An experimental system and method for simulating shield over-excavation

Abstract

The invention relates to the field of shield over-excavation simulation experiments, and discloses an experimental system and method for simulating shield over-excavation. The system comprises a shield machine model, two racks, a placing unit, a pushing unit and a redirecting unit. The end of the shield machine model is placed in a test box, the pushing unit is used to push the rack to drive the shield machine model to move in the test box, the placing unit is used to place any rack, and the redirecting unit is used to redirect the rack after the placing unit releases the placement of any rack when the rack moves. The existing technology cannot accurately and conveniently simulate shield over-excavation, and the over-excavation amount and the settlement amount are obtained by comparing with the theoretical excavation amount and monitoring the surface settlement, so that the influence of the over-excavation of the straight section and the curved section on the settlement can be obtained. At the same time, the influence of the over-excavation of the shield on the surface settlement under different burial depths can be simulated, and the blade selection and excavation parameters are effectively optimized to ensure the safety of tunnel construction and surface buildings.

Description

Technical Field

[0001] The invention relates to the field of shield over-excavation simulation experiments, in particular to an experimental system and method for simulating shield over-excavation. Background Art

[0002] Shield machines are often used to excavate the ground in urban subway construction. If over-excavation occurs and the effect of grouting to compensate for the ground is poor, it will cause ground subsidence and threaten the safety of the building. When the shield encounters a curved section during advancement, it is necessary to open the over-excavation cutter to pre-excavate the soil outside the turn and dig out the space for the shield machine to turn. That is, the over-excavation cutter is opened for a certain time and extension to over-excavate the outer soil. However, if the over-excavation amount and grouting compensation amount are not well controlled or the grouting cannot fill the gap, it is easy to cause soil loss and surface subsidence. The above are the main factors for over-excavation. In addition, when the shield is excavating, over-excavation will also occur due to the presence of a flange on the shield cut ring. Finally, if the excavation speed does not match the speed of the soil ejector, over-excavation will also occur. At present, most of the relevant simulation devices are hollow tube static simulations of shield over-excavation, which are difficult to reflect the dynamic excavation changes on the real site. And there is a lack of experimental simulation of curved excavation. Therefore, there is an urgent need for an experimental system equipment that is simple to operate and can dynamically simulate the impact of shield over-excavation on surface settlement, especially the over-excavation of shield in curved sections. Summary of the invention

[0003] The purpose of the present invention is to overcome the inability of the prior art to accurately and conveniently simulate shield overexcavation, especially to dynamically simulate the overexcavation of the shield during curved advancement. An experimental system and method for simulating shield overexcavation are provided. The experimental system can effectively simulate the overexcavation of the shield during straight excavation and curved excavation. The overexcavation amount and settlement amount are obtained by comparing with the theoretical excavation amount and monitoring the surface settlement, so as to obtain the influence of overexcavation of straight segments and curved segments on settlement. At the same time, the influence of shield overexcavation on surface settlement under different burial depths can also be simulated, so as to effectively optimize the blade selection and excavation parameters, and ensure the safety of tunnel construction and surface buildings.

[0004] The present invention is achieved through the following technical solutions:

[0005] An experimental system simulating shield over-excavation comprises a shield machine model, a test box, two racks, a placement unit, a pushing unit and a redirecting unit. A through hole is provided on the test box, and the end of the shield machine model passes through the through hole and is placed in the test box. The pushing unit is used for pushing the rack to drive the shield machine model to move in the test box. The placement unit is used for placing any rack. The redirecting unit is used for redirecting the rack after releasing the placement of any rack by the placement unit when the rack moves.

[0006] To simulate the over-excavation of a shield machine during dynamic curve advancement, the prior art often requires replacing the pipe ring segments to redirect the straight or curved line of the shield machine. The replacement is not only time-consuming and labor-intensive, but also the data obtained when detecting the settlement is different from the real data. The present invention drives the shield machine model to move in the test box by pushing the rack through the pushing unit, wherein one of the racks is placed in the placing unit. When the rack moves, the redirecting unit releases the placement of the rack by the placing unit, and the other rack is still connected to the shield machine model. Therefore, the thrust on both sides of the shield machine model is inconsistent. At this time, the purpose of steering can be achieved without stopping the operation to replace the pipe ring segments. The over-excavation of the shield machine during curve advancement is dynamically simulated, thereby obtaining the settlement data of the real over-excavation of the straight and curved segments to judge the influence law on the settlement.

[0007] Furthermore, the pushing unit includes a reaction steel plate and a first rotating rod. One end of the shield machine model is open. A cutter disc is rotatably arranged at the open end of the shield machine model. The cutter disc is connected to the first rotating rod. A first bevel gear is arranged at the free end of the first rotating rod. A motor is arranged in the shield machine model. A second bevel gear is arranged at the output end of the motor. The first bevel gear is meshed with the second bevel gear. A third bevel gear is meshed on the second bevel gear. A telescopic bracket is arranged on the third bevel gear. The free end of the telescopic bracket moves through the shield machine model in sequence and is connected to the reaction steel plate. A first gear is also arranged on the telescopic bracket. The first gear is located on the reaction steel plate. Two worms are rotatably arranged on the reaction steel plate. A fourth bevel gear is arranged at the free end of the worm. Each fourth bevel gear is meshed with a rack. The end of the rack is connected to the shield machine model. The free end of the rack moves through the reaction steel plate and extends outward.

[0008] Furthermore, the placement unit includes a first rectangular groove and a second rectangular groove on the closed end of the shield machine, and the placement unit includes a first rectangular groove and a second rectangular groove on the closed end of the shield machine model, the first rectangular groove and the second rectangular groove are connected, a partition is connected to the inner wall of the first rectangular groove, a first connecting plate is vertically provided at the free end of the partition, the first connecting plate is connected to the inner wall of the second rectangular groove through a first telescopic rod, a second connecting plate is also provided on the first connecting plate, and a groove is provided on the second connecting plate.

[0009] Furthermore, the redirection unit includes a plurality of second telescopic rods arranged on the test box, each second telescopic rod is connected to the reaction steel plate, a positioning plate is provided between any two second telescopic rods, a second gear meshing with the first gear is rotatably provided on the positioning plate, a guide rod matching the groove is provided on the second gear, and the end of the guide rod movably passes through the positioning plate.

[0010] Furthermore, each second telescopic rod is connected to the shield machine model through a bearing column. The present invention drives the second telescopic rod to be extended and retracted by moving the shield machine, so the positioning plate moves together with the shield machine. Since the partition separates the first rectangular groove to form a first cavity and a second cavity, one of the two racks is initially placed in the first cavity, and the other rack is fixedly connected to the closed end of the shield machine model. When the guide rod cooperates with the groove, the guide rod drives the partition to move into the second rectangular groove through the second connecting plate and the first connecting plate. At this time, the rack is placed in the second cavity, and the rack placed in the second cavity no longer acts vertically on the shield machine, which reduces the force and produces deflection. Moreover, since the positioning plate moves together with the shield machine, the guide rod can continuously act on the groove to increase the deflection force, thereby deepening the collection of over-excavation data.

[0011] Furthermore, the test box is open at one end, and a plurality of load-bearing brackets are provided at the open end of the test box. A plurality of laser displacement meters are provided on each load-bearing bracket. The plurality of load-bearing brackets are arranged at equal intervals on both sides of the simulated excavation direction, so that the settlement parameters can be efficiently monitored.

[0012] Furthermore, a plurality of laser displacement meters are arranged on the supporting bracket at equal intervals.

[0013] An experimental system simulating shield over-excavation comprises the following steps:

[0014] Step 1: Fill the test box with surrounding rock simulation materials, level it every 10 cm, and when it is close to the lower part of the through hole, install the cutter head, soil bin and shield shell in the shield machine model inside the test box at the through hole, turn off the soil discharge switch, and continue to fill until the test requirements;

[0015] Step 2: Starting from 10 cm away from the through hole along the simulated excavation direction, a load-bearing bracket is arranged at intervals of 13 cm perpendicular to the excavation direction. There are 7 load-bearing brackets in the width direction, and laser displacement meters are arranged along the excavation center line. One is arranged directly above the center line, one is arranged at intervals of 10 cm within 20 cm on both sides of the center line, and only one is arranged outside the 20 cm range, for a total of 49;

[0016] Step 3: Extend the first telescopic rod, and adjust the length of the first telescopic rod after installing the segment ring so that the reaction steel plate faces the end of the shield machine model;

[0017] Step 4: Apply a certain thrust to the shield machine model to balance the pressure acting in front of the shield machine model;

[0018] Step 5: Turn on the soil discharge switch and screw conveyor in the shield machine model, stop loading after the rack applies thrust every 5 cm, turn off the soil discharge switch and screw conveyor, check the soil volume in the soil box and replace it in time, level the soil surface, and use a laser displacement meter to record the settlement data;

[0019] Step 6: Retract the 5 cm long rack and the first telescopic rod at the same time, and repeat step 5 until they are 5 cm away from the other end of the test box;

[0020] Step 7: Turn off the soil discharge switch and screw conveyor, level the soil surface, record the settlement value with the laser displacement meter, and turn off the laser displacement meter;

[0021] Step 8: Weigh the discharged surrounding rock simulation material to obtain the excavated volume.

[0022] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0023] 1. The present invention includes a shield machine model, two racks, a placement unit, a pushing unit and a redirecting unit. The end of the shield machine model is placed in a test box. The pushing unit is used to push the rack to drive the shield machine model to move in the test box. The placement unit is used to place any rack. The redirecting unit is used to redirect the rack after the placement unit releases the placement of any rack when the rack moves. The over-excavation of the shield during curve advancement is dynamically simulated, so as to obtain the settlement data of the over-excavation of the straight segment and the curved segment to determine the influence law on the settlement.

[0024] 2. In the present invention, each first telescopic rod is connected to the shield machine model through a bearing column, so the guide rod can continuously act on the groove, increase the deflection force, and deepen the collection of over-excavation data.

[0025] 3. The present invention has a test box with one end open, and the open end of the test box is provided with a plurality of load-bearing brackets, each of which is provided with a plurality of laser displacement meters. The plurality of load-bearing brackets are arranged at equal distances on both sides of the simulated excavation direction, so that the settlement parameters can be monitored efficiently. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0027] Figure 1 It is a three-dimensional schematic diagram of the overall structure of the present invention;

[0028] Figure 2 is a cross-sectional view of the structure of the present invention;

[0029] Figure 3 It is a schematic end view of the shield machine model of the present invention;

[0030] Figure 4 It is a schematic diagram of the implementation process of the present invention.

[0031] Marks and corresponding parts names in the attached drawings:

[0032] 1-shield machine model; 2-rack; 3-reaction steel plate; 4-first rotating rod; 5-cutter head; 6-motor; 7-first bevel gear; 8-second bevel gear; 9-third bevel gear; 10-telescopic bracket; 11-first gear; 12-fourth bevel gear; 13-first rectangular groove; 14-second rectangular groove; 15-partition; 16-first connecting plate; 17-second connecting plate; 18-second telescopic rod; 19-positioning plate; 20-guide rod; 21-bearing bracket; 22-laser displacement meter; 23-test box; 24-through hole; 25-second gear. DETAILED DESCRIPTION

[0033] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0034] Example:

[0035] like Figure 1-Figure 4As shown, the present invention includes a shield machine model 1, a test box 23, two racks 2, a placement unit, a pushing unit and a redirecting unit. A through hole 24 is opened on the test box 23, and the end of the shield machine model 1 passes through the through hole 24 and is placed in the test box 23. The pushing unit is used to push the rack 2 to drive the shield machine model 1 to move in the test box 23. The placement unit is used to place any rack 2. The redirecting unit is used to release the placement unit from placing any rack 2 when the rack 2 moves to redirect. The pushing unit includes a reaction steel plate 3 and a first rotating rod 4. One end of the shield machine model 1 is open, and a cutter head 5 is rotatably arranged at the open end of the shield machine model 1. The cutter head 5 is connected to the first rotating rod 4. The free end of the first rotating rod 4 is provided with a first bevel gear 7. A motor 6 is provided in the machine model 1, and a second bevel gear 8 is provided at the output end of the motor 6. The first bevel gear 7 is meshed with the second bevel gear 8, and the second bevel gear 8 is meshed with a third bevel gear 9. The third bevel gear 9 is provided with a telescopic bracket 10. The free end of the telescopic bracket 10 is movable through the shield machine model 1 in turn and is connected to the reaction steel plate 3. The telescopic bracket 10 is also provided with a first gear 11, and the first gear 11 is located on the reaction steel plate 3. Two worms are also rotatably arranged on the reaction steel plate 3. The free end of the worm is provided with a fourth bevel gear 12, and each fourth bevel gear 12 is meshed with the rack 2. The end of the rack 2 is connected to the shield machine model 1, and the free end of the rack 2 is movable through the reaction steel plate 3 and extends outward. The placement unit includes a closed end of the shield machine model 1. A first rectangular groove 13 and a second rectangular groove 14 are provided on the test box 23, and the first rectangular groove 13 and the second rectangular groove 14 are connected. A partition 15 is connected to the inner wall of the first rectangular groove 13, and a first connecting plate 16 is vertically provided at the free end of the partition 15. The first connecting plate 16 is connected to the inner wall of the second rectangular groove 14 through a first telescopic rod. The first connecting plate 16 is also provided with a second connecting plate 17, and a groove is provided on the second connecting plate 17. The redirection unit includes a plurality of second telescopic rods 18 arranged on the test box 23, each second telescopic rod 18 is connected to the reaction steel plate 3, and a positioning plate 19 is provided between any two second telescopic rods 18. A second gear 25 meshing with the first gear 11 is rotatably provided on the positioning plate 19, and a guide 25 matching the groove is provided on the second gear 25. The guide rod 20, the end of the guide rod 20 movably passes through the positioning plate 19, each first telescopic rod is connected to the shield machine model 1 through a bearing column, the test box 23 is open at one end, and a plurality of bearing brackets 21 are arranged at the open end of the test box 23, and a plurality of laser displacement meters 22 are arranged on each bearing bracket 21, and the plurality of bearing brackets 21 are arranged equidistantly along both sides of the pipeline axis, and the plurality of laser displacement meters 22 are arranged on the bearing brackets 21 at equidistant intervals; the following steps are included: Step 1: Fill the test box 23 with surrounding rock simulation material, level it every 10 cm, and when it is filled to a position close to the lower part of the through hole 24, install the cutter head 5, soil bin and shield shell in the shield machine model 1 inside the test box 23 at the through hole 24, and close the soil discharge switch, and continue to fill until the experimental requirements;Step 2: Starting from 2410cm away from the through hole along the simulated excavation direction, a load-bearing bracket 21 is arranged perpendicular to the excavation direction at an interval of 13cm, with a total of 7 load-bearing brackets 21 in the width direction, and a laser displacement meter 22 is arranged along the excavation center line, one is arranged directly above the center line, one is arranged at an interval of 10cm on both sides of the center line within a range of 20cm, and only one is arranged outside the range of 20cm, with a total of 49 arranged; Step 3: Extend the first telescopic rod, and adjust the length of the first telescopic rod after installing the segment ring so that the reaction steel plate 3 is facing the end of the shield machine model 1; Step 4: Apply a certain thrust to the shield machine model 1 and a pressure acting in front of the shield machine model 1 Force balance; Step 5: Turn on the soil discharge switch and screw conveyor in the shield machine model 1, stop loading after the rack 2 applies thrust and extends 5cm each time, turn off the soil discharge switch and screw conveyor, check the soil volume in the soil box and replace it in time, level the soil surface, and the laser displacement meter 22 records the settlement data; Step 6: Simultaneously shrink the rack 2 and the second telescopic rod by 5cm in length, repeat step 5 until it is 5cm away from the other end of the test box 23; Step 7, turn off the soil discharge switch and screw conveyor, level the soil surface, and the laser displacement meter 22 records the settlement value, and turn off the laser displacement meter 22; Step 8: Weigh the discharged surrounding rock simulation material to obtain the excavated amount. ;

[0036] Working principle of the present invention:

[0037] The present invention starts the motor 6, and the motor 6 drives the first bevel gear 7 and the third bevel gear 9 to rotate through the second bevel gear 8. The first bevel gear 7 drives the first rotating rod 4 to drive the cutter head 5 to rotate. At the same time, the third bevel gear 9 drives the first gear 11 on the telescopic bracket 10 to drive the two worms to rotate. The fourth bevel gear 12 on the worm drives the rack 2 to move forward. Since the rack 2 is connected to the shield machine model 1, it drives the shield machine model 1 to move forward. The first gear 117 drives the second gear 25 to rotate at the same time. The second gear 25 drives the guide rod 20 to move toward the groove on the second connecting plate 17. Since the partition 15 separates the first rectangular groove 13 to form a first cavity and a second cavity, one of the two racks 2 is initially placed in the first cavity, and the other rack 2 is fixedly connected to the closed end of the shield machine model 1. When the guide rod 20 cooperates with the groove, the guide rod 20 drives the partition 15 to move into the second rectangular groove 14 through the second connecting plate 17 and the first connecting plate 16. At this time, the rack 2 moves down to the second cavity, and the rack 2 placed in the second cavity no longer acts vertically on the shield machine, so that the force becomes smaller and deflection occurs. Since the positioning plate 19 moves together with the shield machine, the guide rod 20 can continue to act on the groove, increase the deflection force, and deepen the collection of over-excavation data. While the telescopic bracket is rotating, since the shield machine model is moving forward, the telescopic bracket will begin to extend, and the distance the shield machine moves is equal to the distance the telescopic bracket is extended.

[0038] The purpose of the present invention is to provide an experimental system that can dynamically simulate shield over-excavation, especially an experimental system and a method for using the shield over-excavation for simulating shield over-excavation in a curved section, in view of the lack of dynamic excavation simulation and over-excavation of the shield in the current shield over-excavation experiment, which leads to the inability to accurately and effectively grasp the law of over-excavation in the curved section and the surface settlement, thereby affecting the construction and the safety of surface buildings. The experimental system comprises a test box, a first telescopic rod, a reaction steel plate 3, a rack 2, a bearing bracket, a laser displacement meter and surrounding rock simulation materials. The rack 2 provides a top thrust to simulate the advance of shield excavation, the advance of the shield machine in the curved section is simulated by different top thrusts on the left and right sides, the direction of the reaction steel plate 3 is changed by controlling the elongation of the first telescopic rod to simulate the bending direction of the curved section segment ring, the settlement is recorded by the laser displacement meter, the different burial depths of the tunnel are simulated by filling the surrounding rock simulation materials with different depths, the over-excavation under different cutter head 5 selections is simulated by different shield machine cutter head 5 models, the blade selection and excavation parameters are optimized according to the experimental results, and the tunnel construction and the safety of surface buildings are guaranteed. A circular through hole is provided in the lower middle part of the test box in the present invention to provide space for the shield machine model 1 to enter the hole. The cutterhead 5 in the shield machine model 1 is obtained by scaling down the actual shield machine cutterhead 5 in proportion, and the elongation of the over-excavation cutter therein can be controlled. The shield machine model 1 also includes a cutterhead 5, a soil bin, a soil discharge switch, a screw conveyor, a soil box, a shield shell and a segment ring. In the present invention, a first telescopic rod is used to connect the test box and the reaction steel plate 3. The first telescopic rod is used to change the direction of the reaction steel plate 3 to simulate the bending direction of the curved segment ring. The present invention simulates the shield machine jack through the rack 2. The present invention fixes the laser displacement meter by bearing, and the laser displacement meter records the settlement of the surrounding rock simulation material. The present invention can effectively simulate the over-excavation of the shield and explore the law between the over-excavation and the surface settlement through the joint action of the first telescopic rod, the reaction steel plate 3, the surrounding rock simulation material, the rack 2 and the shield machine model 1, thereby optimizing the blade selection and excavation parameters to ensure the safety of tunnel construction and surface buildings.

[0039] The height, length and width of the test box can be designed according to 5 times, 3 times and 3 times the excavation diameter respectively. For the convenience of the experiment, the height is designed to be 1.5m, then the excavation diameter is 0.3m. The diameter of the cutter head 5 in the shield machine model 1 is proportionally reduced to 0.3m. To simplify the experiment, the length of the soil bin is 2cm and the length of the shield shell is 8cm. Before the experiment begins, the cutter head 5, soil bin and shield shell are all inside the test box, the soil discharge switch and the screw conveyor are in the closed state, and the shield machine model 1 includes a segment ring with a thickness of 2cm. After the experiment starts, turn on the soil discharge switch and the screw conveyor, put the discharged soil into the soil box and finally calculate and weigh it to get the excavation volume; the lower edge of the through hole is 30cm away from the bottom of the test box, and the center of the through hole passes through the excavation center line; the bearing brackets are arranged in a Ⅱ-shaped structure on both sides along the excavation direction, starting from 10cm away from the through hole along the direction of simulated excavation, and a bracket is arranged perpendicular to the excavation direction at an interval of 13cm. There are 7 bearing brackets in the excavation direction, and the laser displacement meter is installed at the lower part of the bearing bracket in the width direction according to a certain rule.

[0040] In the present invention, in step 1, the properties of the surrounding rock simulation material are determined in advance, and the surrounding rock simulation material is filled into the test box. The soil surface is leveled every 10 cm. When the soil filling reaches the lower part of the through hole, the filling is stopped. The cutter head 5, soil bin and shield shell in the shield machine model 1 are installed on the soil surface inside the test box at the through hole. The soil discharge switch is in the closed state, and the surrounding rock simulation material is continued to be filled to the required depth of the experiment. The surrounding rock simulation material of different depths can be filled to explore the influence of the tunnel burial depth on the surface settlement; step 2, a bracket is arranged at an interval of 13 cm starting from 10 cm away from the through hole along the excavation direction, with a width of 13 cm. There are 7 support structures in total in the direction, and laser displacement meters are arranged along the excavation center line. On a support structure in the width direction, one is arranged directly above the excavation center line, one is arranged at an interval of 10 cm within a range of 20 cm on both sides of the center line, and only one is arranged outside the range of 20 cm. A total of 49 are arranged. When conducting the experiment, the excavation center line is marked on the soil surface in advance; Step three, extend the first telescopic rod, and adjust the length of the first telescopic rod after installing the segment ring so that the reaction steel plate 3 is facing the end of the shield machine model 1; Step four, apply a certain thrust to the shield machine model 1 to balance the pressure acting in front of the shield machine model 1 , level the soil surface during this period. If no displacement occurs, the thrust and pressure are balanced; Step 5, turn on the soil discharge switch and the screw conveyor, and apply thrust to the rack 2. If it is a straight segment, apply the same thrust. If it is a curved segment, keep the difference in thrust on the left and right sides stable. Stop loading after each extension of 5 cm, delay a certain period of time to turn off the soil discharge switch and the screw conveyor to simulate a certain amount of over-excavation, check the amount of soil in the soil box and replace it in time, level the soil surface, and use a laser displacement meter to record the settlement data; Step 6, simultaneously retract the rack 2 and the first telescopic rod by 5 cm in length, and repeat step 6 until it is 5c away from the other end of the test box. m; in step seven, turn off the soil discharge switch and the screw conveyor, level the soil surface, record the settlement value with a laser displacement meter, turn off the laser displacement meter, and sort out the data to obtain the influence of each stage of excavation on the settlement of the surface soil; in step eight, weigh the discharged surrounding rock simulation material to obtain the excavation volume. During the experiment, the over-excavation volume is controlled by controlling the elongation and elongation time of the over-excavation cutter of the cutter head 5 in the shield machine model 1 and the excavation parameters. The over-excavation rate can be obtained by comparing and analyzing with the theoretical excavation volume. By adding the settlement data, the settlement of each position on the soil surface when excavating to different positions can be obtained, and the corresponding law can be obtained by sorting.

[0041] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An experimental system for simulating shield over-excavation, characterized in that it comprises a shield machine model (1), a test box (23), two racks (2), a placement unit, a pushing unit and a redirecting unit, wherein a through hole (24) is provided on the test box (23), an end of the shield machine model (1) passes through the through hole (24) and is placed in the test box (23), the pushing unit is used to push the rack (2) to drive the shield machine model (1) to move in the test box (23), the placement unit is used to place any rack (2), the redirecting unit is used to release the placement unit from any rack (2) when the rack (2) moves, and then redirect the rack (2), the pushing unit comprises a reaction steel plate (3) and a first rotating rod (4), the shield machine model One end of the shield machine model (1) is open, and a cutterhead (5) is rotatably provided at the open end of the shield machine model (1), the cutterhead (5) is connected to a first rotating rod (4), a first bevel gear (7) is provided at the free end of the first rotating rod (4), a motor (6) is provided inside the shield machine model (1), a second bevel gear (8) is provided at the output end of the motor (6), the first bevel gear (7) is meshed with the second bevel gear (8), a third bevel gear (9) is meshed on the second bevel gear (8), a telescopic bracket (10) is provided on the third bevel gear (9), the free end of the telescopic bracket (10) is movably passed through the shield machine model (1) in sequence and then connected to the reaction steel plate (3), and a first gear (11) is also provided on the telescopic bracket (10). ), the first gear (11) is located on the reaction steel plate (3), and two worms are rotatably arranged on the reaction steel plate (3), and the free end of the worm is provided with a fourth bevel gear (12), and each fourth bevel gear (12) is meshed with a rack (2), and the end of the rack (2) is connected to the shield machine model (1), and the free end of the rack (2) is movable through the reaction steel plate (3) and then extends outward, and the placement unit includes a first rectangular groove (13) and a second rectangular groove (14) are opened on the closed end of the shield machine model (1), and the first rectangular groove (13) and the second rectangular groove (14) are connected, and a partition (15) is connected to the inner wall of the first rectangular groove (13), and the free end of the partition (15) is vertically provided with a first connecting plate (1 6), the first connecting plate (16) is connected to the inner wall of the second rectangular groove (14) through the first telescopic rod, the first connecting plate (16) is also provided with a second connecting plate (17), the second connecting plate (17) is provided with a groove, the redirection unit includes a plurality of second telescopic rods (18) arranged on the test box (23), each second telescopic rod (18) is connected to the reaction steel plate (3), a positioning plate (19) is provided between any two second telescopic rods (18), a second gear (25) meshing with the first gear (11) is rotatably provided on the positioning plate (19), the second gear (25) is provided with a guide rod (20) matched with the groove, and the end of the guide rod (20) movably passes through the positioning plate (19).

2. The experimental system for simulating shield over-excavation according to claim 1, characterized in that: Each second telescopic rod (18) is connected to the shield machine model (1) via a bearing column.

3. The experimental system for simulating shield over-excavation according to claim 2, characterized in that: The test box (23) is open at one end, and a plurality of bearing brackets (21) are provided at the open end of the test box (23). Each bearing bracket (21) is provided with a plurality of laser displacement meters (22), and the plurality of bearing brackets (21) are arranged at equal intervals along both sides of the pipeline axis.

4. The experimental system for simulating shield over-excavation according to claim 3, characterized in that: A plurality of laser displacement meters (22) are arranged at equal intervals on the bearing bracket (21).

5. An experimental method for simulating shield over-excavation, characterized in that: An experimental system for simulating shield over-excavation according to claim 4 comprises the following steps: Step 1: Fill the test box (23) with surrounding rock simulation material, leveling it every 10 cm. When the filling reaches the position close to the lower part of the through hole (24), install the cutterhead (5), soil bin and shield shell in the shield machine model (1) inside the test box (23) at the through hole (24), close the soil discharge switch, and continue to fill until the test requirements are met; Step 2: Starting from 10 cm away from the through hole (24) along the simulated excavation direction, a load-bearing bracket (21) is arranged at intervals of 13 cm perpendicular to the excavation direction, with a total of 7 load-bearing brackets (21) in the width direction, and laser displacement meters (22) are arranged along the excavation center line, one is arranged directly above the center line, one is arranged at intervals of 10 cm within a range of 20 cm on both sides of the center line, and only one is arranged outside the range of 20 cm, with a total of 49 arranged; Step 3: Extend the first telescopic rod, and after installing the segment ring, adjust the length of the first telescopic rod so that the reaction steel plate (3) faces the end of the shield machine model (1); Step 4: applying a certain thrust to the shield machine model (1) to balance the pressure acting in front of the shield machine model (1); Step 5: Turn on the soil discharge switch and screw conveyor in the shield machine model (1), stop loading after the rack (2) applies thrust and extends 5 cm each time, turn off the soil discharge switch and screw conveyor, check the soil volume in the soil box and replace it in time, level the soil surface, and use the laser displacement meter (22) to record the settlement data; Step 6: Simultaneously retract the rack (2) and the second telescopic rod by 5 cm in length, and repeat step 5 until they are 5 cm away from the other end of the test box (23); Step 7: Turn off the soil discharge switch and the screw conveyor, level the soil surface, record the settlement value with the laser displacement meter (22), and turn off the laser displacement meter (22); Step 8: Weigh the discharged surrounding rock simulation material to obtain the excavated volume.

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