Centrifugal model test device and method for pile-anchor foundation pit collapse caused by excavation and pipeline leakage under high gravity field

Abstract

A centrifuge model test apparatus and method for simulating the collapse of pile-anchor foundation pits caused by excavation and pipeline leakage under a hypergravity field includes a test chamber, a hydraulically controlled layered excavation device, a leakage device simulating pipeline rupture, anchor bolts and support piles, and a data monitoring system. The layered excavation device is equipped with an independent hydraulic telescopic mechanism, allowing the support baffles to be retracted step-by-step while the centrifuge is running, simulating step-by-step excavation of the foundation pit. The leakage device, through an external water storage tank and a pipe with small holes, simulates constant water pressure leakage without stopping the centrifuge. The anchor bolts are integrally formed from 3D-printed nylon and fiberglass, with a rectangular cross-section in the free section and multiple threads in the anchoring section, achieving mechanical equivalence and facilitating monitoring. This invention avoids interference with the soil stress state during excavation shutdown, eliminates the problems of additional load from the device's self-weight and excessive local stiffness, and can realistically reproduce the entire process of continuous foundation pit collapse induced by leakage, providing an experimental means for foundation pit disaster prevention and control research.

Description

Technical Field

[0001] This invention relates to the field of centrifugal model testing technology in geotechnical engineering, and in particular to a centrifugal model testing device and method for detecting the collapse of pile anchor foundation pits caused by excavation and pipeline leakage under hypergravity. Background Technology

[0002] In urban construction, foundation pit engineering is a crucial aspect of underground space development. With the increasing intensive use of urban underground space, foundation pit projects often face complex surrounding environments, such as adjacent municipal pipelines and existing buildings. Among these, leakage caused by the rupture of municipal pipelines (such as water supply pipes and sewage pipes) outside the foundation pit is a significant contributing factor to the failure of the foundation pit's support structure and even its overall collapse.

[0003] Currently, centrifuge model testing under hypergravity is an important tool for studying geotechnical engineering problems. By placing a scaled-down model in a centrifuge, the model can be subjected to the same stress level as the prototype under a hypergravity field, thus realistically reproducing the mechanical behavior of the prototype geotechnical structure. Therefore, this method is widely used in research fields such as foundation pit excavation and the stress-deformation characteristics of support structures.

[0004] In existing technologies, some studies have used centrifugal model tests to simulate the excavation process of foundation pits. For example, by setting up support structures to simulate the stress state of the foundation pit retaining system, or by embedding components such as anchor bolts and support piles in the model box to study the deformation and internal force development of the support system. However, existing test devices and methods still have the following shortcomings: First, conventional centrifuge model tests for foundation pits often employ a shutdown-and-excavation method, where a portion of the soil is removed manually or mechanically after the centrifuge stops operating to simulate excavation. This shutdown operation alters the stress state of the soil, especially in water-bearing soils, where shutdown can lead to a redistribution of pore water pressure, distorting the moisture distribution and severely affecting the authenticity and reliability of the test results.

[0005] Second, a few existing technologies attempt to simulate excavation using hydraulic devices without shutting down the machine. However, the structural design of these devices does not fully consider the additional load on the test soil caused by the amplified self-weight of the device under hypergravity. Furthermore, when simulating layered excavation, after the support baffles are retracted, the local constraint stiffness of the remaining support structure on the retaining piles becomes excessive, leading to deformation and stress patterns of the retaining structure that do not match actual engineering conditions.

[0006] Third, there is currently no experimental device or method capable of simultaneously simulating the coupled effects of staged excavation of a foundation pit and pipeline leakage under hypergravity conditions without shutting down the system. Existing experiments are unable to reproduce the entire evolution mechanism of water seeping into unsaturated soil after pipeline rupture, which in turn leads to a decrease in anchor bolt anchoring force and continuous collapse of the support system.

[0007] Fourth, regarding anchor bolts, existing centrifugal model tests mostly use metal nails or metal bolts to simulate anchor bolts. These models do not strictly follow the similarity ratio equivalence principle for tensile stiffness and pull-out ultimate bearing capacity, and the metal surfaces are mostly curved, making it difficult to attach strain gauges for axial force monitoring, thus limiting the refined testing of anchor bolt stress behavior. Summary of the Invention

[0008] The purpose of this invention is to propose a centrifuge model test device and method for simulating the collapse of pile anchor foundation pits caused by excavation and pipeline leakage under hypergravity, so as to solve the technical problems in the prior art that cannot simultaneously simulate the coupling effect of step-by-step excavation of foundation pits and pipeline leakage under hypergravity without stopping the centrifuge, and that there are problems such as soil stress state distortion, device self-weight interference, excessive local stiffness, inequivalence of anchor mechanicals, and difficulty in monitoring.

[0009] To achieve the above objectives, the technical solution of the present invention is: a simulation test system for the collapse of pile anchor foundation pits caused by excavation and pipeline leakage under a hypergravity field, comprising a cantilever centrifuge, an oil pump, and a water storage tank, characterized in that the test chamber is fixedly mounted on the rotating arm of the centrifuge, and the test chamber is provided with: The foundation pit layered excavation device is fixedly installed on the upper part of one side of the test box through the support structure. The upper and lower two independent hydraulic telescopic mechanisms are connected to the oil pump respectively, which can control the extension and retraction of the hydraulically driven support rods. A baffle is fixedly connected to the front end of each of the two support rods to provide displacement boundary constraints for the soil between the excavation device and the support piles, so as to simulate the step-by-step excavation process of the foundation pit. The leakage device includes: a pipe connected at one end to a water storage tank and fixed to the test chamber, and the other end extending into the test chamber, with multiple rows of small holes at the center of a preset leakage location. The pipe is used to simulate pipeline leakage under constant water pressure while the centrifuge is running. Multiple anchor bolts-support piles are located on the baffle. The anchor section of the anchor bolt is provided with multiple turns of thread, and the non-anchor section has a rectangular cross-section. A strain gauge for monitoring the axial strain of the anchor bolt is provided on one side of the long side of the non-anchor section. The support piles are inserted into the unsaturated soil. The anchor bolts pass through the gaps between the support piles and are anchored to the capping beam in front of the support piles. A 10cm gap is maintained between the support piles and the baffle. The data monitoring device includes a horizontal displacement meter and a soil vertical settlement meter installed on the steel beam at the top of the anchor rod of the test chamber, a PIV industrial camera on one side of the observation window on the side of the test chamber, a strain gauge on the long side of the free section of the anchor rod, and an earth pressure cell and a support pile bending moment measuring point located on the other side of the test chamber. All of the above devices are buried in unsaturated soil inside the test chamber.

[0010] Furthermore, the support structure includes: The top plate is located on the upper part of the pit layered excavation device and is fixedly connected to the top of the test chamber. The base plate is located at the bottom of the layered excavation device for the foundation pit, and one end is fixedly connected to the test chamber. The rear side plate is located between the pit layer excavation device and the test chamber, and is used to fix two hydraulic telescopic mechanisms to the test chamber. Its lower part is fixedly connected to the bottom plate. The front side plate is fixedly installed on the front side of the hydraulic telescopic mechanism, and its lower part is fixedly connected to the bottom plate. The support rod passes through the front side plate and is fixedly connected to the baffle. Four vertical connecting rods are fixedly connected to the four corners of the top and bottom plates; Multiple horizontal connecting rods are installed between the rear side panel and the front side panel.

[0011] Furthermore, the pipeline is L-shaped on one side of the test chamber and is fixed to the limiting plate by a buckle. The limiting plate is fixed to the test chamber by a first bolt.

[0012] Furthermore, two steel beams are horizontally installed on the top of the test chamber, and horizontal displacement gauges and soil vertical settlement gauges are installed on the steel beams.

[0013] A centrifuge model test method for pile anchor foundation pit collapse induced by excavation and pipeline leakage under a hypergravity field, employing the aforementioned simulation test system for pile anchor foundation pit collapse induced by excavation and pipeline leakage under a hypergravity field, includes the following steps: Step 1, Install the test chamber: Unsaturated soil was filled into the test chamber in stages: (1) First, fill the soil to the bottom of the support piles. When the soil is 38cm away from the top of the test box, fix a row of 30 to 40 support piles vertically and evenly at the preset position. The top of the support piles is 3cm away from the top of the test box. (2) Continue filling the soil to the height of the connecting bottom plate. When the distance from the top of the support pile is 24cm, assemble the bottom plate, vertical connecting rod and top plate into place, connect the rear side plate of the pit layer excavation device to the test box, fix the horizontal connecting rod to the rear side plate and the front side plate, and fix the top plate to the test box. (3) Control the upper and lower support rods to be fully extended, and install baffles at their front ends. Leave a 10cm gap between the upper and lower baffles and the support piles, and fill the gap with test soil. (4) Continue filling the soil to the height of the cap beam. When the distance from the top of the support pile is 3cm, 20 to 30 anchor rods are anchored on the cap beam: the strain gauge is pasted on the long side of the free section of the anchor rod, the anchor rod is passed through the gap between the support piles and anchored to the cap beam in front of the support pile; (5) Arrange a leakage device to simulate pipeline rupture, fix the pipeline to the limiting plate on the upper part of the test chamber, reserve an interface at the end of the pipeline for connecting to the pressurized water pipe, and embed the leakage end with 5 rows of small holes in the preset leakage position. (6) After continuing to fill the soil to the top of the support pile, two steel beams are horizontally set on the top of the test box, and horizontal displacement gauges and soil vertical settlement gauges are installed on the steel beams; the PIV industrial camera is placed on the side of the observation window of the test box, and the soil pressure box and the support pile bending moment measuring point are buried on the side of the support pile far away from the excavation device.

[0014] Step 2. Centrifuge installation and connection: The test chamber is fixed along the rotation radius of the centrifuge to the centrifuge rotating arm, with the support piles and the pit excavation device facing outwards from the centrifuge. The oil pipe and the pressurized water pipe are connected to the oil pump and the water tank, respectively. Step 3. Start the centrifuge: Start the centrifuge, the rotating arm rotates and gradually accelerates to the predetermined acceleration value to simulate the self-weight stress field at the corresponding depth in actual engineering. Step 4. Simulate phased excavation of the foundation pit: Simulated excavation of the upper foundation pit: The oil pump first controls the upper hydraulic telescopic mechanism, causing the upper support rod to retract, which drives the upper baffle to retract. The soil pre-filled between the upper baffle and the support pile loosens and slides down naturally. Simulate the excavation of the lower foundation pit: observe and monitor the data. After the data such as the horizontal displacement of the support piles, soil settlement and anchor axial force stabilize again, the oil pump controls the hydraulic telescopic mechanism below to retract the support rod below, drive the lower baffle to retract, and the test soil between the lower baffle and the support pile slides down. Step 5. Simulate pipeline leakage: After the monitoring data stabilizes again, open the water outlet valve of the water storage tank, control the water flow to enter the pipeline through the pressurized water pipe, and let the water seep out from the 5 rows of small holes at the preset leakage location, gradually seeping into the surrounding unsaturated soil. The water pressure is maintained at 0.6MPa and the flow rate is maintained at 4.0L / min. During the leakage process, the detection data of strain gauges, horizontal displacement gauges, soil vertical settlement gauges, bending moment measuring point pressure cells and the changes in the internal displacement field of the soil continuously captured by PIV industrial cameras are continuously monitored and collected until the anchor bolt-support piles collapse continuously or the monitoring data shows that the test target has been achieved. Step 6. End of experiment: Stop the centrifuge and wait for the rotating arm to come to a complete stop. Remove the test chamber, clean the soil, check the condition of each device, and record the post-test status. The foundation pit collapse simulation test is now complete.

[0015] Furthermore, in step 4, test soil is pre-filled between the baffle and the support pile, with a fill thickness of 10cm, to avoid the influence of excessive local stiffness on the deformation and stress mode of the support structure after the baffle is withdrawn.

[0016] Furthermore, in step 5, the leakage flow rate and velocity are adjusted by the water storage tank to maintain the water pressure at 0.6 MPa and the flow rate at 4.0 L / min, so as to keep the water pressure constant in the pipeline during the leakage process.

[0017] Furthermore, the anchor rod is divided into a free section and an anchoring section. The free section has a rectangular cross-section, and the anchoring section has multiple threads. The anchor rod is made of 3D printed nylon fiberglass material, and its tensile stiffness and pull-out ultimate bearing capacity are designed according to the prototype equivalent. The long side of the rectangular cross-section of the free section is used to attach strain gauges to monitor the axial strain of the anchor rod.

[0018] Furthermore, in steps 4 and 5, the criteria for judging the stability of the monitoring data are: the readings of the horizontal displacement gauge, the readings of the soil vertical settlement gauge, and the readings of the strain gauges on the anchor rod, and the changes in each of the three per minute do not exceed 5% of their respective initial values.

[0019] The beneficial effects of this invention are: to achieve step-by-step excavation without stopping the machine: by using a hydraulic control system to retract the support baffle step by step while the centrifuge is running, the layered excavation of the foundation pit is simulated, which avoids the problems of soil stress state distortion and water distribution disturbance caused by traditional stop-excavation.

[0020] Eliminating interference from the device's own weight: The self-weight of the excavation device under hypergravity is transferred to the test chamber through the top plate, bottom plate, and connecting rods, avoiding additional loads on the test soil and ensuring test accuracy.

[0021] To avoid excessive local stiffness: test soil is reserved between the support baffle and the retaining pile. After the baffle is removed, the soil slides down naturally, which simulates excavation and unloading, and avoids deformation distortion caused by direct rigid contact between the support structure and the retaining pile.

[0022] Simulates constant water pressure leakage without shutting down the machine: By connecting an external water storage tank and pressurized water pipe, the leakage of small holes in the pipe is controlled while the centrifuge is running, and the water pressure is kept constant, realistically simulating the process of water seeping into the soil after the pipeline ruptures.

[0023] The anchor bolts are mechanically equivalent and easy to monitor: the anchor bolts are made of 3D printed nylon glass fiber, achieving equivalent tensile stiffness and pull-out ultimate bearing capacity; the free section is a rectangular cross section, which is convenient for attaching strain gauges to monitor axial force.

[0024] Revealing the entire collapse mechanism: Integrating excavation, seepage, support and monitoring systems, it can continuously simulate the complete process of foundation pit from normal excavation to seepage-induced continuous collapse, providing experimental means for disaster prevention and control research.

[0025] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the casing of the present invention installed on a centrifuge; Figure 2 This is a perspective view of the test chamber of the present invention; Figure 3 This is a side view of the internal structure of the test chamber of the present invention; Figure 4 This is a top view of the internal structure of the test chamber of this invention; Figure 5 This is a schematic diagram of the experimental simulation of the foundation pit before excavation in this invention; Figure 6 This is a schematic diagram of the first step of the experimental simulation of foundation pit excavation in this invention; Figure 7 This is a schematic diagram of the experimental simulation of the excavation of the foundation pit in this invention.

[0027] In the diagram: 2 Front side plate, 4 Bolt, 5 Small hole, 6 Horizontal connecting rod, 7 Vertical connecting rod, 8 Bottom plate, 9 Rear side plate, 11 Support rod, 13 Limiting plate, 14 First bolt, 15 Pipe, 16 Support pile, 17 Anchor rod, 18 Horizontal displacement gauge, 19 Soil vertical settlement gauge, 20 Unsaturated soil, 21 Baffle, 23 Steel beam, 24 Top plate, 25 Oil pipe, 27 Oil pump, 28 Water tank, 30 Crown beam, 51 Hydraulic telescopic mechanism, 100 Test chamber, 101 Observation window, 171 Free section, 172 Anchored section. Detailed Implementation

[0028] Example 1: Centrifuge Model Test Device for Collapse of Pile Anchor Foundation Pit Caused by Excavation and Pipeline Leakage under Hypergravity Field This embodiment provides a centrifugal model test device for the collapse of pile anchor foundation pit caused by excavation and pipeline leakage under a hypergravity field. The specific structure is described in detail below.

[0029] like Figure 1-7 As shown, a simulation test system for pile anchor foundation pit collapse caused by excavation and pipeline leakage under hypergravity includes a cantilever centrifuge, an oil pump, and a water storage tank. The system is characterized in that the test chamber 100 is fixedly mounted on the rotating arm of the centrifuge, and the test chamber 100 is equipped with: The foundation pit layered excavation device is fixedly installed on the upper part of one side of the test box 100 through the support structure. The upper and lower two independent hydraulic telescopic mechanisms 51 are connected to the oil pump 27 respectively, which can control the extension and retraction of the hydraulically driven support rod 11. A baffle 21 is fixedly connected to the front end of each of the two support rods 11 to provide displacement boundary constraints for the soil between the excavation device and the support pile 16, so as to simulate the step-by-step excavation process of the foundation pit. The leakage device includes: a pipe 15 connected at one end to a water storage tank 28, fixed on the test chamber 100, and the other end extending into the test chamber 100, with multiple rows of small holes at the center of the preset leakage position. The pipe 15 is used to simulate pipeline leakage under constant water pressure while the centrifuge is running. Multiple anchor bolts-support piles are located on baffle 21. The anchor section of the anchor bolt 17 is provided with multiple turns of thread, and the non-anchor section has a rectangular cross-section. A strain gauge for monitoring the axial strain of the anchor bolt is provided on the long side of the non-anchor section. The support pile 16 is inserted into the unsaturated soil. The anchor bolt 17 passes through the gap between the support piles 16 and is anchored to the capping beam 30 in front of the support pile. A 10cm gap is maintained between the support pile 16 and the baffle 21. The data monitoring device includes a horizontal displacement meter 18 and a soil vertical settlement meter 19 installed on the steel beam at the top of the anchor rod of the test chamber 100, a PIV industrial camera on one side of the observation window 101 on the side of the test chamber, a strain gauge on the long side of the free section of the anchor rod 17, and an earth pressure cell and a support pile bending moment measuring point located on the other side inside the test chamber 100. All of the above devices are buried in unsaturated soil 20 inside the test chamber.

[0030] In this embodiment, the supporting structure is further configured to include: Top plate 24 is set on the upper part of the foundation pit layered excavation device and is fixedly connected to the top of the test chamber 100; The base plate 8 is located at the lower part of the foundation pit layered excavation device, and one end is fixedly connected to the test chamber 100; The rear side plate 9 is located between the pit layer excavation device and the test chamber 100, and is used to fix two hydraulic telescopic mechanisms 51 to the test chamber 100. Its lower part is fixedly connected to the bottom plate 8. The front side plate 2 is fixedly installed on the front side of the hydraulic telescopic mechanism 51, and its lower part is fixedly connected to the bottom plate 8. The support rod 11 passes through the front side plate 2 and is fixedly connected to the baffle 21. Four vertical connecting rods 7 are fixedly connected to the four corners of the top plate 24 and the bottom plate 8; Multiple horizontal connecting rods 6 are provided between the rear side panel 9 and the front side panel 2.

[0031] In this embodiment, the pipe 15 is L-shaped on one side of the test chamber 100 and is fixed to the limiting plate 13 by a buckle. The limiting plate 13 is fixed to the test chamber 100 by bolts 14.

[0032] In this embodiment, two steel beams 23 are horizontally arranged on the top of the test chamber 100, and a horizontal displacement meter 18 and a soil vertical settlement meter 19 are arranged on the steel beams 23.

[0033] 1. Overall Structure like Figure 1-2 As shown, the device in this embodiment includes a centrifuge, a test chamber 100, a layered excavation device for foundation pits, a leakage device simulating pipeline rupture, an anchor bolt-support pile model, and a data monitoring system.

[0034] The centrifuge has a rotating arm to provide a hypergravity field environment for the experiment. The test chamber 100 is fixed to the rotating arm of the centrifuge, and the interior of the chamber is filled with unsaturated soil 20 to simulate the foundation soil in actual engineering.

[0035] 2. Pit layered excavation device like Figure 3-4 As shown, the layered excavation device for the foundation pit is installed inside the test chamber 100 to simulate the step-by-step excavation process of the foundation pit. The device includes two independent hydraulic telescopic mechanisms 51, a support rod 11, and a baffle 21.

[0036] The upper hydraulic telescopic mechanism 51 is connected to the support rod 11, and the end of the support rod 11 is connected to the upper baffle 21; the lower hydraulic telescopic mechanism 51 is connected to the support rod 11, and the end of the support rod 11 is connected to the lower baffle 2. The upper and lower hydraulic telescopic mechanisms 51 are respectively connected to the oil pump 27 outside the centrifuge via oil pipes 25.

[0037] During the test, the oil pump 27 can drive the upper and lower hydraulic telescopic mechanisms 51 respectively, so that the support rod 11 can extend and retract, thereby driving the upper baffle 21 and the lower baffle 21 to retract, realizing step-by-step excavation control without stopping the centrifuge.

[0038] To prevent the hydraulic telescopic mechanism 51 from shifting laterally under hypergravity and affecting the test accuracy, the device is also equipped with a horizontal connecting rod 6, one end of which is fixed by bolts 4, and the other end is connected to the rear side plate 9 of the excavation device. In addition, the layered excavation device for the foundation pit also includes a vertical connecting rod 7, a bottom plate 8, and a top plate 24. The vertical connecting rod 7 connects the bottom plate 8 and the top plate 24, and the top plate 24 is bolted to the test chamber 100. This structure ensures that the self-weight of the excavation device under hypergravity is mainly borne by the top plate 24 and transferred to the test chamber 100, avoiding additional loads on the test soil 20. Simultaneously, the rear side plate 9 of the excavation device is bolted to the test chamber 100 to prevent horizontal displacement of the device.

[0039] 3. A device to simulate pipeline rupture and leakage. A simulated pipeline rupture leakage device is installed inside the test chamber 100 to simulate the process of water seeping into the soil after a municipal pipeline ruptures. The device includes a pipe 15 and an external water storage tank 28. The pipe 15 is L-shaped on one side of the test chamber 100, with five rows of small holes at the preset leakage location, and is connected to the water storage tank 28 via a pressurized water pipe.

[0040] To prevent the pipe 15 from shifting irregularly in a hypergravity environment, the pipe 15 is fixed to the limiting plate 13 by a buckle. The limiting plate 13 is fixed to the test chamber 100 by the first bolt 14, thereby transferring multiple times the weight of the leakage device to the test chamber 100 and preventing the device from undergoing excessive deformation or settlement.

[0041] During the experiment, the centrifuge remained operational, and water flow was controlled by the water storage tank 28 to enter the pressurized water pipe into the pipeline 15, and then seeped out from the five rows of small holes in the pipeline 15 into the surrounding unsaturated soil 20. The water storage tank 28 can precisely control the flow rate and velocity to maintain a constant water pressure in the pipeline 15 during the leakage process, realistically simulating the constant water pressure leakage condition after a pipeline rupture in actual engineering.

[0042] 4. Anchor Bolt-Support Pile Model The anchor-support pile model includes 30-40 support piles 16 and 20-30 anchor bolts 17. The support piles 16 are hollow aluminum tube piles, designed according to the prototype similarity ratio. The anchor bolts 17 are 3D printed in one piece, made of nylon fiberglass material, and are divided into free section 171 and anchoring section 172.

[0043] The free section 171 has a rectangular cross-section, with its long side used to attach strain gauges to monitor the axial strain of the anchor bolt. The anchoring section 172 has multiple threads, and the number of threads and the thread radius can be changed according to the prototype to adjust the side friction of the anchoring section and achieve a similarity ratio equivalent in pull-out ultimate bearing capacity. The anchor bolt 17 passes through the gap between the support piles 16 and is anchored to the capping beam 30 on the front side of the support piles to realistically simulate the interaction between the anchor bolt and the support pile.

[0044] 5. Data monitoring system Two steel beams 23 are horizontally mounted on the top of the test chamber 100. A horizontal displacement gauge 18 and a soil vertical settlement gauge 19 are mounted on the steel beams 23 to monitor the horizontal displacement of the support piles and the vertical settlement of the soil, respectively. In addition, the monitoring system includes a PIV industrial camera mounted on one side of the observation window 101 on the side of the test chamber, strain gauges attached to the long side of the free section 171 of the anchor bolt 17 for monitoring anchor axial force, an earth pressure cell, and bending moment measuring points for the support piles, all located on the side of the support piles 16 furthest from the excavation device.

[0045] The aforementioned monitoring equipment collects data in real time during the test to analyze the deformation of the support structure, the development of internal forces, and changes in soil settlement during the excavation of the foundation pit and the leakage of the pipeline, until the support system collapses continuously or the test ends.

[0046] 6. Beneficial effects of the device The device in this embodiment achieves step-by-step excavation without stopping the machine under a hypergravity field by setting up two independent hydraulic telescopic mechanisms 51, avoiding the interference of traditional stop-excavation on the soil stress state and moisture distribution. The device's own weight is transferred to the test chamber 100 through the top plate 24, bottom plate 8 and vertical connecting rod 7, eliminating the additional load effect of the device's own weight on the test soil under hypergravity. By leaving a 10cm thick test soil between the upper baffle 21 and the lower baffle 21 and the support pile 16, deformation distortion caused by excessive local stiffness after layered excavation is avoided. The external water storage tank 28 and the pipe 15 with 5 rows of small holes realize the simulation of constant water pressure leakage under a hypergravity field without stopping the machine. The 3D printed nylon fiberglass anchor rod 17 realizes the mechanical equivalence of the anchor rod's tensile stiffness and pull-out ultimate bearing capacity, and facilitates the attachment of strain gauges for axial force monitoring.

[0047] Example 2: Centrifuge Model Test Method for Collapse of Pile Anchor Foundation Pit Caused by Excavation and Pipeline Leakage under Hypergravity Field A test method for the collapse of a pile anchor foundation pit caused by excavation and pipeline leakage under a hypergravity field, using the simulation test system for the collapse of a pile anchor foundation pit caused by excavation and pipeline leakage under a hypergravity field as described in any one of claims 1 to 4, characterized by comprising the following steps: Step 1, Install the test chamber: Unsaturated soil 20 was filled in stages within the test chamber 100: 1. First, when the soil is filled to the bottom of the support pile 16 and 38cm away from the top of the test box 100, a row of 30 to 40 support piles 16 are vertically and evenly fixed at the preset position, with the top of the support pile 16 3cm away from the top of the test box 100. 2. Continue backfilling to the height of the connecting base plate 8. When the distance from the top of the support pile 16 is 24cm, assemble the base plate 8, vertical connecting rod 7 and top plate 24 into place. Connect the rear side plate 9 of the pit layer excavation device to the test box 100. Fix the horizontal connecting rod to the rear side plate 9 and the front side plate 2. Fix the top plate 24 to the test box 100. 3. Control the upper and lower support rods 12 to be fully extended, and install baffles at their front ends. Leave a 10cm gap between the upper baffle 21 and the lower baffle 21 and the support pile 16, and fill the gap with test soil. 4. Continue backfilling to the height of the capping beam 30. When the distance from the top of the support pile 16 is 3cm, 20 to 30 anchor rods 17 are anchored on the capping beam 30. The strain gauge is attached to the long side of the free section of the anchor rod 17. The anchor rod 17 is passed through the gap between the support piles 16 and anchored to the capping beam in front of the support pile. 5. Arrange a leakage device to simulate pipeline rupture. Fix the pipe 15 to the limiting plate 13 on the upper part of the test chamber 100. The end of the pipe 15 is reserved for connecting to the pressurized water pipe. The leakage end with 5 rows of small holes is pre-embedded in the preset leakage position. 6. After continuing to fill the soil to the top of the support pile 16, two steel beams 23 are horizontally set at the top of the test box 100, and a horizontal displacement meter 18 and a soil vertical settlement meter 19 are installed on the steel beams 23; a PIV industrial camera is placed on one side of the observation window 101 on the side of the test box, and the soil pressure cell and the support pile bending moment measuring point are buried on the side of the support pile 16 away from the excavation device.

[0048] Step 2. Centrifuge installation and connection: The test chamber 100 is fixed along the rotation radius of the centrifuge along its length direction, and the support piles 16 and the pit excavation device face outwards from the centrifuge. The oil pipe 25 and the pressurized water pipe are connected to the oil pump 27 and the water tank 28, respectively. Step 3. Start the centrifuge: Start the centrifuge, the rotating arm rotates and gradually accelerates to the predetermined acceleration value to simulate the self-weight stress field at the corresponding depth in actual engineering. Step 4. Simulate phased excavation of the foundation pit: Simulated excavation of the upper foundation pit: The oil pump 27 first controls the upper hydraulic telescopic mechanism 51, causing the upper support rod 11 to retract, which drives the upper baffle 21 to retract. The soil pre-filled between the upper baffle 21 and the support pile 16 loosens and slides down naturally. Simulate the excavation of the lower foundation pit: Observe the monitoring data. After the data such as the horizontal displacement of the support pile 16, soil settlement and axial force of the anchor rod 17 stabilize again, the oil pump 27 controls the hydraulic telescopic mechanism 51 below to retract the support rod 11 below, drive the baffle 21 below to retract, and the test soil between the baffle 21 below and the support pile 16 slides down. Step 5. Simulate pipeline leakage: After the monitoring data stabilizes again, open the outlet valve of the water storage tank 28, control the water flow to enter the pipe 15 through the pressurized water pipe, and let the water seep out from the 5 rows of small holes at the preset leakage position, gradually seeping into the surrounding unsaturated soil 20. The water pressure is maintained at 0.6MPa and the flow rate is maintained at 4.0L / min. During the leakage process, the detection data of strain gauges, horizontal displacement gauges 18, settlement gauges 19, bending moment measuring point pressure cells and the changes in the internal displacement field of the soil continuously captured by PIV industrial cameras were continuously monitored and collected until the anchor bolt-support piles collapsed continuously or the monitoring data showed that the test target had been achieved. Step 6. End of experiment: Stop the centrifuge and wait for the rotating arm to come to a complete stop. Remove the test chamber 100, clean the soil and check the integrity of each device. Record the post-test status. The foundation pit collapse simulation test is now complete.

[0049] In this embodiment, it is further configured that, in step 4, test soil is pre-filled between the upper baffle 21 and the lower baffle 21 and the support pile 16, with a fill thickness of 10cm, in order to avoid the influence of excessive local stiffness on the deformation and stress mode of the support structure after the baffle is withdrawn.

[0050] In this embodiment, it is further configured that in step 5, the leakage flow rate and velocity are adjusted by the water storage tank 28 to keep the water pressure at 0.6MPa and the flow rate at 4.0L / min, so as to keep the water pressure of the pipe 15 constant during the leakage process.

[0051] In this embodiment, the anchor rod 17 is further configured to be divided into a free section 171 and an anchoring section 172. The free section 171 has a rectangular cross-section, and the anchoring section 172 has multiple threads. The anchor rod 17 is made of 3D printed nylon fiberglass material, and its tensile stiffness and pull-out ultimate bearing capacity are designed according to the prototype equivalent. The long side of the rectangular cross-section of the free section 171 is used to attach strain gauges to monitor the axial strain of the anchor rod.

[0052] In this embodiment, the criteria for judging the stability of monitoring data in steps 4 and 5 are as follows: the readings of the horizontal displacement gauge 18, the vertical settlement gauge 19, and the strain gauge on the anchor rod 17, and the changes per minute of each of the three do not exceed 5% of their respective initial values.

[0053] like Figure 5-7 As shown, this embodiment uses the centrifugal model test device described in the above-mentioned device embodiment to provide a test method for the collapse of pile anchor foundation pit caused by excavation and pipeline leakage under hypergravity field. The specific steps are described in detail below.

[0054] 1. Experimental Preparation Stage Steps First, unsaturated soil 20 was filled into the test chamber 100. During the filling process, the soil was compacted in layers according to the density of the prototype soil, and the filling height was controlled.

[0055] When the soil is backfilled to the bottom of the support pile 16 and 38cm away from the top of the test chamber 100, 30 to 40 support piles 16 are fixed with clamps. The top of the support pile 16 is 3cm away from the top of the test chamber 100 to ensure that the position and verticality of the support pile 16 meet the design requirements.

[0056] Continue backfilling to the height of the connecting base plate 8. When the distance from the top of the support pile 16 is 24cm, install the layered excavation device for the foundation pit. Assemble the base plate 8, vertical connecting rod 7, and top plate 24 into place. Connect the top plate 24 to the test chamber 100 with bolts, and connect the rear side plate 9 to the test chamber 100 with bolts. Control the upper and lower support rods 11 to be fully extended, and install baffles at their front ends to maintain a 10cm gap between the upper baffle 21 and the lower baffle 21 and the support pile 16. Fill the gap with test soil.

[0057] Continue backfilling to the height of the capping beam 30. When the distance from the top of the support pile 16 is 3cm, install 20-30 anchor rods 17. The anchor rod 17 is integrally molded from 3D printed nylon fiberglass material, consisting of a free section 171 and an anchoring section 172. The free section 171 has a rectangular cross-section, and the anchoring section 172 has multiple threads. Adhere strain gauges to the long side of the free section 171 of the anchor rod 17, pass the anchor rod 17 through the gap between the support piles 16, and anchor it to the capping beam 30 in front of the support piles. At the same time, install a leakage device simulating pipeline rupture. Fix the L-shaped pipe 15 to the limiting plate 13 with clips. The limiting plate 13 is fixed to the test chamber 100 with the first bolt 14. The L-shaped end of the pipe 15 has a reserved interface for connecting to a pressurized water pipe. The pipe 15 has 5 rows of small holes at the preset leakage position.

[0058] After continuing to fill the soil to the top of the support pile 16, two steel beams 23 are horizontally installed at the top of the test chamber 100, and a horizontal displacement meter 18 and a soil vertical settlement meter 19 are installed on the steel beams 23. A PIV industrial camera is placed on one side of the observation window 101 on the side of the test chamber, and the earth pressure cell and the support pile bending moment measuring point are buried on the side of the support pile 16 away from the excavation device.

[0059] 2. Centrifuge Installation and Connection Steps The test chamber 100 is fixed along the centrifuge's rotation radius along its length onto the centrifuge's rotating arm, with the support piles 16 and the pit excavation device facing outwards from the centrifuge. The oil pipe 25 of the pit excavation device is connected to the oil pump 27 outside the centrifuge, and the pressurized water pipe of the simulated pipeline rupture leakage device is connected to the water storage tank 28 outside the centrifuge. All connecting pipes are checked to ensure reliable sealing and no leaks.

[0060] 3. Steps to start the centrifuge Start the centrifuge to allow the rotating arm to begin rotating, gradually accelerating to a predetermined acceleration value. In this embodiment, the predetermined acceleration value is preferably 80g to simulate the self-weight stress field at the corresponding depth in actual engineering. During acceleration, observe the changing trends of various monitoring data to ensure stable operation of the device.

[0061] 4. Simulate the step-by-step excavation process of the foundation pit. After the monitoring data stabilizes, a step-by-step excavation simulation of the foundation pit is conducted. In this embodiment, the criteria for judging the stability of the monitoring data are: the readings of the horizontal displacement gauge 18, the soil vertical settlement gauge 19, and the strain gauge readings on the anchor rod 17, all of which change by no more than 5% of their respective initial values ​​per minute.

[0062] With the centrifuge running continuously, the hydraulic telescopic mechanism 51 at the top is controlled by the oil pump 27, causing the upper support rod 11 to retract and the upper baffle 21 to move backward. After the upper baffle 21 moves backward, the 10cm thick test soil pre-filled between the upper baffle 21 and the support pile 16 loses its displacement constraint, loosens, and slides down naturally, simulating the excavation of the first upper layer of the foundation pit. After observing and monitoring the data, once the horizontal displacement of the support pile 16, soil settlement, and axial force of the anchor rod 17 stabilize again, the hydraulic telescopic mechanism 51 at the bottom is controlled by the oil pump 27, causing the lower support rod 11 to retract and the lower baffle 21 to move backward. After the lower baffle 22 moves backward, the 10cm thick test soil between the lower baffle 21 and the support pile 16 also slides down, simulating the excavation of the second lower layer of the foundation pit, thus completing the simulation of the step-by-step excavation process of the foundation pit from top to bottom.

[0063] It should be noted that the 10cm thick test soil pre-filled between the baffle 21 and the support pile 16 is not only used to simulate the excavation and unloading effect of the soil in the passive zone of the foundation pit, but more importantly, it avoids the problem of excessive local stiffness caused by the remaining support structure directly rigidly contacting the support pile after the baffle is withdrawn, so that the deformation and stress mode of the support structure are closer to the actual engineering situation.

[0064] 5. Simulation of pipeline leakage steps After the monitoring data stabilizes again, the criteria for judging the stability of the monitoring data are the same as in step 4. Pipeline leakage simulation is then performed while the centrifuge remains running. The outlet valve of the water tank 28 is opened, controlling the water flow through the pressurized water pipe into pipe 15. The water seeps out from five rows of small holes at the preset leakage location in pipe 15, gradually seeping into the surrounding unsaturated soil 20. In this embodiment, the leakage flow rate and velocity are adjusted by the water tank 28 to maintain the water pressure at 0.6 MPa and the flow rate at 4.0 L / min, simulating actual pipeline leakage conditions. The precise control capability of the water tank 28 maintains a constant water pressure in pipe 15 during the leakage process, realistically reproducing the constant water pressure leakage process after a pipeline rupture.

[0065] During the leakage process, the following key data are continuously monitored: the axial force change of anchor bolt 17 is collected by strain gauges; the horizontal displacement of support pile 16 is collected by horizontal displacement gauge 18; the vertical settlement of the soil is collected by soil vertical settlement gauge 19; the bending moment of support pile is collected by bending moment measuring points; and the earth pressure change is collected by earth pressure cell. A PIV industrial camera continuously captures the displacement field changes inside the soil through observation window 101.

[0066] As seepage continues, the water saturation of the unsaturated soil 20 gradually increases, reducing the soil matrix suction and causing a decrease in the side friction of the anchor section 172 of anchor 17, resulting in changes in the axial force of the anchor. When the bearing capacity of a local anchor drops below its limit, the anchor fails, and the load it bears is transferred to adjacent anchors through the capping beam 30 and the support piles 16, potentially triggering a continuous failure process and ultimately leading to the overall collapse of the support system.

[0067] 6. Procedures for ending the experiment Continue the above monitoring until the support system experiences continuous collapse or the monitoring data shows that the test objective has been achieved. Stop the centrifuge and, after the rotating arm has completely stopped, dismantle the test chamber 100, clean the soil and check the integrity of each device, record the post-test status, and the foundation pit collapse simulation test is complete.

[0068] 7. Beneficial effects of the method The method in this embodiment, through the organic combination of steps 1 to 5, achieves continuous simulation of the coupled effect of step-by-step excavation of foundation pits and pipeline leakage under hypergravity. Compared with existing technologies, this method can simulate two key working conditions—step-by-step excavation and pipeline leakage—sequentially without stopping the centrifuge, avoiding interference from shutdown operations on soil stress state and water distribution. By reserving a 10cm thick test soil between the baffle 21 and the support pile 16, the problem of excessive local stiffness after layered excavation is solved. By precisely controlling the leakage flow rate and velocity while maintaining constant water pressure, a realistic simulation of pipeline leakage is achieved. Through the design of the rectangular cross-section and threaded anchor section of the 3D-printed anchor rod 17, the mechanical equivalence and refined monitoring of the anchor rod are realized. This method can fully reveal the entire evolution mechanism of foundation pits from normal excavation to leakage-induced continuous collapse, providing a reliable experimental means for foundation pit disaster prevention and control research.

Claims

1. A centrifugal model test device for pile anchor foundation pit collapse caused by excavation and pipeline leakage under hypergravity, comprising a cantilever centrifuge, an oil pump, and a water storage tank, characterized in that, The test chamber (100) is fixedly mounted on the rotating arm of the centrifuge, and the test chamber (100) is provided with: The foundation pit layered excavation device is fixedly installed on the upper part of one side of the test box (100) through the support structure. The upper and lower two independent hydraulic telescopic mechanisms (51) are connected to the oil pump (27) respectively, which can control the extension and retraction of the hydraulic transmission support rod (11). The front ends of the two support rods (11) are respectively fixedly connected to a baffle (21) to provide displacement boundary constraints for the soil between the excavation device and the support pile (16) to simulate the step-by-step excavation process of the foundation pit. The leakage device includes: a pipe (15) with one end connected to the water storage tank (28), fixed on the test chamber (100), and the other end extending into the test chamber (100), with multiple rows of small holes at the center of the preset leakage position. The pipe (15) is used to simulate pipeline leakage under constant water pressure while the centrifuge is running. Multiple anchor bolts-support piles are located on the baffle (21). The anchor section of the anchor bolt (17) is provided with multiple turns of thread, and the non-anchor section is rectangular in cross-section. A strain gauge for monitoring the axial strain of the anchor bolt is provided on the long side of the non-anchor section. The support pile (16) is inserted into the unsaturated soil. The anchor bolt (17) passes through the gap between the support piles (16) and is anchored to the front capping beam (30) of the support pile. A 10cm gap is maintained between the support pile (16) and the baffle (21). The data monitoring device includes a horizontal displacement meter (18) and a soil vertical settlement meter (19) installed on the steel beam at the top of the anchor rod of the test chamber (100), a PIV industrial camera on one side of the observation window (101) on the side of the test chamber, a strain gauge on the long side of the free section of the anchor rod (17), and an earth pressure cell and a support pile bending moment measuring point located on the other side inside the test chamber (100). All of the above devices were buried in unsaturated soil (20) inside the test chamber.

2. The centrifuge model test device for pile anchor foundation pit collapse caused by excavation and pipeline leakage under hypergravity field as described in claim 1, characterized in that, The support structure includes: The top plate (24) is set on the upper part of the foundation pit layered excavation device and is fixedly connected to the top of the test box (100); The base plate (8) is set at the lower part of the foundation pit layered excavation device, and one end is fixedly connected to the test chamber (100); The rear side plate (9) is set between the foundation pit layer excavation device and the test box (100) for fixing two hydraulic telescopic mechanisms (51) to the test box (100), and the lower part is fixedly connected to the bottom plate (8); The front side plate (2) is fixedly installed on the front side of the hydraulic telescopic mechanism (51), and its lower part is fixedly connected to the bottom plate (8). The support rod (11) passes through the front side plate (2) and is fixedly connected to the baffle (21). Four vertical connecting rods (7) are fixedly connected to the four corners of the top plate (24) and the bottom plate (8); Multiple horizontal connecting rods (6) are provided between the rear side plate (9) and the front side plate (2).

3. The centrifuge model test device for pile anchor foundation pit collapse caused by excavation and pipeline leakage under hypergravity field as described in claim 1, characterized in that, The pipe (15) is L-shaped on one side of the test chamber (100) and is fixed to the limiting plate (13) by a buckle. The limiting plate (13) is fixed to the test chamber (100) by a first bolt (14).

4. The centrifuge model test device for pile anchor foundation pit collapse caused by excavation and pipeline leakage under hypergravity field as described in claim 1, characterized in that, The test chamber (100) has two steel beams (23) horizontally installed on its top, and a horizontal displacement meter (18) and a soil vertical settlement meter (19) are installed on the steel beams (23).

5. A centrifuge model test method for pile anchor foundation pit collapse caused by excavation and pipeline leakage under a hypergravity field, comprising the centrifuge model test apparatus for pile anchor foundation pit collapse caused by excavation and pipeline leakage under a hypergravity field as described in any one of claims 1 to 4, characterized in that, Includes the following steps: Step 1, Install the test chamber: Unsaturated soil (20) was filled in stages inside the test chamber (100): First, fill the soil to the bottom of the support pile (16) and when it is 38cm away from the top of the test box (100), fix a row of 30 to 40 support piles (16) vertically and evenly at the preset position. The top of the support pile (16) is 3cm away from the top of the test box (100).

2. Continue filling the soil to the height of the connecting bottom plate (8). When the distance from the top of the support pile (16) is 24cm, assemble the bottom plate (8), vertical connecting rod (7) and top plate (24) into place. Connect the rear side plate (9) of the pit layer excavation device to the test box (100). Fix the horizontal connecting rod to the rear side plate (9) and the front side plate (2). Fix the top plate (24) to the test box (100).

3. Control the upper and lower support rods (12) to be fully extended, and install baffles at their front ends. Leave a 10cm gap between the upper and lower baffles (21) and the support piles (16), and fill the gap with test soil.

4. Continue filling the soil to the height of the capping beam (30). When the distance from the top of the support pile (16) is 3cm, 20 to 30 anchor rods (17) are anchored on the capping beam (30): the strain gauge is pasted on the long side of the free section of the anchor rod (17), the anchor rod (17) is passed through the gap between the support piles (16) and anchored to the capping beam in front of the support pile; 5. Arrange a leakage device to simulate pipeline rupture. Fix the pipe (15) on the limiting plate (13) on the upper part of the test chamber (100). The end of the pipe (15) is reserved for connecting the pressurized water pipe. The leakage end with 5 rows of small holes is pre-embedded in the preset leakage position.

6. After continuing to fill the soil to the top of the support pile (16), two steel beams (23) are horizontally set on the top of the test box (100), and a horizontal displacement meter (18) and a soil vertical settlement meter (19) are installed on the steel beams (23); the PIV industrial camera is placed on one side of the observation window (101) on the side of the test box, and the soil pressure cell and the support pile bending moment measuring point are buried on the side of the support pile (16) away from the excavation device; Step 2. Centrifuge installation and connection: The test chamber (100) is fixed along the rotation radius of the centrifuge on the centrifuge rotating arm, and the support pile (16) and the pit layer excavation device face the outside of the centrifuge. The oil pipe (25) and the pressurized water pipe are connected to the oil pump (27) and the water tank (28) respectively. Step 3. Start the centrifuge: Start the centrifuge, the rotating arm rotates and gradually accelerates to the predetermined acceleration value to simulate the self-weight stress field at the corresponding depth in actual engineering. Step 4. Simulate phased excavation of the foundation pit: Simulated excavation of the upper foundation pit: The oil pump (27) first controls the upper hydraulic telescopic mechanism (51) to retract the upper support rod (11), which drives the upper baffle (21) to retreat. The soil pre-filled between the upper baffle (21) and the support pile (16) loosens and slides down naturally. Simulate the excavation of the lower foundation pit: observe the monitoring data, and after the horizontal displacement of the support pile (16), soil settlement and axial force of the anchor (17) stabilize again, the oil pump (27) controls the hydraulic telescopic mechanism (51) below to retract the support rod (11) below, drive the baffle (21) below to move backward, and the test soil between the baffle (21) below and the support pile (16) slides down; Step 5. Simulate pipeline leakage: After the monitoring data stabilizes again, open the outlet valve of the water storage tank (28) and control the water flow to enter the pipeline (15) through the pressurized water pipe. The water flow seeps out from the five rows of small holes at the preset leakage position and gradually seeps into the surrounding unsaturated soil (20). The water pressure is maintained at 0.6MPa and the flow rate is maintained at 4.0L / min. During the leakage process, the detection data of strain gauges, horizontal displacement gauges (18), soil vertical settlement gauges (19), bending moment measuring point pressure cells and the changes in the internal displacement field of the soil continuously captured by PIV industrial cameras were continuously monitored and collected until the anchor bolt-support piles collapsed continuously or the monitoring data showed that the test target had been achieved. Step 6. End of experiment: Stop the centrifuge and wait for the rotating arm to stop completely. Remove the test chamber (100), clean the soil and check the condition of each device. Record the post-test status. The foundation pit collapse simulation test is now complete.

6. The test method according to claim 5, characterized in that, In step 4, test soil is pre-filled between the baffle (21) and the support pile (16), with a filling thickness of 10cm, to avoid the influence of excessive local stiffness on the deformation and stress mode of the support structure after the baffle is withdrawn.

7. The test method according to claim 5, characterized in that, In step 5, the leakage flow rate and velocity are adjusted by the water storage tank (28) to keep the water pressure at 0.6MPa and the flow rate at 4.0L / min, so as to keep the water pressure of the pipeline (15) constant during the leakage process.

8. The test method according to claim 5, characterized in that, The anchor rod (17) is divided into a free section (171) and an anchoring section (172). The free section (171) has a rectangular cross section, and the anchoring section (172) has multiple threads. The anchor rod (17) is made of 3D printed nylon fiberglass material. Its tensile stiffness and pull-out ultimate bearing capacity are designed according to the prototype equivalent. The long side of the rectangular cross section of the free section (171) is used to attach strain gauges to monitor the axial strain of the anchor rod.

9. The test method according to claim 5, characterized in that, In steps 4 and 5, the criteria for judging the stability of the monitoring data are: the readings of the horizontal displacement gauge (18), the vertical settlement gauge (19) of the soil, and the strain gauge readings on the anchor rod (17) all have a change per minute that does not exceed 5% of their respective initial values.

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