A visual model test device and test method for simulating the uplift, deformation and failure of soil at the bottom of a foundation pit

Abstract

The present invention provides a visualization model test device and test method for simulating the uplift, deformation and destruction of soil at the bottom of a foundation pit, wherein the test device comprises a CT scanning mechanism, a bearing base, a model box and a lifting control mechanism installed on a base plate, the CT scanning mechanism comprises an X-ray transmitter and an array detector, a vertical frame is respectively arranged on both sides of the upper end surface of the base plate, an adjustment component is arranged on each vertical frame, a support plate is arranged on each adjustment component, the X-ray transmitter and the array detector are symmetrical to each other and are respectively fixed on two support plates, the positions of the X-ray transmitter and the array detector are respectively adjusted by two adjustment components, the bearing base is located between the X-ray transmitter and the array detector, the model box is located on the bearing base, and the lifting control mechanism controls a slotting machine to simulate foundation pit excavation.

Description

Technical Field

[0001] The invention belongs to the technical field of geotechnical engineering and structural engineering, and particularly relates to a visual model test device and a test method for simulating the uplift, deformation and damage of soil at the bottom of a foundation pit. Background Art

[0002] The continuous increase in my country's urbanization rate and the establishment of regional economic zones have led to an increasingly tight supply of construction land, especially in large and medium-sized cities, where land resources are increasingly scarce, becoming one of the important constraints on urban economic and social development. Therefore, the development and utilization of underground space resources has gradually become the development direction of urban planning and construction. During the construction process, a large number of foundation pit projects have appeared, and foundation pit projects have gradually become a research hotspot.

[0003] The safety and stability of the foundation pit in the foundation pit project is related to the success or failure of the project, and the safety of the bottom of the foundation pit is particularly important. Among them, whether the bulge deformation of the bottom of the foundation pit is within the safety range is an important issue in engineering construction. Foundation pit uplift refers to the upward bulge of the soil at the bottom of the pit caused by the unbalanced force of the soil body during the excavation of the foundation pit, when the bearing capacity of the bottom of the foundation pit is lower than the total value of the deadweight of the soil outside the supporting structure and the ground load outside the foundation pit. If a foundation pit accident occurs, it will not only cause huge losses to the national economy and personal and property safety, but also have a huge impact on urban construction. For these engineering problems, ensuring the safety, economy and stability of the foundation pit project is an urgent problem to be solved. Therefore, it is of great significance to carry out research on foundation pit support design and stability research.

[0004] At present, there are mainly theoretical analysis methods, field measurement methods, and numerical analysis methods for the analysis of the stability of the bottom of the foundation pit against uplift. Among them, the theoretical analysis method includes the limit equilibrium method, the limit analysis method, the nonlinear finite element method, and the reliability analysis method. The system is well developed, but it is difficult to accurately reflect the soil stress under actual conditions. Moreover, it is assumed that the soil is an ideal rigid-plastic body. The calculation process is complicated and the safety factor obtained is related to the shape and position of the artificially assumed sliding surface. Although the field measurement method is an in-situ test and the results are real and effective, it is not repeatable and cannot accurately reveal the stress distribution law and damage characteristics of the bottom of the foundation pit when it is uplifted. In the simulation analysis process, the numerical analysis method often simplifies the boundary conditions and material properties, which affects the analysis results. Moreover, the different forms of structural discretization result in different results and accuracy, and the randomness is relatively large. In addition, the above methods cannot have a real-time observation of the actual uplift deformation of the bottom of the foundation pit and the whole process of the interaction between the support structure and the soil, and cannot detect the spatial configuration of the development and evolution of the deformation and damage of the foundation pit.

[0005] With the development of industrial CT, it has become possible to study the digital and visual characterization of the entire process of uplift, deformation and failure of the soil at the bottom of the foundation pit. The key to the technology lies in the development of visual model tests and methods to simulate the uplift, deformation and failure of the soil at the bottom of the foundation pit.

[0006] The invention with patent application number 201510281093.4 and authorization announcement number CN 104912123 B discloses a foundation pit uplift model test device, including a model box and a liquid container, a connecting pipe is provided between the liquid container and the bottom of the model box, two parallel model plates and a supporting rod for supporting the model plates are provided in the model box, a suspended gap is provided between the lower end of the model plate and the bottom surface of the model box, a partition is fixedly provided in the suspended gap, small holes are arranged in an array on the partition, and the connecting port between the connecting pipe and the model box is located below the partition. A foundation pit uplift model test method is also disclosed. The foundation pit uplift model test device and test method of the present invention are provided by setting a model box and a model plate, the model plate is vertically installed in the model box, the silty clay is consolidated in layers above the partition, and water is then injected into the liquid container, so that the silty clay in the model box can be subjected to a foundation pit uplift model test, which has the advantages of simple operation, good accuracy, and good repeatability. However, this structure cannot simulate the entire process of foundation pit support and excavation on site, and cannot realize the visualization and digital representation of the entire process of dynamic destruction of the base. At the same time, since the model box cannot rotate 360 ​​degrees, three-dimensional imaging of the foundation pit model cannot be achieved. Summary of the invention

[0007] In view of the above problems, the present invention provides a visual model test device and test method for simulating the uplift deformation and damage of the bottom soil of a foundation pit, simulating the influence of different geological conditions and foundation pit support design on the deformation of the base uplift. The system is based on the high-energy X-ray industrial CT technology of the array detector, which can not only intuitively monitor the deformation response characteristics and instability failure mode of the bottom soil during the base uplift process, but also obtain high-definition CT images of different depths inside the bottom of the foundation pit during the excavation process in real time, reconstruct the foundation pit in three dimensions, and then know the deformation mechanism and instability failure evolution process of the base soil uplift caused by the foundation pit support design, realize the visualization and digital representation of the whole process of base dynamic failure, help to reveal the stress distribution law and dynamic failure instability mechanism of the base soil under different support conditions, and provide reference for the early warning and prevention of pit bottom uplift damage and the determination of the design and construction method of the foundation pit support structure.

[0008] The technical solution adopted by the present invention is:

[0009] A visualization model test device for simulating the uplift, deformation and destruction of soil at the bottom of a foundation pit, comprising a CT scanning mechanism, a bearing base, a model box and a lifting control mechanism installed on a base plate, wherein the CT scanning mechanism comprises an X-ray transmitter and an array detector, a vertical frame is respectively arranged on both sides of the upper end surface of the base plate, an adjustment component is arranged on each vertical frame, and a support plate is arranged on each adjustment component, the X-ray transmitter and the array detector are symmetrical to each other and are respectively fixed on two support plates, and the positions of the X-ray transmitter and the array detector are respectively adjusted by two adjustment components, the bearing base is located between the X-ray transmitter and the array detector, the model box is located on the bearing base, and the lifting control mechanism controls a slotting machine to simulate foundation pit excavation.

[0010] Preferably, the adjustment assembly includes a transmission motor, a transmission reducer, a transmission motor seat and a lead screw, the transmission motor and the transmission motor seat are arranged on the upper side wall of the vertical frame, the transmission motor and the transmission reducer are fixed by screws, the transmission reducer and the transmission motor seat are connected by screws, the lower side wall of the vertical frame is provided with a transmission bearing seat, the upper and lower ends of the lead screw are respectively connected to the transmission motor seat and the transmission bearing seat, the support plate is installed on the lead screw, guide rods are symmetrically arranged on both sides of the lead screw, the support plate is located on the guide rod and can slide along the guide rod, and a plurality of equally spaced positioning holes are also provided on the end wall of the vertical frame for installing and debugging the relative positions of the array detector and the X-ray transmitter.

[0011] Preferably, the model box includes an outer frame of the model box, tempered glass baffles are embedded on all sides of the outer frame of the model box, a foundation pit model is placed inside the outer frame of the model box, the foundation pit model includes ground-connected wall steel plates, cross braces and steel cages, the ground-connected wall steel plates are supported on both sides of the foundation pit, the steel cages are evenly spaced on the back of the ground-connected wall steel plates, and the cross braces are evenly spaced and supported between the ground-connected wall steel plates on both sides.

[0012] Preferably, the lifting control mechanism includes a support beam, an elevator and a control console, both ends of the support beam are built on a platform, the platform is installed and fixed on the vertical frames on both sides, a pulley is fixed on the support beam, the wire rope on the elevator passes through the pulley and is connected to the slotting machine, a grab is integrally connected to the bottom of the slotting machine, and the control console is connected to the elevator through a pipeline.

[0013] Preferably, a column is installed at the bottom of the supporting base, a rotating assembly is provided at the upper end of the supporting base, the model box is located above the rotating assembly, and the model box is rotated 360 degrees by the rotating assembly to achieve three-dimensional imaging of the foundation pit model.

[0014] Preferably, the rotating assembly includes a turntable and a turntable, the model box is located on the turntable, and a limiting hole is provided at the bottom of the model box, a turntable outer ring is provided at the bottom of the turntable, and the turntable outer ring is fixedly connected to the bearing base by screws, an installation cavity is provided inside the turntable, and the top of the installation cavity penetrates the top wall of the turntable to form an open groove structure, a center column and a driving motor are provided on the bottom wall of the installation cavity, the upper end of the center column is connected to the turntable through a first bearing, and the bottom wall of the installation cavity is also provided with an annular table surface, and the annular table surface is provided with an annular sliding groove along its circumferential direction, a plurality of equally spaced vertical poles are provided on the inner wall of the turntable, and a sliding wheel is provided at the lower end of the vertical pole, and the sliding wheel is located in the annular sliding groove, a sleeve is provided on the outer side of the center column, and a second bearing is provided between the inner wall of the sleeve and the outer wall of the center column, a driven wheel and a first connecting rod are provided on the outer wall of the sleeve, and the first connecting rod is connected to the vertical pole, and a driving wheel is provided on the driving shaft of the driving motor, and the driving wheel is meshed with the driven wheel.

[0015] Preferably, an annular movable hole is provided on the turntable, a matching annular movable seat is provided in the annular movable hole, an annular groove is provided at the bottom of the annular movable seat along its circumferential direction, an inner bearing and an outer bearing are provided in the first annular groove, a support plate is provided on the center column, a fixing ring is provided on the support plate, a second annular groove corresponding to the first annular groove is provided on the upper end surface of the fixing ring, a compression spring is provided between the first annular groove and the second annular groove, the lower end of the compression spring is fixedly connected to the bottom wall of the second annular groove, the upper end of the compression spring is located between the inner bearing and the outer bearing, a second connecting rod is provided on the outer wall of the bottom of the annular movable seat, the second connecting rod is connected to the limit rod through a transmission assembly, the upper end of the limit rod can move in the guide hole on the turntable and be inserted into the limit hole at the bottom of the model box, a limit groove is provided on the outer wall of the limit rod, and a convex strip matching the limit groove is provided in the guide hole.

[0016] Preferably, the transmission assembly includes a fixed plate, the upper end of the fixed plate is connected to the inner wall of the turntable, the fixed plate is provided with a vertical guide groove, the side wall of the fixed plate is provided with a notch connected to the guide groove, a guide block and a gear are provided in the guide groove, the side wall of the guide block is provided with teeth meshing with the gear, the free end of the second connecting rod passes through the notch and is connected to the guide block, a horizontal plate is provided on the outer wall of the fixed plate, a vertical plate and a fixed seat are provided on the horizontal plate, a worm is provided between the vertical plate and the fixed plate, One end of the worm penetrates the side wall of the fixed plate and extends into the guide groove and is rotatably connected to the inner wall of the guide groove. The gear is installed on the rotating shaft of the worm. The fixed seat is located behind the worm and is provided with a vertical movable groove. The upper end of the movable groove penetrates the top of the fixed seat. The inner wall of the fixed seat is also provided with a horizontal annular groove, which is connected to the movable groove. One side of the annular groove penetrates the side wall of the fixed seat. A worm wheel is provided in the annular groove. The inner wall of the worm wheel is threadedly connected to the threaded section on the limiting rod, and the outer wall of the worm wheel is meshed with the worm.

[0017] Preferably, a circle of second balls is provided on the top wall and the bottom wall of the annular groove, and the upper and lower arms of the worm wheel are in rolling contact with the second balls.

[0018] A visual model test method for simulating the uplift, deformation and failure of soil at the bottom of a foundation pit, the test method comprising the following steps:

[0019] Step 1: Determine the basic parameters of the model foundation pit, namely the length, width and height of the model;

[0020] Step 2: Based on the designed simulated foundation pit size, apply similarity theory to determine the ratio of the actual foundation pit size to the model foundation pit size in the simulation test, and design and process the corresponding model box;

[0021] Step 3: Use similarity theory to derive the corresponding physical and mechanical parameters of the simulation model, including elastic modulus, saturated density, cohesion, internal friction angle, Poisson's ratio, and gravitational acceleration. Select appropriate similar materials to conduct similar material ratio tests to obtain the optimal ratio corresponding to the on-site foundation pit soil.

[0022] Step 4: Prepare the similar materials required for the test, configure the materials in similar ratios according to the similarity relationship, weigh each similar material using an electronic scale, and mix the materials evenly;

[0023] Step 5: When making the model, use a marker to draw the design dimension line of the model on the side of the model box, and then take a certain amount of the stirred similar material and pour it into the model box;

[0024] Step 6: After the foundation pit model is prepared, it needs to be consolidated for 48 hours before testing. During the consolidation process, the part of the foundation pit in contact with the air is sealed with a plastic film for moisture retention;

[0025] Step 7: After the foundation pit model is consolidated, the underground continuous wall support is carried out. First, the guide wall is constructed, and the center line of the guide wall coincides with the ground continuous wall;

[0026] Step 8: After the guide wall construction is completed, fix the model box on the upper part of the turntable and check that the model box and the turntable are well connected;

[0027] Step 9: Trench construction, the console controls the operation of the grab bucket through the elevator and starts excavation;

[0028] Step 10: After cleaning the bottom of the trench, insert the prepared steel cage and ground-connected wall steel plate into the trench;

[0029] Step 11: Pour concrete through the reserved conduit to make the ground-connected wall steel plate and the steel cage form a whole;

[0030] Step 12: Start the X-ray machine, select the preheating mode and preheat according to the length of time since the last shutdown. After the preheating is completed, the X-ray machine emits rays through the X-ray emission hole, and the X-rays pass through the foundation pit model. Part of the rays are absorbed by the foundation pit model, and the transmitted rays are received by the area array detector to achieve a three-dimensional CT scan of the foundation pit model;

[0031] Step 13: Adjust the height of the slotting machine, excavate the foundation pit, and install the support beam every time a certain depth is excavated;

[0032] Step 14: Start the driving motor to drive the turntable and the model box to rotate to perform CT scanning, obtain the CT image of the inside of the foundation pit during the excavation process in real time, and obtain the three-dimensional reconstruction data of the foundation pit;

[0033] Step 15: Continue excavation until the bottom of the foundation pit bulges and becomes unstable, the X-ray machine stops emitting beams, all mechanisms stop working, the radiation source of the CT machine is turned off, the foundation pit model is dismantled, and the test ends;

[0034] Step 16: Steps 1-12 are a CT scanning test of the foundation pit model instability. Steps 1-12 are repeated according to the designed test plan to conduct multiple groups of tests;

[0035] Step 17: After all detection tasks are completed, wait for the X-ray machine to cool down, turn off the power of the X-ray machine, and disconnect the switches of each subsystem;

[0036] Step 18: Use computer-aided software to organize and analyze the obtained data, obtain the dynamic instability evolution information of the foundation pit, and realize the visualization and digital representation of the entire process of foundation pit deformation and instability.

[0037] Beneficial effects of the present invention:

[0038] 1. The present invention, combined with industrial CT scanning, can not only intuitively monitor the deformation response characteristics and instability failure mode of the pit bottom soil during the entire process of base uplift, but also obtain high-definition CT images at different depths inside the pit bottom during excavation in real time, thereby realizing the visualization and digital representation of the entire process of base dynamic destruction.

[0039] 2. The present invention utilizes a lifting control mechanism to simulate the entire process of foundation pit support and excavation. At the same time, the control console can adjust the excavation height and speed of the slotting machine to control the construction progress and more accurately simulate the actual state of foundation pit excavation.

[0040] 3. The model box device can be processed and modified to achieve different purposes. The experimental purpose effect of the above patent can be achieved by processing and modifying the model box device, and the model box device is made of high-strength, low-density, transparent aviation glass material, which has more advantages such as light weight and good repeatability.

[0041] 4. The present invention also adds a turntable and a turntable, and installs the model box on the turntable. The limit rod on the turntable is adjusted by the transmission component to move up and down and insert into the limit hole at the bottom of the model box, so that the model box can be limited to improve the stability of the model box during rotation. At the same time, the driving motor drives the active wheel to engage the driven wheel to rotate, and then the turntable is driven to rotate through the first connecting rod, thereby realizing three-dimensional imaging of the foundation pit model. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0043] Figure 1 It is a structural schematic diagram of a visual model test system for simulating the uplift, deformation and failure of soil at the bottom of a foundation pit according to the present invention;

[0044] Figure 2 It is a front view of a visual model test system for simulating the uplift, deformation and failure of soil at the bottom of a foundation pit according to the present invention;

[0045] Figure 3 A side view of a visual model test system for simulating the uplift, deformation and failure of soil at the bottom of a foundation pit according to the present invention;

[0046] Figure 4 It is a schematic diagram of the industrial CT assembly structure of the present invention;

[0047] Figure 5 It is a schematic diagram of the structure of the model box device of the present invention;

[0048] Figure 6 is a cross-sectional view of the rotating assembly of the present invention;

[0049] Figure 7 for Figure 6 The enlarged view of point A in the middle;

[0050] Figure 8 is a schematic diagram of a worm gear;

[0051] Fig. 9 is a schematic diagram of the guide block;

[0052] Fig.10 is a cross-sectional view of the fixing seat;

[0053] Fig.11 Schematic diagram of the limit rod.

[0054] The reference numerals are as follows:

[0055] Among them, 1-vertical frame; 2-array detector; 3-X-ray transmitter; 4-X-ray emission hole; 5-transmission motor; 6-transmission reducer; 7-transmission motor seat; 8-transmission screw; 9-transmission bearing seat; 10-positioning hole; 11-bottom plate; 12-bearing base; 13-column; 14-turntable; 1401-annular moving hole; 15-turntable; 1501-installation cavity; 1502-annular table; 1503-annular sliding groove; 16-turntable outer ring; 17-model box outer frame; 18-tempered glass baffle; 19-foundation pit model; 20-ground wall steel plate; 21-reinforcement cage; 22-cross bracing beam; 23-grooving machine; 24-grab bucket; 25-wire rope; 26-pulley; 27-support beam; 28-capping platform; 29-elevator; 30-control The control table; 31- pipeline; 32- center column; 33- sleeve; 34- second bearing; 35- washer; 36- driven wheel; 37- driving motor; 38- driving wheel; 39- vertical rod; 3901- sliding wheel; 40- first connecting rod; 41- supporting plate; 42- fixing ring; 43- compression spring; 44, annular movable seat; 45- second connecting rod; 46- guide block; 4601- teeth; 47- fixing plate; 4701- guide groove; 4702- notch; 48- horizontal plate; 49- worm; 50- gear; 51- vertical plate; 52- fixing seat; 5201- movable groove; 5202- annular groove; 53- limiting rod; 5301- threaded section; 5302- limiting groove; 54- worm wheel; 55- second ball; 56- first bearing; 57- first ball. DETAILED DESCRIPTION

[0056] To make the purpose, technical solution and advantages of the embodiments of the present invention more clear, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0057] This embodiment specifically provides a visual model test device for simulating the uplift, deformation and failure of the soil at the bottom of a foundation pit. Figure 1 and Figure 2 As shown, it includes a CT scanning mechanism installed on a base plate 11, a bearing base 12, a model box and a lifting control mechanism, the CT scanning mechanism includes an X-ray transmitter 3 and an array detector 2, a vertical frame 1 is arranged on both sides of the upper end surface of the base plate 11, each vertical frame 1 is arranged with an adjustment component, each adjustment component is arranged with a support plate, the X-ray transmitter 3 and the array detector 2 are symmetrical to each other and are respectively fixed on two support plates, the positions of the X-ray transmitter 3 and the array detector 2 are respectively adjusted by two adjustment components, the bearing base 12 is located between the X-ray transmitter 3 and the array detector 2, the model box is located on the bearing base 12, and the lifting control mechanism controls the slotting machine 23 to simulate foundation pit excavation.

[0058] In this embodiment, if Figure 3 and Figure 4 As shown, the adjustment component includes a transmission motor 5, a transmission reducer 6, a transmission motor seat 7 and a lead screw 8. The transmission motor 5 and the transmission motor 5 seat are arranged on the upper side wall of the vertical frame. The transmission motor 5 and the transmission reducer 6 are fixed by screws. The transmission reducer 6 and the transmission motor seat 7 are connected by screws. A transmission bearing seat is arranged on the lower side wall of the vertical frame. The upper and lower ends of the lead screw are respectively connected to the transmission motor seat 7 and the transmission bearing seat. The support plate is installed on the lead screw 8. Guide rods are symmetrically arranged on both sides of the lead screw 8. The support plate is located on the guide rod and can slide along the guide rod. A plurality of equally spaced positioning holes 10 are also arranged on the end wall of the vertical frame for installing and debugging the relative positions of the array detector and the X-ray transmitter. The X-ray emission hole 4 is located at the center of the X-ray transmitter 3.

[0059] like Figure 5 As shown, the model box includes a model box outer frame 17, and a tempered glass baffle 18 is embedded around the model box outer frame 17. A foundation pit model 19 is placed inside the model box outer frame 17. The foundation pit model 19 includes a ground-connected wall steel plate 20, a cross brace and a steel cage 21. The ground-connected wall steel plate 20 is supported on both sides of the foundation pit, and the steel cage 21 is evenly distributed on the back of the ground-connected wall steel plate 20. The cross brace beam 22 is evenly supported between the ground-connected wall steel plates 20 on both sides. The model box is made of high-strength, low-density, transparent aviation glass material. Aviation glass not only has excellent optical properties, thermoplastic and processing properties, and anti-aging properties, but also has the characteristics of low specific gravity, high mechanical strength, and outstanding compressive and tensile properties. Compared with metal materials, it improves the attenuation of X-ray energy when passing through while meeting functional requirements. Transparent materials also realize the visualization of deformation and damage of the foundation pit.

[0060] like Figure 1 , 2 As shown in Figure 3, the lifting control mechanism includes a support beam 27, a lift 29 and a control console 30. Both ends of the support beam 27 are built on a base 28. The base 28 is installed and fixed on the vertical frames 1 on both sides. A pulley 26 is fixed on the support beam 27. The wire rope 25 on the lift 29 passes through the pulley 26 and is connected to the slotting machine 23. A grab bucket 24 is integrally connected to the bottom of the slotting machine 23. The control console 30 is connected to the lift 29 through a pipeline 31.

[0061] like Figure 1 and Figure 2 As shown, a column 13 is installed at the bottom of the supporting base 12, and a rotating component is provided at the upper end of the supporting base 12. The model box is located above the rotating component. The model box is rotated 360 degrees by the rotating component to realize three-dimensional imaging of the foundation pit model 19.

[0062] Before the experiment, a foundation pit model 19 of equal size is configured according to engineering experience and on-site investigation. After the experiment begins, the model box device is placed on the upper part of the rotating assembly. The CT scanning system and the lifting control mechanism are powered on for preheating to reach the working state. After everything is ready, the turntable 15 starts to rotate, and the X-ray transmitter 3 emits rays through the X-ray emission hole 4. The X-rays pass through the foundation pit model 19, and some of the rays are absorbed by the foundation pit model 19. The transmitted rays are received by the array detector 2 to realize the three-dimensional CT scanning of the foundation pit model 19. At the same time, the console 30 adjusts the length of the wire rope 25 to realize the lifting and lowering of the slotting machine 23. The slotting machine 23 controls the opening and closing of the grab bucket 24 to excavate the foundation pit. Every time a certain depth is excavated, the foundation pit is supported accordingly until the bottom of the foundation pit rises and becomes unstable and damaged. The dynamic deformation and damage of the foundation pit soil during the whole process of instability can be visualized through CT scanning.

[0063] The CT scanning mechanism uses the high-energy X-ray CT technology of the DR system conversion screen + array detector 2. Using cone beam rays, the projection acquisition system adopts a scintillating crystal screen (conversion screen) + array detector 2 structure. The conversion screen converts the transmitted X-rays into visible light, which is coupled to the array CCD detector by the lens. A two-dimensional projection image of the entire foundation pit model 19 can be obtained in one scan. The CT scanning system based on the array detector 2 can improve the scanning speed and ray utilization rate.

[0064] like Figure 6-11As shown, the rotating assembly includes a turntable 15 and a turntable 14, the model box is located on the turntable 14, and a limiting hole is set at the bottom of the model box, a turntable outer ring 16 is set at the bottom of the turntable 15, and the turntable outer ring 16 is fixedly connected to the bearing base 12 by screws, and an installation cavity 1501 is set inside the turntable 15, and the top of the installation cavity 1501 passes through the top wall of the turntable 15 to form an open groove structure, and a center column 32 and a driving motor 37 are set on the bottom wall of the installation cavity 1501, and the upper end of the center column 32 is connected to the turntable 14 through a first bearing 56, and the installation cavity 150 The inner bottom wall is also provided with an annular table 1502, and the annular table 1502 is provided with an annular sliding groove 1503 along its circumferential direction. The inner wall of the rotating disk 14 is provided with a plurality of equally spaced vertical rods 39, and a sliding wheel 3901 is provided at the lower end of the vertical rod 39, and the sliding wheel 3901 is located in the annular sliding groove 1503. The outer side of the central column 32 is sleeved with a sleeve 33, and a second bearing 34 is provided between the inner wall of the sleeve 33 and the outer wall of the central column 32. A washer 35 is provided at the bottom or top of the second bearing 34, and the washer 35 is fixed on the outer wall of the central column 32. A driven wheel 36 and a first connecting rod 40 are provided on the outer wall of the sleeve 33, and the first connecting rod 40 is connected to the vertical rod 39. A driving wheel 38 is provided on the driving shaft of the driving motor 37, and the driving wheel 38 is meshed with the driven wheel 36. A circle of first balls 57 is arranged on the upper end surface of the turntable 15 along the circumferential direction thereof, and the inner bottom surface of the turntable 14 is in rolling contact with the first balls 57 .

[0065] When the turntable 14 needs to drive the model box to rotate, the driving motor 37 is started, and the driving wheel 38 on the driving motor 37 meshes with the driven wheel 36, thereby driving the sleeve 33 to rotate, and then carrying the first connecting rod 40 to rotate synchronously. Under the traction of the first connecting rod 40, the vertical rod 39 drives the sliding wheel 3901 at the bottom to rotate around the sliding groove, and the turntable 14 realizes synchronous rotation. The driving mechanism formed by the driving wheel 38, the driven wheel 36, the sleeve 33, the first connecting rod 40, the vertical rod 39 and the sliding wheel 3901 can realize the uniform and stable rotation of the turntable 14, thereby ensuring the uniformity of the rotation of the model box.

[0066] In order to improve the stability of the model box placed on the turntable 14, an annular moving hole 1401 is provided on the turntable 14, and a matching annular moving seat 44 is provided in the annular moving hole 1401. The bottom of the annular moving seat 44 is provided with an annular groove along its circumferential direction. An inner bearing and an outer bearing are provided in the first annular groove. A support plate 41 is provided on the center column 32, and a fixing ring 42 is provided on the support plate 41. A second annular groove corresponding to the first annular groove is provided on the upper end surface of the fixing ring 42. The first annular groove and the second annular groove are provided with a plurality of annular grooves. A compression spring 43 is arranged between the two parts, the lower end of the compression spring 43 is fixedly connected to the bottom wall of the second annular groove, the upper end of the compression spring 43 is located between the inner bearing and the outer bearing, a second connecting rod 45 is arranged on the outer wall of the bottom of the annular movable seat 44, the second connecting rod 45 is connected to the limiting rod 53 through a transmission assembly, the upper end of the limiting rod 53 can move in the guide hole on the turntable 14 and be inserted into the limiting hole at the bottom of the model box, a limiting groove 5302 is arranged on the outer wall of the limiting rod 53, and a convex strip matching the limiting groove 5302 is arranged in the guide hole.

[0067] The transmission assembly includes a fixed plate 47, the upper end of which is connected to the inner wall of the turntable 14, a vertical guide groove 4701 is provided on the fixed plate 47, a notch 4702 communicating with the guide groove 4701 is provided on the side wall of the fixed plate 47, a guide block 46 and a gear 50 are provided in the guide groove 4701, a tooth 4601 meshing with the gear 50 is provided on the side wall of the guide block 46, the free end of the second connecting rod 45 passes through the notch 4702 and is connected to the guide block 46, a horizontal plate 48 is provided on the outer wall of the fixed plate 47, a vertical plate 51 and a fixing seat 52 are provided on the horizontal plate 48, a worm 49 is provided between the vertical plate 51 and the fixed plate 47, and the worm 49 is provided between the vertical plate 51 and the fixed plate 47. One end of the gear 50 penetrates the side wall of the fixing plate 47 and extends into the guide groove 4701 and is rotatably connected with the inner wall of the guide groove 4701. The gear 50 is mounted on the rotating shaft of the worm 49. The fixing seat 52 is located behind the worm 49 and is provided with a vertical movable groove 5201. The upper end of the movable groove 5201 penetrates the top of the fixing seat 52. The inner wall of the fixing seat 52 is also provided with a horizontal annular groove 5202, which is connected with the movable groove 5201. One side of the annular groove 5202 penetrates the side wall of the fixing seat 52. A worm wheel 54 is provided in the annular groove 5202. The inner wall of the worm wheel 54 is threadedly connected with the threaded section 5301 on the limiting rod 53, and the outer wall of the worm wheel 54 is meshed with the worm 49. A circle of second balls 55 are provided on the top and bottom walls of the annular groove 5202, and the upper and lower arms of the worm wheel 54 are in rolling contact with the second balls 55.

[0068] When the model box is placed on the turntable 14, the annular movable seat 44 will be squeezed to move downward along the annular movable hole 1401, and the guide block 46 will be driven to move downward in the movable groove 5201 through the second connecting rod 45. Since the gear 50 is engaged with the teeth 4601 on the outer wall of the guide block 46, the gear 50 is driven to rotate, and the worm 49 rotates synchronously, which is engaged with the worm wheel 54, driving the worm wheel 54 to rotate. Since the inner wall of the worm wheel 54 is threadedly connected with the threaded section 5301 on the limit rod 53, the limit rod 53 is moved upward and inserted into the limit hole at the bottom of the model box, thereby positioning the model box.

[0069] The material ratio is determined based on the similarity principle and the physical and mechanical parameters of the original samples taken from the foundation pits in multiple regions, and the model similarity material is developed. After many research and tests, it is determined that refined iron powder, barite powder, quartz sand and rosin alcohol solution can be used as the main similarity materials for most foundation pit soils, which have the advantages of high density, stable performance, simple manufacturing process, and non-toxicity.

[0070] The ground-anchored wall steel plate 20 uses a uniform specification and is marked with scales, which can qualitatively and quantitatively analyze the deformation of the base and the soil around the foundation pit.

[0071] The pulley 26 can move along the support beam 27, and the grab bucket 24 adopts a rotating design, thereby increasing the flexibility and maneuverability of the slotting machine 23 and realizing multi-angle and multi-directional excavation of the foundation pit.

[0072] The above test device is used to conduct a visualization test of the uplift, deformation and failure of the soil at the bottom of the foundation pit, including the following steps:

[0073] Step 1: Determine the basic parameters of the model foundation pit, namely the length, width and height of the model;

[0074] Step 2: Based on the designed simulated foundation pit size, apply similarity theory to determine the ratio of the actual foundation pit size to the model foundation pit size in the simulation test, and design and process the corresponding model box;

[0075] Step 3: Use similarity theory to derive the corresponding physical and mechanical parameters of the simulation model, including elastic modulus, saturated density, cohesion, internal friction angle, Poisson's ratio, and gravitational acceleration. Select appropriate similar materials to conduct similar material ratio tests to obtain the optimal ratio corresponding to the on-site foundation pit soil.

[0076] Step 4: Prepare the similar materials required for the test, configure the materials in similar ratios according to the similarity relationship, weigh each similar material using an electronic scale, and mix the materials evenly;

[0077] Step 5: When making the model, use a marker to draw the design dimension line of the model on the side of the model box, and then take a certain amount of the stirred similar material and pour it into the model box;

[0078] Step 6: After the foundation pit model is prepared, it needs to be consolidated for 48 hours before testing. During the consolidation process, the part of the foundation pit in contact with the air is sealed with a plastic film for moisture retention;

[0079] Step 7: After the foundation pit model 19 is consolidated, the underground continuous wall support is carried out. First, the guide wall is constructed, and the center line of the guide wall coincides with the ground continuous wall;

[0080] Step 8: After the guide wall construction is completed, fix the model box on the upper part of the turntable 14, and check that the model box and the turntable 14 are well connected;

[0081] Step 9: Trench construction, the control console 30 controls the operation of the grab bucket 24 through the elevator 29 to start excavation;

[0082] Step 10: After the bottom of the groove is cleaned, the prepared steel cage 21 and the ground-connected wall steel plate 20 are inserted into the groove;

[0083] Step 11: pouring concrete through the reserved conduit to form the ground-connected wall steel plate 20 and the steel cage 21 into a whole;

[0084] Step 12: Start the X-ray machine, select the preheating mode and preheat according to the length of time since the last shutdown. After the preheating is completed, the X-ray machine emits rays through the X-ray emission hole 4, and the X-rays pass through the foundation pit model 19. Part of the rays are absorbed by the foundation pit model 19, and the transmitted rays are received by the area array detector 2, so as to realize the three-dimensional CT scanning of the foundation pit model 19;

[0085] Step 13: Adjust the height of the slotting machine 23, excavate the foundation pit, and install the support beam 27 every time a certain depth is excavated;

[0086] Step 14: Start the driving motor 37 to drive the turntable 14 and the model box to rotate to perform CT scanning, obtain the CT image of the inside of the foundation pit during the excavation process in real time, and obtain the three-dimensional reconstruction data of the foundation pit;

[0087] Step 15: Continue excavating until the bottom of the foundation pit bulges and becomes unstable, the X-ray machine stops emitting beams, all mechanisms stop working, the radiation source of the CT machine is turned off, the foundation pit model 19 is removed, and the test ends;

[0088] Step 16: Steps 1-12 are a CT scanning test of the instability of the foundation pit model 19. Steps 1-12 are repeated according to the designed test plan to conduct multiple groups of tests;

[0089] Step 17: After all detection tasks are completed, wait for the X-ray machine to cool down, turn off the power of the X-ray machine, and disconnect the switches of each subsystem;

[0090] Step 18: Use computer-aided software to organize and analyze the obtained data, obtain the dynamic instability evolution information of the foundation pit, and realize the visualization and digital representation of the entire process of foundation pit deformation and instability.

[0091] The above description is only used to illustrate the technical solution of the present invention rather than to limit it. Other modifications or equivalent substitutions made to the technical solution of the present invention by ordinary technicians in this field should be included in the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solution of the present invention.

Claims

1. A visual model test device for simulating the uplift, deformation and failure of the soil at the bottom of a foundation pit, characterized in that: It comprises a CT scanning mechanism, a bearing base, a model box and a lifting control mechanism installed on a bottom plate, wherein the CT scanning mechanism comprises an X-ray transmitter and an array detector, a vertical rack is respectively arranged on both sides of the upper end surface of the bottom plate, an adjustment component is arranged on each vertical rack, and a support plate is arranged on each adjustment component, the X-ray transmitter and the array detector are symmetrical to each other and are respectively fixed on two support plates, and the positions of the X-ray transmitter and the array detector are respectively adjusted by two adjustment components, the bearing base is located between the X-ray transmitter and the array detector, the model box is located on the bearing base, and the lifting control mechanism controls the slotting machine to simulate foundation pit excavation; The model box includes an outer frame of the model box, tempered glass baffles are embedded around the outer frame of the model box, a foundation pit model is placed inside the outer frame of the model box, and the foundation pit model includes ground-connected wall steel plates, cross braces and steel cages, the ground-connected wall steel plates are supported on both sides of the foundation pit, the steel cages are evenly spaced on the back of the ground-connected wall steel plates, and the cross braces are evenly spaced and supported between the ground-connected wall steel plates on both sides; A column is installed at the bottom of the bearing base, a rotating assembly is arranged at the upper end of the bearing base, the model box is located above the rotating assembly, and the model box is rotated 360 degrees by the rotating assembly to realize three-dimensional imaging of the foundation pit model; The rotating assembly includes a turntable and a turntable. The model box is located on the turntable, and a limiting hole is provided at the bottom of the model box. A turntable outer ring is provided at the bottom of the turntable, and the turntable outer ring is fixedly connected to the bearing base by screws. An installation cavity is provided inside the turntable, and the top of the installation cavity penetrates the top wall of the turntable to form an open groove structure. A center column and a driving motor are provided on the bottom wall of the installation cavity. The upper end of the center column is connected to the turntable through a first bearing. An annular table is also provided on the bottom wall of the installation cavity, and an annular sliding groove is provided on the annular table along its circumferential direction. A plurality of equally spaced vertical poles are provided on the inner wall of the turntable, and a sliding wheel is provided at the lower end of the vertical pole, and the sliding wheel is located in the annular sliding groove. A sleeve is provided on the outer side of the center column, and a second bearing is provided between the inner wall of the sleeve and the outer wall of the center column. A driven wheel and a first connecting rod are provided on the outer wall of the sleeve, and the first connecting rod is connected to the vertical pole. A driving wheel is provided on the driving shaft of the driving motor, and the driving wheel is meshed with the driven wheel.

2. A visual model test device for simulating the uplift, deformation and failure of the soil at the bottom of a foundation pit according to claim 1, characterized in that: The adjustment assembly includes a transmission motor, a transmission reducer, a transmission motor seat and a lead screw. The transmission motor and the transmission motor seat are arranged on the upper side wall of the vertical frame. The transmission motor and the transmission reducer are fixed by screws. The transmission reducer and the transmission motor seat are connected by screws. A transmission bearing seat is arranged on the lower side wall of the vertical frame. The upper and lower ends of the lead screw are respectively connected to the transmission motor seat and the transmission bearing seat. The support plate is installed on the lead screw. Guide rods are symmetrically arranged on both sides of the lead screw. The support plate is located on the guide rod and can slide along the guide rod. A plurality of equally spaced positioning holes are also arranged on the end wall of the vertical frame for installing and debugging the relative positions of the array detector and the X-ray transmitter.

3. A visual model test device for simulating the uplift, deformation and failure of the soil at the bottom of a foundation pit according to claim 1, characterized in that: The lifting control mechanism includes a support beam, an elevator and a control console. Both ends of the support beam are built on a supporting platform, and the supporting platform is installed and fixed on the vertical frames on both sides. A pulley is fixed on the support beam. The wire rope on the elevator passes over the pulley and is connected to the slotting machine. A grab bucket is integrally connected to the bottom of the slotting machine, and the control console is connected to the elevator through a pipeline.

4. A visual model test device for simulating the uplift, deformation and failure of the soil at the bottom of a foundation pit according to claim 1, characterized in that: The turntable is provided with an annular movable hole, a matching annular movable seat is provided in the annular movable hole, an annular groove is provided at the bottom of the annular movable seat along its circumferential direction, an inner bearing and an outer bearing are provided in the first annular groove, a support plate is provided on the center column, a fixing ring is provided on the support plate, a second annular groove corresponding to the first annular groove is provided on the upper end surface of the fixing ring, a compression spring is provided between the first annular groove and the second annular groove, the lower end of the compression spring is fixedly connected to the bottom wall of the second annular groove, the upper end of the compression spring is located between the inner bearing and the outer bearing, a second connecting rod is provided on the outer wall of the bottom of the annular movable seat, the second connecting rod is connected to the limit rod through a transmission assembly, the upper end of the limit rod can move in the guide hole on the turntable and be inserted into the limit hole at the bottom of the model box, a limiting groove is provided on the outer wall of the limit rod, and a convex strip matching the limiting groove is provided in the guide hole.

5. A visual model test device for simulating the uplift, deformation and failure of the soil at the bottom of a foundation pit according to claim 4, characterized in that: The transmission assembly includes a fixed plate, the upper end of the fixed plate is connected to the inner wall of the turntable, a vertical guide groove is arranged on the fixed plate, a notch connected to the guide groove is arranged on the side wall of the fixed plate, a guide block and a gear are arranged in the guide groove, teeth meshing with the gear are arranged on the side wall of the guide block, the free end of the second connecting rod passes through the notch and is connected to the guide block, a horizontal plate is arranged on the outer wall of the fixed plate, a vertical plate and a fixed seat are arranged on the horizontal plate, a worm is arranged between the vertical plate and the fixed plate, and the worm One end of the rod passes through the side wall of the fixed plate and extends into the guide groove and is rotatably connected to the inner wall of the guide groove. The gear is installed on the rotating shaft of the worm. The fixed seat is located behind the worm and is provided with a vertical movable groove. The upper end of the movable groove passes through the top of the fixed seat. The inner wall of the fixed seat is also provided with a horizontal annular groove, which is connected to the movable groove. One side of the annular groove passes through the side wall of the fixed seat. A worm wheel is provided in the annular groove. The inner wall of the worm wheel is threadedly connected to the threaded section on the limiting rod, and the outer wall of the worm wheel is meshed with the worm.

6. A visual model test device for simulating the uplift, deformation and failure of the soil at the bottom of a foundation pit according to claim 5, characterized in that: A circle of second balls is arranged on the top wall and the bottom wall of the annular groove, and the upper and lower arms of the worm wheel are in rolling contact with the second balls.

7. The test method of a visual model test device for simulating the uplift, deformation and failure of soil at the bottom of a foundation pit according to any one of claims 1 to 6, characterized in that: The test method comprises the following steps: Step 1: Determine the basic parameters of the model foundation pit, namely the length, width and height of the model; Step 2: Based on the designed simulated foundation pit size, apply similarity theory to determine the ratio of the actual foundation pit size to the model foundation pit size in the simulation test, and design and process the corresponding model box; Step 3: Use similarity theory to derive the corresponding physical and mechanical parameters of the simulation model, including elastic modulus, saturated density, cohesion, internal friction angle, Poisson's ratio, and gravitational acceleration. Select appropriate similar materials to conduct similar material ratio tests to obtain the optimal ratio corresponding to the on-site foundation pit soil. Step 4: Prepare the similar materials required for the test, configure the materials in similar ratios according to the similarity relationship, weigh each similar material using an electronic scale, and mix the materials evenly; Step 5: When making the model, use a marker to draw the design dimension line of the model on the side of the model box, and then take a certain amount of the stirred similar material and pour it into the model box; Step 6: After the foundation pit model is prepared, it needs to be consolidated for 48 hours before testing. During the consolidation process, the part of the foundation pit in contact with the air is sealed with a plastic film for moisture retention; Step 7: After the foundation pit model is consolidated, the underground continuous wall support is carried out. First, the guide wall is constructed, and the center line of the guide wall coincides with the ground continuous wall; Step 8: After the guide wall construction is completed, fix the model box on the upper part of the turntable and check that the model box and the turntable are well connected; Step 9: Trench construction, the console controls the operation of the grab bucket through the elevator and starts excavation; Step 10: After cleaning the bottom of the trench, insert the prepared steel cage and ground-connected wall steel plate into the trench; Step 11: Pour concrete through the reserved conduit to make the ground-connected wall steel plate and the steel cage form a whole; Step 12: Start the X-ray machine, select the preheating mode and preheat according to the length of time since the last shutdown. After the preheating is completed, the X-ray machine emits rays through the X-ray emission hole, and the X-rays pass through the foundation pit model. Part of the rays are absorbed by the foundation pit model, and the transmitted rays are received by the area array detector to achieve a three-dimensional CT scan of the foundation pit model; Step 13: Adjust the height of the slotting machine, excavate the foundation pit, and install the support beam every time a certain depth is excavated; Step 14: Start the driving motor to drive the turntable and the model box to rotate to perform CT scanning, obtain the CT image of the inside of the foundation pit during the excavation process in real time, and obtain the three-dimensional reconstruction data of the foundation pit; Step 15: Continue excavation until the bottom of the foundation pit bulges and becomes unstable, the X-ray machine stops emitting beams, all mechanisms stop working, the radiation source of the CT machine is turned off, the foundation pit model is dismantled, and the test ends; Step 16: Steps 1-12 are a CT scanning test of the foundation pit model instability. Steps 1-12 are repeated according to the designed test plan to conduct multiple groups of tests; Step 17: After all detection tasks are completed, wait for the X-ray machine to cool down, turn off the power of the X-ray machine, and disconnect the switches of each subsystem; Step 18: Use computer-aided software to organize and analyze the obtained data, obtain the dynamic instability evolution information of the foundation pit, and realize the visualization and digital representation of the entire process of foundation pit deformation and instability.

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