Test device and method for influence of multi-side foundation pit excavation on foundation and structure between pits

Abstract

The application discloses a kind of test device and method of the influence of multi-side foundation pit excavation to foundation and structure between pits, the test device includes model box, retaining wall board (4), existing structure (6), support rod piece (15), model soil (19), movable counterforce component, drainage component and data acquisition component;Model box is the box type structure of top opening, existing structure is located in the middle of model box, and several retaining wall boards are respectively inserted in model box, and form excavation foundation pit on the both sides of existing structure;Drainage component is arranged at the bottom of model box, movable counterforce component is arranged at the top of model box, data acquisition component is arranged on model box, retaining wall board, existing structure and support rod piece, and model soil is filled in model box.The application can solve the problem that existing technology cannot simulate the influence of multi-side foundation pit excavation to foundation soil body and existing structure between pits.

Description

Technical Field

[0001] This invention relates to a test apparatus and method for underground engineering construction, and more particularly to a test apparatus and method for the impact of multi-sided foundation pit excavation on the foundation and structure between pits. Background Technology

[0002] In recent years, against the backdrop of comprehensive development and deep integration of urban underground space, large and deep foundation pit clusters have frequently appeared across the country. Complex boundary foundation pits with various irregular shapes, such as polygonal and concave-convex polygonal types, are commonplace in densely populated urban areas. This has led to an increasing number of adjacent buildings and structures facing multi-sided foundation pit excavation and unloading, resulting in more complex mechanical properties and superimposed deformation characteristics of the foundation soil under multi-sided excavation and unloading, and repeated disturbance. These new engineering problems undoubtedly present numerous new difficulties and challenges to foundation pit design, and significantly increase construction difficulty and risks. Therefore, researching the disturbance mechanism of ground stress caused by multi-sided foundation pit excavation and unloading, and the deformation control measures for multi-sided foundation pit excavation, is of great significance.

[0003] Currently, indoor model testing is one of the widely used research methods for simulating complex geotechnical engineering problems. Numerous model tests have been conducted on foundation pit excavation. These typically involve setting up retaining structures under simulated geological conditions within a model chamber, followed by foundation pit excavation and support installation, and then observing the changes in stress and deformation of the retaining structure, as well as soil deformation and stress state, during the test.

[0004] However, existing model devices and testing methods mainly simulate single-sided foundation pit excavation under two-dimensional plane strain conditions, rarely addressing the situation of multiple foundation pits being excavated sequentially or simultaneously in three-dimensional space. It is evident that traditional model test chambers and testing devices are insufficient to specifically simulate the problem of unloading soil in increasingly limited areas of large cities due to multi-sided foundation pit excavation. Therefore, there is a need to provide a testing device and method for the impact of multi-sided foundation pit excavation on the foundation soil and existing structures between the pits, solving the problem that existing technologies cannot simulate the impact of multi-sided foundation pit excavation on the foundation soil and existing structures between the pits. Summary of the Invention

[0005] The purpose of this invention is to provide a test device and method for the impact of multi-sided foundation pit excavation on the foundation and structure between the pits, which can solve the problem that the existing technology cannot simulate the impact of multi-sided foundation pit excavation on the foundation soil and existing structure between the pits.

[0006] This invention is implemented as follows:

[0007] An experimental device for assessing the impact of multi-sided excavation on the foundation and structure between pits includes a model box, retaining wall panels, an existing structure, supporting rods, model soil, a movable reaction assembly, a drainage assembly, and a data acquisition assembly. The model box is a box-shaped structure with an open top. The existing structure is located in the middle of the model box, and several retaining wall panels are movably inserted into the model box, forming excavation pits on both sides of the existing structure. The drainage assembly is located at the bottom of the model box, the movable reaction assembly is located at the top of the model box, and the data acquisition assembly is located on the model box, retaining wall panels, existing structure, and supporting rods. The model soil fills the model box.

[0008] The model box includes a model box, a box frame, and casters; the box frame is installed on the inner wall of the model box, and several casters are installed at intervals on the bottom of the model box; several sliding grooves are formed at intervals on the inner wall of the box frame, allowing the retaining wall panels to be slidably inserted into the model box through the sliding grooves; a movable reaction force assembly is installed on the top of the box frame; the data acquisition assembly includes a dial gauge and a displacement acquisition device, with several dial gauges spaced at intervals on the top of the box frame and facing the model soil, and all dial gauges are electrically connected to the displacement acquisition device.

[0009] The retaining wall panel has multiple walers spaced apart on its outer wall; the retaining wall panel has several support holes spaced apart, and the support holes penetrate the retaining wall panel and the walers, so that the support rods can be horizontally supported between two adjacent retaining wall panels through the support holes; the data acquisition component includes strain gauges, a strain acquisition instrument, a miniature earth pressure gauge and a pore water pressure gauge, several miniature earth pressure gauges and pore water pressure gauges are arranged vertically on the outer wall of the retaining wall panel, and multiple strain gauges are arranged in a matrix and attached to the retaining surface and the back soil surface of the retaining wall panel and electrically connected to the strain acquisition instrument.

[0010] The supporting rods include a first supporting rod, a second supporting rod, springs, connecting plates, and fixing components. One end of the first supporting rod has a threaded hole, and one end of the second supporting rod has a screw thread that matches the threaded hole, allowing the first and second supporting rods to be movably screwed together. The other ends of the first and second supporting rods are respectively rotatably connected to one end of two springs via rolling bearings. The other ends of the two springs are respectively fixed to the support holes of two oppositely arranged retaining wall panels via connecting plates and fixing components, so that the supporting rods are horizontally supported between the two retaining wall panels. The data acquisition component includes a displacement sensor and a displacement acquisition device. A displacement sensor is installed between the first and second supporting rods, and a displacement sensor is installed between the two connecting plates and the retaining wall panels they are connected to.

[0011] Each of the aforementioned sliding grooves includes a tenon, a wedge, and a handle; one side of the tenon is vertically set on the inner wall of the box frame, and the other side of the tenon forms a wedge-shaped groove, with the wedge fitted into the wedge-shaped groove of the tenon, and the handle is set on the top of the wedge.

[0012] The two ends of the existing structure's main body penetrate the model box, and the two ends of the existing structure are sealed by an interface sealing device; the data acquisition component includes an LVDT displacement sensor, an earth pressure gauge, and a displacement acquisition device. Multiple displacement sensors are installed horizontally and vertically inside the main body of the structure through fixed supports and are electrically connected to the displacement acquisition device. Several earth pressure gauges are installed at intervals on the outer wall of the main body of the structure.

[0013] The interface sealing device includes an interface cover plate and a sealing gasket. A flange is formed at the outer edge of the interface cover plate, and the sealing gasket is attached to the inner wall of the flange. When the inner side of the interface cover plate is inserted into the existing structure, the outer flange of the interface cover plate is sealed and fixed to the end face of the existing structure and the outer wall of the model box by the sealing gasket.

[0014] The movable reaction force assembly includes a movable reaction beam, a jack, and a loading plate. The movable reaction beam is set on the top of the box frame of the model box, and the jack is set at the bottom of the movable reaction beam. The output end of the jack is connected to the loading plate, so that the loading plate presses against the surface of the model soil. The data acquisition assembly includes a weighing device and a weighing display. The weighing device is set at the connection between the movable reaction beam and the jack, and the weighing device and the weighing display are electrically connected.

[0015] The drainage component includes an openable / closeable water outlet and a permeable bottom plate. The permeable bottom plate is laid on the bottom surface inside the model box, and several openable / closeable water outlets are respectively arranged at intervals on both sides of the bottom of the model box and connected to the permeable bottom plate.

[0016] A test method for an experimental apparatus to test the impact of multi-sided foundation pit excavation on the foundation and structure between pits includes the following steps:

[0017] Step 1: Determine the spacing of the foundation pits according to the experimental requirements;

[0018] Step 2: Determine the dimensions of the retaining wall panels and fabricate four retaining wall panels;

[0019] Step 3: Install a data acquisition component on the retaining wall panel and use the data acquisition component to measure the deflection of the retaining wall panel caused by the excavation of the foundation pit, so as to calculate the horizontal deformation of the retaining wall panel;

[0020] Step 4: Set the existing structure inside the model box and install the data acquisition components on the existing structure;

[0021] Step 5: Install the retaining wall panels inside the model box according to the spacing of the foundation pits, and form foundation pits on both sides of the existing structure;

[0022] Step 6: Lay drainage components at the bottom of the model box according to the type of drainage to be simulated;

[0023] Step 7: Prepare model soil according to the required soil type, turn off the drainage components, seal the gap between the existing structure and the model box, and fill the model soil into the model box;

[0024] Step 8: During the filling of model soil, the data acquisition components are buried in the predetermined positions in the pit according to the test plan, for measuring the horizontal and vertical earth pressure in the pit.

[0025] Step 9: After the model soil is filled, let it stand to allow the soil inside the model box to stabilize.

[0026] Step 10: Install the movable reaction force assembly directly above the desired loading position;

[0027] Step 11: Install the data acquisition unit on top of the model soil and record the initial readings;

[0028] Step 12: According to the excavation sequence and method determined in the test plan, excavate the foundation pit soil between the retaining wall panels in layers and erect support rods; according to the medium of the model soil and the test drainage conditions, set the drainage components to normally closed, normally open or open in stages during the excavation of the foundation pit soil.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] 1. Because the present invention is equipped with a retaining wall plate, it can be flexibly installed and adjusted through a sliding groove, overcoming the drawbacks of traditional foundation pit excavation test devices. It can simultaneously simulate the disturbance effect of multi-sided foundation pit excavation on the foundation soil between the pits under two-dimensional and three-dimensional conditions, and obtain data such as surface settlement, retaining wall bending moment and horizontal displacement, earth pressure on the retaining wall and earth pressure inside the foundation soil between the pits. It can also simultaneously consider multiple factors such as foundation pit spacing, excavation sequence, and depth asymmetry, providing scientific and accurate test data for revealing the disturbance mechanism of multi-sided foundation pit excavation on the foundation soil between the pits and the earth pressure calculation method for finite soil.

[0031] 2. Because the present invention is equipped with a retaining wall panel, it can be flexibly installed and adjusted through a sliding groove. It can not only simulate the excavation of multiple foundation pits, but also simulate the response of existing buildings (structures) such as pit tunnels and shallow foundation buildings under the unloading of multiple foundation pits, providing a basis for the protection of existing buildings (structures) under the disturbance of multiple excavations.

[0032] 3. This invention is not only applicable to foundation pit excavation in sandy soil, but also to soils such as saturated clay. By controlling the drainage conditions, it can reflect the changes in stress and pore water pressure of the foundation soil between pits over time under multi-sided excavation and unloading conditions, providing an effective means to simulate and evaluate the long-term and short-term effects of the foundation soil between pits after multiple disturbances. Attached Figure Description

[0033] Figure 1 This is a cross-sectional view (without support rods) of the test device for the impact of multi-sided foundation pit excavation on the foundation and structure between pits according to the present invention.

[0034] Figure 2 This is a top view of the test device for the impact of multi-sided foundation pit excavation on the foundation and structure between pits according to the present invention (without support rods installed).

[0035] Figure 3 This is a side sectional view of the test device for the impact of multi-sided foundation pit excavation on the foundation and structure between pits according to the present invention;

[0036] Figure 4 yes Figure 2 Sectional view of AA in the middle;

[0037] Figure 5 This is a top view of the sliding groove in the test device for the impact of multi-sided foundation pit excavation on the foundation and structure between pits according to the present invention.

[0038] Figure 6 This is a schematic diagram of the back soil surface of the retaining wall panel in the test device for the impact of multi-sided foundation pit excavation on the foundation and structure between pits in this invention.

[0039] Figure 7 This is a schematic diagram of the soil-facing surface of the retaining wall panel in the test device for the impact of multi-sided foundation pit excavation on the foundation and structure between pits according to the present invention.

[0040] Figure 8 This is a front view of the interface cover plate in the experimental device for testing the impact of multi-sided foundation pit excavation on the foundation and structure between pits according to the present invention.

[0041] Figure 9 yes Figure 8 Cross-sectional view of the middle section (BB);

[0042] Figure 10 This is a cross-sectional view of the existing structure in the test device for the impact of multi-sided foundation pit excavation on the foundation and structure between pits according to the present invention.

[0043] Figure 11 This is a cross-sectional view of the support rod in the test device for the impact of multi-sided foundation pit excavation on the foundation and structure between pits according to the present invention.

[0044] In the diagram, 1. Model box; 2. Box frame; 3. Interface sealing device; 4. Retaining wall panel; 5. Casters; 6. Existing structure; 7. Movable reaction beam; 8. Weighing device; 9. Jack; 10. Weighing digital display; 11. Sliding groove; 12. Strain gauge; 13. Dial gauge; 14. Miniature earth pressure gauge and pore water pressure gauge; 15. Support rods; 16. Open / closed water outlet; 17. Permeable base plate; 18. Loading plate; 19. Model soil; 20. Displacement acquisition device; 3-1 Interface cover plate; 3-2 Bolt and nut assembly; 3-3 Sealing gasket; 4-1 Support hole; 4-2 Waler; 4-3 Strain gauge; 6-1 Main structure; 6-2 LVDT displacement sensor; 6-3 fixed support; 6-4 earth pressure gauge; 11-1 tenon; 11-2 wedge; 11-3 handle; 15-1 first support rod; 15-2 second support rod; 15-3 rolling bearing; 15-4 spring; 15-5 connecting plate; 15-6 fastener; 15-7 displacement sensor; 15-8 baffle. Detailed Implementation

[0045] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0046] Please see the appendix Figure 1 To be continued Figure 4 An experimental device for assessing the impact of multi-sided excavation on the foundation and structure between pits includes a model box, retaining wall panels 4, existing structure 6, supporting rods 15, model soil 19, a movable reaction assembly, a drainage assembly, and a data acquisition assembly. The model box is a box-shaped structure with an open top. The existing structure 6 is located in the middle of the model box. Several retaining wall panels 4 are movably inserted into the model box, forming excavation pits on both sides of the existing structure 6. The drainage assembly is located at the bottom of the model box, the movable reaction assembly is located at the top of the model box, and the data acquisition assembly is located on the model box, retaining wall panels 4, existing structure 6, and supporting rods 15. The model soil 19 fills the model box.

[0047] Preferably, the retaining wall panel 4 can be made of polypropylene material, which is highly workable and can be processed according to size requirements. It can be flexibly inserted into different positions within the model box to meet the simulation needs of excavation pits of different sizes, locations, and numbers, thereby enabling experiments on the impact of multi-sided excavation on the foundation or existing structure 6. By flexibly combining and configuring retaining wall panels 4 in different positions and quantities, two-dimensional and three-dimensional test conditions can be simulated. The model soil 19 can use sand or cohesive soil as the soil medium, and the soil consolidation and drainage conditions are controlled by the drainage components at the bottom. Support rods 15 are used to support the retaining wall panel 4, and movable reaction components are used to apply different pressures to the model soil 19 to simulate the impact of ground overload and other conditions on the soil between pits and the existing structure 6. The data acquisition component is used to deploy various sensors and other equipment required for data collection, facilitating the acquisition and processing of data during the experiment.

[0048] Please see the appendix Figure 1 To be continued Figure 4 The model box includes a model box 1, a box frame 2, and casters 5. The box frame 2 is installed on the inner wall of the model box 1, and several casters 5 are installed at intervals on the bottom of the model box 1. Several sliding grooves 11 are formed at intervals on the inner wall of the box frame 2, so that the retaining wall plate 4 is slidably inserted into the model box 1 through the sliding grooves 11. The movable reaction force assembly is installed on the top of the box frame 2. The data acquisition assembly includes a dial gauge 13 and a displacement acquisition device 20. Several dial gauges 13 are respectively arranged at intervals on the top of the box frame 2 and facing the model soil 19. Several dial gauges 13 are electrically connected to the displacement acquisition device 20.

[0049] Waterproof sealant is filled in the gaps between the side walls and bottom plate of model box 1 and the box frame 2 to prevent water and soil from leaking out of the model box 1 during the test. The box frame 2 can be made of steel and manufactured according to the size of model box 1 to improve the structural strength of model box 1. The casters 5 facilitate flexible movement of the entire device of the present invention. The dial indicator 13 can be a magnetic dial indicator 13 of the prior art, and the displacement acquisition device 20 can be computer equipment to facilitate the collection of data from the dial indicator 13 via a serial port through a data cable.

[0050] Please see the appendix Figure 6 and attached Figure 7The retaining wall panel 4 has multiple walers 4-2 spaced apart on its outer wall; the retaining wall panel 4 has a number of support holes 4-1 spaced apart, and the support holes 4-1 penetrate the retaining wall panel 4 and the walers 4-2, so that the support rods 15 can be horizontally supported between two adjacent retaining wall panels 4 through the support holes 4-1; the data acquisition component includes strain gauges 4-3, strain acquisition instrument 12, and miniature earth pressure gauges and pore water pressure gauges 14. A number of miniature earth pressure gauges and pore water pressure gauges 14 are arranged vertically on the outer wall of the retaining wall panel 4, and multiple strain gauges 4-3 are arranged in a matrix and attached to the retaining surface and the back soil surface of the retaining wall panel 4 and electrically connected to the strain acquisition instrument 12.

[0051] Strain gauges 4-3 are attached to the retaining and back soil surfaces of the retaining wall panel 4 using adhesive methods to detect deformation of these surfaces. A strain gauge acquisition instrument 12 is used in conjunction with strain gauges 4-3. A miniature earth pressure gauge and a pore water pressure gauge 14 are used; the miniature earth pressure gauge collects earth pressure, and the pore water pressure gauge collects pore water pressure. Pressure data can be acquired via a computer device through a data cable.

[0052] Please see the appendix Figure 11 The support rod 15 includes a first support rod 15-1, a second support rod 15-2, a spring 15-4, a connecting plate 15-5, and a fixing member 15-6. One end of the first support rod 15-1 has a screw hole, and one end of the second support rod 15-2 has a screw that matches the screw hole, so that the first support rod 15-1 and the second support rod 15-2 are movably screwed together. The other ends of the first support rod 15-1 and the other ends of the second support rod 15-2 are respectively rotatably sleeved to one end of the two springs 15-4 through rolling bearings 15-3. The other ends of the two springs 15-4 are respectively fixed to the support holes 4-1 of the two opposite retaining wall plates 4 through the connecting plate 15-5 and the fixing member 15-6, so that the support rod 15 is horizontally supported between the two retaining wall plates 4; the data acquisition component includes a displacement sensor 15-7 and a displacement acquisition device 20. The displacement sensor 15-7 is installed between the first support rod 15-1 and the second support rod 15-2 through the baffle 15-8, and the displacement sensor 15-7 is installed between the two connecting plates 15-5 and the retaining wall plates 4 they are connected to.

[0053] The first support rod 15-1 and the second support rod 15-2 can adjust their connection length by rotating the screw in the screw hole. The rolling bearing 15-3 reduces the end friction during the adjustment of the first support rod 15-1 and the second support rod 15-2, thereby ensuring the reliability of the support for retaining wall panels 4 with different spacing. The spring 15-4 can undergo compression deformation after the retaining wall panel 4 is subjected to force, thus facilitating displacement measurement. The fastener 15-6 can be a bolt and nut, used for installation and connection with the pre-reserved support hole 4-1 on the retaining wall panel 4. The displacement sensor 15-7 can be connected to an external computer device to detect the relative displacement between the first support rod 15-1 and the second support rod 15-2, and the relative displacement between the connecting plate 15-5 and the connected retaining wall panel 4, and transmit the displacement data to the computer device via data cable or other means.

[0054] Please see the appendix Figure 5 Each of the sliding grooves 11 includes a tenon 11-1, a wedge 11-2, and a handle 11-3; one side of the tenon 11-1 is vertically set on the inner wall of the box frame 2, and the other side of the tenon 11-1 forms a wedge-shaped groove, the wedge 11-2 is fitted into the wedge-shaped groove of the tenon 11-1, and the handle 11-3 is set on the top of the wedge 11-2.

[0055] In the unused sliding groove 11, its wedge-shaped opening is closed by a wedge 11-2 to prevent the model soil 19 from clogging the sliding groove 11. When the sliding groove 11 is in use, the wedge 11-2 is pulled out upward by the handle 11-3. The end of the retaining wall plate 4 can form a wedge 11-2 that matches the wedge-shaped opening, which is used to reliably insert the retaining wall plate 4 into the model box 1.

[0056] Please see the appendix Figure 10 The two ends of the main body 6-1 of the existing structure 6 penetrate the model box, and the two ends of the existing structure 6 are sealed by the interface sealing device 3; the data acquisition component includes LVDT (Linear Variable Displacement Transducer) displacement sensor 6-2, earth pressure gauge 6-4 and displacement acquisition device 20. Multiple displacement sensors 6-2 are installed horizontally and vertically in the main body 6-1 through fixed supports 6-3 and are electrically connected to the displacement acquisition device 20. Several earth pressure gauges 6-4 are installed at intervals on the outer wall of the main body 6-1.

[0057] Preferably, the existing structure 6 is mostly a tunnel, with a hollow cylindrical structure. The main body 6-1 is a tunnel segment. The penetration between the existing structure 6 and the model box 1 is sealed by an interface sealing device 3 to prevent mud and water leakage. LVDT displacement sensors 6-2 and earth pressure gauges 6-4 are used to detect the displacement and earth pressure on the existing structure 6 during multi-sided foundation pit excavation. Data from the LVDT displacement sensors 6-2 and earth pressure gauges 6-4 can be collected using external computer equipment.

[0058] Please see the appendix Figure 8 and attached Figure 9 The interface sealing device 3 includes an interface cover plate 3-1 and a sealing gasket 3-3. A flange is formed on the outer edge of the interface cover plate 3-1 (i.e., the side away from the existing structure 6). The sealing gasket 3-3 is attached to the inner wall of the flange. When the inner side of the interface cover plate 3-1 (i.e., the side close to the existing structure 6) is inserted into the existing structure 6, the flange on the outer side of the interface cover plate 3-1 is sealed and attached to the end face of the existing structure 6 and the outer wall of the model box 1 by the sealing gasket 3-3, and is fixed by multiple bolt and nut groups 3-2.

[0059] Preferably, the sealing gasket 3-3 can be made of rubber to ensure the sealing of the gaps between the two ends of the existing structure 6 and the model box 1. The interface cover plate 3-1 can be made of steel, and its size and shape can be determined according to the size and shape of the existing structure 6.

[0060] Please see the appendix Figure 1 To be continued Figure 4 The movable reaction force assembly includes a movable reaction beam 7, a jack 9, and a loading plate 18. The movable reaction beam 7 is located on the top of the box frame 2 of the model box, and the jack 9 is located at the bottom of the movable reaction beam 7. The output end of the jack 9 is connected to the loading plate 18, so that the loading plate 18 presses against the surface of the model soil 19. The data acquisition assembly includes a weighing device 8 and a weighing digital display 10. The weighing device 8 is located at the connection between the movable reaction beam 7 and the jack 9, and the weighing device 8 is electrically connected to the weighing digital display 10.

[0061] The movable reaction beam 7 can be set at the location required for the applied pressure and can be temporarily fixed by bolts or other means. This facilitates pressure loading tests on the model soil 19 via the loading plate 18 using jacks 9, simulating surcharge and other pressure conditions on the soil and the existing structure 6 below it. The weighing device 8 measures the load applied by the jacks 9 and displays it in real time via a digital weighing display 10, allowing for timely adjustments to the load during the test.

[0062] Please see the appendix Figure 1 To be continued Figure 4The drainage component includes an openable and closable outlet 16 and a permeable bottom plate 17. The permeable bottom plate 17 is laid on the bottom surface inside the box frame 2 of the model box. Several openable and closable outlets 16 are respectively arranged at intervals on both sides of the bottom of the model box 1 of the model box and are connected to the permeable bottom plate 17.

[0063] Preferably, a switch valve can be installed on the open / closed outlet 16 to control the opening and closing state of the open / closed outlet 16. When the switch valve is opened, the water in the model box 1 can seep down through the permeable bottom plate 17 and be discharged from the open / closed outlet 16. When the switch valve is closed, the water is sealed in the model box 1 to simulate groundwater conditions.

[0064] Please see the appendix Figure 1 To be continued Figure 11 A test method for an experimental apparatus for assessing the impact of multi-sided excavation on the foundation and structure between excavations includes the following steps:

[0065] Step 1: Determine the spacing of the foundation pits according to the needs of the experiment.

[0066] Step 2: Determine the dimensions of the retaining wall panel 4 and fabricate four retaining wall panels 4.

[0067] Specifically, the dimensions of the retaining wall panel 4 required for the model test corresponding to the prototype in the actual project are obtained by converting the bending stiffness similarity ratio, and four polypropylene panels of the same size are processed as retaining wall panels 4. The walers 4-2 are fixedly installed on the retaining wall panel 4 by means of drilling or pasting, and the installation positions of the support rods are marked on the walers 4-2.

[0068] Step 3: Install data acquisition components on the retaining wall panel 4 and perform surface waterproofing and anti-corrosion treatment. Use the data acquisition components to measure the deflection of the retaining wall panel 4 caused by the excavation of the foundation pit, and use this measurement to calculate the horizontal deformation of the retaining wall panel 4.

[0069] Specifically, strain gauges 4-3 are attached from top to bottom to the soil-facing and soil-repellent surfaces of the retaining wall panel 4. These strain gauges 4-3 are used to measure the deflection and deformation of the retaining wall panel 4 caused by the model soil 19 during excavation, thereby calculating the horizontal deformation of the retaining wall panel 4. A miniature earth pressure gauge and a pore water pressure gauge 14 are installed on the soil-facing surface of the retaining wall panel 4. The miniature earth pressure gauge can be used to monitor the lateral earth pressure between the soil layers and the lateral earth pressure on the soil at the far side after unloading during excavation.

[0070] Step 4: Set the existing structure 6 inside the model box and install the data acquisition component on the existing structure 6.

[0071] If the test only involves the impact of multi-sided excavation on the soil between the pits, step 4 can be skipped. If it is necessary to test the impact of multi-sided excavation on the existing structure 6, the existing structure 6 should be installed inside the model box. The existing structure 6 is preferably located in the middle of the model box 1 to facilitate the layout of the pits on both sides.

[0072] Specifically, mounting holes for the existing structure 6 are pre-drilled on both sides of the model box 1. The two ends of the existing structure 6 pass through the mounting holes. The two ends of the existing structure 6 are sealed by the interface cover plate 3-1 and the sealing gasket 3-3, and are circumferentially locked and fixed by multiple bolt and nut groups 3-2 to ensure the sealing between the two ends of the existing structure 6 and the model box 1.

[0073] Fixed supports 6-3 are adhered to the inner wall of the main structure 6-1 using adhesive material, and LVDT displacement sensors 6-2 are fixed to the fixed supports 6-1. A set of LVDT displacement sensors 6-2 are fixed in both the horizontal and vertical directions to measure the convergence deformation of the existing structure 6 caused by the excavation and unloading. Starting from the arch top of the main structure 6-1, an earth pressure gauge 6-4 is installed every 45° to measure the changes in external earth pressure on the existing structure 6 caused by the excavation and unloading.

[0074] Step 5: Install the retaining wall panel 4 into the model box according to the spacing of the foundation pits, and form foundation pits on both sides of the existing structure 6.

[0075] Specifically, the retaining wall panels 4 are installed by inserting the sliding grooves 11 on the inner wall of the box frame 2, so that the four retaining wall panels 4 form a foundation pit on both sides of the existing structure 6.

[0076] Step 6: Depending on the type of drainage to be simulated, selectively lay drainage components at the bottom of the model box.

[0077] Specifically, a permeable panel 17, thoroughly soaked in water, is laid at the bottom of the model box, and a layer of filter paper is placed on top of the permeable panel 17. If the simulated test does not require drainage, the permeable panel 17 may not be laid.

[0078] Step 7: Prepare model soil 19 according to the required soil type, close the open and closed outlet 16 of the drainage component, seal the gap between the existing structure 6 and the model box, that is, seal both ends of the existing structure 6 through the interface sealing device 3, and fill the model soil 19 into the model box.

[0079] Preferably, if the model soil 19 is sandy soil, it can be filled into the model box 1 in layers and evenly using the rain method, and then compacted. If the model soil 19 is saturated clay, it can be filled in layers by a combination of manual and mechanical methods. Record the weight of the soil and the height of the soil layer in each round of filling into the model box 1.

[0080] Step 8: During the filling of model soil 19, the miniature earth pressure gauge and pore water pressure gauge 14 of the data acquisition component are buried in the predetermined position in the pit according to the test plan, in order to measure the horizontal earth pressure and vertical earth pressure in the pit.

[0081] The location and number of miniature earth pressure gauges and pore water pressure gauges 14 can be determined according to actual test requirements. The wiring of the miniature earth pressure gauges and pore water pressure gauges 14 is led out from the side wall of the model box 1 and protected to prevent excessive disturbance to the miniature earth pressure gauges and pore water pressure gauges 14 during the backfilling process, which could cause a large deviation in their position and affect the measurement accuracy.

[0082] When excavating a double-sided foundation pit in a simulated sandy soil stratum, pore water pressure gauges are not required due to the low moisture content of the soil. However, when excavating a double-sided foundation pit in a simulated saturated clay stratum, pore water pressure gauges are necessary due to the high moisture content of the soil. The placement of the pore water pressure gauges can be determined based on the actual simulation conditions.

[0083] Step 9: After filling the model soil 19, let it stand for 24 hours to allow the soil in the model box 1 to stabilize.

[0084] After the soil in model box 1 has stabilized, a static cone penetrometer can be used to penetrate the soil to determine the initial stratum properties. The penetration location should be representative, but should not have a significant impact on the soil stress state in the main study area.

[0085] Step 10: Install the movable reaction force assembly directly above the desired loading position.

[0086] Specifically, the movable reaction beam 7 is installed on the box frame 2 directly above the desired loading position. A weighing device 8 and a jack 9 are then installed sequentially using bolts and nuts. The weighing device 8 is electrically connected to a digital weighing display 10 to acquire and record the additional load value in real time. A loading plate 18 is connected to the loading end of the jack 9. Different jacking forces of the jack 9 are used to load the model soil 18 to simulate different overload effects from earthmoving vehicles, excavating machinery, and traffic roads. The additional load value is acquired and recorded in real time using the weighing device 8 and the digital weighing display 10. If a loading test is not required, step 10 can be skipped.

[0087] Step 11: Install the data acquisition component on top of model soil 19 and record the initial readings.

[0088] Specifically, the dial indicator 13 is fixed to the top of the box frame 2 of the model box 1 using a magnetic support, and the dial indicator 13 is connected to the displacement acquisition device 20; the displacement acquisition device 20 and the strain acquisition instrument 12 are turned on, and the initial readings are recorded.

[0089] Step 12: According to the excavation sequence and method determined in the test plan, excavate the foundation pit soil between the retaining wall panels 4 in layers and erect the support rods 15; according to the medium of the model soil 19 and the test drainage conditions, set the drainage components to various states such as normally closed, normally open or phased opening during the excavation of the foundation pit soil.

[0090] During the excavation of the foundation pit, the soil pressure, pore water pressure, displacement, etc. of the soil between the two foundation pits or the existing building 6 can be measured by the data acquisition component, so as to determine the degree of impact of the excavation of the foundation pits on the soil between the pits or the existing building 6.

[0091] After the experiment is completed, save all data, turn off the data acquisition device 20 and other devices, and summarize and analyze the data.

[0092] In simulating the short- and long-term effects of double-sided foundation pit excavation on soil disturbance in saturated clay strata, the open-closed outlet 16 of the drainage component was closed before excavation. Following the excavation sequence and method determined in the experimental plan, the soil was excavated in layers to simulate the short-term behavior of the foundation pit excavation. After excavation, the open-closed outlet 16 was opened to simulate the dissipation of excess pore water pressure caused by the unloading during excavation. Data monitoring was conducted using a micro earth pressure gauge and the pore water pressure gauge 14 to study the long-term effects of stress and deformation changes in the inter-pit strata after excavation.

[0093] When measuring the axial force of the support during the excavation of the foundation pit, after the excavation and unloading, the force balance inside and outside the pit is broken. The soil pressure outside the pit is transmitted to the retaining wall plate 4, and then to the support member 15, causing the spring 15-4 to compress. The displacement sensor 15-7 on the two retaining wall plates 4 can measure the horizontal deformation of the retaining wall plate 4. Based on the compression of the spring 15-4 and its stiffness k and the horizontal deformation of the retaining wall plate 4, the axial force of the support can be calculated. This is quick and convenient, and can quickly assess the excavation of the foundation pit.

[0094] By actively adjusting the length of support rod 15, the effect of increasing or decreasing axial force on the deformation of the foundation pit can be simulated. The method for adjusting the length of support rod 15 and measuring axial force is as follows: First, determine whether the adjustment target is to increase or decrease the axial force; then, rotate the second support rod 15-2 counterclockwise or clockwise to move it away from the first support rod 15-1. At this time, the axial force increases; conversely, it decreases. The change in axial force after the support rod 15 extends or shortens can be obtained by processing the displacement changes measured by displacement sensors 15-7 at points A, B, and C. For example, when support rod 15 extends, the changes in displacement sensors 15-7 at points A, B, and C are respectively ΔS... A , △S B and △S CAt this time, the change in the supporting axial force ΔF N Through △F N =(△S A -△S B -△S C )·k is obtained.

[0095] The function of the aforementioned support rod 15 is not limited to this. The reasonable application of the aforementioned support rod 15 provides good support for verifying the control mechanism and control effect of the active adjustment of the support axial force on the soil disturbance of multi-face excavation and unloading.

[0096] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the invention. Therefore, any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A test apparatus for the impact of multi-sided foundation pit excavation on the foundation and structure between pits, characterized in that: The model box includes a model box, retaining wall panels (4), existing structure (6), support rods (15), model soil (19), movable reaction components, drainage components, and data acquisition components. The model box is a box-shaped structure with an open top. The existing structure (6) is located in the middle of the model box. Several retaining wall panels (4) are movably inserted into the model box and excavation pits are formed on both sides of the existing structure (6). The drainage components are set at the bottom of the model box, the movable reaction components are set at the top of the model box, and the data acquisition components are set on the model box, retaining wall panels (4), existing structure (6), and support rods (15). The model soil (19) is filled in the model box. The outer wall of the retaining wall panel (4) is provided with multiple walers (4-2) at intervals; the retaining wall panel (4) is provided with a number of support holes (4-1) at intervals, and the support holes (4-1) penetrate the retaining wall panel (4) and the walers (4-2), so that the support rod (15) can be horizontally supported between two adjacent retaining wall panels (4) through the support holes (4-1); the data acquisition component includes strain gauges (4-3), strain acquisition instrument (12) and micro earth pressure gauges and pore water pressure gauges (14), a number of micro earth pressure gauges and pore water pressure gauges (14) are arranged vertically on the outer wall of the retaining wall panel (4), and multiple strain gauges (4-3) are arranged in a matrix and attached to the retaining surface and back soil surface of the retaining wall panel (4) and electrically connected to the strain acquisition instrument (12); The support rod (15) includes a first support rod (15-1), a second support rod (15-2), a spring (15-4), a connecting plate (15-5), and a fixing member (15-6). One end of the first support rod (15-1) has a screw hole, and one end of the second support rod (15-2) has a screw that matches the screw hole, so that the first support rod (15-1) and the second support rod (15-2) are movably screwed together. The other ends of the first support rod (15-1) and the second support rod (15-2) are respectively rotatable through rolling bearings (15-3) and one end of the two springs (15-4). The two springs (15-4) are connected in a sleeve manner. The other ends of the two springs (15-4) are fixed to the support holes (4-1) of the two opposite retaining wall plates (4) through the connecting plate (15-5) and the fixing member (15-6), so that the support rod (15) is horizontally supported between the two retaining wall plates (4). The data acquisition component includes a displacement sensor (15-7) and a displacement acquisition device (20). The displacement sensor (15-7) is installed between the first support rod (15-1) and the second support rod (15-2), and the displacement sensor (15-7) is installed between the two connecting plates (15-5) and the retaining wall plates (4) they are connected to.

2. The experimental apparatus for assessing the impact of multi-sided foundation pit excavation on the inter-pit foundation and structure as described in claim 1, characterized in that: The model box includes a model box (1), a box frame (2), and casters (5); the box frame (2) is installed on the inner wall of the model box (1), and several casters (5) are installed at intervals on the bottom of the model box (1); several sliding grooves (11) are formed at intervals on the inner wall of the box frame (2), so that the retaining wall plate (4) is slidably inserted into the model box (1) through the sliding grooves (11); the movable reaction component is installed on the top of the box frame (2); the data acquisition component includes a dial gauge (13) and a displacement acquisition device (20), several dial gauges (13) are respectively set at intervals on the top of the box frame (2) and facing the model soil (19), and several dial gauges (13) are electrically connected to the displacement acquisition device (20).

3. The test apparatus for assessing the impact of multi-sided foundation pit excavation on the inter-pit foundation and structure according to claim 2, characterized in that: Each of the aforementioned sliding grooves (11) includes a tenon (11-1), a wedge (11-2), and a handle (11-3); one side of the tenon (11-1) is vertically set on the inner wall of the box frame (2), and the other side of the tenon (11-1) forms a wedge-shaped groove, the wedge (11-2) is fitted into the wedge-shaped groove of the tenon (11-1), and the handle (11-3) is set on the top of the wedge (11-2).

4. The test apparatus for assessing the impact of multi-sided foundation pit excavation on the inter-pit foundation and structure according to claim 1, characterized in that: The two ends of the main body (6-1) of the existing structure (6) penetrate the model box, and the two ends of the existing structure (6) are sealed by the interface sealing device (3); the data acquisition component includes LVDT displacement sensor (6-2), earth pressure gauge (6-4) and displacement acquisition device (20). Multiple LVDT displacement sensors (6-2) are installed horizontally and vertically in the main body (6-1) through fixed supports (6-3) and are electrically connected to the displacement acquisition device (20). Several earth pressure gauges (6-4) are installed at intervals on the outer wall of the main body (6-1).

5. The test apparatus for assessing the impact of multi-sided foundation pit excavation on the inter-pit foundation and structure according to claim 4, characterized in that: The interface sealing device (3) includes an interface cover plate (3-1) and a sealing gasket (3-3). A flange is formed at the outer edge of the interface cover plate (3-1). The sealing gasket (3-3) is attached to the inner wall of the flange. When the inner side of the interface cover plate (3-1) is inserted into the existing structure (6), the flange on the outer side of the interface cover plate (3-1) is sealed and attached to the end face of the existing structure (6) and the outer wall of the model box (1) by the sealing gasket (3-3) and fixed.

6. The test apparatus for assessing the impact of multi-sided foundation pit excavation on the inter-pit foundation and structure according to claim 2, characterized in that: The movable reaction component includes a movable reaction beam (7), a jack (9), and a loading plate (18); the movable reaction beam (7) is set on the top of the box frame (2) of the model box, the jack (9) is set on the bottom of the movable reaction beam (7), and the output end of the jack (9) is connected to the loading plate (18) so that the loading plate (18) presses against the surface of the model soil (19); the data acquisition component includes a weighing device (8) and a weighing digital display (10), the weighing device (8) is set at the connection between the movable reaction beam (7) and the jack (9), and the weighing device (8) is electrically connected to the weighing digital display (10).

7. The test apparatus for assessing the impact of multi-sided foundation pit excavation on the inter-pit foundation and structure according to claim 1, characterized in that: The drainage component includes an openable and closed outlet (16) and a permeable base plate (17). The permeable base plate (17) is laid on the bottom surface inside the model box. Several openable and closed outlets (16) are respectively arranged at intervals on both sides of the bottom of the model box (1) of the model box and are connected to the permeable base plate (17).

8. A test method for the test apparatus of claim 1 for the impact of multi-sided foundation pit excavation on the foundation and structure between pits, characterized in that: Includes the following steps: Step 1: Determine the spacing of the foundation pits according to the experimental requirements; Step 2: Determine the dimensions of the retaining wall panel (4) and make four retaining wall panels (4); Step 3: Set up a data acquisition component on the retaining wall panel (4) and measure the deflection of the retaining wall panel (4) caused by the excavation of the foundation pit through the data acquisition component to calculate the horizontal deformation of the retaining wall panel (4); Step 4: Set the existing structure (6) inside the model box and install the data acquisition component on the existing structure (6); Step 5: Install the retaining wall panels (4) into the model box according to the pit spacing, and form pits on both sides of the existing structure (6); Step 6: Lay drainage components at the bottom of the model box according to the type of drainage to be simulated; Step 7: Prepare model soil (19) according to the required soil type, close the drainage components, seal the gap between the existing structure (6) and the model box, and fill the model soil (19) into the model box; Step 8: During the filling of model soil (19), the data acquisition component is buried in the predetermined position between the pits according to the test plan, for measuring the horizontal earth pressure and vertical earth pressure between the pits; Step 9: After the model soil (19) is filled, let it stand to stabilize the soil in the model box (1); Step 10: Install the movable reaction force assembly directly above the desired loading position; Step 11: Install the data acquisition component on top of the model soil (19) and record the initial readings; Step 12: According to the excavation sequence and method determined by the test plan, excavate the foundation pit soil between the retaining wall panels (4) in layers and erect support rods (15); according to the medium of the model soil (19) and the test drainage conditions, set the drainage components to normally closed, normally open or open in stages during the excavation of the foundation pit soil.

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