Test device and method for simulating double-cabin slurry balance shield tunneling under supergravity

Abstract

The invention discloses a test device and method for simulating double-cabin slurry balance shield tunneling under supergravity. The shield body and the slurry feeding and discharging system are fixed through the bottom plate and placed on the geotechnical centrifuge, the soil box and the shield power system are connected through the shield body, the shield body is further connected with the slurry feeding and discharging system, the working cabin is divided into a slurry cabin and an air cushion cabin through the front partition plate, and the shield power system is used for driving the cutter head to rotate and meanwhile driving the main shaft to advance forwards. And the slurry feeding and discharging system is used for conveying slurry and discharging muck into the slurry cabin and the air cushion cabin. Slurry in the slurry cabin is pressed out and permeates into a film by utilizing gas pressure in the air cushion cabin, so that the whole process of tunneling and excavation of the slurry balance shield under large burial depth and high water pressure is simulated, the cutting and forward tunneling actions of an actual shield cutter head are simulated, and the pressure of the slurry in the slurry cabin and the slurry feeding and discharging flow are accurately controlled.

Description

Technical Field

[0001] The invention belongs to the field of slurry shield model test, and in particular relates to a double-chamber slurry shield excavation test device and method under simulated overgravity. Background Art

[0002] As a common method for constructing cross-river and cross-sea tunnels, slurry shield uses pressurized mud to penetrate the stratum and form a mud film in front of the excavation face, so that the mud pressure acts on the mud film in the form of surface force to balance the lateral water and soil pressure in front of the excavation face and maintain the stability of the excavation face. The support pressure of the double-chamber slurry shield is dominated by gas pressure and will not fluctuate greatly due to changes in mud density. Therefore, compared with the single-chamber slurry shield, the support pressure of the double-chamber slurry shield is easier to control during the excavation process.

[0003] At present, most of the excavation tests of slurry shield are carried out under normal gravity. However, since the test under normal gravity cannot restore the real stress level of the stratum and the real scale of the shield, it is not certain whether the simulated slurry shield excavation process and excavation face instability mode conform to the actual working conditions. Geotechnical centrifuge physical simulation is an effective means to restore the stress level of large-scale media under normal gravity in small-scale media, which solves the problem of stress field dissimilarity. The manufactured hypergravity environment can restore the real soil stress level and water pressure outside the slurry tank and the gradient mud pressure inside the slurry tank, which provides the possibility of simulating the actual slurry shield excavation process and excavation face instability mode. However, since the mud is made of two substances with different densities, bentonite and water, increasing the gravity field strength through the hypergravity centrifuge will intensify the relative driving force between the two substances, thereby accelerating the phase separation of the two substances, resulting in uneven mud density, and unable to simulate the actual mud penetration law and mud film formation type. Excessive gravity will aggravate the deposition of excavated soil and block the pipeline during shield excavation, making it difficult to control the slurry discharge flow and the slurry pressure. Therefore, in the study of complex strata with large burial depth and high water pressure, how to solve the above problems, restore the excavation process of slurry shield, and master the support pressure control mechanism of double-chamber slurry shield are the current problems that need to be solved urgently. Summary of the invention

[0004] In order to solve the problems existing in the background technology, the purpose of the present invention is to provide a double-chamber slurry balance shield excavation test device and method under simulated hypergravity, so as to solve the problem that hypergravity aggravates the deposition of shield excavation debris and blockage of pipelines, resulting in difficulty in controlling the slurry discharge flow and inability to accurately control the mud pressure.

[0005] The scheme adopted by the present invention is as follows:

[0006] 1. A double-chamber slurry shield tunneling test device simulating high gravity:

[0007] It includes a soil box, a shield body, a shield power system and a slurry introduction and discharge system. Soil is stored in the soil box. The soil box and the shield power system are connected through the shield body. The shield power system is used to drive the shield body to move forward and backward along the excavation direction, so that the shield body can excavate the soil in the soil box. The shield body is connected to the slurry introduction and discharge system. A pressure maintaining system for balancing the air pressure inside the shield body is provided in the shield body. The soil box, the shield power system and the slurry introduction and discharge system are all fixed on the bottom plate, and the bottom plate is placed in the basket of the geotechnical centrifuge.

[0008] The shield body includes a hull with a working cabin inside, a cutterhead, an annular front bulkhead and a main shaft; the front bulkhead is located inside the hull and divides the working cabin into a mud and water cabin and an air cushion cabin, the cutterhead is located on a side close to the mud and water cabin, one end of the main shaft is connected to the shield power system, and the other end of the main shaft passes through the air cushion cabin, the front bulkhead and the mud and water cabin in sequence and is coaxially connected to the cutterhead; one end of the hull with the mud and water cabin is movably connected to the opening of the soil box so as to be movable forward and backward, and one end of the hull with the air cushion cabin is fixedly connected to the shield power system, the shield power system is used to drive the cutterhead to rotate and at the same time drive the main shaft to excavate forward along its own axial direction, the mud and water cabin and the cutterhead are both arranged at the opening position of the soil box; a connecting pipe is connected to the front bulkhead, the connecting pipe is used to transmit the pressure in the air cushion cabin to the mud and water cabin, and the shield power system realizes closed-loop control through a servo valve.

[0009] The slurry inlet and discharge system comprises a mud water tank, a mud pump, a slag box, a separation box and a screw conveying device; the mud pump is connected to the output end of the mud water tank, the mud pump is communicated with the mud water tank through a first slurry inlet pipe, and the mud pump is communicated with the air cushion tank through a second slurry inlet pipe, and the first slurry inlet pipe and the second slurry inlet pipe are respectively provided with a first electromagnetic ball valve and a second electromagnetic ball valve, one end of the first overflow pipe passes through the air cushion tank and the opening on the front bulkhead and extends into the mud water tank, the other end of the first overflow pipe is connected to the atmosphere, one end of the second overflow pipe extends into the air cushion tank, and the other end of the second overflow pipe is connected to the atmosphere, and the first overflow pipe and the second overflow pipe are respectively provided with a third electromagnetic ball valve and a fourth electromagnetic ball valve, a bypass pipe is also provided between the mud water tank and the mud pump, one end of the bypass pipe is connected to the mud water tank, and the other end is respectively communicated with the mud pump, the first slurry inlet pipe and the second slurry inlet pipe, and the bypass pipe is provided with a bypass ball valve;

[0010] One end of the screw conveyor extends into the mud and water tank, and the other end is connected to the slag box through a pipeline. The sixth solenoid valve, separation box and switching valve group are arranged in sequence on the pipeline from the screw conveyor to the slag box. The mud pump is powered by the hydraulic pressure of the geotechnical centrifuge.

[0011] The switching valve group is mainly composed of two branch pipelines, a slag inlet pipeline and a slag outlet pipeline. One end of the slag inlet pipeline is connected to the separation box, and the other end of the slag inlet pipeline is respectively connected to the input ends of the two branch pipelines. The output ends of the two branch pipelines are connected to one end of the slag outlet pipeline, and the other end of the slag outlet pipeline is connected to the slag box. The two branch pipelines are both provided with a seventh solenoid valve and a damper, and the slag outlet pipeline is provided with a second electromagnetic flowmeter;

[0012] The slurry discharge flow rate in the slag discharge pipe is obtained according to the following formula:

[0013]

[0014] Where, Q is the slurry discharge flow rate; C d is the damping coefficient of the damping; A is the cross-sectional area of ​​the slag discharge pipe; ΔP is the pressure drop; ρ d It is the density of mud mixed with slag.

[0015] Three layers of filters with different apertures are arranged inside the separation box. The axial direction of the filter is perpendicular to the mud flow direction. The mud output by the spiral conveying equipment flows into the separation box from the input end, is filtered by the three layers of filters in sequence, and then flows out of the separation box. The apertures of the three layers of filters decrease in sequence from the inlet to the outlet of the separation box. The aperture of the third layer of filter is smaller than the maximum particle size that can pass through the second electromagnetic flowmeter.

[0016] The relationship between the mud pressure and soil water pressure at the shield excavation surface satisfies the following expression:

[0017] P g +ρ s g(h-D+z)≥γ w (H+z)+K a γ'(H+z)

[0018] P g +ρ s g(h-D+z)≤γ w (H+z)+K p γ'(H+z)

[0019] Where P g is the gas pressure; ρ s is the density of mud; g is the acceleration of gravity; h is the height of the air cushion cabin liquid level; D is the diameter of the shield; z is the vertical coordinate of the excavation surface; γ w is the density of water; H is the burial depth of the shield top; γ' is the effective density of soil; K a is the active earth pressure coefficient; K p is the passive earth pressure coefficient.

[0020] The thrust F provided by the shield power system dAnd torque T is obtained according to the following formula:

[0021]

[0022] In the formula, F 1 F is the frontal thrust resistance during shield tunneling; 2 is the friction between the shield shell and the surrounding soil; K is the lateral earth pressure coefficient; γ is the weight of the soil; f is the friction coefficient between the shield shell and the surrounding soil; L is the length of the shield machine; W is the weight of the shield machine per unit length; T 1 is the friction torque between the cutterhead and the soil; T 2 The formation resistance torque when the cutterhead cuts the soil; η is the cutterhead opening rate; P 0 is the mud pressure in the mud water tank; p is the penetration rate.

[0023] The expression of the cutter head speed is as follows:

[0024]

[0025] Wherein, λ(n) is the ratio of the cutterhead speed under supergravity to that under normal gravity; λ(v) is the ratio of the excavation speed under supergravity to that under normal gravity; λ(s) is the ratio of the excavation distance under supergravity to that under normal gravity; λ(t) is the ratio of the test time under supergravity to the excavation time under normal gravity; λ(p) is the ratio of the penetration under supergravity to that under normal gravity.

[0026] The pressure maintaining system includes an air inlet pipe, an air exhaust pipe, a pressure transmitter, an exhaust valve and an air inlet valve; an air inlet and an air outlet are provided on the front baffle, one end of the air inlet pipe is connected with the mud and water tank after passing through the air inlet, the other end of the air inlet pipe is connected with the air outlet of the geotechnical centrifuge, one end of the exhaust pipe is connected with the mud and water tank after passing through the exhaust port, and the other end of the exhaust pipe is connected to the atmosphere; the air inlet valve and the exhaust valve are respectively provided on the air inlet pipe and the exhaust pipe, the pressure transmitter is connected to the front baffle, and the air inlet valve, the exhaust valve and the pressure transmitter are all connected to the control system.

[0027] 2. A double-chamber slurry shield tunneling test method simulating high gravity, comprising the following steps:

[0028] Step 1: Prepare mud with a preset ratio of bentonite and water, and inject the mud into the mud-water tank, remove the soil box from the bottom plate, and then prepare soil samples in layers in the soil box and bury earth pressure sensors in the soil samples;

[0029] Step 2: Use a saturation box to saturate the soil sample in the soil box. When the soil sample is saturated, hoist the soil box as a whole into the geotechnical centrifuge and push the shield into the hole of the soil box;

[0030] Step 3: Turn on the mud pump to fill the mud water tank with mud, and make the mud reach 2 / 3 of the liquid level of the air cushion tank. When mud seeps out of the first overflow pipe and the second overflow pipe, close the third electromagnetic ball valve and the fourth electromagnetic ball valve, and stop feeding the mud;

[0031] Step 4: Start the geotechnical centrifuge and gradually increase the centrifugal acceleration of the geotechnical centrifuge to a preset Ng. When the geotechnical centrifuge reaches the target Ng value, control the air intake valve of the pressure-maintaining system to inlet air and open the sixth solenoid valve to control the liquid level of the air cushion cabin to remain at 2 / 3 of the height;

[0032] Step 5: Control the shield to advance forward. When the shield advances forward stably for a preset period of time, use the shield power system to control the shield to stop advancing. Control the pressure-maintaining system to control the gas pressure in the air cushion cabin. At the same time, observe the damage of the contact surface between the shield and the soil sample to simulate the actual working conditions when the slurry shield excavation face undergoes active and passive damage, and then obtain the stability law of the slurry shield excavation face.

[0033] The technical solution principle of the present invention is as follows:

[0034] For prototype soil sample: σ=ρgh'

[0035] For a 1 / N times scaled model: σ 1 =ρ·g·h' / N

[0036] For a 1 / N times scaled model under N times hypergravity: σ 2 =ρ·Ng·h' / N=ρg h'

[0037] Among them, σ represents the stress of the prototype soil sample, ρ represents the natural density of the soil, g represents the gravitational acceleration, h' represents the depth of the formation, and σ 1 represents the stress of the 1 / N-fold scale model, σ 2 It represents the stress of 1 / N times scaled model under N times hypergravity, where N represents the ratio of centrifugal acceleration of geotechnical centrifuge to gravitational acceleration;

[0038] It is easy to see that σ=σ 2 , that is, the stress level of the prototype soil sample is equal to that of the 1 / N times scaled model under N times hypergravity, that is, the stress field of the prototype can be replicated under hypergravity, thereby greatly improving the similarity of the slurry shield tunneling test.

[0039] The shield body and the slurry inlet and outlet system of the present invention are fixed by a bottom plate and placed on a geotechnical centrifuge. A supergravity field is created by centrifugal rotation to restore the real shield excavation process. A variety of pipeline installation interfaces are set on the front partition plate to realize functions such as slurry inlet and outlet, pressure transmission and monitoring equipment connection. Considering the circulation of mud in the pipeline during the g-lift process, the cutter disc is connected to a ring-shaped stirring rod, and a blade-type stirring rod is designed in the mud water tank to avoid separation and precipitation of mud under supergravity. A separation box is set on the slurry discharge pipeline, intending to retain large particles in the separation box under supergravity to prevent particles from clogging the electromagnetic flowmeter and pipeline. After the g value stabilizes, the stratum soil samples in the excavation box are manipulated by the slurry balance shield machine, and the monitoring data of the sensor is collected in real time during the process to simulate the dynamic cutting process of the mud film and the soil disturbance during the actual shield excavation process; after the shield body has stably advanced forward for a preset period of time, in order to simulate the working condition of instability of the shield excavation face, the shield power system is used to control the shield body to stop excavation, and the pressure maintaining system is used to adjust the gas pressure. The mud pressure is accurately controlled through the pressure transmission method, and then the ultimate support pressure and the excavation face stability law are obtained.

[0040] The working cabin of the slurry shield is divided into an air cushion cabin and a slurry cabin by the front partition, that is, the excavation face support pressure is divided into two parts: gas pressure and pressure generated by the mud's own weight. The gas pressure is adjusted by the pressure-maintaining system, and the pressure generated by the mud's own weight is adjusted by the slurry inlet and outlet flow. The present invention utilizes the hypergravity environment generated by the geotechnical centrifuge, and according to the similar scale relationship, the shield body can restore the real slurry shield scale, the stratum stress level and the slurry gradient pressure to the real situation, so that the working conditions of the slurry shield excavation in the actual project can be restored.

[0041] The beneficial effects of the present invention are:

[0042] 1. The present invention has a high degree of mechanization and restoration, and can simulate the actual shield cutter cutting, forward excavation action, and accurately control the mud pressure and mud inlet and outlet flow in the mud and water tank.

[0043] 2. Using N times hypergravity environment to conduct 1 / N times slurry shield tunneling excavation and excavation face stability tests greatly improved the similarity of the model test.

[0044] 3. The present invention avoids the influence of the hypergravity effect on the mud separation and sedimentation by designing different types of stirring rods on the cutter head and in the mud water tank and designing a method for circulating the mud in the pipeline during the g-raising process.

[0045] 4. The present invention designs a separation box and damping for the slurry discharge pipeline. By designing a combination of different damping, the slurry discharge pressure in the pipeline is regulated, and then the slurry discharge flow rate is controlled. The separation box is designed to filter large particles to prevent large particles from clogging the electromagnetic flowmeter and pipeline. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 is a structural diagram of the device of the present invention;

[0047] Figure 2 It is a schematic diagram of the internal structure of the device of the present invention;

[0048] Figure 3 It is a schematic diagram of the internal structure of the shield body of the present invention;

[0049] Figure 4 It is a schematic diagram of the slurry inlet and outlet system;

[0050] Figure 5 is a schematic diagram of a separation box;

[0051] Figure 6 It is a schematic diagram of the hydraulic system;

[0052] Figure 7 It is a schematic diagram of the pressure holding system;

[0053] Figure 8 This is the structural diagram of the cutter disc;

[0054] Fig. 9 It is a structural schematic diagram of the screw conveying equipment;

[0055] Fig.10 This is a schematic diagram of a mud water tank;

[0056] Fig.11 Schematic diagram of a geotechnical centrifuge.

[0057] In the figure: 1. Soil box; 2. Shield; 3. Mud and water tank; 4. Muck box; 5. Power box; 6. Driving motor; 7. Mud pump; 8. Separation box; 9. Screw conveyor; 10. Bottom plate; 11. Cutter head; 12. Mud and water tank; 13. Front partition; 14. Air cushion cabin; 15. Main shaft; 16. Torque sensor; 17. First slurry inlet pipe; 18. Second slurry inlet pipe; 19. First electromagnetic flowmeter; 20. Pressure maintaining system; 21. Ball guide rail; 22. Oil cylinder; 23. , second electromagnetic flowmeter; 24, seventh electromagnetic valve; 25, geotechnical centrifuge; 26, control system; 27, thin aluminum plate; 28, first overflow pipe; 29, first overflow pipe; 30, connecting pipe; 31, third electromagnetic ball valve; 32, first electromagnetic ball valve; 33, fourth electromagnetic ball valve; 34, fifth electromagnetic ball valve; 35, second electromagnetic ball valve; 36, bypass ball valve; 37, sixth electromagnetic valve; 38, mud tank; 39, third slurry inlet pipe; 40, switching valve group; 41 , damping; 201, pressure transmitter; 202, exhaust valve; 203, intake valve; 301, stirring motor; 302, stirring blade; 701, gear flowmeter; 702, first proportional speed regulating valve; 703, second proportional speed regulating valve; 704, reversing valve; 705, pressure reducing valve; 706, two-position two-way electromagnetic ball valve; 707, second ball valve; 708, third rotary joint; 709, fourth rotary joint; 801, filter screen; 901, hard tube cylinder; 9 02, hose barrel; 903, dynamic torque sensor; 904, reducer; 905, servo motor; 111, stirring rod; 221, servo valve; 222, one-way valve; 223, filter; 224, first rotary joint; 225, first ball valve; 251, first hanging basket; 252, counterweight; 253, second hanging basket; 254, swing arm; 255, air outlet; 256, oil outlet; 257, camera; 258, cable; 259, oil return port. DETAILED DESCRIPTION

[0058] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0059] like Figure 1As shown, the device includes a soil box 1, a shield body 2, a shield power system and a slurry introduction and discharge system. Soil is stored in the soil box 1. The soil box 1 and the shield power system are connected through the shield body 2. The shield power system is used to drive the shield body 2 to move forward and backward along the excavation direction, so that the shield body 2 excavates the soil in the soil box 1. The shield body 2 is connected to the slurry introduction and discharge system. The slurry stored in the slurry introduction and discharge system is injected into the shield body 2 through a pipeline. The slag generated during the excavation of the device is discharged from the shield body 2 through a pipeline to the slurry introduction and discharge system. A pressure maintaining system 20 for balancing the internal air pressure of the shield body 2 is provided in the shield body 2. The pressure maintaining system 20 is used to control and adjust the gas pressure in the air cushion cabin 14. The soil box 1, the shield power system and the slurry introduction and discharge system are all fixed on the base plate 10, and the base plate 10 is placed in the hanging basket of the geotechnical centrifuge 25. The pressure maintaining system 20, the shield power system and the slurry introduction and discharge system are all electrically connected to the external control system 26.

[0060] like Fig.11 As shown, the geotechnical centrifuge 25 includes a first hanging basket 251, a second hanging basket 253 and a centrifuge base; the first hanging basket 251 and the second hanging basket 253 are respectively fixedly mounted on both sides of the centrifuge base through a rotating arm 254, a counterweight 252 is placed inside the first hanging basket 251, and the bottom plate 10 is fixedly mounted on the second hanging basket 253. A camera 257 is installed on the rotating arm 254 connecting the second hanging basket 253 and the centrifuge base, and an air outlet 255, an oil outlet 256 and an oil return port 259 are provided on the rotating arm 254.

[0061] like Figure 2-Figure 3 As shown, the shield body 2 includes a hull with a working cabin inside, a cutter head 11, an annular front baffle 13 and a main shaft 15; the front baffle 13 is located inside the hull and divides the working cabin into a mud and water cabin 12 and an air cushion cabin 14, the cutter head 11 is located on a side close to the mud and water cabin 12, one end of the main shaft 15 is connected to the shield power system, and the other end of the main shaft 15 passes through the air cushion cabin 14, the front baffle 13 and the mud and water cabin 12 in sequence and is coaxially connected to the cutter head 11; the end of the hull with the mud and water cabin 12 can be moved forward and backward between the opening of the soil box 1 The shield power system is used to drive the cutter head 11 to rotate and drive the main shaft 15 to advance forward along its own axial direction. The mud and water chamber 12 and the cutter head 11 are both arranged at the opening position of the soil box 1; a connecting pipe 30 is connected to the front partition plate 13, and the connecting pipe 30 is used to transfer the pressure in the air cushion chamber 14 to the mud and water chamber 12. The oil cylinder 22 in the shield power system realizes closed-loop control through the servo valve 221 in the control system 26.

[0062] A pressure sensor is arranged on one side of the front bulkhead 13 near the mud and water tank 12, and the pressure sensor transmits the collected mud pressure signal to the control system 26. A connecting pipe opening for installing a connecting pipe 30 is provided on the front bulkhead 13, and the two ends of the connecting pipe 30 are respectively connected to the mud and water tank 12 and the air cushion tank 14. The setting of the connecting pipe 30 enables gas conduction between the air cushion tank 14 and the mud and water tank 12.

[0063] The shield power system includes a power box 5, a drive motor 6, a ball guide 21 and a cylinder 22; the ball guide 21 is fixed on the base plate 10, and the cylinder 22 can be installed on the ball guide 21 for reciprocating motion along the extension direction of the ball guide 21; the power box 5 is fixedly installed on the cylinder 22, and the drive motor 6 is arranged inside the power box 5; the side wall of the power box 5 is fixedly connected to one end of the cabin shell; an opening is provided on the side wall of the power box 5 close to the shield body 2 as a power box outlet; one end of the main shaft 15 passes through the power box outlet and is connected to the output shaft of the drive motor 6; a torque sensor 16 is provided on the outer surface of the main shaft 15 close to the drive motor 6; the torque sensor 16 transmits the collected torque signal to the control system 26, and the cylinder 22 is connected to the oil outlet 256 of the geotechnical centrifuge 25. The driving motor 6 makes the spindle 15 reach the set torque value according to the electrical signal of the torque sensor 16, and the torque is transmitted to the cutter head 11 through the spindle 15, and the oil cylinder 22 pushes the power box 5 to move forward, and the power box 5 transmits the thrust to the cutter head 11 through the spindle 15. The oil cylinder 22 is connected to the oil outlet 256 and the oil return port 259 through pipelines.

[0064] like Figure 4-Figure 6 As shown, the slurry inlet and outlet system includes a mud water tank 3, a mud pump 7, a slag box 4, a separation box 8 and a screw conveying device 9; the mud pump 7 is connected to the output end of the mud water tank 3, the mud pump 7 is communicated with the mud water tank 12 through a first slurry inlet pipe 17, and the mud pump 7 is communicated with the air cushion cabin 14 through a second slurry inlet pipe 18. The first slurry inlet pipe 17 and the second slurry inlet pipe 18 are respectively provided with a first electromagnetic ball valve 32 and a second electromagnetic ball valve 35, and the second slurry inlet pipe 18 is also provided with a first electromagnetic flowmeter 19, one end of the first overflow pipe 28 passes through the openings on the air cushion cabin 14 and the front partition 13 and then extends into the mud water tank 12, and the other end of the first overflow pipe 28 One end of the second overflow pipe 29 is connected to the atmosphere, one end of the second overflow pipe 29 extends into the air cushion cabin 14, and the other end of the second overflow pipe 29 is connected to the atmosphere. The first overflow pipe 28 and the second overflow pipe 29 are respectively provided with a third electromagnetic ball valve 31 and a fourth electromagnetic ball valve 33. A bypass pipe is also provided between the mud water tank 3 and the mud pump 7. One end of the bypass pipe is connected to the mud water tank 3, and the other end is respectively connected to the mud pump 7, the first slurry inlet pipe 17 and the second slurry inlet pipe 18, and a bypass ball valve 36 is provided on the bypass pipe; the mud water tank 12 is also connected to the external mud tank 38 through the third slurry inlet pipe 39, and the third slurry inlet pipe 39 is provided with a fifth electromagnetic ball valve 34.

[0065] One end of the screw conveying device 9 extends into the mud and water tank 12, and the other end is connected to the slag box 4 through a pipeline. The sixth solenoid valve 37, the separation box 8 and the switching valve group 40 are sequentially arranged on the pipeline from the screw conveying device 9 to the slag box 4. The mud pump 7 is powered by the hydraulic pressure of the geotechnical centrifuge 25.

[0066] The mud water tank 3, the mud pump 7, the slag box 4 and the separation box 8 are all placed on the bottom plate 10. Fig.10 As shown, a stirring motor 301 is provided on the top of the mud water tank 3, and a stirring blade 302 is connected to the output shaft of the stirring motor 301. The stirring blade 302 is located in the mud water tank 3 and is used to stir the mud to prevent the mud from being separated and precipitated in a supergravity environment. The oil outlet 256 of the geotechnical centrifuge 25 is connected to the input end of the mud pump 7 through a pipeline. The mud pump 7 is used to transport the mud in the mud water tank 3 to the mud water tank 12 and the air cushion tank 14. An electromagnetic flowmeter for real-time flow monitoring is arranged on the slurry inlet pipes 17 and 18. The first electromagnetic flowmeter 19 transmits the signal to the control system 26 through the cable 258; a slurry discharge pipe opening is provided at the bottom of the front partition 13, and one end of the screw conveying device 9 is connected to the mud water tank 12 after passing through the slurry discharge pipe opening, and the other end of the screw conveying device 9 is connected to the input end of the separation box 8 and controlled by the sixth electromagnetic valve 37. The first overflow pipe 28 is arranged at the top of the mud and water tank 12, and the second overflow pipe 29 is arranged at a liquid level 2 / 3 of the distance from the bottom of the air cushion tank 14. The electromagnetic ball valve in the slurry discharge system is connected to the control system 26.

[0067] The switching valve group 40 is mainly composed of two branch pipes, a slag inlet pipe and a slag outlet pipe. One end of the slag inlet pipe is connected to the separation box 8, and the other end of the slag inlet pipe is respectively connected to the input ends of the two branch pipes. The output ends of the two branch pipes are connected to one end of the slag outlet pipe, and the other end of the slag outlet pipe is connected to the slag box 4. The two branch pipes are provided with a seventh electromagnetic valve 24 and a damper 41. The slag outlet pipe is provided with a second electromagnetic flowmeter 23. The flow resistance of the damper 41 realizes the regulation of the slurry discharge flow rate.

[0068] The slurry discharge flow rate in the slag discharge pipe is obtained according to the following formula:

[0069]

[0070] Where, Q is the slurry discharge flow rate; C d is the damping coefficient of damping 41; A is the cross-sectional area of ​​the slag discharge pipe; ΔP is the pressure drop; ρ d It is the density of mud mixed with slag.

[0071] like Figure 5As shown, three layers of filter screens 801 with different apertures are arranged inside the separation box 8, and the axial direction of the filter screen 801 is perpendicular to the mud flow direction. The mud output by the screw conveying device 9 flows into the separation box 8 from the input end, and flows out of the separation box 8 after being filtered by the three layers of filter screens in sequence. The apertures of the three layers of filter screens 801 decrease in sequence from the inlet to the outlet of the separation box 8. The aperture of the third layer of filter screen 801 (i.e., the filter screen 801 with the smallest aperture) is smaller than the maximum particle size that can pass through the second electromagnetic flowmeter 23. The horizontal height of the input / output end of the separation box 8 is consistent with the horizontal height of the screw conveying device 9.

[0072] In order to ensure the stability of the excavation face in front of the cutterhead and prevent active and passive damage, the gas pressure adjusted by the pressure-maintaining system should be such that the relationship between the mud pressure and soil-water pressure at any position z in the vertical direction of the excavation face satisfies the following formula.

[0073] The relationship between the mud pressure and soil water pressure at the excavation surface of shield 2 satisfies the following expression:

[0074] P g +ρ s g(h-D+z)≥γ w (H+z)+K a γ'(H+z)

[0075] P g +ρ s g(h-D+z)≤γ w (H+z)+K p γ'(H+z)

[0076] Where P g is the gas pressure; ρ s is the density of mud; g is the acceleration of gravity; h is the liquid level of the air cushion cabin; D is the diameter of the shield; z is the vertical coordinate of the excavation surface; γ w is the density of water; H is the burial depth of the shield top; γ' is the effective density of soil; K a is the active earth pressure coefficient; K p is the passive earth pressure coefficient.

[0077] By γ w +K a γ'-ρ s g>0、γ w +K p γ'-ρ s g>0, we know that:

[0078] (γ w +K a γ')(H+D)-ρ s gh≤P g ≤(γ w +Kp γ')H+ρ s g(Dh)

[0079] The thrust F provided by the hydraulic cylinder 22 in the shield power system d The torque T provided by the driving motor 6 is obtained by the following formula:

[0080]

[0081] In the formula, F d The thrust provided to the shield power system; F 1 F is the frontal thrust resistance during shield tunneling; 2 is the friction between the shield shell and the surrounding soil; K is the lateral earth pressure coefficient; γ is the weight of the soil; f is the friction coefficient between the shield shell and the surrounding soil; L is the length of the shield machine; W is the weight of the shield machine per unit length; T is the torque provided by the shield power system; T 1 is the friction torque between the front and side of the cutterhead and the soil; T 2 The formation resistance torque when the cutterhead cuts the soil; η is the cutterhead opening rate; P 0 is the mud pressure in the mud water tank; p is the penetration rate.

[0082]

[0083]

[0084] Among them, λ(F d ) is the ratio of the thrust under supergravity to the thrust under normal gravity; N is the gravity magnification of the supergravity test; λ(T 1 ) is the ratio of the friction torque under super gravity to the friction torque under normal gravity; λ(T 2 ) is the ratio of the stratum resistance torque under super gravity to the stratum resistance torque under normal gravity; λ(p) is the ratio of the penetration under super gravity to the penetration under normal gravity. The height of the cutter head 11 is greater than or equal to the penetration of the cutter head 11. Since the foundation soil actually cut by the shield belongs to a continuous medium, the penetration of the cutter head is considered to be a certain multiple of the average particle size d of the foundation soil. 50 , such as 20d 50 , 30d 50 or 40d 50 .

[0085] like Figure 8As shown, a stirring rod 111 is fixedly connected to one side of the cutter head 11 near the mud and water chamber 12. There are two types of stirring rod arrangement designs. One stirring rod is flat and mounted on the panel of the cutter head 11. The other stirring rod is hook-shaped and arranged circumferentially along the main shaft 15. The stirring rod is driven to stir by the rotation of the main shaft 15. Considering that the shield excavation parameters under super gravity and the shield excavation parameters under normal gravity have a similar scale relationship, the expression of the rotation speed of the cutter head 11 under super gravity is as follows:

[0086]

[0087] Where λ(n) is the ratio of the cutterhead speed under hypergravity to that under normal gravity; λ(v) is the ratio of the excavation speed under hypergravity to that under normal gravity; λ(s) is the ratio of the excavation distance under hypergravity to that under normal gravity; λ(t) is the ratio of the test time under hypergravity to the excavation time under normal gravity.

[0088] like Figure 7 As shown, the pressure maintaining system 20 includes an air inlet pipe, an air exhaust pipe, a pressure transmitter 201, an exhaust valve 202 and an air inlet valve 203; an air inlet and an air outlet are provided on the front baffle 13, one end of the air inlet pipe is connected to the mud and water tank 12 after passing through the air inlet, and the other end of the air inlet pipe is connected to the air outlet 255 of the geotechnical centrifuge 25, one end of the exhaust pipe is connected to the mud and water tank 12 after passing through the exhaust port, and the other end of the exhaust pipe is connected to the atmosphere; the air inlet valve 203 and the exhaust valve 202 are respectively provided on the air inlet pipe and the exhaust pipe, the pressure transmitter 201 is connected to the front baffle 13, and is used to measure the gas pressure in the air cushion cabin 14, the air inlet valve 203, the exhaust valve 202 and the pressure transmitter 201 are all connected to the control system 26 through the cable 258, and the control system 26 is used to control the opening and closing degree of the exhaust valve 202 and the air inlet valve 203, thereby controlling the inlet and outlet flow rates of the gas in the air inlet pipe and the exhaust pipe.

[0089] The oil cylinder 22 is controlled by the servo valve 221 in a closed loop: the oil outlet 256 of the geotechnical centrifuge 25 is connected to the input end of the ball valve 225, the output end of the first ball valve 225 is connected to the oil inlet P of the servo valve 221 through a pipeline, the first rotary joint 224, the filter 223 and the one-way valve 222 are sequentially arranged on the pipeline from the first ball valve 225 to the servo valve 221, the oil return port T of the servo valve 221 is connected to the oil return port 259 through the second rotary joint 226, and the oil outlet B of the servo valve 221 is connected to the oil cylinder 22. The filter 223 is used to prevent the metal debris generated by the rotary joint from damaging the servo valve 221 in the control system 26, and the three-position four-way servo valve 221 can realize the reversing function.

[0090] The mud pump 7 is powered by the hydraulic pressure of the geotechnical centrifuge 25. The oil outlet 256 of the geotechnical centrifuge 25 is connected to the input end of the second ball valve 707 through a pipeline, and the output end of the second ball valve 707 is connected to the oil inlet of the mud pump 7 through a pipeline. The pipeline from the second ball valve 707 to the mud pump 7 is sequentially provided with a third rotary joint 708, a two-position two-way electromagnetic ball valve 706, a pressure reducing valve 705, a reversing valve 704, proportional speed regulating valves 702, 703 and a gear flowmeter 701. The oil return port of the mud pump 7 is connected to the oil return port 259 of the geotechnical centrifuge 25 through a fourth rotary joint 709. The pressure reducing valve 705 is used to balance the rated working pressure of the mud pump 7 and the oil cylinder 22, and the oil return port of the pressure reducing valve 705 is connected to the input end of the fourth rotary joint 709.

[0091] like Fig. 9 As shown, the screw conveying device 9 includes a hard tube cylinder 901, a soft tube cylinder 902 and a servo motor 905; the hard tube cylinder 901 extends into the mud and water tank 12, and the soft tube cylinder 902 is arranged inside the air cushion cabin 14 and communicated with the separation box 8; the hard tube cylinder 901 is mainly composed of a first cylinder wall and a first spiral blade, and the first spiral blade is rotatably arranged inside the first cylinder wall, and the soft tube cylinder 902 is mainly composed of a second cylinder wall and a second spiral blade, and the second spiral blade is rotatably arranged inside the second cylinder wall, the first cylinder wall and the second cylinder wall are coaxially fixedly connected, and one end of the first spiral blade and the second spiral blade are coaxially fixedly connected, and the output shaft of the servo motor 905 is coaxially fixedly connected to the other end of the second spiral blade through a coupling and a reducer 904, and the servo motor 905 is used to drive the first spiral blade and the second spiral blade to rotate, thereby preventing the screw conveying device 9 from being blocked, and a dynamic torque sensor 903 for monitoring the torque of the screw conveying device 9 is arranged on the coupling connected to the servo motor 905.

[0092] The embodiment of the present invention includes the following steps:

[0093] Preliminary preparation: Determine the shield parameters: including shield diameter, shield burial depth, excavation speed and cutterhead speed. According to the shield diameter, shield burial depth and foundation soil and water pressure, determine the target Ng value that the geotechnical centrifuge 25 needs to provide, and then determine the gas pressure of the air cushion cabin 14. According to the ratio of the volume of slag cut by the cutter head 11 per unit time to the slurry flow rate of 1:11.7, the slurry flow rate is determined in combination with the excavation speed. According to the conservation relationship of inlet and outlet mass, determine the slurry discharge flow rate. Calculate the slurry discharge flow rate based on the mud pressure in the mud and water tank 12, compare the calculated value with the preset value, and determine the damping 41.

[0094] Step 1: Prepare slurry with bentonite and water in a preset ratio, and inject the slurry into the mud and water tank 3 in the slurry inlet and outlet system, remove the soil box 1 from the bottom plate 10, seal the hole on the side wall of the soil box with a thin aluminum plate 27, and then prepare soil samples in layers in the soil box 1 and bury soil pressure sensors in the soil samples;

[0095] In the specific implementation, bending element sensors, micro soil pressure gauges, micro pore pressure sensors and TDR sensors are also buried in the soil sample, and a wire brush is used to perform a 2 mm polishing treatment on the top of the foundation soil.

[0096] Step 2: Use a saturation box to saturate the soil sample in the soil box 1. When the soil sample is saturated, the soil box 20 is hoisted into the geotechnical centrifuge 25 as a whole, and the shield body 2 is pushed into the hole of the soil box 1. The cutter head 11 is pressed against the thin aluminum plate 27, and the slurry discharge pipeline is closed;

[0097] Specifically, the soil box 1 is placed in the saturated box, and the airless water in the saturated box is pumped into the soil box 1 by vacuuming. After the airless water is extracted, the soil box 1 is re-fixed on the base plate 10, the counterweight block 252 is hoisted into the first hanging basket 251, and the base plate 10 is hoisted into the second hanging basket 253.

[0098] Step 3: Turn on the mud pump 7, and fill the mud tank 12 with mud through the mud inlet pipes 17 and 18, so that the mud reaches the 2 / 3 liquid level of the air cushion tank 14. When mud seeps out of the first overflow pipe 28 and the second overflow pipe 29 in the mud inlet and outlet system, close the third electromagnetic ball valve 31 and the fourth electromagnetic ball valve 33, and stop the mud inlet. At this time, the mud pressure in the shield body 2 is 0-2.5kPa;

[0099] Install the mud tank 38 and the third slurry inlet pipe 39, open the fifth electromagnetic ball valve 34 on the third slurry inlet pipe 39, control the height and liquid level of the mud tank 38 so that the pressure of the mud tank 12 is slightly higher than the lateral water and soil pressure of the soil sample in the soil box 1, lift the thin aluminum plate 27 to allow the pressurized mud in the mud tank 14 to penetrate the soil layer, close the fifth electromagnetic ball valve 34 when the mud film is formed, and remove the mud tank 38 and the third slurry inlet pipe 39;

[0100] Step 4: Start the geotechnical centrifuge 25, and gradually increase the centrifugal acceleration of the geotechnical centrifuge 25 to a preset value Ng. During the centrifugal acceleration increase process, close all electromagnetic ball valves (the first electromagnetic ball valve 32, the second electromagnetic ball valve 35, the third electromagnetic ball valve 31, the fourth electromagnetic ball valve 33, and the sixth electromagnetic valve 37) to keep the mud full of the mud and water tank 12 and the air cushion tank 14. The mud pressure in the mud and water tank 12 increases with the increase of the acceleration Ng value. During the centrifugal acceleration increase process, the cutter head 11 idles to prevent the mud in the mud and water tank 12 from segregating and settling. Sedimentation, at the same time, the stirring rod 302 in the mud water tank 3 continues to stir to prevent the mud in the mud water tank 3 from segregating and settling, the mud pump 7 and the bypass ball valve 36 are opened, so that the mud circulates in the pipeline connected to the mud water tank 3 to prevent segregation and precipitation in the pipeline, when the geotechnical centrifuge 25 reaches the target Ng value, the air inlet valve 203 of the pressure holding system 20 is controlled to inlet air and the sixth solenoid valve 37 is opened to control the liquid level of the air cushion cabin 14 to be maintained at 2 / 3 of the height of the air cushion cabin 14, wherein the damping 41 is set according to the change in the liquid level height of the air cushion cabin 14 and the theoretical value of the mud pressure;

[0101] Step 5: Control the shield body 2 to advance forward. After the shield body 2 has advanced forward stably for a preset period of time, use the shield power system to control the shield body 2 to stop advancing, close all valves on the pipelines, and control the pressure maintaining system 20 to achieve the gas pressure in the air cushion cabin 14. At the same time, observe the damage of the contact surface between the shield body 2 and the soil sample to simulate the working conditions when the slurry shield excavation face undergoes active and passive damage under real working conditions, thereby obtaining the stability law of the slurry shield excavation face.

Claims

1. A double-chamber slurry shield tunneling test device simulating high gravity, characterized in that: The invention comprises a soil box (1), a shield body (2), a shield power system and a slurry feeding and discharging system. Soil is stored in the soil box (1). The soil box (1) and the shield power system are connected via the shield body (2). The shield power system is used to drive the shield body (2) to move forward and backward along the excavation direction, thereby enabling the shield body (2) to excavate the soil in the soil box (1). The shield body (2) and the slurry feeding and discharging system are connected. A pressure maintaining system (20) for balancing the internal air pressure of the shield body (2) is arranged in the shield body (2). The soil box (1), the shield power system and the slurry feeding and discharging system are all fixed on a bottom plate (10). The bottom plate (10) is placed in the hanging basket of a geotechnical centrifuge (25).

2. The double-chamber slurry shield tunneling test device for simulating high gravity according to claim 1, characterized in that: The shield body (2) comprises a hull with a working cabin provided therein, a cutter head (11), an annular front bulkhead (13) and a main shaft (15); the front bulkhead (13) is located inside the hull and divides the working cabin into a mud and water cabin (12) and an air cushion cabin (14); the cutter head (11) is located on a side close to the mud and water cabin (12); one end of the main shaft (15) is connected to the shield power system; the other end of the main shaft (15) passes through the air cushion cabin (14), the front bulkhead (13) and the mud and water cabin (12) in sequence and is coaxially connected to the cutter head (11); one end of the mud and water cabin (12) provided in the hull is connected to the soil box The opening of the soil box (1) is movably connected to each other so as to be movable forward and backward. One end of the air cushion cabin (14) is fixedly connected to the shield power system. The shield power system is used to drive the cutter head (11) to rotate and drive the main shaft (15) to dig forward along its own axis. The mud and water cabin (12) and the cutter head (11) are both arranged at the opening position of the soil box (1). A connecting pipe (30) is connected to the front partition (13). The connecting pipe (30) is used to transmit the pressure in the air cushion cabin (14) to the mud and water cabin (12). The shield power system realizes closed-loop control through a servo valve (221).

3. The double-chamber slurry shield tunneling test device for simulating high gravity according to claim 1, characterized in that: The slurry inlet and outlet system comprises a slurry water tank (3), a slurry pump (7), a slag box (4), a separation box (8) and a screw conveying device (9); the slurry pump (7) is connected to the output end of the slurry water tank (3), the slurry pump (7) is connected to the slurry water tank (12) through a first slurry inlet pipe (17), the slurry pump (7) is connected to the air cushion cabin (14) through a second slurry inlet pipe (18), the first slurry inlet pipe (17) and the second slurry inlet pipe (18) are respectively provided with a first electromagnetic ball valve (32) and a second electromagnetic ball valve (35), one end of the first overflow pipe (28) passes through the openings on the air cushion cabin (14) and the front partition (13) and then extends into the In the mud and water tank (12), the other end of the first overflow pipe (28) is connected to the atmosphere, one end of the second overflow pipe (29) extends into the air cushion tank (14), the other end of the second overflow pipe (29) is connected to the atmosphere, the first overflow pipe (28) and the second overflow pipe (29) are respectively provided with a third electromagnetic ball valve (31) and a fourth electromagnetic ball valve (33), a bypass pipe is also provided between the mud and water tank (3) and the mud pump (7), one end of the bypass pipe is connected to the mud and water tank (3), and the other end is respectively connected to the mud pump (7), the first slurry inlet pipe (17) and the second slurry inlet pipe (18), and a bypass ball valve (36) is provided on the bypass pipe; One end of the screw conveying device (9) extends into the mud and water tank (12), and the other end is connected to the slag box (4) through a pipeline. A sixth solenoid valve (37), a separation box (8) and a switching valve group (40) are sequentially arranged on the pipeline from the screw conveying device (9) to the slag box (4). The mud pump (7) is powered by the hydraulic pressure of the geotechnical centrifuge (25).

4. The double-chamber slurry shield tunneling test device for simulating high gravity according to claim 3, characterized in that: The switching valve group (40) is mainly composed of two branch pipelines, a slag inlet pipeline and a slag outlet pipeline. One end of the slag inlet pipeline is connected to the separation box (8), and the other end of the slag inlet pipeline is respectively connected to the input ends of the two branch pipelines. The output ends of the two branch pipelines are connected to one end of the slag outlet pipeline, and the other end of the slag outlet pipeline is connected to the slag box (4). The two branch pipelines are both provided with a seventh electromagnetic valve (24) and a damper (41), and the slag outlet pipeline is provided with a second electromagnetic flowmeter (23); The slurry discharge flow rate in the slag discharge pipe is obtained according to the following formula: Where, Q is the slurry discharge flow rate; C d is the damping coefficient of the damping (41); A is the cross-sectional area of ​​the slag discharge pipe; ΔP is the pressure drop; ρ d It is the density of mud mixed with slag.

5. The double-chamber slurry shield tunneling test device for simulating high gravity according to claim 3, characterized in that: Three layers of filter screens (801) with different apertures are arranged inside the separation box (8). The axial direction of the filter screen (801) is perpendicular to the flow direction of the mud. The mud output by the screw conveying device (9) flows into the separation box (8) from the input end, is filtered by the three layers of filter screens in sequence, and then flows out of the separation box (8). The apertures of the three layers of filter screens (801) decrease in sequence from the inlet to the outlet of the separation box (8). The aperture of the third layer of filter screen (801) is smaller than the maximum particle size that can pass through the second electromagnetic flowmeter (23).

6. The double-chamber slurry shield tunneling test device for simulating high gravity according to claim 1, characterized in that: The relationship between the mud pressure and the soil water pressure at the excavation surface of the shield (2) satisfies the following expression: P g +ρ s g(h-D+z)≥γ w (H+z)+K a γ'(H+z) P g +ρ s g(h-D+z)≤γ w (H+z)+K p γ'(H+z) Where P g is the gas pressure; ρ s is the density of mud; g is the acceleration of gravity; h is the height of the air cushion cabin liquid level; D is the diameter of the shield; z is the vertical coordinate of the excavation surface; γ w is the density of water; H is the burial depth of the shield top; γ' is the effective density of soil; K a is the active earth pressure coefficient; K p is the passive earth pressure coefficient.

7. The double-chamber slurry shield tunneling test device for simulating high gravity according to claim 1, characterized in that: The thrust F provided by the shield power system d And torque T is obtained according to the following formula: Where, F1 is the frontal propulsion resistance during shield tunneling; F2 is the friction between the shield shell and the surrounding soil; K is the lateral earth pressure coefficient; γ is the weight of the soil; f is the friction coefficient between the shield shell and the surrounding soil; L is the length of the shield machine; W is the deadweight of the shield machine per unit length; T1 is the friction torque between the cutterhead and the soil; T2 is the formation resistance torque when the cutterhead cuts the soil; η is the cutterhead opening rate; P0 is the mud pressure in the mud water tank; p is the penetration rate.

8. The double-chamber slurry shield tunneling test device for simulating high gravity according to claim 1, characterized in that: The expression of the rotation speed of the cutter disc (11) is as follows: Where, λ(n) is the ratio of the cutterhead speed under hypergravity to the cutterhead speed under normal gravity; λ(v) is the ratio of the excavation speed under hypergravity to the excavation speed under normal gravity; λ(s) is the ratio of the excavation distance under hypergravity to the excavation distance under normal gravity; λ(t) is the ratio of the test time under hypergravity to the excavation time under normal gravity; λ(p) is the ratio of penetration under super gravity to penetration under normal gravity.

9. The double-chamber slurry shield tunneling test device for simulating high gravity according to claim 1, characterized in that: The pressure maintaining system (20) comprises an air inlet pipe, an air outlet pipe, a pressure transmitter (201), an exhaust valve (202) and an air inlet valve (203); an air inlet and an air outlet are provided on the front baffle (13); one end of the air inlet pipe passes through the air inlet and is connected to the mud and water tank (12); the other end of the air inlet pipe is connected to the air outlet (255) of the geotechnical centrifuge (25); one end of the exhaust pipe passes through the exhaust port and is connected to the mud and water tank (12); the other end of the exhaust pipe is connected to the atmosphere; the air inlet valve (203) and the exhaust valve (202) are respectively provided on the air inlet pipe and the exhaust pipe; the pressure transmitter (201) is connected to the front baffle (13); the air inlet valve (203), the exhaust valve (202) and the pressure transmitter (201) are all connected to the control system (26).

10. A double-chamber slurry shield tunneling test method under simulated hypergravity applied to the device described in any one of claims 1 to 9, characterized in that: The following steps are involved: Step 1: Prepare slurry with bentonite and water in a preset ratio, and inject the slurry into a mud-water tank (3), remove the soil box (1) from the base plate (10), and then prepare soil samples in layers in the soil box (1) and bury soil pressure sensors in the soil samples; Step 2: Using a saturation box to saturate the soil sample in the soil box (1), after the soil sample is saturated, the soil box (20) is hoisted as a whole into the geotechnical centrifuge (25), and the shield (2) is pushed into the hole of the soil box (1); Step 3: Turn on the mud pump (7) to fill the mud and water tank (12) with mud, and make the mud reach 2 / 3 of the liquid level of the air cushion tank (14). When mud seeps out of the first overflow pipe (28) and the second overflow pipe (29), close the third electromagnetic ball valve (31) and the fourth electromagnetic ball valve (33), and stop feeding the mud. Step 4: Start the geotechnical centrifuge (25), gradually increase the centrifugal acceleration of the geotechnical centrifuge (25) to a preset Ng, and when the geotechnical centrifuge (25) reaches the target Ng value, control the air inlet valve (203) of the pressure-maintaining system (20) to inlet air and open the sixth solenoid valve (37), and control the liquid level of the air cushion cabin (14) to be maintained at 2 / 3 of the height; Step 5: Control the shield body (2) to advance forward. When the shield body (2) advances forward stably for a preset period of time, the shield power system is used to control the shield body (2) to stop advancing. The gas pressure in the air cushion cabin (14) is controlled by controlling the pressure maintaining system (20). At the same time, the damage of the contact surface between the shield body (2) and the soil sample is observed to simulate the working conditions when the active and passive damage occurs on the excavation surface of the slurry shield under real working conditions, thereby obtaining the stability law of the excavation surface of the slurry shield under real working conditions.

Images