shield, a wooden wedge is driven into the gap between the guide rail of the starting bracket and the outer diameter of the negative ring to support the negative ring; and a steel wire rope plus a turnbuckle bolt or a guide chain is used to tighten the back of the negative ring segment to increase the rigidity of the negative ring segment;

[0089] S70310. After the front half of the negative ring is assembled, the shield machine cutterhead cuts into the soil, and the subsequent assembly of the negative ring is consistent with the assembly of the initial excavation section segments.

[0090] S8. Start trial excavation of the shield machine in time.

[0091] S801. Calculation of main parameters, including soil pressure calculation and thrust calculation.

[0092] Earth pressure calculation: During the shield tunnel construction process, the cutterhead disturbance changes the static elastic equilibrium state of the original natural soil, thereby generating active earth pressure or passive earth pressure in the soil near the cutterhead.

[0093] When the shield is advancing, if the earth pressure in the soil bin is set too low, the soil in front of the working face will move or slide slightly toward the shield cutterhead, and the soil will tend to slide downward. In order to resist the downward sliding trend of the soil, the shear resistance of the soil will gradually increase. When the lateral stress of the soil is reduced to a certain extent and the shear strength of the soil is fully exerted, the lateral earth pressure of the soil is reduced to the minimum value, and the soil is in a limit equilibrium state, that is, the active limit equilibrium state. The corresponding earth pressure is called active earth pressure Ea. When the shield is advancing, if the earth pressure in the soil bin is set too high, the lateral stress of the cutterhead on the soil will gradually increase, and the soil in front of the cutterhead will tend to slide upward. In order to resist the upward sliding trend of the soil, the shear resistance of the soil will gradually increase, and the soil will be in another limit equilibrium state, that is, the passive limit equilibrium state. The corresponding earth pressure is called passive earth pressure Ep, such as Figure 2 shown.

[0094] When the shield advances, if the earth pressure in the soil bin is set too high, the lateral stress of the cutterhead on the soil will gradually increase, and the soil in front of the cutterhead will tend to slide upward. In order to resist the upward sliding trend of the soil, the shear force of the soil will gradually increase, and the soil will be in another limit equilibrium state, that is, the passive limit equilibrium state. The corresponding earth pressure is called passive earth pressure Ep, such as Figure 3 shown.

[0095] Earth pressure calculation includes static earth pressure calculation, active earth pressure calculation, passive earth pressure calculation, groundwater pressure calculation and preparatory pressure calculation.

[0096] (1) Calculation of static earth pressure

[0097] The static earth pressure is the earth pressure of the original natural soil in a static elastic equilibrium state, that is, the earth pressure when it is not disturbed by shield construction. At depth z, the principal stress on the vertical plane, that is, the static earth pressure is

[0098] σZ=γz

[0099] σ horizontal side pressure = k0γz

[0100] Where: k0—static lateral pressure coefficient of soil;

[0101] γ—soil bulk density, kN / m 3 ;

[0102] z—depth of calculation point, m.

[0103] K0 can also be determined empirically: sand k0 = 0.34 ~ 0.45; hard clay, compacted sandy soil k0 = 0.5 ~ 0.7; extremely soft clay, loose sandy soil k0 = 0.5 ~ 0.7.

[0104] According to the characteristics of shield and the construction principle of shield, combined with the specific experience of railway tunnel design and construction in my country, the Rankine theory is used to calculate the active earth pressure and passive earth pressure.

[0105] (2) Calculation of active earth pressure

[0106] When the thrust of the shield machine is too small, the soil is in a limit equilibrium state of sliding downward. The minimum earth pressure required to keep the soil in front of the cutterhead from sliding downward is the active earth pressure of the soil:

[0107] σa=σztan2(45°-φ / 2)-2ctan(45°-φ / 2)

[0108] Where: σz - formation self-weight stress at depth z; σz = γz

[0109] c-soil adhesion;

[0110] z – depth of formation;

[0111] φ - internal friction angle of the formation.

[0112] (3) Passive earth pressure calculation

[0113] When the thrust of the shield is too large, the soil is in an extreme equilibrium state of sliding upward.

[0114] σp=σ1=σz tan2(45°+φ / 2)+2ctan(45°+φ / 2)

[0115] Where, σz is the formation self-weight stress at depth z;

[0116] c-soil adhesion;

[0117] z – depth of formation;

[0118] φ - internal friction angle of the formation.

[0119] (4) Calculation of groundwater pressure

[0120] When the groundwater level is higher than the top of the tunnel, lateral groundwater pressure is formed due to the presence of pores and cracks in the formation. The magnitude of groundwater pressure is related to the hydraulic gradient, formation permeability coefficient, mortar setting time behind the pipe segment, permeability coefficient and penetration time. Since groundwater flows through the soil and generates head loss due to the resistance of the soil, the water pressure acting on the cutterhead is generally less than the theoretical head pressure at the formation.

[0121] During the excavation process, as the cutterhead continues to move forward, the pressure in the soil bin is close to the original soil pressure value. Considering the resistance of water flowing in the soil, the water pressure in the stratum during excavation can be considered as appropriate based on the permeability coefficient of the stratum.

[0122] When the shield machine stops for some reason, due to the pressure head difference in the stratum, groundwater will inevitably continue to flow into the soil bin until the pressure head difference in the stratum is eliminated. At this time, the water pressure in the soil bin is:

[0123] σw before the cutter head = q × γ water h

[0124] Where, q is an empirical value determined based on the permeability coefficient of the soil layer, q = 0.5 ~ 1.0 for sandy soil, q = 0.1 ~ 0.5 for clay soil, and q = 0 ~ 0.5 for weathered rock layer;

[0125] γwater – specific gravity of water;

[0126] h - the height of the groundwater level from the top of the cutterhead.

[0127] (5) Calculation of preliminary pressure

[0128] Due to many unforeseen factors in construction, the construction soil pressure is less than the static soil pressure in the original soil. According to construction experience, when calculating the soil pressure in areas with strict settlement requirements, a pressure of 0.01 to 0.02 MPa is usually considered as a preliminary pressure based on theoretical calculations.

[0129] The soil bin setting value is σ initial setting = σ horizontal side pressure + σ water pressure + σ adjustment

[0130] Earth pressure management and control generally give an appropriate range. According to the construction site, stratum, and construction environment, an upper limit value of earth pressure and a lower limit value of earth pressure are given. When the geological conditions of the stratum are good and the stability is good, the earth pressure is low. When the stratum changes greatly and the settlement requirements are high, the earth pressure is high.

[0131] (Upper limit) Pmax = groundwater pressure + (passive earth pressure or static pressure) + preparation pressure;

[0132] (Lower limit) Pmin = groundwater pressure + active earth pressure.

[0133] The shield machine propulsion must ensure that the shield has sufficient thrust to maintain and balance the earth pressure balance pressure, excavation resistance, friction resistance between the shield shell and the surrounding rock, and traction force of the rear supporting equipment.

[0134] F1 Peripheral reaction force during shield advancement, kN

[0135] (1) For sandy soil

[0136] F1=μ1(πDLP m +w)

[0137] Where: μ1—friction coefficient between the formation and the shield, is the friction angle within the soil;

[0138] P m —Average earth pressure acting on the shield machine, kPa, P m =(2Pe+2K0Pe+K0γD) / 4

[0139] Pe—vertical earth pressure at the top of the shield, kPa, equal to γH, where H is the burial depth of the top of the shield;

[0140] W—weight of shield machine, kN;

[0141] D--outer diameter of shield machine, m;

[0142] L--shield machine length, m;

[0143] K—static pressure coefficient of soil;

[0144] γ—soil bulk density, kN / m 3 .

[0145] (2) For clay soil

[0146] F1=πDLC

[0147] Where: D is the outer diameter of the shield machine, m;

[0148] L is the length of the shield machine, m;

[0149] C is the cohesion of the soil on the excavation surface, kPa.

[0150] F2 Pushing resistance of the cutter head panel, kN

[0151] F2=0.25πD 2 P

[0152] Where: P is the pressure in front of the excavation face: for slurry shield, it is the designed slurry pressure in the soil bin; for earth pressure shield, it is the designed soil pressure in the soil bin, kPa.

[0153] F3 Friction resistance between the segment and the shield tail, kN

[0154] F3=n1W s μ2+πD s B T n2μ2

[0155] Where: F3 is the friction resistance between the segment and the shield tail, KN;

[0156] n1 is the number of segments inside the shield tail;

[0157] Ws is the weight of one ring of segments, KN;

[0158] μ2 is the friction coefficient between the shield tail and the segment, which is taken as 0.3;

[0159] Ds is the outer diameter of the segment, m;

[0160] b is the contact length between each shield tail brush and the segment, m;

[0161] PT is the grease pressure in the shield tail brush, kPa;

[0162] n2 is the number of layers of the shield tail brush.

[0163] F4 Resistance of the cut ring to penetrate the soil layer, kN

[0164] (1) For sandy soil

[0165] F4=π(D 2 -D1 2 )P+πDtK p P m

[0166] Where: D—front shield outer diameter, m;

[0167] D1—inner diameter of front shield, m;

[0168] t—the depth of the cut ring inserted into the formation, m, taken as 0.5;

[0169] K p — passive earth pressure coefficient;

[0170] P m —Average earth pressure acting on the shield machine, kPa.

[0171] (2) For clay

[0172] F4=π(D 2 -D1 2 )P+πDtC

[0173] Where: t is the depth of the cut ring inserted into the formation, m, taken as 0.5;

[0174] D—front shield outer diameter, m;

[0175] D1—inner diameter of front shield, m;

[0176] C—Cohesion of soil on the excavation surface, kpa.

[0177] Traction resistance of F5 rear supporting trolley, kN

[0178] F5=G h ·sinθ+μ g G h cosθ

[0179] Where: G h is the weight of the shield tail trolley, kN;

[0180] θ is the slope;

[0181] sinθ≈tgθ;

[0182] cosθ≈1;

[0183] μ g is the rolling friction, μ g =0.05.

[0184] F6 steering resistance, kN

[0185] F6=RS

[0186] R—resisting earth pressure (passive earth pressure), kPa;

[0187] S—projected area of ​​the resistance plate in the excavation direction, m 2 .

[0188] Turning resistance only exists during curved construction or when serpentine appears during shield advancement. Since the projection calculation of the resistance plate in the direction of the tunneling plate is relatively complicated, turning resistance is generally not calculated. When determining the total thrust, factors such as shield curved construction, serpentine and correction are considered to leave necessary margin.

[0189] S802. Conduct trial excavation of 100 rings for summary and acceptance.

[0190] After excavating to the 100th ring, the 100-ring acceptance inspection is carried out. The purpose is to adjust the adaptability of the shield machine. Through the 100-ring summary report, the understanding of the interval strata is improved, various adaptability parameters are collected, and the total thrust, excavation speed, cutter head speed and cutter head torque of the shield machine are adjusted to make the shield machine reach the optimal working state, pass through various risk sources safely and smoothly, and complete the construction task quickly and efficiently.

[0191] S803. Control, adjustment and correction of excavation posture.

[0192] The tunneling posture is controlled by using the shield automatic guidance system and manual measurement to assist in shield posture monitoring, and by using zoned operation of the shield machine's propulsion cylinder to control the shield tunneling direction.

[0193] S804. Start synchronous grouting after the shield tail passes the seal.

[0194] After the initial grouting, synchronous grouting is carried out to fill the annular gap behind the shield tail segment in time to ensure that the slurry is fully filled and the surface is stable. Grouting is carried out from the shield tail using the synchronous grouting pipeline provided by the shield machine, and the grouting pressure is 1.1 to 1.2 times the set value of the soil bin pressure.

[0195] The theoretical grouting volume per ring is Q 理 =V =π[(D / 2) 2 -(d / 2)2 ]L

[0196] Where: V is the filling volume;

[0197] D is the excavation diameter;

[0198] d is the outer diameter of the segment;

[0199] L is the segment ring width.

[0200] The actual grouting volume per ring is: Q 实 =V*μ

[0201] Where: V is the filling volume;

[0202] μ is the filling coefficient. According to the construction experience in different strata, the synchronous grouting situation in the Taizhong section and the shield construction manual, the actual synchronous grouting volume is 1.4 to 1.6 times the theoretical grouting volume.

[0203] S9. Shield tunneling is proceeding normally.

[0204] During the shield tunneling process, the shield tunneling direction is controlled and the shield tunneling posture is adjusted and corrected.

[0205] The shield tunneling direction control includes equipping the shield machine with an automatic total station and partition-operated shield machine propulsion cylinders to control the shield tunneling direction.

[0206] By equipping the shield machine with an automatic total station, the current position and theoretical position of the shield machine can be reflected in real time, and adjustment instructions can be provided. The deviation and trend between the current position of the shield machine and the tunnel design axis can be dynamically displayed in the shield machine main control room around the clock. Based on this, the excavation direction of the shield machine can be adjusted and controlled to keep it within the allowable deviation range.

[0207] The zoned operation of the shield machine's thrust cylinders controls the shield machine's excavation direction by dividing the thrust cylinders 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.

[0208] 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.

[0209] The shield machine's excavation posture adjustment and correction is carried out in actual construction. Due to incorrect segment selection, operating errors by the shield machine driver, etc., the shield machine's advancement direction may deviate from the design axis and exceed the management warning value; 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, large deviations may occur. At this time, it is necessary to adjust the shield machine's posture and correct the deviation in time.

Claims

1. Shield construction technology for subway tunnel in silty clay layer, characterized by: It includes the following steps: S1. Before shield construction, the starting shaft and receiving shaft ends are reinforced by grouting in the tunnel, and the tunnel door is chiseled out; S2. Install the starting base: According to the height, width and length requirements of the starting base, combined with the outer diameter of the shield and the center of the starting hole and the elevation requirements of the tunnel bottom, adjustments are made based on the deviations obtained from actual measurements to determine the spatial position of the starting base in the shield shaft. At the same time, according to the determined position, a steel structure supporting starting frame is made in the clearance from the bottom of the base to the bottom plate to install the starting base; S3. Install and lay the supporting running tracks for shield tunneling and battery car running tracks in the station; S4. Post-assembly and shield machine assembly and no-load commissioning; S5. Install the reaction frame in the station and support and reinforce the reaction frame: Before installing the reaction frame, check whether the center line of the reaction frame, the center line of the bracket, and the center line of the tunnel coincide; S6. Install the door sealing device; S7. Install the negative ring segment to the reaction frame to bear the force; S8. Shield machine starts trial excavation in time; S9. Shield tunneling is proceeding normally.

2. The shield construction process for subway tunnel in silty clay layer according to claim 1 is characterized by: In the step S1, after the initial bottom end is reinforced, core sampling is performed in the reinforced area and 9 horizontal exploration holes are evenly arranged in a "M" shape at the tunnel entrance to detect the reinforcement effect.

3. The shield construction process for subway tunnel in silty clay layer according to claim 1 is characterized by: In step S1, the chiseling of the tunnel portal is divided into three stages: the first chiseling of the tunnel portal is carried out manually, and the chiseling is carried out in the order of first top and then bottom, first middle and then both sides; the second chiseling of the tunnel portal removes the remaining concrete, and retains no less than 5 steel bars on the inside. After the chiseling is completed, the concrete surface around the tunnel portal is trimmed with a pneumatic pick to make the area around the tunnel portal round and smooth; the third chiseling of the tunnel portal removes the remaining reinforced concrete on the periphery, trims and cuts the steel bars around the tunnel portal to make it round and smooth, thereby shortening the time when the tunnel portal soil is unsupported.

4. The shield construction process for subway tunnel in silty clay layer according to claim 1 is characterized by: In step S3, the rails are connected by rail clamps, hot-rolled channel steel is used as a sleeper under the rails, and the rails and the sleeper are fixed by standard fasteners.

5. The shield construction process for subway tunnel in silty clay layer according to claim 1 is characterized by: In step S6, the construction of the portal sealing device is carried out in two steps. The first step is to bury the starting portal steel ring during the construction of the station structure. During the burying process, the embedded parts must be connected with the station structure steel bars. The second step is to clean the slag at the portal before the shield is officially started. Before installation, the threaded holes of the circular ring plate should be cleaned with steel wire and greased, and then the portal sealing device should be installed.

6. The shield construction process for subway tunnel in silty clay layer according to claim 1, characterized in that: In step S7, the installation of the negative ring segment includes the following steps: S701. Determine the number of negative ring segments; S702. Install the negative ring segment support system; S703. Assemble negative ring segments; The assembly method of the negative ring segment is: S7031. According to the segment installation sequence, retract the jacks at the locations where the segments are to be installed to leave space for segment assembly; S7032. To ensure the shield tail gap, it is placed in the range of the inverted arch, and steel bars with a thickness not less than the shield tail gap are installed in the shield shell to ensure the position of the segment in the shield shell. It can be removed after the second ring is assembled; S7033. The segment installation is operated by remote control. The installation head must be adjusted relative to the segment, and then the segment is lifted for installation; S7034. Rotate the segments to their final correct positions and take temporary fixing measures for the segments in the shield shell; S7035. Put on the bolts, tighten the nuts, and only install the ring bolts; S7036. Assemble the A-type segment, B-type segment, and K-type segment in sequence; when installing the A1 segment and A2 segment, take temporary fixing measures inside the shield to prevent the segment from sagging; S7037. After the last negative ring is formed, use the jack to push the ring backward as a whole. The extension speed of the jack should not be too fast. S7038. The segment conveyor continues to convey the last negative ring segment to the installation position and repeats the above steps to assemble into a complete ring and connect it with the last negative ring with longitudinal bolts; S7039. When the last negative ring is separated from the shield, a wooden wedge is driven into the gap between the guide rail of the starting bracket and the outer diameter of the negative ring to support the negative ring; and a steel wire rope plus a turnbuckle bolt or a guide chain is used to tighten the back of the negative ring segment to increase the rigidity of the negative ring segment; S70310. After the front half of the negative ring is assembled, the shield machine cutterhead cuts into the soil, and the subsequent assembly of the negative ring is consistent with the assembly of the initial excavation section segments.

7. The shield construction process for subway tunnel in silty clay layer according to claim 1, characterized in that: In step S8, the construction method of starting and trial excavation includes the following steps: S801. Calculation of main parameters, including soil pressure and thrust; S802. Conduct trial excavation of 100 rings for summary and acceptance; S803. Control, adjustment and deviation correction of excavation posture; S804. Start synchronous grouting after the shield tail passes the seal.

8. The shield construction process for subway tunnel in silty clay layer according to claim 1, characterized in that: In step S9, during the shield tunneling process, the shield tunneling direction is controlled and the shield tunneling posture is adjusted and corrected.

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