Multifunctional tunnel model test device and method for testing arching curve of coarse-grained soil

Abstract

The application provides a multifunctional tunnel model test device and method for testing arching curve of coarse-grained soil, which comprises a loading system, a measuring system and a test box; the test box is a cuboid structure composed of a main frame and a pressure-bearing side plate; the upper part of the test box is provided with a force transmission steel plate; the loading system comprises a stand, a pressure lever, a balance weight, a loading frame and a tray; the stand is vertically fixed at the back of the test box, the pressure lever is arranged at the top of the stand, one end of the pressure lever is provided with the balance weight, and the other end of the pressure lever is provided with the tray; the tray is connected with the pressure lever through the loading frame; the top of the stand is a support point of the pressure lever; the measuring system comprises a displacement measuring device and a stress measuring device; the displacement measuring device comprises an adjustable balance screw and a scale; the stress measuring device comprises a strain gauge and a soil pressure cell. Compared with the traditional test device, the application realizes one box with multiple uses and can perform various tests such as soil body arching, settlement displacement and the like.

Description

Technical Field

[0001] This invention relates to the field of testing equipment technology, and in particular, to a multifunctional tunnel model testing device and method for testing the arch curve of coarse-grained soil. Background Technology

[0002] The mechanism of ground settlement caused by shield tunneling in sandy and gravelly soil is currently unclear. Unlike fine-grained soil strata, ground settlement caused by ground loss in sandy and gravelly strata is sudden and random. Specifically, it manifests as sudden settlement that occurs some time after the shield tunneling has passed through (ranging from several days to several months). The important influencing factors are the arching capacity of the sand and gravel and the failure of the stress arch. Existing monitoring and measurement technologies are difficult to accurately predict the occurrence of settlement.

[0003] Scholars have studied the arch formation curve of the collapse arch after shield tunneling in sand and gravel soil, but a quantitative descriptive model of the arch formation curve under the influence of multiple factors is lacking. Currently, most experimental studies on collapse arches are limited to a certain construction state, with certain discontinuities in time and space. There is a lack of a comprehensive dynamic study that can continuously study the overall dynamic development of the excavation net width from 0 to the target net width.

[0004] Numerous results have been achieved in using numerical simulation to study the impact of shield tunnel excavation on strata in sandy and gravelly soil. However, the physical parameters used in these simulations fundamentally rely on experimental calibration, and the validity of the results depends on verification using experimental or monitoring data. Currently, shield tunnel model testing equipment is extremely expensive, lacks versatility, and requires significant manpower and resources for each test. Furthermore, these models are highly specific and insufficient for simulating tunnel excavation in complex strata in real-world engineering projects.

[0005] Therefore, the industry urgently needs a new technology for a simple and practical multifunctional tunnel model test device that can adjust the width of the collapsed arch and measure surface settlement. Summary of the Invention

[0006] The purpose of this invention is to provide a multifunctional tunnel model test device and method that can adjust the width of the collapse arch and measure settlement, in order to solve the problems existing in the excavation of sand and gravel shield tunnels, and to study the mechanism of soil collapse and settlement caused by associated factors in sand and gravel soil. The multifunctional tunnel model test device provided by this invention has the advantages of convenient sample loading, easy measurement operation, and accurate and reliable measurement results.

[0007] To achieve the above objectives, the present invention provides a multifunctional tunnel model test device for testing the arching curve of coarse-grained soil. The multifunctional tunnel model test device includes a loading system, a measurement system, and a test chamber.

[0008] The test chamber is a cuboid structure consisting of a main frame and pressure-bearing side plates. The main frame is formed by two steel frames, each welded together as a whole, connected by bolts with rollers. The pressure-bearing side plates consist of three steel plates on the left, right, and rear sides of the chamber, an acrylic plate at the front, and a bottom plate. The bottom plate consists of an upper bottom partition and a lower sliding bottom plate. A force-transmitting steel plate is provided on the upper part of the test chamber.

[0009] The loading system includes a column, a pressure lever, a counterweight, a loading frame, and a tray;

[0010] The column is vertically fixed to the back of the test chamber. The pressure lever is located on the top of the column. One end of the pressure lever is equipped with a counterweight, and the other end is equipped with a tray. The tray is connected to the pressure lever through a loading frame. The top of the column is the support point of the pressure lever.

[0011] The measurement system includes a displacement measuring device and a stress measuring device;

[0012] The displacement measuring device includes an adjustable balance screw for measuring soil settlement and a scale for measuring slump. The balance screw is set on a pressure lever between the support point and the tray. The loading force is transmitted to the soil through the balance screw. The pressure lever is kept in a horizontal position by adjusting the rise and fall of the balance screw.

[0013] The stress measurement device consists of strain gauges for monitoring stress changes in tunnel support structures under different working conditions and earth pressure cells for monitoring soil stress states. The acrylic plate in front of the test chamber has a hole in the middle, the diameter and shape of which are determined according to the test requirements. A thin-walled component simulating tunnel lining with an equal outer diameter is installed inside the hole, and the strain gauge is installed on the thin-walled component.

[0014] Furthermore, the pressure lever is connected to the support point of the column via bearings and bolts.

[0015] Furthermore, the loading frame is a hook-type bracket that can be hung on the pressure lever.

[0016] Furthermore, the balance screw is equipped with a handwheel for adjusting the balance screw.

[0017] Furthermore, the support point between the top of the column and the pressure lever is located at a 5-point interval on the pressure lever near the end of the balance weight.

[0018] Furthermore, the loading system is provided in multiple parts, each column is welded to the main frame of the test chamber, and is symmetrically distributed at equal intervals from the midpoint of the long side of the test chamber to both sides.

[0019] Furthermore, each pressure lever in the loading system is 1500mm long; each pressure lever can apply a maximum force of 20kN; and each balance screw is a screw with an outer diameter of 15mm and a length of 300mm.

[0020] Furthermore, the balance screw is positioned on the pressure lever between the support point and the tray at a distance of 300mm from the support point.

[0021] Furthermore, the base plate consists of two layers: the upper bottom partition is composed of a series of steel strips of different widths that are in contact with the test soil, and the lower sliding base plate is composed of two steel plates of equal length that can slide to both sides.

[0022] The present invention also provides a method for measuring settlement using the above-mentioned multifunctional tunnel model test device, comprising:

[0023] Step 1: Assemble the main frame, rollers, and pressure-bearing side plates into a test chamber as needed;

[0024] Step Two: Based on the requirements, conduct model tests:

[0025] Scenario 1: Fill the assembled test chamber with the soil sample to be studied and compact it. After the soil sample is filled, place the force-transmitting steel plate on the surface of the soil sample.

[0026] Scenario 2: During the process of filling and compacting the soil sample to be studied into the assembled test chamber, a tunnel lining model with strain gauges attached is installed at the opening in the middle of the front acrylic plate. Soil pressure cells are embedded in the soil sample according to the test requirements. After the soil sample is filled, a force-transmitting steel plate is placed on the surface of the soil sample.

[0027] Step 3: Adjust the counterweight to make the pressure lever horizontal, and then adjust the balance screw to make it just contact the force transmission steel plate without applying force.

[0028] Step 4: According to the load requirements, place a certain number of weights on the tray, and observe whether the pressure lever is in a horizontal state. Adjust the balance screw to keep it in a horizontal state and maintain the pressure. When the soil settlement rate is less than a certain value that meets the test requirements, the settlement can be considered to be complete.

[0029] Step 5: Based on the experimental requirements, monitor the slump, soil deformation, structural stress state, and other test data.

[0030] If step two uses case one, then this step uses the following operation:

[0031] Scenario 3: Pull the sliding base plate outwards, remove the bottom partitions one by one, and measure the amount of the corresponding collapsed arch;

[0032] In the case of using scenario two in step two, this step uses the following operation:

[0033] Case 4: During the loading process in step four, strain gauges are used to monitor the changes in the stress state of the tunnel structure and the changes in the stress in the soil in real time. In this case, the test ends at this step.

[0034] Scenario 5: Pull the sliding bottom plate outward, remove the bottom partitions one by one, and measure the amount of collapsed arch; while pulling, monitor the changes in the stress state of the tunnel and the changes in the stress in the soil.

[0035] Step Six: Collapse Arch Stability Test: After the lower collapse arch has formed and remained stable, the collapse arch is quantitatively destroyed, and the settlement of the soil sample is detected to end the test.

[0036] The present invention has the following beneficial effects:

[0037] 1. Compared to traditional tunnel simulation test chambers, this invention provides a multifunctional tunnel model test device that can adjust the width of the collapse arch and measure settlement. This device features a detachable test chamber, resulting in lower costs, easier operation, and significant savings in manpower and resources. During the test, the pressure lever is kept in equilibrium by adjusting the balance screw. The change in length of the force-bearing part of the balance screw represents the soil settlement. Therefore, by measuring the change in length of the balance screw in real time, it is possible to monitor soil settlement and collapse conditions in real time while simulating the stress state of the tunnel.

[0038] 2. The present invention provides a multifunctional tunnel model test device that can adjust the width of the collapsed arch and measure soil settlement. The test box used is an assembled test box. Different test box volumes can be obtained by different assembly methods (adjusting the length of the roller, the width of the front and rear steel plates, etc.). Therefore, the assembled test box of the present invention can be flexibly assembled to carry out multi-condition tests according to actual needs.

[0039] 3. Compared to traditional testing devices, the measurement system of this invention, a multifunctional tunnel model testing device that can adjust the width of the collapse arch and measure settlement, is simple and can directly observe the settlement characteristics of the soil. This invention achieves quantitative description in three ways: first, by using a transparent acrylic plate (i.e., the observation window) and combining it with PIV image processing technology, it monitors the settlement of the surrounding soil caused by tunnel excavation, achieving quantitative description; second, by pulling open the sliding bottom plate to simulate the tunnel excavation width, it achieves a quantitative description of the relationship between the fill particle size distribution and the excavation width on soil disturbance (stress changes, collapse arch size, and surface settlement); third, by disturbing the collapse arch, it achieves a quantitative description of soil stability and secondary settlement. In this device, the lower bottom plate is pulled open to both sides to simulate dynamic tunnel excavation and monitor the dynamic development of the collapse arch. This invention can monitor soil settlement in real time while testing the stress state of the tunnel lining structure, and test important parameters such as the soil's arching ability and critical stability state.

[0040] 4. Compared to traditional testing devices, this invention achieves multiple uses with a single unit, enabling testing of various aspects such as tunnel stress state, soil collapse, and settlement. Furthermore, this invention features a simple structure, novel and reasonable design, diverse functions, convenient implementation, strong practicality, good performance, and ease of promotion.

[0041] In addition to the objectives, features and advantages described above, other objectives, features and advantages of the present invention will be further described in detail below with reference to illustrations. Attached Figure Description

[0042] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0043] Figure 1 This is a three-dimensional structural diagram of the test chamber without side plates in the multifunctional tunnel model test device of the present invention;

[0044] Figure 2 This is a three-dimensional structural diagram of the test chamber including the side plates in the multifunctional tunnel model test device of the present invention;

[0045] Figure 3 This is a front view of the multifunctional tunnel model test device of the present invention;

[0046] Figure 4 This is a left view of the multifunctional tunnel model test device of the present invention;

[0047] Figure 5 This is a top view of the multifunctional tunnel model test device of the present invention;

[0048] Figure 6 This is a structural diagram of the loading system in the multifunctional tunnel model test device of the present invention;

[0049] Figure 7 This is a detailed view of the rollers in the test chamber of the device of the present invention;

[0050] Figure 8 This is a detailed view of the transparent acrylic plate (i.e., the observation window) in front of the test chamber in the device of the present invention;

[0051] The components include: 1. counterweight; 2. pressure lever; 3. balance screw; 4. handwheel; 5. loading frame; 6. tray; 7. column; 8. weight; 9. bearing; 10. main frame; 11. roller; 12. steel plate; 13. acrylic plate; 14. sliding base plate; 15. bottom partition; 16. pre-set screw holes; 17. tunnel lining model; 18. bolt; 19. hole; 20. force transmission steel plate; 21. strain gauge. Detailed Implementation

[0052] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the present invention can be implemented in many different ways as defined and covered by the claims.

[0053] See Figures 1 to 8 This invention provides a multifunctional tunnel model test device that can adjust the width of the collapse arch and measure soil settlement. The tunnel model test device includes a loading system, a measurement system, and an assembled test chamber. The loading system consists of a series of pressure levers connected to a column vertically welded and fixed to the back of the test chamber via bearings and bolts. The levers are equipped with balance screws and loading trays for easy adjustment of the lever state and application of pressure. The measurement system includes displacement measuring devices and stress measuring devices. Furthermore, since the front of the chamber is made of a transparent acrylic panel, the corresponding soil settlement and collapse changes can be observed directly. The assembled test chamber is a cuboid structure composed of a main frame and pressure-bearing side plates on each load-bearing surface. The main frame consists of two steel frames connected by rollers and bolts. Different roller installation methods can result in test chambers of different volumes. The pressure-bearing side plates on each load-bearing surface consist of left, right, and rear steel plates 12, a transparent acrylic plate 13 at the front, and a bottom plate.

[0054] Specifically, the assembled test chamber is a cuboid structure composed of a main frame 10 and pressure-bearing side plates. The main frame 10 plays the main load-bearing role and is composed of two steel frames welded together from the front and back. During assembly, they are connected by rollers 11 and bolts 18. Different roller lengths and different roller assembly methods can achieve the effect of using test chambers of different sizes. Each load-bearing plate consists of three 6mm thick steel plates 12 on the left, right, and rear sides. The plates are designed with different sizes according to the front frame. The front panel is composed of steel plates and acrylic plates 13 to consider stress limitations. A transparent acrylic plate 13 with a side length of 1000mm*1000mm and a thickness of 15mm (i.e., observation window) is set in the middle near the bottom edge. Except for the acrylic plate, the front panel is filled with steel plates with a thickness of 3mm to complete the entire panel. A hole 19 with a diameter of 150mm is opened in the middle of the acrylic plate 13, and a tunnel lining model 17 with the same outer diameter is set inside. Strain gauges 21 are attached to the inner wall to detect stress changes. The base plate consists of two layers: an upper bottom partition 15 and a lower sliding base plate 14. The upper bottom partition 15 is composed of a series of steel strips of different widths that contact the test soil, specifically 40*2+12*20+40*2mm. The lower sliding base plate 14 consists of two steel plates of equal length that can slide to both sides. The upper layer is arranged in sequence and placed on the lower base plate, which is then placed on a roller at the bottom. During the test, the lower steel plate is first slid outwards and pulled out, allowing the upper steel strips to fall naturally, causing the soil inside the box to naturally collapse into an arch. The bottom partition 15 ensures that the soil is not affected by the sliding friction of the lower plate throughout the process. This device uses thin-walled components to simulate the tunnel lining structure, and strain gauges are attached to the inside to monitor changes in the tunnel's stress state. In the specific experiment: when the soil is filled to the corresponding height, the tunnel lining model 17 is installed, and then the soil is filled again until the required test height is reached, after which the subsequent test is conducted. The changes in key time points (i.e., initial strain gauge values, changes upon completion of backfilling, and changes after applying load) during the aforementioned process can be used to simulate the stress state during actual tunnel excavation. In the test step of opening the bottom plate, the changes are detected to study the mutual influence between tunnels that are spatially distributed vertically. The upper part of the test chamber is equipped with a force-transmitting steel plate 20. The loading system of this invention uses lever loading; the concentrated force generated by the lever acts on the center of the force-transmitting steel plate, and is converted by the steel plate into a uniformly distributed load acting on the upper surface of the soil. Under the maximum pressure conditions required for the test, the deformation of the steel plate is negligible; therefore, dividing the concentrated force by the area of ​​the force-transmitting steel plate yields the upper distributed load on the soil.

[0055] In one specific embodiment, the overall external dimensions of the test chamber are 2000mm*500mm*1700mm (length*width*height). The internal dimensions of the test chamber vary depending on the assembly method, with three options: 1000mm*500mm*1500mm (length*width*height), 500mm*500mm*1500mm (length*width*height), and 2000mm*250mm*1500mm (length*width*height). Assembly and testing can be performed according to actual needs.

[0056] The test chamber frame is equipped with pre-set screw holes 16 as described above, for connecting corresponding rollers 11 and bolts 18. The rollers are available in two lengths: 500mm and 250mm. The final assembled frame consists of welded square steel pipes on both the front and rear sides, in seven pairs from bottom to top. Each steel pipe has pre-set screw holes 16 drilled at 500mm intervals. The frame is supported by steel pipes at the four corners, which are square steel pipes with outer sides of 50mm x 50mm and a wall thickness of 6mm. Steel pads are placed underneath (the support columns are hollow square tubes to prevent them from puncturing the ground and causing instability). This results in a total height of 1500mm for the test chamber, with the test chamber 200mm from the ground. The frame is connected on both sides by bolts 18 and rollers 11, in seven pairs from bottom to top. A roller is placed at every 200mm along the bottom of the frame, for a total of 11 rollers.

[0057] The loading system includes a column 7, a pressure lever 2, a counterweight 1, a loading frame 5, and a tray 6. The column 7 is vertically fixed to the side of the test chamber. The pressure lever 2 is located on top of the column 7, with the counterweight 1 at one end and the tray 6 at the other. The tray 6 is connected to the pressure lever 2 via the loading frame 5. The top of the column 7 serves as the support point for the pressure lever 2. In one specific embodiment, a loading system includes seven pressure levers 2. Each pressure lever 2 is 1500mm long, and five equal division points near the end of the counterweight 1 are used as fulcrums, which are welded to the rear frame of the main frame via the column 7. The pressure lever 2 and the column 7 are connected by bearings 9 and bolts 18 to ensure that the pressure lever 2 is subjected to minimal external friction. The five equal division points are the result of finite element calculations, representing the optimal result considering the maximum load, lever section parameters, and safety factor. The short section of the pressure lever is connected to the counterweight 1 to balance the external forces such as the weight of the pressure lever. An adjustable balance screw 3 is installed on the long section of the pressure lever at a distance of 300mm from the fulcrum. The loading force is transmitted to the soil through the balance screw 3. Adjusting the balance screw 3 ensures that the pressure lever 2 remains in a horizontal position. Considering the thickness of the test chamber, the point of force application at 300mm is located in the center of the chamber to avoid eccentric loading on the soil. A hook-type bracket is installed at the end of the long section of the pressure lever, and weights 8 are placed on the tray 6 of the loading frame 5 to achieve the loading purpose.

[0058] Each pressure lever 2 in the loading system can apply a maximum force of 20kN, so the maximum force that one loading system can apply is 7 * 20kN. The column 7 is 1700mm high and made of the same material as the front and rear frames. It is a square steel tube with an outer side length of 50mm * 50mm and a wall thickness of 6mm, welded to the rear frame, and symmetrically distributed at 333mm intervals from the middle point outwards. Bearings 9 are welded to the support points of the pressure levers 2 and 7. The pressure levers are cylindrical steel tubes with a diameter of 50mm and a total length of 1500mm. The counterweight 1 is adjustable according to the weight of the empty lever, ensuring the balance of the lever when there are no weights 8 on the loading frame 5. The balance screw 3 is a screw with an outer diameter of 15mm and a length of 300mm. The balance screw 3 is equipped with a handwheel 4, which can adjust the position of the balance screw 3 as needed. The loading frame 5 is a hook-type bracket that can be hung on the pressure levers 2, and has a tray 6 on it.

[0059] The measurement system includes a displacement measuring device and a stress measuring device. The displacement measuring device includes a balancing screw 3 for measuring soil settlement and a scale; its probe can be used to measure the specific collapse amount when measuring the collapse arch. The balancing screw 3 is mounted on a pressure lever 2 between the support point and the tray 6; the loading force is transmitted to the soil through the balancing screw 3, and the pressure lever 2 is kept horizontal by adjusting the balancing screw 3. The stress measuring device is a strain gauge 21 mounted on a simulated tunnel lining pipe, which can measure the stress changes of tunnel support measures under different conditions and the stress changes of the soil tested by an earth pressure cell embedded in the soil.

[0060] This invention also provides a test method for a multifunctional tunnel model test device that can adjust the width of the collapsed arch and measure soil settlement, the test steps of which are as follows:

[0061] Step 1: Assemble the test chamber as needed: Assemble the main frame 10 and the corresponding rollers 11, and assemble the corresponding side steel plates 12, front acrylic plate 13, bottom plate and other pressure-bearing side plates.

[0062] Step Two: Based on the requirements, conduct model tests:

[0063] Scenario 1: Fill the assembled test chamber with the soil sample to be studied and compact it. After the soil sample is filled, place the force transmission steel plate 20 on the top of the test chamber to convert the concentrated force into stress.

[0064] Scenario 2: During the process of filling and compacting the corresponding research soil sample into the assembled test chamber, a tunnel lining model with strain gauges 21 attached is installed at the middle hole 19 of the front acrylic plate 13. Soil pressure cells are embedded in the soil sample according to the test requirements. After the soil sample is filled, a force transmission steel plate 20 is installed on the top of the test chamber to convert the concentrated force into stress.

[0065] Step 3: Adjust the counterweight 1 so that the pressure lever 2 is in a horizontal state, and adjust the balance screw 3 so that it is in just contact with the force transmission steel plate 20 without applying force, so that the load calculation is simpler and more efficient, and the test error is reduced.

[0066] Step 4: According to the load requirements, place the corresponding weights 8 on the tray 6, and observe whether the pressure lever 2 is in a horizontal state. Adjust the balance screw 3 to keep it in a horizontal state and maintain the pressure. When the soil settlement rate is less than a certain value that meets the test requirements, the settlement is considered to be complete.

[0067] Step 5: Based on the experimental requirements, monitor the slump, soil deformation, structural stress state, and other test data.

[0068] If step two uses case one, then this step uses the following operation:

[0069] Scenario 3: Pull the sliding base plate 14 outwards and remove the bottom partition 15 from the middle to both sides in sequence to measure the collapse volume, the shape and curvature of the collapse arch, and the soil settlement. Specifically, take a picture at the front plexiglass and combine it with image analysis technology to preliminarily determine the two-dimensional planar shape of the collapse arch. After clearing the fallen soil, insert calipers into the exposed part of the collapse arch at the bottom of the box through the 200mm space to measure the depth. Combining the above two measurements, the numerical three-dimensional reproduction of the collapse arch can be achieved, that is, the measurement of the collapse arch volume can be completed.

[0070] In the case of using scenario two in step two, this step uses the following operation:

[0071] Scenario 4: During the loading process in step four, strain gauges are used to monitor the changes in the stress state of the tunnel and the stress changes in the soil in real time; specifically, strain gauges and strain testing instruments can be used to monitor the changes in the stress state of the tunnel lining model in real time, and the test ends in this step.

[0072] Scenario 5: Pull the sliding base plate 14 outwards and remove the bottom partitions 15 one by one to measure the collapse volume, the shape and curvature of the collapse arch, and the soil settlement. During the pulling process, monitor changes in the tunnel's stress state and soil stress. Specifically, take photos at the front plexiglass area and combine them with image analysis technology to preliminarily determine the two-dimensional planar shape of the collapse arch. After clearing the fallen soil, insert calipers into the exposed area of ​​the collapse arch at the bottom of the box body through the 200mm space to measure the depth. Combining these two measurements allows for a three-dimensional numerical reconstruction of the collapse arch, thus completing the measurement of the collapse arch volume. Strain gauges and strain gauges can be used to monitor changes in the stress state of the tunnel lining model in real time.

[0073] Step Six: Collapse Arch Stability Test: After the lower collapse arch forms and is maintained in this state for a period of time, the collapse arch is quantitatively destroyed, and the settlement of the soil sample is detected. Specifically, as mentioned in Step Four, the pressure lever 2 is kept horizontal throughout the entire test by adjusting the balance screw 3. Therefore, the settlement of the soil sample can be obtained by comparing the length of the balance screw before and after the test.

[0074] The arching ability of coarse-grained soil is influenced by numerous factors (particle size distribution, stress level, degree of consolidation, moisture content, etc.), and currently there is no mature theory to accurately predict it. The device of this invention can effectively control these influencing factors and study the formation and evolution of soil collapse arches by controlling the opening width of the bottom sliding plate. It can also directly observe the arching morphology of the collapse arch. Related experimental research has positive significance for improving the theoretical system regarding the arching ability and stability assessment of coarse-grained soil.

[0075] The delayed settlement of coarse-grained soil has long been a major challenge in the construction of tunnels in gravel and sandy soils. However, the mechanism of delayed settlement is not clear. Based on existing research, several important influencing factors have been identified. The device of this invention can address these factors by quantitatively analyzing their impact on soil settlement, such as the influence of soil particle size distribution and moisture content, superload on the soil, and excavation width. It can also simulate the settlement state caused by tunnel excavation, providing a theoretical basis for engineering construction.

[0076] With the large-scale construction of tunnels, the distance between newly built (planned) tunnels and existing tunnels is getting closer and closer. From the perspective of soil mechanics, the two must have mutual influence. Compared with traditional tunnel model test devices, the device of this invention realizes the simulation of the mutual influence between the tunnel under construction and the existing tunnel. The lining model of the existing tunnel is set at a specific position in the model box, and its stress state is monitored. The impact of the excavation of the tunnel under construction on the existing tunnel can be simulated by pulling open the sliding bottom plate, and the impact of the existing tunnel on the excavation stability of the tunnel under construction can also be analyzed.

[0077] In summary, this invention provides a multifunctional tunnel model testing device that can adjust the width of the collapse arch and measure soil settlement. This device features a simple structure, low cost, novel design, flexible assembly and disassembly, and easy expansion. The testing operation is simple, significantly saving manpower and resources. The test uses a pressure lever for loading, and the adjustable balance screw ensures it remains in a balanced state, resulting in stable loading. Soil settlement is monitored by real-time measurement of the length change of the load-bearing section of the balance screw. Adjusting the opening width of the sliding bottom plate allows for testing the range and stability of the soil collapse arch. Tunnel model tests can measure important parameters such as soil settlement, stress changes, and the stress state of the tunnel support structure caused by tunnel excavation. This invention achieves multiple uses in one unit, capable of testing various aspects including soil collapse, settlement, stress state, tunnel stress state, and the mutual influence of multiple tunnel excavations. Its diverse functions, strong practicality, and good performance make it suitable for widespread application.

[0078] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A multifunctional tunnel model test device for testing the arching curve of coarse-grained soil, characterized in that, The multifunctional tunnel model test device includes a loading system, a measurement system, and a test chamber; The test chamber is a cuboid structure consisting of a main frame and pressure-bearing side plates. The main frame is formed by welding two steel frames, one at the front and one at the back, together with rollers and bolts. The pressure-bearing side plates consist of three steel plates on the left, right, and rear sides of the chamber, an acrylic plate at the front, and a bottom plate. The bottom plate consists of an upper bottom partition and a lower sliding bottom plate. The top of the test chamber is equipped with a force-transmitting steel plate. The loading system includes columns, pressure levers, counterweights, loading frames, and trays; the loading system has multiple columns, each of which is welded to the main frame of the test chamber and is symmetrically distributed at equal intervals from the center of the long side of the test chamber to both sides. The column is vertically fixed to the back of the test chamber. The pressure lever is set on the top of the column. One end of the pressure lever is equipped with a counterweight, and the other end is equipped with a tray. The tray is connected to the pressure lever through a loading frame. The top of the column is the support point of the pressure lever. The support point between the top of the column and the pressure lever is located at the 5th division point on the pressure lever near the end of the counterweight. The measurement system includes a displacement measuring device and a stress measuring device; The displacement measuring device includes an adjustable balance screw for measuring soil settlement and a scale for measuring slump. The balance screw is connected to a pressure lever between the support point and the tray connection point. The loading force is transmitted to the soil through the balance screw, and the pressure lever is always kept in a horizontal position by adjusting the rise and fall of the balance screw. The stress measurement device consists of strain gauges for monitoring stress changes in tunnel support structures under different working conditions and earth pressure cells for monitoring soil stress states. The acrylic plate in front of the test chamber has a hole in the middle, the diameter and shape of which are determined according to the test requirements. A thin-walled component simulating tunnel lining with an equal outer diameter is installed inside the hole, and the strain gauge is installed on the thin-walled component.

2. The multifunctional tunnel model test device for testing the arch curve of coarse-grained soil according to claim 1, characterized in that, The pressure lever is connected to the support point of the column by bearings and bolts.

3. The multifunctional tunnel model test device for testing the arch curve of coarse-grained soil according to claim 1, characterized in that, The loading frame is a hook-type bracket that can be hung on a pressure lever.

4. The multifunctional tunnel model test device for testing the arch curve of coarse-grained soil according to claim 1, characterized in that, The balance screw is equipped with a handwheel for adjusting the raising and lowering of the balance screw.

5. The multifunctional tunnel model test device for testing the arch curve of coarse-grained soil according to claim 1, characterized in that, Each pressure lever in the loading system is 1500mm long; each pressure lever can apply a maximum force of 20kN; each balance screw is a screw with an outer diameter of 15mm and a length of 300mm.

6. A multifunctional tunnel model test device for testing the arch curve of coarse-grained soil according to claim 5, characterized in that, The balance screw is positioned on the pressure lever between the support point and the tray, approximately 300 mm from the support point.

7. A multifunctional tunnel model test device for testing the arch curve of coarse-grained soil according to claim 1, characterized in that, The base plate consists of two layers. The upper layer has a bottom partition composed of a series of steel strips of different widths that are in contact with the test soil. The lower layer has a sliding base plate composed of two steel plates of equal length that can slide to the sides.

8. A method for measuring the settlement of test soil using a multifunctional tunnel model test device as described in any one of claims 1 to 7, characterized in that, include: Step 1: Assemble the main frame, rollers, and pressure-bearing side plates into a test chamber as needed; Step Two: Based on the requirements, conduct model tests: Scenario 1: Fill the assembled test chamber with the soil sample to be studied and compact it. After the soil sample is filled, place the force-transmitting steel plate on the surface of the soil sample. Scenario 2: During the process of filling and compacting the soil sample to be studied into the assembled test chamber, a tunnel lining model with strain gauges attached is installed at the opening in the middle of the front acrylic plate. Soil pressure cells are embedded in the soil sample according to the test requirements. After the soil sample is filled, a force-transmitting steel plate is placed on the surface of the soil sample. Step 3: Adjust the counterweight to make the pressure lever horizontal, and then adjust the balance screw to make it just contact the force transmission steel plate without applying force. Step 4: According to the load requirements, place a certain number of weights on the tray, and observe whether the pressure lever is in a horizontal state. Adjust the balance screw to keep it in a horizontal state and maintain the pressure. When the soil settlement rate is less than a certain value that meets the test requirements, the settlement is considered to be complete. Step 5: Based on the experimental requirements, monitor the slump, soil deformation, structural stress state, and other test data. If step two uses case one, then this step uses the following operation: Scenario 3: Pull the sliding base plate outwards, remove the bottom partitions one by one, and measure the amount of the corresponding collapsed arch; In the case of using scenario two in step two, this step uses the following operation: Case 4: During the loading process in step four, strain gauges are used to monitor the changes in the stress state of the tunnel structure and the changes in the stress in the soil in real time. In this case, the test ends at this step. Scenario 5: Pull the sliding bottom plate outward, remove the bottom partitions one by one, and measure the amount of collapsed arch; while pulling, monitor the changes in the stress state of the tunnel and the changes in the stress in the soil. Step Six: Collapse Arch Stability Test: After the lower collapse arch has formed and remained stable, the collapse arch is quantitatively destroyed, and the settlement of the soil sample is detected to end the test.

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