A test method for simulating instability mode conversion of a shield tunnel face

Abstract

The application discloses a kind of test methods for simulating the instability mode conversion of shield tunnel excavation face, comprising the following steps: step S1, the test soil is layered and rammed, and the array arrangement of soil pre-embedded earth pressure sensor is pre-embedded in the soil along the direction of excavation face travel, then install soil displacement sensor;Step S2, simulate active instability conversion to passive instability of excavation face;Make excavation face uniform speed horizontal withdrawal, when excavation face is withdrawn to set position, adjust motion parameters, make excavation face uniform speed horizontal advance until passive instability occurs in excavation face;Step S3, simulate passive instability conversion to active instability of excavation face;Make excavation face uniform speed horizontal advance, when excavation face advances to set position, make excavation face uniform speed horizontal withdrawal until active instability occurs in excavation face, step S2, step S3 do not have precedence and sequence;With the advantages of simulating and restoring actual field soil changes, high accuracy of test data, reflecting subtle changes in soil and the like.

Description

Technical Field

[0001] This invention belongs to the field of simulation of shield tunnel excavation face instability technology, specifically relating to an experimental method for simulating the transformation of instability modes of shield tunnel excavation face. Background Technology

[0002] Instability at the excavation face of a shield tunnel refers to the situation where, during shield tunneling, the internal pressure of a soil chamber or slurry chamber is used to balance the soil pressure in front of the excavation face and maintain its stability. If the pressure inside the chamber is too low, active instability will occur, causing soil collapse and surface subsidence. Conversely, excessive pressure will lead to passive instability, causing soil to erupt and the surface to heave. Once instability occurs during shield tunneling, it can trigger a series of engineering accidents, such as uneven settlement of buildings and rupture of municipal pipelines. Therefore, controlling the stability of the excavation face is a crucial guarantee for the quality and safety of shield tunnel projects.

[0003] In existing indoor model tests of shield tunnel excavation face instability, the displacement control method is generally used to simulate the instability of the excavation face. During the test, active instability of the excavation face is simulated by retracting the baffle, and passive instability is simulated by advancing the baffle.

[0004] However, in actual engineering, the pressure inside the soil chamber is constantly changing during shield tunneling. If the soil chamber pressure is too low, it is easy to cause active instability; if the soil chamber pressure is too high, it is easy to cause passive instability. Therefore, the active and passive instability of the excavation face are constantly changing during shield tunneling. This change in instability mode is still very rare in the existing indoor model tests of shield tunnel excavation face instability.

[0005] However, most of the existing tests simulate single working conditions of active or passive instability at the excavation face of shield tunnels, which obviously cannot match the actual field conditions, resulting in experimental data that cannot be well adapted to reality. Summary of the Invention

[0006] The present invention aims to provide a test method for simulating the transformation of instability modes at the excavation face of a shield tunnel. It combines actual conditions and continuously transforms active instability and passive instability modes, solving the problem that current single-condition tests simulating active or passive instability at the excavation face of a shield tunnel cannot fully simulate the actual situation on site.

[0007] Therefore, the technical solution adopted in this invention is: a test method for simulating the instability mode transformation of the shield tunnel excavation face, comprising the following steps:

[0008] Step S1: The test soil is compacted in layers, and soil pressure sensors are pre-embedded in an array in the soil along the direction of excavation. Then, soil displacement sensors are installed in an "L" shape and inserted into the test soil. Finally, the surface of the test soil is leveled and left to stand for more than 24 hours.

[0009] Step S2: Simulate the conversion of active instability of the excavation face into passive instability; make the excavation face retreat horizontally at a uniform speed, so that the excavation face will experience active instability, observe the deformation of the soil in front of the excavation face, and after the excavation face retreats to the set position, adjust the motion parameters to make the excavation face advance horizontally at a uniform speed until the excavation face experiences passive instability. Record the changes in the soil throughout the process by collecting data from the soil pressure sensor and the soil displacement sensor embedded in the soil.

[0010] Step S3: Simulate the conversion of passive instability of the excavation face into active instability; make the excavation face advance horizontally at a uniform speed, so that the excavation face will experience passive instability. When the excavation face advances to the set position, adjust the motion parameters to make the excavation face retreat horizontally at a uniform speed until the excavation face experiences active instability. Record the changes in the soil throughout the process by collecting data from the soil pressure sensor and the soil displacement sensor embedded in the soil.

[0011] Steps S2 and S3 are not in any particular order.

[0012] As a preferred embodiment of the above scheme, in step S1, the array of soil pressure sensors is arranged in three rows and three columns, with a row and column spacing of D / 2, where D is the diameter of the excavation face. The horizontal distance between the soil pressure sensor closest to the excavation face and the end of the excavation face travel path is D / 2. Since the soil changes most significantly in the direction of the excavation face travel, multiple soil pressure sensors need to be deployed, which is reasonable.

[0013] The soil displacement sensor located at the intersection of the "L"-shaped layout faces directly above the end of the excavation face's travel path. Starting from the intersection, three soil displacement sensors are arranged at intervals along the excavation face's travel direction with a spacing of D. Two soil displacement sensors are arranged perpendicular to the excavation face's travel direction with spacings ranging from D / 2 to D, respectively. This arrangement is designed to estimate the extent of unstable soil. Soil instability is usually most pronounced along the excavation face's travel direction, making the layout reasonable.

[0014] More preferably, in step S2, the excavation face is first withdrawn at a speed of 5 mm / min to 7 mm / min for 15 mm to 20 mm, and then the motion parameters are adjusted to advance forward at a speed of 10 mm / min to 14 mm / min for 40 mm to 50 mm, which is reasonable in both speed and distance.

[0015] More preferably, in step S3, the excavation face first advances forward 15mm to 20mm at a speed of 20mm / min to 25mm / min, and then the motion parameters are adjusted to advance forward 40mm to 50mm at a speed of 10mm / min to 14mm / min, which is reasonable in both speed and distance.

[0016] More preferably, the test method is based on a device for simulating the instability mode conversion of a shield tunnel excavation face. This device includes a test module, a drive module, a control module, and a monitoring module. The test module includes an open test chamber filled with dredged sand, a shield tunnel model with a semi-circular shell structure installed on the inner wall of the rear side plate of the open test chamber, and a piston matched to the inner wall of the shield tunnel model. In the initial state, the front end of the piston is flush with the front end of the shield tunnel model. The shield tunnel model and the left side plate of the open test chamber are tightly fitted to form a cavity for horizontal piston movement. All side plates of the open test chamber, except the rear side plate, are made of transparent material. A sealing strip is provided on the contact surface between the shield tunnel model and the left side plate of the open test chamber. The drive module includes a mounting base, an electric push rod, a servo motor, and a power supply base. The bottom bolt of the electric push rod is installed on the mounting base. The electric push rod's front end horizontally passes through the rear panel of the uncovered test chamber and is fixed to the rear end of the piston. The servo motor and the rear end of the electric push rod are flush with each other and spaced vertically on a vertical power supply base. The control module includes an electrical control box support frame and an electrical control box mounted on the support frame and connected to the servo motor circuit. The monitoring module includes a piston displacement sensor, several piston earth pressure sensors, a data acquisition card, a real-time monitoring computer, a soil change camera, and a spotlight. The piston displacement sensor is mounted on the electric push rod and connected to the piston. The piston earth pressure sensor is mounted on the excavation surface at the front end of the piston to record the earth pressure acting on the piston at the excavation surface during the test. The data acquisition card is connected to the piston displacement sensor, the piston earth pressure sensor, and the real-time monitoring computer via wiring. The soil change camera is mounted on a height-adjustable tripod to adjust the shooting height to align with the piston.

[0017] Compared to the small-sized shield tunnel excavation face instability model test device that uses a manual knob to push the piston horizontally back and forth, this solution uses an electrical control box to precisely control the piston's moving speed and distance through a servo motor, effectively reducing the workload of experimental personnel, improving experimental efficiency, and more accurately simulating the actual situation of shield tunnel excavation face instability.

[0018] Compared to the small-sized shield tunnel excavation face instability model test device where the earth pressure data measurement error is large, the piston displacement sensor is installed on the electric push rod and connected to the piston, and the piston earth pressure sensor is installed on the excavation face at the front end of the piston. The two sensors accurately record the movement data and earth pressure data acting on the piston at the excavation face when the piston moves horizontally backward to simulate the active failure of the shield tunnel excavation face and when the piston moves horizontally forward to simulate the passive failure of the shield tunnel excavation face. The experimental data are real and reliable.

[0019] Preferably, the side panels of the uncovered test chamber, except for the rear side panel, are all made of transparent glass for easy observation and photography. The bottom plate and rear side panel of the uncovered test chamber are both made of steel plate, and the bottom plate extends rearward to accommodate the mounting base and electrical control box support frame for integrated installation. The bottom plate of the uncovered test chamber is provided with an openable and closable soil discharge port for discharging blown sand, which facilitates sand discharge. The four corners of the bottom plate of the uncovered test chamber are equipped with directional wheels for easy movement and parking.

[0020] Further preferably, the piston is made of polyoxymethylene (POM). POM is commonly used in industry to make bearings, and currently no one uses this material to make pistons for shield tunnel excavation face models. The choice of material is excellent. Pistons made of POM can effectively reduce the friction between the piston and the shield tunnel model. The inner wall of the shield tunnel model is coated with lubricant, which not only lubricates the surface but also prevents sand and soil from seeping into the interior of the shield tunnel model.

[0021] A further preferred embodiment is that the rear end of the piston is fitted with a connecting screw via a flange, and the front end of the electric push rod is threadedly matched with the connecting screw, resulting in a secure threaded connection that is easy to install and disassemble.

[0022] A further preferred embodiment is that the lower front part of the shield tunnel model is provided with a model support plate installed on the bottom plate of the uncovered test chamber, which ensures that the front end of the shield tunnel model can also be fixed while the rear end is fixed, so that the left and right forces are balanced and the fixation is reliable.

[0023] More preferably, the universal joint at the front end of the piston displacement sensor passes through the uncovered test chamber and abuts against the flange, and the middle end is equipped with a positioning clamp for fixing it to the electric push rod. The position is firmly installed, connecting the piston and the electric push rod, ensuring accurate monitoring of the piston speed.

[0024] The beneficial effects of this invention are:

[0025] (1) Compared with the current single working condition of simulating active or passive instability of the excavation face of shield tunnel, this scheme adopts the conversion of active instability of the excavation face into passive instability and the conversion of passive instability of the excavation face into active instability. The two instability modes are converted, and the simulation more accurately reflects the actual soil changes on site. The test data obtained are more valuable for reference.

[0026] (2) The soil pressure sensor array is pre-embedded in the soil and the soil displacement sensor is distributed in an "L" shape and inserted into the test soil. It records the dynamic changes when the soil becomes unstable. Compared with the existing method of recording the soil by squeezing the excavation surface and then transmitting the data to the soil pressure box through the connecting bracket, the pre-embedded soil pressure sensor and soil displacement sensor are arranged in a regular manner in the soil. The data is obviously more accurate and can reflect the subtle changes in the soil more in a timely manner.

[0027] In summary, it has advantages such as simulating and reproducing actual soil changes in the field, high accuracy of test data, and reflecting subtle changes in the soil. Attached Figure Description

[0028] Figure 1 This is a flowchart illustrating steps S2 and S3 of the present invention.

[0029] Figure 2 This is a top view of the test soil where soil pressure sensors are embedded.

[0030] Figure 3 This is a top view of the test soil where soil displacement sensors are installed.

[0031] Figure 4 A front view of a model test device for the instability of the excavation face of a shield tunnel in a dredged sand stratum.

[0032] Figure 5 for Figure 4 The right view (connected to a data acquisition card, real-time monitoring computer, soil change camera and spotlight).

[0033] Figure 6 for Figure 1 Top view. Detailed Implementation

[0034] The present invention will be further described below with reference to the embodiments and accompanying drawings:

[0035] Combination Figure 1 — Figure 6 As shown, a test method for simulating the instability mode transformation of a shield tunnel excavation face is described, and the specific implementation steps are as follows:

[0036] Step S1: The test soil is compacted in layers, and soil pressure sensors a are pre-embedded in an array in the soil along the direction of excavation. Then, soil displacement sensors b are installed in an "L" shape and inserted into the test soil. Finally, the surface of the test soil is leveled and left to stand for more than 24 hours.

[0037] In step S1, the array of soil pressure sensors a embedded in the soil is arranged in three rows and three columns, with a row and column spacing of D / 2, where D is the diameter of the excavation face. The horizontal distance between the soil pressure sensor a embedded in the soil closest to the excavation face and the end of the excavation face travel path is D / 2. The soil displacement sensor b located at the intersection of the "L"-shaped layout is directly above the end of the excavation face travel path. There are 3 soil displacement sensors b arranged at intervals along the excavation face travel direction starting from the intersection, with a spacing of D. There are 2 soil displacement sensors b along the direction perpendicular to the excavation face travel direction, with spacings from small to large, namely D / 2 and D.

[0038] Step S2: Simulate the conversion of active instability of the excavation face into passive instability; make the excavation face retreat horizontally at a uniform speed, thereby causing active instability of the excavation face, observe the deformation of the soil in front of the excavation face, and after the excavation face retreats to the set position, adjust the motion parameters to make the excavation face advance horizontally at a uniform speed until the excavation face becomes passively unstable. Record the changes in the soil throughout the process by collecting data from the soil pressure sensor a and the soil displacement sensor b embedded in the soil.

[0039] Step S3: Simulate the conversion of passive instability of the excavation face into active instability; make the excavation face advance horizontally at a uniform speed, so that the excavation face will experience passive instability. When the excavation face advances to the set position, adjust the motion parameters to make the excavation face retreat horizontally at a uniform speed until the excavation face experiences active instability. Record the changes in the soil throughout the process by collecting data from the soil pressure sensor a and the soil displacement sensor b embedded in the soil.

[0040] Steps S2 and S3 are not in any particular order.

[0041] In step S2, the excavation face is first withdrawn at a speed of 5 mm / min to 7 mm / min for 15 mm to 20 mm, and then the motion parameters are adjusted to advance forward at a speed of 10 mm / min to 14 mm / min for 40 mm to 50 mm.

[0042] In step S3, the excavation face first advances 15mm to 20mm at a speed of 20mm / min to 25mm / min, and then the motion parameters are adjusted to advance 40mm to 50mm at a speed of 10mm / min to 14mm / min.

[0043] The test method is based on a device for converting the instability mode of a shield tunnel excavation face. The device consists of a test module 1, a drive module 2, a control module 3, and a monitoring module 4.

[0044] The test module 1 consists of an open test chamber 11 filled with dredged sand, a shield tunnel model 12 with a semi-circular shell structure installed on the inner wall of the rear side plate of the open test chamber 11, and a piston 13 that matches the inner wall of the shield tunnel model 12.

[0045] Except for the rear side panel, all four side panels of the uncovered test chamber 11 are made of transparent material. A sealing strip 121 is provided on the contact surface between the shield tunnel model 12 and the left side panel of the uncovered test chamber 11.

[0046] Except for the rear side panel, the four side panels of the uncovered test chamber 11 are all made of transparent glass. The bottom plate and rear side panel of the uncovered test chamber 11 are all made of steel plate, and the bottom plate extends backward to provide space for the mounting base 21 and the electrical control box support frame 31.

[0047] The bottom plate of the uncovered test chamber 11 is provided with an openable and closable soil discharge port 112 for discharging blown sand, and directional wheels 111 are installed at the four corners of the bottom plate of the uncovered test chamber 11.

[0048] The shield tunnel model 12 and the left side plate of the uncovered test chamber 11 are closely fitted to form a cavity for the piston 13 to move horizontally.

[0049] The inner wall of the shield tunnel model 12 is coated with lubricant, and a sealing strip 121 is provided on the contact surface between the shield tunnel model 12 and the left side plate of the uncovered test chamber 11.

[0050] The shield tunnel model 12 has a model support plate 122 installed on the bottom plate of the uncovered test chamber 11 at the lower front.

[0051] In the initial state, the front end of piston 13 is flush with the front end of shield tunnel model 12.

[0052] Piston 13 is preferably made of polyoxymethylene material.

[0053] The piston 13 has a connecting screw 132 mounted on its rear end via a flange 131, and the front end of the electric push rod 22 is threadedly matched with the connecting screw 132.

[0054] The drive module 2 consists of a mounting base 21, an electric push rod 22, a servo motor 23, and a power supply base 24.

[0055] The bottom bolt of the electric push rod 22 is installed on the mounting base 21, and the front end of the electric push rod 22 passes horizontally through the rear side plate of the uncovered test chamber 11 and is fixed to the rear end of the piston 13.

[0056] The rear ends of the servo motor 23 and the electric push rod 22 are flush with each other and spaced apart on the vertical power supply base 24.

[0057] The control module 3 consists of an electrical control box support frame 31 and an electrical control box 32 mounted on the electrical control box support frame 31 and connected to the servo motor 23.

[0058] The monitoring module 4 consists of a piston displacement sensor 41, several piston earth pressure sensors 42, a data acquisition card 43, a real-time monitoring computer 44, a soil change camera 45, and a spotlight 46.

[0059] The piston displacement sensor 41 is mounted on the electric push rod 22 and connected to the piston 13.

[0060] The universal joint 411 at the front end of the piston displacement sensor 41 passes through the uncovered test chamber 11 and abuts against the flange 131, and the middle end is equipped with a positioning clamp 412 for fixing to the electric push rod 22.

[0061] Piston earth pressure sensor 42 is installed on the front end of piston 13 on the excavation surface to record the earth pressure acting on the piston on the excavation surface during the test.

[0062] The data acquisition card 43 is connected to the piston displacement sensor 41, the piston earth pressure sensor 42, and the real-time monitoring computer 44 via a line.

[0063] The soil change camera 45 is mounted on a height-adjustable tripod 451, thereby adjusting the shooting height to align with the piston 13.

Claims

1. A test method for simulating the instability mode transition of a shield tunnel face, characterized in that, It comprises the following steps: Step S1, stratified compaction of the test soil body, and pre-embedding of the arrayed soil pressure sensors (a) in the soil body along the direction of the excavation face, then installing the soil displacement sensors (b) in the form of "L" type distribution inserted into the test soil body, and finally leveling the surface of the test soil body and standing still for more than 24 hours; In the step S1, the arrayed soil pressure sensors (a) are arranged in three rows and three columns, and the row and column spacing is D / 2, D is the diameter of the excavation face, the horizontal distance between the soil pressure sensor (a) closest to the excavation face and the end of the excavation face travel path is D / 2, the soil displacement sensor (b) at the intersection of the "L" type arrangement is directly above the end of the excavation face travel path, the soil displacement sensors (b) spaced apart from the intersection along the direction of the excavation face travel path are three and the spacing is D, and the soil displacement sensors (b) perpendicular to the direction of the excavation face travel path are two and the spacing from small to large is D / 2 and D respectively; Step S2, simulating the conversion of the active instability of the excavation face to passive instability; uniformly withdrawing the excavation face horizontally, so that the excavation face is in active instability, observing the deformation of the soil mass in front of the excavation face, adjusting the motion parameters when the excavation face is withdrawn to the set position, and uniformly advancing the excavation face until the passive instability of the excavation face occurs, and recording the changes of the soil body during the whole process through the collected data of the soil pressure sensors (a) and the soil displacement sensors (b); In the step S2, the excavation face is first withdrawn at a speed of 5mm / min~7mm / min for 15mm~20mm, and then the motion parameters are adjusted to advance at a speed of 10mm / min~14mm / min for 40mm~50mm; Step S3, simulating the conversion of the passive instability of the excavation face to active instability; uniformly advancing the excavation face, so that the excavation face is in passive instability, adjusting the motion parameters when the excavation face advances to the set position, and uniformly withdrawing the excavation face until the active instability of the excavation face occurs, and recording the changes of the soil body during the whole process through the collected data of the soil pressure sensors (a) and the soil displacement sensors (b); In the step S3, the excavation face is first advanced at a speed of 20mm / min~25mm / min for 15mm~20mm, and then the motion parameters are adjusted to advance at a speed of 10mm / min~14mm / min for 40mm~50mm; The steps S2 and S3 are not in a specific order.

2. The test method for simulating the instability mode conversion of a shield tunnel face according to claim 1, characterized in that: The test method is based on a simulation shield tunnel excavation face instability mode conversion device, the simulation shield tunnel excavation face instability mode conversion device includes test module (1), drive module (2), control module (3) and monitoring module (4), the test module (1) includes the filling of the sand without cover test box (11), the shield tunnel model (12) of the half circular shell structure of the rear side plate inner wall of the installation without cover test box (11) and the piston (13) with the inner wall matching of shield tunnel model (12), the initial state of piston (13) front end with shield tunnel model (12) front end flush, the shield tunnel model (12) and the left side plate of without cover test box (11) are closely attached to form the cavity for the horizontal movement of piston (13), the left side plate of without cover test box (11) is except rear side plate all adopts transparent material, the contact surface of shield tunnel model (12) and the left side plate of without cover test box (11) is equipped with sealing rubber strip (121), the drive module (2) includes installation base (21), electric push rod (22), servo motor (23) and power supply seat (24), the bottom bolt installation of electric push rod (22) is on installation base (21), the front end of electric push rod (22) passes through the rear side plate of without cover test box (11) and is fixed with the rear end of piston (13), the servo motor (23), the rear end of electric push rod (22) flush is installed on the vertical power supply seat (24) with interval; The control module (3) includes electric control box support frame (31) and the electric control box (32) installed on electric control box support frame (31) and connected with servo motor (23) line; The monitoring module (4) includes piston displacement sensor (41), several piston soil pressure sensors (42), data acquisition card (43), real-time monitoring computer (44), soil body change camera (45) and spotlight (46), the piston displacement sensor (41) is installed on electric push rod (22) and is connected with piston (13), the piston soil pressure sensor (42) is installed on the front end excavation face of piston (13), for recording the soil pressure on the piston of excavation face in the test process, the data acquisition card (43) is connected with piston displacement sensor (41), piston soil pressure sensor (42) and real-time monitoring computer (44) through line, the soil body change camera (45) is installed on the height adjustable tripod (451), so as to adjust the shooting height to align with piston (13).

3. The test method for simulating the instability mode conversion of a shield tunnel face according to claim 2, characterized in that: The four side plates of the coverless test box (11) are made of transparent glass plates except the rear side plate, the bottom plate and the rear side plate of the coverless test box (11) are made of steel plates, and the bottom plate continues to extend backward for mounting the installation base (21) and the electric control box support frame (31), the bottom plate of the coverless test box (11) is provided with an open-close type soil outlet (112) for discharging the sand, and the directional wheels (111) are installed at the four corners of the bottom plate of the coverless test box (11).

4. The test method for simulating the instability mode conversion of a shield tunnel face according to claim 2, characterized in that: The piston (13) is made of polyformaldehyde material, and the inner wall of the shield tunnel model (12) is coated with lubricating liquid.

5. The test method for simulating the instability mode conversion of a shield tunnel face according to claim 2, characterized in that: The rear end of the piston (13) is provided with a connecting screw rod (132) through a flange (131), and the front end of the electric push rod (22) is threadedly matched with the connecting screw rod (132).

6. The test method for simulating the instability mode conversion of a shield tunnel face according to claim 2, characterized in that: The front lower part of the shield tunnel model (12) is provided with a model support plate (122) installed on the bottom plate of the coverless test box (11).

7. The test method for simulating the instability mode conversion of a shield tunnel face according to claim 5, characterized in that: The universal joint (411) at the front end of the piston displacement sensor (41) penetrates through the coverless test box (11) and abuts against the flange (131), and the middle end is provided with a positioning clamp (412) for fixing on the electric push rod (22).

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