Simulation foundation pit cross support failure test device, system and method thereof

Abstract

The application discloses a simulation foundation pit cross support failure test device, a system and a method thereof, the test device comprises a test box body, a soil body, a deep pit supporting mechanism and a cross support failure mechanism, the system comprises the test device, the test device is located in a basket of a soil centrifuge, and the method is suitable for the soil centrifuge model test system for simulating foundation pit cross support failure. The system optimizes the foundation pit supporting test through multi-link design. The test box body is fixedly installed with a reference, can reproduce various soil layers and pore water environments, is in line with actual stress, can reproduce pile row, surrounding purlin and cross support structures, can adjust parameters to adapt to different working conditions, and can restore a real failure mode. The cross support failure mechanism realizes dynamic evolution from single root to overall instability, and can also simulate sudden and gradual failure. In addition, the centrifugal compatible monitoring equipment is also provided, multi-parameter synchronous acquisition is adopted, anti-interference wireless transmission is matched, data accuracy is ensured, and support is provided for analyzing the coupling relationship between soil and supporting 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 impact 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.

[0003] 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.

[0004] 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 under 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.

[0005] The chain reaction caused by this 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 load originally borne by the supporting pile will be quickly transferred to the adjacent supporting pile under the action of soil pressure. Since the design stage does not consider this load mutation, the adjacent supporting pile may fail successively 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 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

[0006] Pile row + 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 continuous damage caused by local damage of internal support pile row support structure are urgently needed to be studied. As shown in Figure 1 The internal support pile row support structure is generally composed of support (steel support or concrete support), surrounding purlin (crown beam and waist beam) and pile row (diaphragm wall).

[0007] In actual engineering, local damages such as support and corbel connection damage, support yielding and support pile breaking may occur. From the current research status of continuous damage of structure engineering and foundation pit engineering, it can be obtained that the local damage of structure or component may induce the continuous collapse of the whole building. It is necessary to understand the influence of local component failure on the whole supporting structure for the internally braced row pile (diaphragm wall) supported foundation pit. SUMMARY

[0008] 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:

[0009] a test box body for providing an installation carrier for components of the test device;

[0010] a soil body for simulating the soil layer in underground engineering;

[0011] a deep pit supporting mechanism for simulating the deep foundation pit support in underground engineering; the deep pit supporting mechanism is located in the soil body;

[0012] a cross support failure mechanism 4 for applying a failure condition to the deep pit supporting mechanism to simulate the support and corbel connection damage, support yielding and support pile breaking in the deep foundation pit support; the cross support failure mechanism is installed on the test box body 1 and located above the deep pit supporting mechanism.

[0013] Further, the deep pit supporting mechanism comprises:

[0014] a foundation pit opened in the soil body;

[0015] at least two row piles respectively located at opposite inner vertical surfaces of the foundation pit; each of the row piles is composed of a plurality of single piles vertically inserted side by side in the foundation pit;

[0016] at least two surrounding purlins respectively fixedly installed on each single pile of the corresponding row pile;

[0017] a plurality of bolts respectively fixedly installed on the surrounding purlins, and the bolts correspond one-to-one to the single piles;

[0018] a plurality of supporting units respectively installed between the two surrounding purlins at an interval of one bolt.

[0019] Further, each of the supporting units comprises:

[0020] at least two support rods arranged side by side;

[0021] 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 with the other support hinge seat through a pin shaft, thereby connecting the two support rods and forming a complete foundation pit support rod.

[0022] 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 near the bolt, and the ball head of each of the support ball head pins is overlapped in the corresponding bolt.

[0023] Further, the cross brace failure mechanism comprises:

[0024] At least two loading tracks are installed on the upper end of the test box and are parallel to the support rods;

[0025] A track mounting plate is installed between the two loading tracks; the track mounting plate is provided with a through slot along the length direction thereof;

[0026] A plurality of bolt positioning members are fixedly installed on the track mounting plate on one side of the through slot at equal distances;

[0027] A plurality of hanging units are installed between the through slot and the support hinged 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 one by one; the hanging unit is used to provide an upward tension to the support rod;

[0028] A sliding and pushing unit is fixedly installed on the track mounting plate; the sliding and pushing unit is used to gradually trigger the hanging unit, so that the support rod loses the upward tension, simulates the situation that the middle part of the support rod is broken and folded, and further simulates the working condition that the two side enclosures lose the support of the support rod;

[0029] A driving unit is fixedly installed on the track mounting plate; the driving unit is used to provide power to the sliding and pushing unit.

[0030] Further, each of the hanging units comprises:

[0031] A metal rod; two ends of each of the metal rods span on the through slot;

[0032] A hanging rope hook is installed on the support hinged seat;

[0033] 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.

[0034] Further, the sliding and pushing unit comprises:

[0035] A sliding rail is fixedly installed on the track mounting plate and is parallel to the through slot;

[0036] A sliding block is installed on the sliding rail; the sliding block moves along the length direction of the sliding rail;

[0037] A push plate is installed on the sliding block;

[0038] At least one push block 4064 is installed on the push plate 4063, and the surface of the push block 4064 is in contact with the metal rod 4051.

[0039] Further, the driving unit comprises:

[0040] A hydraulic cylinder is fixedly installed on the rail mounting plate and is parallel to the slide rail.

[0041] Two pulley seats are installed on the rail mounting plate and correspond to the slide rail and the hydraulic cylinder respectively.

[0042] Two pulleys are installed on the corresponding pulley seats respectively.

[0043] A drag rope is connected to the extension end of the hydraulic cylinder through a pull rod at one end and connected to the side surface of the sliding block through the two pulleys at the other end.

[0044] Another technical solution adopted by the present application is a soil centrifuge model test system for simulating the failure of foundation pit cross bracing, which comprises the above-mentioned simulation foundation pit cross bracing failure test device, and the simulation foundation pit cross bracing failure test device is located in a soil centrifuge basket.

[0045] Another technical solution adopted by the present application is a simulation foundation pit cross bracing failure test method, which is applicable to the above-mentioned soil centrifuge model test system for simulating the failure of foundation pit cross bracing, and the method comprises:

[0046] 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 rotation speed and vibration value of the soil centrifuge in real time during the acceleration process;

[0047] S2, when the soil centrifuge is stabilized 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, and the push plate on the sliding block moves synchronously with the push block, the push block contacts the metal rod, and then gradually applies a pushing force, the metal rod rotates, and then peels off from the through slot of the rail mounting plate, causing the hanging rope to lose support and fall off;

[0048] 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 foundation pit peripheral soil body, after the support falls off, 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.

[0049] Compared with the prior art, the present application has the following beneficial effects: by providing a test box, a unified installation reference is provided, test errors caused by part displacement and inclination are avoided, and the relative position of the supporting structure and the failure mechanism is ensured to comply with the logic of the real foundation pit supporting system; the soil body can reproduce different soil layer characteristics, even simulate multi-layer heterogeneous soil and pore water environment, so that the stress state of the test is highly consistent with the actual engineering, and the problem of data distortion in traditional simplified simulation is solved.

[0050] 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 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 the 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, and providing a reliable physical model for studying the failure mechanism.

[0051] 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 progressive triggering of the push block, the dynamic evolution process from single cross brace failure to multiple cross brace chain failure to overall support instability can be realized, and three core failure scenarios of support and crown beam connection damage, support yield and support pile breakage can be reproduced.

[0052] By setting the critical sliding force of the metal rod of the mounting unit and the adjustable triggering rate of the sliding push unit, both the sudden failure of the cross brace fracture caused by earthquakes and the gradual failure of the 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.

[0053] The system is equipped with monitoring equipment compatible with the centrifugal environment: strain gauges monitor the stress of the supporting structure, laser displacement sensors monitor the displacement of the soil body and row pile, piezoelectric soil pressure cells monitor the soil pressure distribution, and high-speed cameras record the failure dynamic process, realizing the synchronous acquisition of stress, displacement, soil pressure and image, covering the whole cycle from before failure to during failure to after failure.

[0054] The wireless transmission module is resistant to centrifugal interference and has small data synchronization error, ensuring stable and accurate monitoring data in high centrifugal environment, avoiding data deviation caused by equipment interference, and providing a complete data set for subsequent quantitative analysis of the coupling relationship between soil deformation and supporting failure. BRIEF DESCRIPTION OF DRAWINGS

[0055] Figure 1 The figure is a structural schematic diagram of the simulation foundation pit cross brace failure test device of the present application.

[0056] Figure 2 The figure is a structural schematic diagram of the cross brace failure mechanism of the present application.

[0057] Figure 3 This is a schematic diagram of the support unit and mounting unit of the present invention.

[0058] Figure 4 This is a schematic diagram of the geotechnical centrifuge model test system for simulating the failure of cross bracing in a foundation pit, as presented in this invention.

[0059] The components include: 1. Test chamber; 2. Soil; 3. Deep pit support mechanism; 301. Foundation pit; 302. Piles; 3021. Single pile; 303. Waler; 304. Bolt; 305. Support unit; 3051. Support rod; 3052. Support hinge seat; 3053. Pin; 3054. Support ball head pin; 4. Cross brace failure mechanism; 401. Loading track; 402. Track mounting plate; 403. Through groove. ; 404, Bolt positioning component; 405, Mounting unit; 4051, Metal rod; 4052, Rope hook; 4053, Rope; 406, Sliding actuation unit; 4061, Slide rail; 4062, Slider; 4063, Push plate; 4064, Actuating block; 407, Drive unit; 4071, Hydraulic cylinder; 4072, Pulley seat; 4073, Pulley; 4074, Towing rope; 4075, Pull cap. Detailed Implementation

[0060] The technical solutions of the simulated foundation pit cross brace failure test device and equipment provided by the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0061] Example 1

[0062] 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.

[0063] The experimental setup also includes: soil 2, which is used to simulate soil layers in underground engineering.

[0064] In this embodiment, the foundation pit excavation and the bracing force in underground engineering are always closely related to the surrounding soil layer. The density, water content, cohesion, internal friction angle and other parameters of different soil layers will directly affect the stress distribution of the foundation pit support structure and the bearing requirement of the bracing. The soil body 2 can make the test environment infinitely close to the real underground working condition by accurately reproducing the soil layer characteristics of the target engineering scene.

[0065] The staff can construct a complex soil layer model such as a heterogeneous soil of multi-layer upper cohesive soil + lower sand, saturated soil containing pore water, composite soil containing particle impurities such as gravel according to the test requirements, so as to simulate the bracing failure test under different engineering scenes. For example, when simulating the foundation pit in coastal areas, the soil body 2 can be configured as saturated sand to study the influence of seawater seepage on the bracing force; when simulating the foundation pit in mountainous areas, large pieces of gravel can be mixed to analyze the inducing effect of local stress concentration on bracing failure. This flexibility enables the test device to cover more complex engineering scenes and provide test support for solving the safety problem of foundation pit under special working conditions.

[0066] As shown in Figure 1 , the test device further comprises: a deep pit support mechanism 3 for simulating deep foundation pit support in underground engineering; the deep pit support mechanism 3 is located in the soil body 2.

[0067] Further, the deep pit support mechanism 3 comprises:

[0068] 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, while simulating the foundation pit space formed after excavation in underground engineering. Its advantages are to avoid simplified simulation without foundation pit space, make the stress, deformation and failure process of the support component completely based on the engineering logic of the soil body after excavation, ensure that the test results are consistent with the actual foundation pit support failure law, and improve the data reference value; the spatial structure of the foundation pit 301 can accommodate monitoring equipment such as displacement sensor and soil pressure cell, facilitating the synchronous collection of data such as soil body deformation and support structure stress, and supporting multi-dimensional failure mechanism analysis.

[0069] At least two pile rows 302 are respectively located at the opposite inner vertical surfaces of the foundation pit 301; each pile row 302 is composed of a plurality of single piles 3021 inserted vertically side by side in the soil body 2 inside the surface of the foundation pit 301. Specifically, by inserting a plurality of single piles 3021 vertically side by side into the soil body 2 inside the surface of the foundation pit 301, the core function of the pile row such as cast-in-place pile and precast pile in actual engineering as a foundation pit side wall support is reproduced, resisting the lateral extrusion of the soil body 2 and preventing the collapse of the foundation pit side wall. The lower end of the single pile 3021 is inserted into the deep part of the soil body 2 to simulate the characteristic that the actual pile row is embedded in the stable soil layer, and the soil pressure load of the foundation pit side wall is transmitted to the deep stable soil body, avoiding the premature instability of the support structure due to insufficient embedding.

[0070] At least two walers 303 are fixedly installed on each individual pile 3021 of the corresponding pile group 302. Specifically, in actual foundation pits, the pile group is the first line of defense against earth pressure. The pile group 302, through the adjustable arrangement density and insertion depth of the individual piles 3021, can simulate the support capacity of pile groups in different engineering scenarios, such as densely packed pile groups in soft soil areas or sparsely packed pile groups in hard rock areas, meeting diverse test requirements. The individual piles 3021 are in direct contact with the soil 2. During the test, the horizontal displacement and bending stress of the individual piles 3021 can be monitored to analyze the impact of soil deformation (such as soil creep) on the cracking of individual piles on the pile group, and the collapse mode of the soil 2 after pile failure can be observed to deepen the research on the interaction between support and soil.

[0071] Multiple bolts 304 are fixedly installed on the waler 303, with each bolt 304 corresponding to a single pile 3021. Specifically, multiple single piles 3021 on the same side are connected into a rigid whole by the waler 303, preventing individual single piles 3021 from deforming or failing due to uneven stress, thus replicating the effect of coordinating the stress of the pile rows and distributing the load in an actual waler. The surface of the waler 303 is flat and perpendicular to the single piles 3021, providing a stable installation carrier for the subsequent bolts 304 and support units 305, ensuring that the support units 305 can horizontally connect the pile rows on both sides, simulating the connection relationship between the actual cross brace and the waler.

[0072] In this embodiment, the waler is a key node connecting the piles and the cross bracing in the actual foundation pit. The waler 303 transforms the support system in the experiment from a dispersed single pile to a pile-waler collaborative structure, which is closer to the actual stress state of the project and avoids load transfer distortion caused by the lack of walers. The rigid connection of the waler 303 can reduce the lateral displacement of the single pile 3021, prevent the support structure from affecting the test data due to its own instability in the early stage of the test, and at the same time facilitate the study of the effect of waler stiffness on the failure resistance of the overall support system by replacing walers 303 with different materials and cross-sectional dimensions.

[0073] like Figure 3 As shown, multiple support units 305 are installed between two walers 303 at intervals of one bolt 304. The support unit 305 is the core component simulating the cross bracing of an actual foundation pit, and its modular design achieves accurate replication of the cross bracing function and failure simulation.

[0074] Further, each of the support units 305 comprises: at least two support rods 3051 arranged side by side. Specifically, the support rods 3051 serve as the core load-bearing members of the support unit, directly bearing the earth pressure load transmitted by the two side enclosing purlins 303, simulating the lateral displacement resistance function of the actual foundation pit lateral bracing, and preventing the deformation of the two side row piles towards the inside of the foundation pit. The side-by-side arrangement of the plurality of support rods 3051 can disperse the concentrated load transmitted by the enclosing purlin 303 into a uniformly distributed load, avoiding the premature failure of a single support rod due to excessive load, while simulating the support form of multiple lateral bracings in parallel in actual engineering. The support rods 3051 can be made of steel or acrylic material or have an adjusted cross-sectional size, so as to accurately control the bearing capacity thereof. In the test, the bending, breaking and other typical failure modes of the support rods can be achieved by loading, so as to restore the actual failure process of the lateral bracing. By replacing the support rods 3051 with different numbers and different stiffnesses, the influence of the number and stiffness of the lateral bracing on the stability of the support system can be studied, thereby providing data support for the selection of the lateral bracing in actual engineering.

[0075] At least two support hinge seats 3052 are used to connect the two support rods 3051; one end of each of the support hinge seats 3052 is mounted 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, 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, thereby simulating the hinged characteristics of the connecting joint between the actual foundation pit lateral bracing and the enclosing purlin. The support rods are allowed to produce a slight rotation under stress, thereby 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, thereby ensuring the integrity of the load transmission path of the entire support unit. In this embodiment, the end of the actual lateral bracing is rigidly connected, which is easy to cause bending moment concentration, while the hinged joint can release the bending moment. The provision of the support hinge seat 3052 makes the stress state of the support rod in the test more close to the actual situation, thereby 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, thereby studying the influence of the wear and looseness of the hinged joint on the bearing capacity of the support unit, and providing a basis for optimizing the design of the actual hinged joint.

[0076] At least two support ball head pins 3054; each of the support ball head pins 3054 is mounted on the end face of the corresponding support rod 3051 close to the bolt 304, and the ball head of each of the support ball head pins 3054 is overlapped in the corresponding bolt 304.

[0077] Specifically, the ball head of the support ball head pin 3054 can rotate freely in the reserved hole of the bolt 304, simulating the universal adjustment function of the actual bracing and the surrounding purlin connection, adapting to the small angle deviation of the support rod 3051 due to soil deformation in the test. The close lap 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 due to connection misalignment. In the actual foundation pit excavation process, the supporting structure will produce small displacement or inclination due to uneven soil deformation. The universal adjustment capability of the support ball head pin 3054 can adapt to this deformation, avoid the premature failure of the supporting unit due to connection jamming in the test, and ensure that the test can completely simulate the whole process from soil deformation to supporting 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 the test installation. The ball head lap design of the support ball head pin 3054 can accommodate certain installation errors, reduce the interference of insufficient installation precision on the test data, and improve the test repeatability and reliability.

[0078] As shown in Figure 2 The test device further comprises: a bracing failure mechanism 4 for applying failure conditions to the deep pit supporting mechanism 3 to simulate the connection damage between bracing and crown beam, bracing yield and supporting pile breakage in deep foundation pit supporting; the bracing failure mechanism 4 is installed on the test box 1 and located above the deep pit supporting mechanism 3. The bracing failure mechanism 4 is the core functional module of the simulation of the bracing failure test of the foundation pit. The core function of the bracing failure mechanism 4 is to actively apply and accurately control the failure working condition of the supporting system, which can reproduce three typical failure scenarios of the connection damage between bracing and crown beam, bracing yield and supporting pile breakage in deep foundation pit engineering, and provide controllable test conditions for studying the soil deformation and supporting structure stress response law in the failure process. It breaks through the limitation of traditional one-time destruction test and can simulate the failure evolution process from local to gradual to whole in engineering, which is highly consistent with the dynamic characteristics of the actual foundation pit supporting failure.

[0079] Further, the bracing 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 alignment accuracy of the bracing failure mechanism and the deep pit supporting 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.

[0080] A track mounting plate 402 is mounted between two loading tracks 401; the track mounting plate 402 is provided with a through slot 403 along its length direction. The track mounting plate 402 carries all sub-components such as bolt positioning members 404, hanging units 405, sliding and pushing units 406, etc. The track mounting plate 402 serves as the mounting reference of various components, ensuring the relative position stability between components. Modular integration of the cross brace failure mechanism is achieved, facilitating overall disassembly, maintenance. The through slot 403 provides a cross-mounted installation space for the metal rod 4051, allowing slight adjustment of the metal rod 4051 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 triggering displacement requirements of the metal rod 4051, without limiting the movement of key components.

[0081] A plurality of bolt positioning members 404 are fixedly installed at equal intervals on the track mounting plate 402 on one side of the through slot 403. The bolt positioning members 404 are used to laterally limit the metal rod 4051 of the adjacent hanging unit 405, preventing the metal rod 4051 from moving along the through slot 403 in the non-triggering state, and also marking the initial installation position of the hanging unit 405, ensuring the consistency of the initial state of each test. 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.

[0082] As shown in Figure 3 A plurality of hanging units 405 are 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; the hanging unit 405 is used to provide upward tension for the support rod 3051.

[0083] Further, each hanging unit 405 comprises:

[0084] A metal rod 4051; both ends of each metal rod 4051 span across the through slot 403. The metal rod 4051 serves 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 pushing block 4064, and the tension is released through its displacement and rotation. The rigid structure of the metal rod 4051 ensures stable tension transmission without significant deformation causing tension loss. The cylindrical design of the metal rod 4051 facilitates the rotation of the pushing block, ensuring smooth triggering action.

[0085] A hanging rope hook 4052 is installed on the support hinged seat 3052. The hanging rope hook 4052 is fixed on the support hinged seat 3052 to provide a lower connection point for the hanging rope 4053, ensuring that the hanging rope tension accurately acts on the hinged 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 the test. 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.

[0086] A hanging rope 4053; one end of each of the hanging ropes 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 the upward tension, and its flexible characteristics allow for small angle adjustments to accommodate 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 both tensile strength and low elastic deformation, and high tension stability.

[0087] A sliding push unit 406 is fixedly installed on the track mounting plate 402; the sliding push unit 406 is used to trigger the mounting unit 405 step by step to make the support rod 3051 lose upward tension, simulate the situation where the middle part of the support rod 3051 breaks and breaks, and further simulate the working condition where the two side enclosures 303 lose the support of the support rod 3051.

[0088] Further, the sliding push unit 406 includes:

[0089] A sliding rail 4061 is fixedly installed on the track mounting plate 402 and parallel to the through slot 403. The sliding rail 4061 provides a linear motion track for the sliding block 4062, limits the movement direction of the sliding block, ensures the stability of the sliding block movement, and avoids lateral deviation. The linear track design of the sliding rail 4061 enables the push block 4064 to accurately act on each metal rod 405.

[0090] 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. The sliding block 4062 is used to carry the push plate 4063 and the push block 4064, moves along the sliding rail under the power of the driving unit, and transmits the traction force of the driving unit to convert it into linear motion of the push block. The rigid structure of the sliding block 4062 ensures that the power transmission is lossless, drives the push block to move stably, and the sliding block 4062 and the sliding rail have high cooperation precision to avoid triggering interruption caused by movement jamming.

[0091] A push plate 4063 is installed on the sliding block 4062. The push plate 4063 is used to connect the sliding block 4062 and the push block 4064, adjust the installation height of the push block, and ensure the synchronization of the movement of multiple push blocks 4064. The push plate 4063 can adjust the height of the push block by replacing push plates of different thicknesses, and adapt to metal rods of different diameters. At the same time, by unifying the power transmission path, the failure sequence confusion caused by the asynchronous movement of multiple push blocks is avoided.

[0092] At least one push block 4064 is installed on the push plate 4063; the surface of the push block 4064 is in contact with the metal rod 4051. The push block 4064 is in contact with the surface of the metal rod 4051, and pushes the metal rod to move on one side by a pushing force, while the other side is blocked by 404 and rotates as a whole, so that the metal rod is separated from the force point of the hanging rope 4053, and the tension is removed. The contact surface of the push block 4064 is made of smooth and wear-resistant polytetrafluoroethylene material to reduce the frictional resistance of the metal rod and trigger more smoothly. At the same time, the number of push blocks can be increased or decreased to control the number of support rods triggered at a time.

[0093] A drive unit 407 is fixedly installed on the track mounting plate 402; the drive unit 407 is used to provide power for the sliding push unit 406.

[0094] Further, the drive unit 407 includes:

[0095] A hydraulic cylinder 4071 is fixedly installed on the track mounting plate 402 and parallel to the sliding rail 4061. The hydraulic cylinder 4071 provides linear driving force, and drives the pulling rope 4074 to move through the extension / retraction of the telescopic 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 can accurately adjust the triggering speed to simulate different failure development rates.

[0096] Two pulley seats 4072 are installed on the track mounting plate 402 and correspond to the sliding rail 4061 and the hydraulic cylinder 4071 respectively. The pulley seat 4072 is used to fix the installation position of the pulley 4073, ensure that the pulley is aligned with the center axis of the hydraulic cylinder and the sliding rail, provide stable support for the pulley, and 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 sliding rail, avoid the lateral stress of the rope caused by the deviation of the rope, can improve the installation stability of the pulley, and reduce the power transmission loss.

[0097] Two pulleys 4073, which are respectively installed on the corresponding pulley seats 4072. The pulley 4073 changes the force direction of the drag rope 4074, converts the axial driving force of the hydraulic cylinder into the axial traction force of the sliding block, and the rolling friction of the pulley 4073 reduces the friction loss of the drag rope and the pulley. The advantage is that the power transmission direction can be flexibly changed, the hydraulic cylinder can be installed at any convenient position of the track mounting plate, the rope wear is reduced, the service life of the drag rope is prolonged, and the test interruption caused by friction rupture is avoided.

[0098] The drag rope 4074 is connected to the extension end of the hydraulic cylinder 4071 through the pull bar 4075 at one end, and is connected to the side of the sliding block 4062 in sequence at the other end through the two pulleys 4073. The drag rope 4074 is used to connect the extension end of the hydraulic cylinder and the sliding block 4062, transmit the driving force, and adapt to the steering requirement of the pulley due to the flexible characteristic, so as to realize smooth transmission of power. The drag rope 4074 is selected from a high-strength steel wire rope, which has high tensile strength and small elastic deformation, so as to ensure accurate power transmission. At the same time, the flexible structure can avoid the impact of rigid connection on the hydraulic cylinder or the sliding block, and protect the components. The pull bar 4075 fixes the connection between the drag rope 4074 and the extension end of the hydraulic cylinder, and prevents the rope from falling off. At the same time, the contact stress between the rope and the extension end can be dispersed, and the rope rupture caused by excessive local stress can be avoided.

[0099] 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 groove 403 and is limited by the single-sided bolt positioning piece 404, and cannot move along the through groove; one end of the hanging rope 4053 is connected to the metal rod 4051, and the other end is connected to the support hinged seat 3052 through the hanging rope hook 4052, so as to apply a upward pre-tension to the support rod 3051; the sliding 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 drag rope 4074 is kept tensioned.

[0100] 2. When the cross brace failure needs to be simulated, the hydraulic cylinder 4071 is started, the extension end of the hydraulic cylinder 4071 is slowly extended, and the drag rope 4074 is pulled through the pull bar 4075; the drag rope 4074 changes direction along the pulley 4073, converts the extension force of the hydraulic cylinder into the traction force in the direction of the slide rail 4061, and pulls the sliding block 4062; under the action of the traction force, the sliding block 4062 moves at a constant speed along the slide rail 4061 towards the hanging unit 405.

[0101] 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.

[0102] 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.

[0103] 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.

[0104] Example 2

[0105] 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.

[0106] This experimental system utilizes the high centrifugal acceleration provided by a geotextile centrifuge to reproduce the stress field of soil under its own weight and the stress state of the support structure in real underground engineering. This system overcomes the limitations of size effects in traditional ambient temperature and pressure model tests, achieving accurate simulation of the failure process of cross bracing in foundation pits, and providing a more practical experimental platform for research on the safety of deep foundation pit support.

[0107] The geotechnical centrifuge mainly consists of a rotating arm, a driving system, a hanging basket, and a control system. The rotating arm is usually 3-10 m long, one end is connected to the driving system, and the other end suspends the hanging basket, which provides centrifugal acceleration for the test device in the hanging basket through high-speed rotation. The driving system uses a variable frequency motor or a hydraulic motor to accurately adjust the rotation speed, realize stable output and dynamic regulation of centrifugal acceleration. The hanging 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 centrifugal acceleration, rotation speed, and hanging basket posture in real time through sensors, automatically adjusts the running state according to the preset program, and ensures the stability of the centrifugal environment during the test.

[0108] 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 hanging 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 support unit 305, and the structural stress change is collected in real time through the wireless transmission module. The 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 hanging basket. The piezoelectric soil pressure sensor is buried between the soil 2 and the row pile 302 for pressure monitoring, and the lateral pressure distribution of the soil on the supporting structure under the centrifugal environment is collected. The high-speed camera records the deformation of the supporting structure and the collapse trajectory of the soil during the failure of the cross brace, which facilitates subsequent analysis of the failure evolution law.

[0109] Example 3

[0110] The method is applicable to the soil centrifuge model test system for simulating the failure of the cross brace of the foundation pit as described in the above embodiment 2, and the method comprises:

[0111] 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.

[0112] Specifically, S101, input the test parameters such as the preset acceleration value, the acceleration increase rate, and the stable duration through the control system of the geotechnical centrifuge.

[0113] S102, start the driving system, the rotating arm drives the hanging basket to rotate slowly, gradually increase the rotation speed to reach the preset acceleration: during the process, the rotation speed is monitored in real time through the rotation speed sensor installed on the rotating arm, the actual acceleration is calculated according to the formula, compared with the preset value, and the rotation speed is automatically adjusted when the deviation exceeds the preset deviation value. The formula for calculating the centrifugal acceleration is: ​wherein is the angular velocity, is the radius of rotation.

[0114] S103, vibration monitoring and abnormal processing, through the vibration sensor of the hanging basket side wall, 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, the vibration reason is investigated, and the system is restarted after the processing is completed.

[0115] S104, soil stress balance observation: in the stable stage, the stress change of the soil 2 is monitored by 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 prolonged until the balance condition is met.

[0116] S2, when the soil centrifuge is stabilized at a preset acceleration, the control system sends an instruction 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 shifting block 4064, and the shifting block 4064 contacts the metal rod. After the metal rod 4051 rotates, the metal rod 4051 is stripped from the through slot 403 of the track mounting plate 402, causing the hanging rope 4053 to lose support and fall.

[0117] S201, send an instruction 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 of the test design 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 and affect the authenticity of the test data.

[0118] S202, the shifting block contacts the metal rod. The sliding block 4062 moves along the sliding rail 4061, drives the push plate 4063 and the shifting block 4064 to move synchronously to the metal rod 4051, and records the initial contact force through the force sensor at the moment of contact to confirm that the contact position is centered.

[0119] S203, critical sliding trigger. When the push force is gradually increased to the rotation of the metal rod 4051, the metal rod 4051 falls from the through slot 403, the hanging rope 4053 loses support and falls freely, the supporting rod 3051 loses upward tension, and the horizontal support failure is simulated; in the process, a high-speed camera continuously shoots, and the metal rod stripping moment, the hanging rope falling trajectory, and the initial deformation state of the supporting rod are recorded.

[0120] S204, Abnormal situation response. If the thrust exceeds the critical value and the metal rod does not slide, the hydraulic cylinder needs to be stopped immediately, the cause needs to be investigated, whether there are impurities in the slot that increase friction or metal rod installation offset problems, and handle it after re-triggering; if the thrust does not reach the critical value, the metal rod slides early, the test is invalid, the metal rod needs to be reinstalled and the thrust threshold needs to be calibrated before retrying.

[0121] S3, Use the preset high-speed camera to record and observe the support falling process and situation, and monitor the horizontal displacement of the row pile 302 and the settlement of the surrounding soil 2 of the foundation pit through the preset displacement sensor. After the support falls, gradually reduce the acceleration of the soil centrifuge to zero, stop the test system, and save the test data for subsequent analysis.

[0122] S301, During the failure triggering process, each monitoring device collects data at a preset frequency to ensure time consistency. Among them, displacement monitoring, the laser displacement sensor collects the horizontal displacement of the row pile 302 at a preset time interval, focusing on monitoring the top, middle and bottom of the pile, and the settlement of the surrounding soil 2 of the foundation pit. 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, the steel wire rope tension sensor collects the tension change of the hanging rope 4053 at a preset time interval, captures the complete process from stable tension to start descending to zero, and clearly shows the tension mutation characteristics at the failure triggering moment. Stress monitoring, the strain gauge on the surface of the row pile 302 and the support rod 3051 collects stress data at a preset time interval, and analyzes the stress redistribution law of the supporting structure after failure.

[0123] 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 too fast 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 down; Before opening the protective cabin, the rotating arm needs to be completely stationary through the speed sensor to avoid safety risks to personnel.

[0124] 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. Use local + cloud mode for double backup, store locally on a dedicated server, and upload to an encrypted database in the cloud to avoid data loss; After backup, check the data integrity to ensure that there is no missing data.

[0125] S304, take out the test box 1, visually 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 cracks appear in the soil 2 around the foundation pit, the width of the cracks, the collapse range, analyze the correlation between soil instability and cross support failure, sample typical deformation areas, and supplement test data dimensions. Among them, the deformation of the row pile 302 includes whether bending or breaking occurs, and 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.

[0126] 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 within the scope of the present application should still be attributed to the patent 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); 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 the two surrounding purlins (303) at intervals of one bolt (304); each support unit (305) comprises: at least two support rods (3051) arranged side by side; at least two support hinge seats (3052) for connecting the 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); 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 mounting units (405) installed between the through slot (403) and the support hinge seat (3052), and each mounting unit (405) is located between the bolt positioning members (404); the position of each mounting unit (405) corresponds one-to-one to the support rod (3051); the mounting 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).

2. The simulated failure test device for a cross-brace of an excavation pit according to claim 1, 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).

3. The simulated failure test apparatus for a cross-brace of an excavation pit according to claim 2, 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).

4. The simulated failure test apparatus for a cross-brace of an excavation pit according to claim 3, 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.

5. 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 1-4, and the simulation foundation pit cross support failure test device is located in a hanging basket of a geotechnical centrifuge.

6. 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 5, 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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