Test device, system and method for simulating failure of foundation pit cross brace

Abstract

The invention discloses a test device, system and method for simulating foundation pit cross brace failure, the test device comprises a test box body, a soil body, a deep pit supporting mechanism and a cross brace failure mechanism, the system comprises the test device, the test device is located in a hanging basket of a geotechnical centrifuge, and the test box body is located in the soil engineering centrifuge. The method is suitable for the geotechnical centrifugal model test system for simulating the failure of the foundation pit cross brace. According to the system, the foundation pit supporting test is optimized through multi-link design. The test box body sets an installation reference, reproduces various soil layers and pore water environments, and fits actual stress; and the row piles, the enclosing purlins and the cross braces are re-carved, parameters can be adjusted to adapt to different working conditions, and a real failure mode is restored. The cross brace failure mechanism realizes dynamic evolution from a single rod to overall instability, and can also simulate sudden and progressive failures. Centrifugal compatible monitoring equipment is further arranged, multi-parameter synchronous acquisition is achieved, anti-interference wireless transmission is matched, data accuracy is guaranteed, and support is provided for analyzing the coupling relation between the soil body and the support failure.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of test simulation, in particular to a simulation device and system for failure test of a foundation pit cross brace and a method thereof. BACKGROUND

[0002] Under the background of continuous deepening of urban underground space development, deep foundation pit support engineering has become a key link for the safety of underground structure construction and the protection of the surrounding environment. Essentially, deep foundation pit support is a systematic engineering technology system, and its core purpose is to create a safe and stable working space for underground structure construction through scientific support, reinforcement and protection measures, while minimizing the occurrence of serious accidents such as foundation pit sidewall collapse, water leakage, and effectively reducing the adverse effects of the construction process on the surrounding environment such as adjacent buildings, underground pipelines, road facilities, etc. From the actual engineering scene, the application of this technology is directly related to the safety of construction personnel, the progress and cost control of engineering projects, and the normal operation of urban existing infrastructure, and is an indispensable important part of modern civil engineering field. The high uncertainty, complexity and contingency of deep foundation pit engineering itself make it a high-risk type in the field of engineering construction. On the one hand, the construction environment of deep foundation pit engineering is greatly affected by geological conditions and hydrological conditions, and there are significant differences in soil layer distribution, soil physical and mechanical properties, groundwater level changes and other factors in different regions. Even in the same engineering site, local geological conditions may mutate, bringing many unpredictable challenges to engineering design and construction. On the other hand, the deep foundation pit construction process involves many procedures, such as earthwork excavation, support structure construction, and dewatering, etc. Each link is interrelated and interdependent, and any problem in one link may trigger a chain reaction. More importantly, the foundation pit support structure, as a temporary protection system, usually has lower safety reserves compared to the main structure of the building. In the design stage, based on economic considerations, the material consumption and structure size are usually controlled as much as possible on the premise of meeting the basic safety requirements, which makes the support structure relatively weak in resisting risks when facing sudden loads, abnormal changes in geological conditions, etc. Currently, the design method of deep foundation pit support structure is generally based on the core of components. This design idea has obvious limitations, that is, it lacks overall consideration of the whole support system. Specifically, the designer usually analyzes the stress and calculates the strength of each component such as supporting pile, anchor, waterproof curtain, etc. separately to ensure that each component can meet the safety standard under its own working condition. However, this design mode of "divide and rule" ignores the synergistic effect between components and the overall stress state of the whole support system when bearing external load. In fact, the deep foundation pit support system is an organic whole, and each component bears the external load such as soil pressure and water pressure together through interaction. The stress change of a component will inevitably affect other components. Due to the lack of consideration of the redundancy of the whole support system in the design process, when the local component fails due to design defects, construction quality problems or external environmental changes, the whole support system lacks sufficient standby bearing capacity to make up for the load imbalance caused by local failure. The chain reaction caused by local failure often leads to serious accidents such as large-scale continuous collapse of deep foundation pit. For example, when the supporting pile of foundation pit fails due to construction deviation, the local fracture of the pile body under the action of soil pressure will cause the load originally borne by the supporting pile to be quickly transferred to the adjacent supporting pile. Since the design stage does not consider this load mutation, the adjacent supporting pile may fail in turn due to exceeding the design bearing capacity, and then cause the overall collapse of the supporting structure. At the same time, the local damage of the waterproof curtain may cause a large amount of groundwater to flow into the foundation pit, which not only aggravates the soil pressure of the foundation pit side wall, but also may cause the permeation damage of the soil around the foundation pit, leading to secondary disasters such as ground subsidence and adjacent building inclination. A large number of engineering practices show that the occurrence of deep foundation pit accidents is not accidental, and its root cause is often the local failure of foundation pit support structure. The neglect of the overallity and redundancy of the support system in the design method further amplifies the risk of large-scale accidents caused by local failure The row pile + horizontal internal support foundation pit support system is often used in the case of large engineering scale, complex surrounding environmental conditions and variable surrounding load of foundation pit. The mechanism, process and control of the overall safety of the foundation pit caused by the local damage of the row pile + horizontal internal support foundation pit support system are urgently needed to be studied. Figure 1 As shown in the figure, the internal support row pile support structure is generally composed of support (steel support or concrete support), surrounding purlin (crown beam and waist beam) and row pile (diaphragm wall).

[0003] In actual engineering, local damage such as connection damage between support and crown beam, yield of support and fracture of supporting pile may occur. From the current research status of continuous damage of structure engineering and foundation pit engineering, it can be seen that the local damage of structure or component may induce the continuous collapse of the whole building. It is necessary to find out the influence of local component failure on the whole support structure for the internal support row pile (diaphragm wall) support foundation pit. SUMMARY

[0004] To achieve the above technical problems, one of the technical solutions adopted by the present application is: a simulation foundation pit cross support failure test device, the test device comprising: a test box body for providing an installation carrier for components of the test device; a soil body for simulating soil layers in underground engineering; a deep pit support mechanism for simulating deep foundation pit support in underground engineering; the deep pit support mechanism is located in the soil body; a cross support failure mechanism 4 for applying failure conditions to the deep pit support mechanism to simulate the destruction of support and crown beam connection, support yielding and support pile breaking in deep foundation pit support; the cross support failure mechanism is installed on the test box body 1 and located above the deep pit support mechanism.

[0005] Further, the deep pit support mechanism comprises: a foundation pit opened in the soil body; at least two rows of piles respectively located at opposite inner vertical surfaces of the foundation pit; each of the rows of piles is composed of a plurality of single piles inserted vertically side by side in the foundation pit; at least two surrounding purlins respectively fixedly installed on each single pile of the corresponding row of piles; a plurality of bolts respectively fixedly installed on the surrounding purlins, and the bolts correspond one-to-one to the single piles; a plurality of support units respectively installed between the two surrounding purlins at an interval of one bolt.

[0006] Further, each of the support units comprises: at least two support rods arranged side by side; at least two support hinge seats for connecting the two support rods; one end of each of the support hinge seats is installed on the end face of the support rod, and the other end is hingedly connected to the other support hinge seat through a pin shaft, thereby connecting the two support rods and forming a complete foundation pit support rod; at least two support ball head pins; each of the support ball head pins is installed on the end face of the corresponding support rod close to the bolt, and the ball head of each of the support ball head pins is overlapped in the corresponding bolt.

[0007] Further, the cross support failure mechanism comprises: at least two loading tracks installed parallel to each other on the upper end of the test box body and parallel to the support rods; a track mounting plate installed between the two loading tracks; the track mounting plate is provided with a through slot along the length direction thereof; a plurality of bolt positioning members respectively fixedly installed at equal distances on the track mounting plate on one side of the through slot; A plurality of hanging units are installed between the through slot and the support hinge seat, and each of the hanging units is located between the bolt positioning members, and the position of each of the hanging units corresponds to the support rod; the hanging units are used to provide upward tension to the support rod; A sliding pushing unit is fixedly installed on the track mounting plate; the sliding pushing unit is used to trigger the hanging units step by step, so that the support rod loses the upward tension, the situation that the middle part of the support rod is broken is simulated, and then the working condition that the two side enclosures lose the support of the support rod is simulated; A driving unit is fixedly installed on the track mounting plate; the driving unit is used to provide power for the sliding pushing unit.

[0008] Further, each of the hanging units comprises: A metal rod; two ends of each of the metal rods span on the through slot; A hanging rope hook is installed on the support hinge seat; A hanging rope; one end of each of the hanging ropes is connected with the metal rod, and the other end is connected with the hanging rope hook.

[0009] Further, the sliding pushing unit comprises: A sliding rail is fixedly installed on the track mounting plate and is parallel to the through slot; A sliding block is installed on the sliding rail; the sliding block moves along the length direction of the sliding rail; A push plate is installed on the sliding block; At least one pushing block 4064 is installed on the push plate 4063; the surface of the pushing block 4064 is in contact with the metal rod 4051.

[0010] Further, the driving unit comprises: A hydraulic cylinder is fixedly installed on the track mounting plate and is parallel to the sliding rail; Two pulley seats are both installed on the track mounting plate and correspond to the sliding rail and the hydraulic cylinder respectively; Two pulleys are respectively installed on the corresponding pulley seats; A pulling rope is connected with the extension end of the hydraulic cylinder through a pull rod at one end, and is connected with the side surface of the sliding block in sequence at the other end.

[0011] Another technical scheme adopted by the present application is a soil centrifuge model test system for simulating the failure of a foundation pit cross brace, wherein the soil centrifuge model test system for simulating the failure of the foundation pit cross brace comprises the test device for simulating the failure of the foundation pit cross brace.

[0012] Another technical scheme adopted by the present application is a test method for simulating the failure of a foundation pit cross brace, which is suitable for the soil centrifuge model test system for simulating the failure of the foundation pit cross brace, and the test method comprises the following steps of: S1, start the soil centrifuge, gradually increase the acceleration according to the preset program until the preset acceleration of the test design is reached, and monitor the running parameters of the rotation speed and vibration value of the soil centrifuge in real time during the acceleration process; S2, when the soil centrifuge is stable at the preset acceleration, the control system sends an instruction to the hydraulic cylinder to drive the hydraulic cylinder to move at a preset speed, which drives the push plate on the sliding block to move synchronously with the driving block, and after the driving block contacts the metal rod, the push force is gradually applied, the metal rod rotates, and then the metal rod is peeled off from the through slot of the track mounting plate, causing the hanging rope to lose support and fall off; S3, a preset high-speed camera is used to record and observe the support falling process and situation, and a preset displacement sensor is used to monitor the horizontal displacement of the row pile and the settlement of the surrounding soil of the foundation pit, after the support falls off, the acceleration of the soil centrifuge is gradually reduced to zero, and the test system is stopped, and the test data is saved for subsequent analysis.

[0013] Compared with the prior art, the present application has the following beneficial effects: by providing a unified installation reference for the test box, avoiding test errors caused by component displacement and inclination, and ensuring that the relative position of the supporting structure and the failure mechanism conforms to the logic of the real foundation pit supporting system; the soil can reproduce different soil layer characteristics, even simulate multi-layer heterogeneous soil and pore water environment, so that the test stress state is highly consistent with the actual engineering, and the problem of data distortion in traditional simplified simulation is solved.

[0014] By setting the deep pit supporting mechanism, the real supporting structure of the row pile, the surrounding purlin and the cross brace is completely reproduced: the row pile can be adjusted by adjusting the insertion depth and arrangement density of the single pile, and different working conditions such as soft soil dense row pile and hard rock sparse row pile can be simulated; the surrounding purlin realizes the overall stress of the row pile, avoiding uneven stress of single pile; the hinge seat and ball head pin of the supporting unit restore the hinge support and universal adjustment characteristics of the cross brace node, ensuring that the deformation and failure mode of the supporting structure are consistent with the actual situation, providing a reliable physical model for studying the failure mechanism.

[0015] By setting the cross brace failure mechanism, it breaks through the limitation of traditional one-time destruction, and through the precise driving of the hydraulic cylinder and the gradual triggering of the driving block, it can realize the dynamic evolution process from single cross brace failure to multiple cross brace chain failure to overall support instability, reproduce three core failure scenarios of support and corbel connection damage, support yield and support pile breakage.

[0016] By setting the critical sliding force of the metal rod of the mounting unit and the adjustable triggering rate of the sliding driving unit, both sudden failure such as cross brace fracture caused by earthquake and gradual failure such as cross brace load accumulation caused by soft soil creep can be simulated, meeting the research needs of different engineering risk scenarios and providing multi-condition data support for foundation pit safety warning.

[0017] The system is equipped with monitoring devices compatible with the centrifugal environment: strain gauges monitor the stress of the support structure, laser displacement sensors monitor the displacement of the soil and the row piles, piezoelectric earth pressure cells monitor the distribution of earth pressure, and high-speed cameras record the dynamic process of failure, realizing the synchronous acquisition of stress, displacement, earth pressure and images covering the whole cycle from before failure to during failure and after failure.

[0018] The wireless transmission module is resistant to centrifugal interference and has small data synchronization error, ensuring stable and accurate monitoring data in a high centrifugal environment, avoiding data deviation caused by device interference, and providing a complete data set for subsequent quantitative analysis of the coupling relationship between soil deformation and support failure. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 It is a structural schematic diagram of the simulation foundation pit cross brace failure test device of the present application.

[0020] Figure 2 It is a structural schematic diagram of the cross brace failure mechanism of the present application.

[0021] Figure 3 It is a structural schematic diagram of the support unit and the mounting unit of the present application.

[0022] Figure 4 It is a structural schematic diagram of the soil centrifugal model test system for simulating foundation pit cross brace failure of the present application.

[0023] 1, test box; 2, soil; 3, deep pit support mechanism; 301, foundation pit; 302, row pile; 3021, single pile; 303, surrounding purlin; 304, bolt; 305, support unit; 3051, support rod; 3052, support hinge seat; 3053, pin shaft; 3054, support ball pin; 4, cross brace failure mechanism; 401, loading track; 402, track mounting plate; 403, through slot; 404, bolt positioning piece; 405, mounting unit; 4051, metal rod; 4052, rope hook; 4053, rope; 406, sliding and pushing unit; 4061, sliding rail; 4062, sliding block; 4063, push plate; 4064, pushing block; 407, driving unit; 4071, hydraulic cylinder; 4072, pulley seat; 4073, pulley; 4074, pulling rope; 4075, pull rod. DETAILED DESCRIPTION

[0024] The technical solutions of the simulation foundation pit cross brace failure test device and the equipment thereof provided by the present application will be described clearly and completely in the embodiments of the present application combined with the drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0025] Example 1 like Figure 1 As shown, a test device for simulating the failure of cross braces in a foundation pit is provided. This device includes a test chamber 1, which serves as a mounting platform for the components of the test device. Specifically, the test chamber 1 provides a unified and fixed mounting reference for various components of the test device, such as simulated foundation pit structural components, deep pit support mechanisms, cross brace failure mechanisms, and monitoring sensors. Compared to decentralized installation methods without a fixed platform, this effectively avoids problems such as displacement, tilting, or swaying of components due to a lack of stable support.

[0026] The experimental setup also includes: soil 2, which is used to simulate soil layers in underground engineering.

[0027] In this embodiment, the excavation of the foundation pit and the stress on the cross bracing in underground engineering are always closely related to the surrounding soil layers. Parameters such as density, water content, cohesion, and internal friction angle of different soil layers directly affect the stress distribution of the foundation pit retaining structure and the bearing capacity requirements of the cross bracing. Soil 2 accurately reproduces the soil layer characteristics of the target engineering scenario, allowing the test environment to closely resemble real underground working conditions.

[0028] Staff can construct complex soil layer models, such as heterogeneous soil with an upper layer of cohesive soil and a lower layer of sand, saturated soil containing pore water, and composite soil containing gravel and other particulate impurities, to simulate cross-bracing failure tests under different engineering scenarios, depending on the experimental requirements. For example, when simulating a foundation pit in a coastal area, soil mass 2 can be configured as saturated sand to study the impact of seawater seepage on the stress on the cross-bracing; when simulating a foundation pit in a mountainous area, large pieces of gravel can be added to analyze the inducing effect of local stress concentration on cross-bracing failure. This flexibility allows the experimental device to cover more complex engineering scenarios, providing experimental support for solving foundation pit safety problems under special working conditions.

[0029] like Figure 1 As shown, the test device also includes a deep pit support mechanism 3, which is used to simulate deep foundation pit support in underground engineering; the deep pit support mechanism 3 is located in the soil 2.

[0030] Furthermore, the deep pit support mechanism 3 includes: A foundation pit 301 is opened in the soil body 2. Specifically, a recessed area consistent with the actual deep foundation pit shape is formed inside the soil body 2 to provide an installation reference for subsequent support components such as pile row 302 and surrounding purlin 303, and to simulate the foundation pit space formed after excavation in underground engineering. The advantage is to avoid simplified simulation without a foundation pit space, so that the stress, deformation and failure process of the support component are completely based on the engineering logic of the soil body after excavation, ensuring that the test results are consistent with the actual foundation pit support failure law, and improving the data reference value; the spatial structure of the foundation pit 301 can accommodate monitoring equipment such as displacement sensors and soil pressure cells, facilitating the simultaneous collection of data such as soil deformation and support structure stress, supporting multi-dimensional failure mechanism analysis.

[0031] At least two pile rows 302 are respectively located at the opposite inner vertical surfaces of the foundation pit 301; each of the pile rows 302 is composed of a plurality of single piles 3021 inserted vertically side by side in the foundation pit 301. Specifically, by inserting a plurality of single piles 3021 vertically side by side into the soil body 2 on the inner surface of the foundation pit 301, the core function of the pile row in the actual engineering such as cast-in-place pile and precast pile is reproduced to resist the lateral extrusion of the soil body 2 and prevent the collapse of the side wall of the foundation pit. The lower end of the single pile 3021 is inserted into the deep part of the soil body 2 to simulate the characteristics of the actual pile row embedded in the stable soil layer, and to transfer the soil pressure load of the side wall of the foundation pit to the deep stable soil body, avoiding the instability of the support structure due to insufficient embedding.

[0032] At least two surrounding purlins 303 are respectively fixedly installed on each single pile 3021 of the corresponding pile row 302. Specifically, the pile row in the actual foundation pit is the first line of defense against soil pressure, and the pile row 302 can simulate the support capacity of the pile row in different engineering scenarios such as dense pile row in soft soil area or sparse pile row in hard rock area through the arrangement density and insertion depth adjustability of the single pile 3021, meeting the diversified test requirements. The single pile 3021 is in direct contact with the soil body 2, and in the test, the horizontal displacement and bending stress of the single pile 3021 can be monitored to analyze the influence of soil body 2 deformation (such as soil creep) on the pile row and other structures, and the collapse mode of the soil body 2 after the failure of the pile row can be observed to deepen the research on the interaction between support and soil.

[0033] A plurality of bolts 304 are respectively fixedly installed on the surrounding purlin 303, and the bolt 304 corresponds to the single pile 3021 one by one. Specifically, the plurality of single piles 3021 on the same side are connected into a rigid whole through the surrounding purlin 303 to avoid the separate deformation or failure of a single single pile 3021 due to uneven stress, reproducing the effect of coordinating the stress of the pile row and dispersing the load in the actual surrounding purlin. The surface of the surrounding purlin 303 is flat and perpendicular to the single pile 3021, providing a stable installation carrier for the subsequent bolts 304 and support units 305, ensuring that the support unit 305 can be connected horizontally to the pile rows on both sides to simulate the connection relationship between the actual cross brace and the surrounding purlin.

[0034] In the present embodiment, the co-ridge is the key node connecting the row pile and the cross brace in the actual foundation pit. The setting of the co-ridge 303 changes the supporting system in the test from the dispersed single pile to the pile-ridge collaborative structure, which is closer to the actual stress state of the engineering and avoids the load transmission distortion caused by the lack of co-ridge. The rigid connection of the co-ridge 303 can reduce the lateral displacement of the single pile 3021 and prevent the supporting structure from affecting the test data due to its own instability in the early stage of the test. At the same time, it is convenient to replace the co-ridge 303 with different materials and cross-sectional sizes to study the influence of the co-ridge stiffness on the anti-failure ability of the overall supporting system.

[0035] As shown in Figure 3 , a plurality of supporting units 305 are installed between the two co-ridges 303 at intervals of a bolt 304. The supporting unit 305 is the core component of the cross brace simulating the actual foundation pit, which realizes the precise replication and failure simulation of the cross brace function through modular design.

[0036] Further, each supporting unit 305 comprises at least two support rods 3051 arranged side by side. Specifically, the support rod 3051 is the core load-bearing member of the supporting unit, which directly bears the soil pressure load transmitted by the two co-ridges 303, simulates the anti-lateral displacement function of the cross brace in the actual foundation pit, and prevents the row piles on both sides of the foundation pit from deforming inward. The plurality of support rods 3051 arranged side by side can disperse the concentrated load transmitted by the co-ridge 303 into a uniformly distributed load, avoid the premature failure of a single support rod due to excessive load, and at the same time simulate the supporting form of multiple cross braces in parallel in the actual engineering. The support rod 3051 can be made of steel or acrylic material or have an adjusted cross-sectional size to precisely control its carrying capacity. In the test, the bending, breaking and other typical failure modes of the support rod can be realized by loading, and the destruction process of the actual cross brace is restored. By replacing the support rods 3051 with different numbers and stiffnesses, the influence of the number and stiffness of the cross brace on the stability of the supporting system can be studied, which provides data support for the selection of the actual engineering cross brace.

[0037] At least two support hinge seats 3052 are used to connect two support rods 3051; one end of each support hinge seat 3052 is mounted on the end face of a support rod 3051, and the other end is hingedly connected to another support hinge seat 3052 through a pin shaft 3053, thereby completing the connection of the two support rods 3051. Through the cooperation of the support hinge seat 3052 and the pin shaft 3053, the two support rods 3051 can rotate around the pin shaft, simulating the hinged characteristics of the actual cross-bracing and surrounding purlin connection joint. The support rod is allowed to produce a small rotation under stress, avoiding stress concentration caused by rigid connection. While allowing rotation, the support hinge seat 3052 can transmit the axial horizontal support force of one side support rod 3051 to the other side support rod, ensuring the integrity of the load transmission path of the whole support unit. In this embodiment, the end of the actual cross-bracing is rigidly connected, which is easy to produce bending moment concentration, while the hinged joint can release the bending moment. The arrangement of the support hinge seat 3052 makes the stress state of the support rod in the test more close to the actual situation, avoiding the distortion of the failure mode caused by the simplification of the connection mode. The connection gap and rotation angle of the support hinge seat 3052 and the pin shaft 3053 can be monitored by a displacement sensor, which can study the influence of the wear and looseness of the hinged joint on the bearing capacity of the support unit, and provide a basis for optimizing the design of the actual hinged joint.

[0038] At least two support ball head pins 3054; each support ball head pin 3054 is mounted on the end face of the corresponding support rod 3051 near the bolt 304, and the ball head of each support ball head pin 3054 is overlapped in the corresponding bolt 304.

[0039] Specifically, the ball head of the support ball head pin 3054 can freely rotate in the reserved hole of the bolt 304, simulating the universal adjustment function of the actual cross-bracing and surrounding purlin connection, and adapting to the small angle deviation of the support rod 3051 caused by soil deformation in the test. The close overlap of the ball head and the bolt 304 can ensure that the axial load of the support rod 3051 can be transmitted to the surrounding purlin 303 through the support ball head pin 3054, avoiding the interruption of load transmission caused by connection misalignment. During the actual excavation of the foundation pit, the support structure will produce a small displacement or inclination due to the uneven deformation of the soil, and the universal adjustment capability of the support ball head pin 3054 can make the support unit adapt to this deformation, avoid the premature failure of the support unit caused by connection jamming in the test, and ensure that the test can completely simulate the whole process from soil deformation to support adaptation to final failure. It is difficult to ensure that the two surrounding purlins 303 are completely parallel and the support rod 3051 is completely horizontal during installation. The ball head overlap design of the support ball head pin 3054 can accommodate certain installation errors, reduce the interference of insufficient installation precision on test data, and improve the repeatability and reliability of the test.

[0040] As Figure 2As shown, the test device further comprises: a cross brace failure mechanism 4 for applying failure conditions to the deep pit support mechanism 3 to simulate the destruction of the support and the crown beam connection, the yield of the support and the breaking of the support pile in the deep foundation pit support; the cross brace failure mechanism 4 is installed on the test box 1 and located above the deep pit support mechanism 3. The cross brace failure mechanism 4 is the core functional module of the simulation of the cross brace failure test of the foundation pit, and the core function of the cross brace failure mechanism 4 is to actively apply and accurately control the failure working condition of the support system. It can reproduce three typical failure scenarios of support and crown beam connection destruction, support yield and support pile breaking in deep foundation pit engineering, and provide controllable test conditions for studying the deformation of soil and the stress response law of support structure in the failure process. Breakthrough the limitation of traditional one-time destruction test, can simulate the failure evolution process from local to gradual to whole in engineering, which is highly consistent with the dynamic characteristics of actual foundation pit support failure.

[0041] Further, the cross brace failure mechanism 4 comprises: at least two loading tracks 401, which are installed on the upper end of the test box 1 and are parallel to the support rod 3051. The loading track 401 provides a parallel installation reference for the track installation plate 402, ensures that it is parallel to the support rod 3051 below, limits the installation position of the track installation plate 402, and ensures the positioning accuracy of the cross brace failure mechanism and the deep pit support mechanism 3. Avoid the inclination of the loading unit 405 due to installation deviation, and ensure that the stress direction of the support rod 3051 meets the design expectation.

[0042] The track installation plate 402 is installed between the two loading tracks 401; the track installation plate 402 is provided with a through slot 403 along the length direction. The track installation plate 402 bears all sub-components such as bolt positioning piece 404, loading unit 405 and sliding push unit 406. The track installation plate 402 serves as the installation reference of each component to ensure the stability of the relative position between components. It realizes the modular integration of the cross brace failure mechanism, and is convenient for overall disassembly, maintenance. The through slot 403 provides a cross installation space for the metal rod 4051, allowing the metal rod 4051 to be slightly adjusted along the slot length direction; the through slot 403 can realize the vertical stress path of the hanging rope 4053, avoiding the friction between the hanging rope and the plate body. The through slot 403 adapts to the installation and trigger displacement requirements of the metal rod 4051, without limiting the movement of the key components.

[0043] A plurality of bolt positioning pieces 404 are fixedly installed on the track installation plate 402 on one side of the through slot 403 at equal distances. The bolt positioning piece 404 is used to laterally limit the metal rod 4051 of the adjacent loading unit 405, preventing the metal rod 4051 from moving along the through slot 403 in the non-trigger state, and also marking the initial installation position of the loading unit 405 to ensure that the initial state of each test is consistent. Thus, the tension of the support rod 3051 in the non-failure state is stable, avoiding the deviation of the initial test conditions caused by the displacement of the metal rod.

[0044] As shown in Figure 3 A plurality of mounting units 405 are installed between the through slot 403 and the support hinge seat 3052, and each mounting unit 405 is located between the bolt positioning member 404, and the position of each mounting unit 405 corresponds to the support rod 3051; the mounting unit 405 is used to provide upward tension to the support rod 3051.

[0045] Further, each mounting unit 405 includes: A metal rod 4051; both ends of each metal rod 4051 span across the through slot 403. The metal rod 4051 acts as an upper force carrier of the hanging rope 4053 and can transmit upward tension. At the same time, the metal rod 4051 is in contact with the push block 4064, and the tension is released through its own displacement and rotation. The rigid structure of the metal rod 4051 ensures stable tension transmission and no significant deformation caused by tension loss. The cylindrical design of the metal rod 4051 facilitates the rotation of the push block and smooth triggering action.

[0046] A hanging rope hook 4052 is installed on the support hinge seat 3052. The hanging rope hook 4052 is fixed on the support hinge seat 3052 to provide a lower connection point for the hanging rope 4053 and ensure that the hanging rope tension accurately acts on the hinge position of the support rod 3051. In this embodiment, the hanging rope hook 4052 is firmly connected to avoid sudden failure caused by unhooking during testing. The tension point of the hanging rope hook 4052 is consistent with the stress node of the cross brace in actual engineering, improving the simulation authenticity.

[0047] A hanging rope 4053; one end of each hanging rope 4053 is connected to the metal rod 4051, and the other end is connected to the hanging rope hook 4052. The hanging rope 4053 is used to connect the metal rod 4051 and the hanging rope hook 4052 to transmit upward tension, and its flexible characteristics allow for small angle adjustments to adapt to slight deformation of the support rod 3051. The flexible transmission of the hanging rope 4053 can avoid additional bending moments on the support rod 3051 caused by rigid connection. The hanging rope 4053 is made of high-strength fiber rope, which has high tensile strength and low elastic deformation, and high tension stability.

[0048] A sliding push unit 406 is fixedly installed on the track mounting plate 402; the sliding push unit 406 is used to gradually trigger the mounting unit 405 to make the support rod 3051 lose upward tension, simulate the condition that the middle part of the support rod 3051 breaks and folds, and further simulate the working condition that the two side enclosures 303 lose support from the support rod 3051.

[0049] Further, the sliding push unit 406 includes: A slide rail 4061 is fixedly installed on the rail mounting plate 402 and parallel to the through slot 403. The slide rail 4061 provides a linear motion track for the sliding block 4062, limits the motion direction of the sliding block, ensures the stability of the motion of the sliding block, and avoids lateral deviation. The linear track design of the slide rail 4061 enables the actuator 4064 to accurately act on each metal rod 405.

[0050] The sliding block 4062 is installed on the slide rail 4061 and moves along the length direction of the slide rail 4061. The sliding block 4062 is used to carry the push plate 4063 and the actuator 4064 and moves along the slide rail under the power of the driving unit, and transmits the traction of the driving unit to convert into linear motion of the actuator. The rigid structure of the sliding block 4062 ensures that the power transmission is lossless and drives the actuator to move stably. The sliding block 4062 has high cooperation precision with the slide rail, which avoids triggering interruption caused by motion jamming.

[0051] The push plate 4063 is installed on the sliding block 4062. The push plate 4063 is used to connect the sliding block 4062 and the actuator 4064, adjust the installation height of the actuator, and ensure the motion synchronization of multiple actuators 4064. The push plate 4063 can adjust the height of the actuator by replacing push plates of different thicknesses, which is suitable for metal rods of different diameters. At the same time, by unifying the power transmission path, the failure sequence confusion caused by the asynchronous action of multiple actuators is avoided.

[0052] At least one actuator 4064 is installed on the push plate 4063, and the surface of the actuator 4064 is in contact with the metal rod 4051. The actuator 4064 is in contact with the surface of the metal rod 4051, and the metal rod is pushed to move on one side by the pushing force, while the other side is rotated as a whole because of the block 404, so that the metal rod is separated from the stress point of the hanging rope 4053, and the tension is removed. The contact surface of the actuator 4064 is made of smooth and wear-resistant polytetrafluoroethylene material, which reduces the friction resistance with the metal rod and triggers more smoothly. At the same time, the number of actuators can be increased or decreased to control the number of support rods triggered at a time.

[0053] The driving unit 407 is fixedly installed on the rail mounting plate 402, and the driving unit 407 is used to provide power for the sliding actuator unit 406.

[0054] Further, the driving unit 407 includes: The hydraulic cylinder 4071 is fixedly installed on the rail mounting plate 402 and parallel to the slide rail 4061. The hydraulic cylinder 4071 provides linear driving force and drives the pulling rope 4074 to move through the extension / retraction of the extension / retraction end. The hydraulic cylinder 4071 can adjust the extension / retraction speed through the hydraulic system to control the moving speed of the sliding block 4062. The hydraulic driving output force of the hydraulic cylinder 4071 is stable and controllable, and the triggering speed can be accurately adjusted to simulate different failure development rates.

[0055] Two pulley seats 4072 are mounted on the rail mounting plate 402, and correspond to the slide rail 4061 and the hydraulic cylinder 4071 respectively. The pulley seat 4072 is used to fix the installation position of the pulley 4073, to ensure that the pulley is aligned with the center axis of the hydraulic cylinder and the slide rail, to provide stable support for the pulley, and to avoid the pulley from shaking when under stress. The pulley seat 4072 can ensure that the movement direction of the pulling rope 4074 is parallel to the slide rail, avoid the lateral stress of the slide block caused by the deviation of the rope, improve the installation stability of the pulley, and reduce the power transmission loss.

[0056] Two pulleys 4073 are mounted on the corresponding pulley seats 4072 respectively. The pulley 4073 changes the stress direction of the pulling rope 4074, converts the axial driving force of the hydraulic cylinder into the axial traction force of the slide block, and the rolling friction of the pulley 4073 reduces the friction loss between the pulling rope and the pulley. The benefits are that the power transmission direction can be flexibly changed, the hydraulic cylinder can be installed at any convenient position of the rail mounting plate, the rope wear is reduced, the service life of the pulling rope is prolonged, and the test interruption caused by friction rupture is avoided.

[0057] The pulling rope 4074 is connected to the telescopic end of the hydraulic cylinder 4071 through the pull ring 4075 at one end, and is connected to the side surface of the slide block 4062 in sequence through the two pulleys 4073 at the other end. The pulling rope 4074 is used to connect the telescopic end of the hydraulic cylinder and the slide block 4062, to transmit the driving force, to adapt to the steering requirements of the pulley with the flexible characteristics, and to realize the smooth transmission of power. The pulling rope 4074 is selected from high-strength steel wire rope, which has high tensile strength and small elastic deformation, to ensure the accuracy of power transmission. At the same time, the flexible structure can avoid the impact on the hydraulic cylinder or the slide block caused by rigid connection, and protect the components. The pull ring 4075 fixes the connection between the pulling rope 4074 and the telescopic end of the hydraulic cylinder, to prevent the rope from falling off. At the same time, it can disperse the contact stress between the rope and the telescopic end, to avoid the rupture of the rope caused by excessive local stress.

[0058] The movement process of the cross brace failure mechanism 4 is as follows: 1. Before the test starts, the metal rod 4051 is transversely arranged on the through slot 403 and is limited by the one-sided bolt positioning member 404, and cannot move along the through slot; the hanging rope 4053 is connected to the metal rod 4051 at one end, and is connected to the support hinge seat 3052 through the hanging rope hook 4052 at the other end, to exert an upward pre-tension on the support rod 3051; the slide block 4062 of the sliding push unit 406 is located at the initial end of the slide rail 4061, and the push block 4064 is not in contact with the metal rod 4051; the hydraulic cylinder 4071 of the drive unit 407 is in a retracted state, and the pulling rope 4074 is kept tensioned.

[0059] 2. When it is necessary to simulate the failure of the cross brace, the hydraulic cylinder 4071 is activated. The telescopic end of the hydraulic cylinder 4071 slowly extends, pulling the towing rope 4074 through the pull cap 4075. The towing rope 4074 changes direction along the pulley 4073, converting the extension force of the hydraulic cylinder into a traction force along the slide rail 4061, which pulls the slider 4062. Under the action of the traction force, the slider 4062 moves at a constant speed along the slide rail 4061 towards the mounting unit 405.

[0060] 3. During the movement of slider 4062, push plate 4063 and actuating block 4064 move synchronously. The first actuating block 4064 first contacts the metal rod 4051 closest to the initial end. As slider continues to move, actuating block applies horizontal pushing force to metal rod. Under the action of pushing force, metal rod 4051 overcomes the limit of bolt positioning part 404, causing metal rod 4051 to start rotating. Since the lower part of metal rod 4051 is arc-shaped, after metal rod 4051 rotates, it is easy for metal rod 4051 to fall out of through groove 403. At this time, the upward pulling force on support rod 3051 is instantly removed, completing the simulated failure of the first support rod 3051.

[0061] 4. The slider 4062 continues to move along the slide rail, and the subsequent actuating blocks 4064 contact and push the remaining metal rods 4051 in sequence. In order from near to far, each metal rod 4051 falls down along the through groove and detaches from the hanging rope support point, and the corresponding hanging rope tension is released one by one. The support rods 3051 corresponding to the metal rods simulate failure in sequence according to the preset order, realizing the progressive failure process from local cross bracing to multiple cross bracings and then to the overall cross bracing. If it is necessary to simulate the simultaneous failure of multiple cross bracings, actuating blocks with the same spacing as the metal rod spacing can be installed on the push plate 4063, so that multiple actuating blocks push multiple metal rods at the same time.

[0062] 5. After all the support rods 3051 that need to simulate failure have had their tension removed, the telescopic end of the hydraulic cylinder 4071 is retracted, and the slider 4062 is pulled back to the initial end along the slide rail by the drag rope; each metal rod 4051 is manually pushed back to the initial position in the through groove and repositioned by the bolt positioning part 404; the hanging rope 4053 is adjusted and reconnected to the metal rod 4051 to restore the pre-tension on the support rod 3051, and the device returns to the initial state, ready for the next failure simulation test.

[0063] Example 2 like Figure 4 As shown, a geotechnical centrifuge model test system for simulating the failure of cross bracing in a foundation pit is provided. This system includes the test device for simulating the failure of cross bracing in a foundation pit as described in Example 1 above. The test device for simulating the failure of cross bracing in a foundation pit is located in the basket of the geotechnical centrifuge.

[0064] The high centrifugal acceleration provided by the geotechnical centrifuge reproduces the stress field of the soil self-weight and the stress state of the supporting structure in the real underground engineering. The system breaks through the size effect limitation of the traditional normal temperature and pressure model test, realizes the precise simulation of the failure process of the lateral support of the foundation pit, and provides a more practical test platform for the safety research of the deep foundation pit support.

[0065] The geotechnical centrifuge mainly consists of a rotating arm, a driving system, a basket and a control system. The rotating arm is usually 3-10 m long, one end is connected to the driving system, the other end is suspended with the basket, and the basket provides centrifugal acceleration for the test device in the basket through high-speed rotation. The driving system adopts a variable frequency motor or a hydraulic motor, which can accurately adjust the rotation speed to realize stable output and dynamic control of the centrifugal acceleration. The basket, as a carrying container for the test device, has a fixed interface inside, which can firmly fix the test box 1, and has structure strength against vibration and impact to avoid displacement or damage of the test device during centrifugal rotation. The control system monitors the parameters such as centrifugal acceleration, rotation speed and basket posture in real time, and automatically adjusts the running state according to the preset program to ensure the stability of the centrifugal environment during the test.

[0066] At the same time, the system also needs to be equipped with monitoring equipment compatible with the centrifugal environment, integrated in the test device and the basket, to realize multi-parameter and real-time data acquisition. For example, the stress monitoring of the resistance strain gauge is installed on the surface of the single pile 3021 of the row pile 302 and the support rod 3051 of the supporting unit 305, and the wireless transmission module is used to collect the stress change of the structure in real time. Laser displacement sensor is used for displacement monitoring of the horizontal displacement and settlement of the side wall soil 2 of the foundation pit 301. The laser displacement sensor is installed in the basket. Piezoelectric soil pressure sensor is buried between the soil 2 and the row pile 302 for pressure monitoring to collect the lateral pressure distribution of the soil on the supporting structure under the centrifugal environment. The high-speed camera records the deformation of the supporting structure and the collapse trajectory of the soil during the failure of the lateral support, which is convenient for subsequent analysis of the failure evolution law.

[0067] Embodiment 3 The method is suitable for the soil centrifuge model test system for simulating the failure of the lateral support of the foundation pit as described in embodiment 2, and the method comprises: S1, start the geotechnical centrifuge, gradually increase the acceleration according to the preset program until the preset acceleration of the test design is reached, and monitor the rotation speed and vibration value of the geotechnical centrifuge in real time during the acceleration process.

[0068] Specifically, S101, input the test parameters such as the preset acceleration value, the acceleration increasing rate and the stable duration through the control system of the geotechnical centrifuge.

[0069] S102, start the driving system, rotate the arm to drive the basket to rotate slowly, gradually increase the rotating speed to reach the preset acceleration: during the process, the rotating speed is monitored in real time through the rotating speed sensor installed on the rotating arm, the actual acceleration is calculated by combining the formula, compared with the preset value, when the deviation exceeds the preset deviation value, the rotating speed is automatically adjusted. Among them, the calculation formula of centrifugal acceleration is: , wherein is the angular velocity, is the radius of rotation.

[0070] S103, vibration monitoring and abnormal processing, through the vibration sensor on the side wall of the basket, the vibration value is collected in real time, when the vibration acceleration exceeds the preset acceleration value, the system automatically triggers the speed reduction program, and the vibration reason is investigated and processed after the processing is completed. Restart.

[0071] S104, soil stress balance observation: in the stable stage, the stress change of the soil 2 is monitored through the soil pressure box, when the stress fluctuation does not exceed the preset range within the continuous preset observation time, it is determined that the soil reaches stress balance, and the next step can be entered; if the stress continues to change, the stable time needs to be extended until the balance condition is met.

[0072] S2, when the soil centrifuge is stabilized at the preset acceleration, the control system sends instructions to the hydraulic cylinder, drives the hydraulic cylinder 4071 to move at a preset speed, drives the push plate 4063 on the sliding block 4062 to move synchronously with the knob 4064, and the knob 4064 contacts the metal rod. After the metal rod 4051 rotates, the metal rod 4051 is peeled off from the through slot 403 of the track mounting plate 402, causing the hanging rope 4053 to lose support and fall.

[0073] S201, send instructions to the hydraulic cylinder 4071 through the control system, set key parameters such as moving speed and push force control mode. Among them, the moving speed is controlled by the hydraulic flow valve according to the failure rate designed by the test to control the moving speed of the hydraulic cylinder; the push force control mode adopts force and displacement composite control, which is pushed in displacement mode in the initial stage, and the push force is slowly increased to the critical value, so as to avoid the sudden increase of the push force causing the metal rod to slide off and affecting the authenticity of the test data.

[0074] S202, the knob contacts the metal rod. The sliding block 4062 moves along the sliding rail 4061, drives the push plate 4063 and the knob 4064 to move synchronously to the metal rod 4051, and records the initial contact force through the force sensor at the moment of contact. Confirm that the contact position is in the middle.

[0075] S203, critical sliding trigger. The pushing force gradually increases to the point where the metal rod 4051 starts to rotate, the metal rod 4051 falls from the through slot 403, the hanging rope 4053 loses support and falls freely, the support rod 3051 loses upward tension, and the simulation of the failure of the cross brace; during the process, a high-speed camera is used to continuously shoot, focusing on recording the instant of metal rod peeling, the trajectory of the hanging rope falling, and the initial deformation state of the support rod.

[0076] S204, abnormal situation response. If the pushing force reaches the critical value and the metal rod does not slide, the hydraulic cylinder needs to be stopped immediately, the reasons need to be investigated, whether there are impurities in the through slot that cause increased friction or the metal rod is installed offset, etc., and after processing, it is triggered again; if the pushing force does not reach the critical value, the metal rod slides prematurely, the test is invalid, the metal rod needs to be reinstalled and the pushing force threshold needs to be calibrated before the test is repeated.

[0077] S3, the preset high-speed camera is used to record and observe the support falling process and situation, and the displacement sensor is used to monitor the horizontal displacement of the row pile 302 and the settlement of the surrounding soil 2 of the foundation pit, and after the support falls, the acceleration of the soil centrifuge is gradually reduced to zero, the test system is stopped, and the test data is saved for subsequent analysis.

[0078] S301, during the failure trigger process, each monitoring device collects data at a preset frequency to ensure time consistency. Among them, displacement monitoring, laser displacement sensor collects the horizontal displacement of row pile 302 at a preset time interval, focuses on monitoring the top, middle and bottom of the pile, and the settlement of the surrounding soil 2 of the foundation pit, and a monitoring point can be set along the edge of the foundation pit at a preset time interval to record the displacement-time curve. Tension monitoring, steel wire rope tension sensor collects the tension change of hanging rope 4053 at a preset time interval, captures the complete process from stable tension to start to decline to zero, and clearly shows the tension mutation characteristics at the moment of failure trigger. Stress monitoring, strain gauges on the surface of row pile 302 and support rod 3051 collect stress data at a preset time interval, and analyze the stress redistribution law of the supporting structure after failure.

[0079] S302, after the support falls, start the speed reduction program. Use stepwise speed reduction to avoid additional stress between the soil 2 and the test device due to rapid speed reduction. After the acceleration is reduced to zero, the centrifuge continues to rotate at a low speed for a period of time, and then stops the drive system after the equipment is completely cooled; before opening the protective cabin, the rotating arm needs to be confirmed to be completely stationary by the speed sensor again to avoid safety risks to personnel.

[0080] S303, export all monitoring data from the data acquisition instrument, arrange in the format of time + parameter + value, including acceleration, speed, vibration value, displacement, tension, stress, etc., and save the video file of the high-speed camera. The local + cloud mode is used for double backup, the local storage is stored in a special server, the cloud is uploaded to an encrypted database to avoid data loss; after backup, check the data integrity to ensure that there is no loss.

[0081] S304, take out the test box 1, directly observe the deformation of the row pile 302, the failure mode of the support rod 3051, measure the damage degree with a tape measure, and take photos for archiving. Record whether the surrounding soil 2 of the foundation pit appears crack width, collapse range, analyze the correlation between soil instability and cross support failure, sample typical deformation area, and supplement test data dimension. Among them, the deformation of the row pile 302 includes whether bending and breaking occur, whether the breaking position is consistent with the stress monitoring concentration area; the failure mode of the support rod 3051 includes whether bending yield occurs and whether the connecting node is damaged; the damage degree includes the maximum horizontal displacement of the row pile and the bending deflection of the support rod.

[0082] The above describes one embodiment of the present application in detail, but the content is only the preferred embodiment of the present application, and cannot be considered as limiting the scope of the present application. Any equivalent changes and improvements made according to the scope of the present application should still belong to the scope of the present application.

Claims

1. A device for simulating the failure of a lateral support of a foundation pit, characterized in that, The test device comprises: a test box (1) for providing an installation carrier for components of the test device; a soil body (2) for simulating a soil layer in underground engineering; a deep pit support mechanism (3) for simulating a deep foundation pit support in underground engineering; the deep pit support mechanism (3) is located in the soil body (2); a cross-bracing failure mechanism (4) for applying a failure condition to the deep pit support mechanism (3) to simulate the destruction of support and corbel connection, the yielding of support and the breaking of support pile in deep foundation pit support; the cross-bracing failure mechanism (4) is installed on the test box (1) and located above the deep pit support mechanism (3).

2. The simulated failure test device for a cross-brace of a foundation pit according to claim 1, wherein The deep pit support mechanism (3) comprises: a foundation pit (301) formed in the soil body (2); at least two row piles (302) located at opposite inner vertical surfaces of the foundation pit (301); each row pile (302) is composed of a plurality of single piles (3021) inserted vertically side by side in the foundation pit (301); at least two surrounding purlins (303) fixedly installed on each single pile (3021) of the corresponding row pile (302); a plurality of bolts (304) fixedly installed on the surrounding purlins (303), and the bolts (304) correspond one-to-one to the single piles (3021); a plurality of support units (305) installed between two surrounding purlins (303) at intervals of one bolt (304).

3. The simulated failure test device for a cross-brace of an excavation pit according to claim 2, wherein Each support unit (305) comprises: at least two support rods (3051) arranged side by side; at least two support hinge seats (3052) for connecting two support rods (3051); one end of each support hinge seat (3052) is installed on the end face of the support rod (3051), and the other end is hingedly connected to another support hinge seat (3052) through a pin shaft (3053) to complete the connection of the two support rods (3051); at least two support ball head pins (3054); each support ball head pin (3054) is installed on the end face of the corresponding support rod (3051) close to the bolt (304), and the ball head of each support ball head pin (3054) is lapped into the corresponding bolt (304).

4. The simulated failure test apparatus for a cross-brace of an excavation pit according to claim 3, wherein The cross-bracing failure mechanism (4) comprises: at least two loading tracks (401) installed parallel to each other on the upper end of the test box (1) and parallel to the support rods (3051); a track mounting plate (402) installed between the two loading tracks (401); the track mounting plate (402) is provided with a through slot (403) along its length direction; a plurality of bolt positioning members (404) fixedly installed at equal distances on the track mounting plate (402) on one side of the through slot (403); a plurality of hanging units (405) installed between the through slot (403) and the support hinge seat (3052), and each hanging unit (405) is located between the bolt positioning members (404), and the position of each hanging unit (405) corresponds to the support rod (3051) one-to-one; the hanging unit (405) is used for providing an upward tension to the support rod (3051). A sliding and poking unit (406) is fixedly installed on the track mounting plate (402); the sliding and poking unit (406) is used for triggering the hanging unit (405) step by step, so that the support rod (3051) loses upward tension, the middle part of the support rod (3051) is simulated to be broken, and then the working condition that the two side enclosures (303) lose the support of the support rod (3051) is simulated; A driving unit (407) is fixedly installed on the track mounting plate (402); the driving unit (407) is used for providing power for the sliding and poking unit (406).

5. The simulated failure test apparatus for a cross-brace of an excavation pit according to claim 4, wherein Each of the hanging units (405) comprises: A metal rod (4051); two ends of each of the metal rods (4051) span on the through groove (403); A hanging rope hook (4052) is installed on the support hinged seat (3052); A hanging rope (4053); one end of each of the hanging ropes (4053) is connected with the metal rod (4051), and the other end is connected with the hanging rope hook (4052).

6. The simulated failure test apparatus for a cross-brace of an excavation pit according to claim 5, wherein The sliding and poking unit (406) comprises: A sliding rail (4061) is fixedly installed on the track mounting plate (402) and is parallel to the through groove (403); A sliding block (4062) is installed on the sliding rail (4061); the sliding block (4062) moves along the length direction of the sliding rail (4061); A push plate (4063) is installed on the sliding block (4062); At least one poking block (4064) is installed on the push plate (4063); the surface of the poking block (4064) is in contact with the metal rod (4051).

7. The simulated failure test apparatus for a cross-brace of an excavation pit according to claim 6, wherein The driving unit (407) comprises: A hydraulic cylinder (4071) is fixedly installed on the track mounting plate (402) and is parallel to the sliding rail (4061); Two pulley seats (4072) are both installed on the track mounting plate (402) and correspond to the sliding rail (4061) and the hydraulic cylinder (4071) respectively; Two pulleys (4073) are respectively installed on the corresponding pulley seats (4072); A dragging rope (4074) is connected with the telescopic end of the hydraulic cylinder (4071) through a pulling lug (4075) at one end and is connected with the side surface of the sliding block (4062) through the two pulleys (4073) in sequence at the other end.

8. A geotechnical centrifuge model test system simulating failure of a lateral support of a foundation pit, characterized by, The system comprises the simulation foundation pit cross support failure test device of any one of claims 1-7, and the simulation foundation pit cross support failure test device is located in a hanging basket of a geotechnical centrifuge.

9. A method for simulating a failure test of a lateral support of a foundation pit, characterized by, The method is suitable for the simulation foundation pit cross support failure geotechnical centrifugal model test system of claim 8, and the method comprises: S1, starting the geotechnical centrifuge, gradually increasing the acceleration according to a preset program until reaching a preset acceleration of a test design, and monitoring the rotation speed and vibration value of the geotechnical centrifuge in real time during the acceleration process. S2, when the geotechnical centrifuge is stabilized at the preset acceleration, the control system sends instructions to the hydraulic cylinder, drives the hydraulic cylinder (4071) to move at a preset speed, drives the push plate (4063) on the sliding block (4062) to move synchronously with the push block (4064), and gradually applies a pushing force after the push block (4064) contacts the metal rod, the metal rod (4051) rotates, and then peels off from the through slot (403) of the track mounting plate (402), causing the hanging rope (4053) to lose support and fall off; S3, a preset high-speed camera is used to record and observe the support falling process and situation, and a preset displacement sensor is used to monitor the horizontal displacement of the pile row (302) and the settlement of the surrounding soil (2) of the foundation pit, after the support falls off, the acceleration of the geotechnical centrifuge is gradually reduced to zero, the test system is stopped, and the test data is saved for subsequent analysis.

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