Three-dimensional automatic control pile foundation vertical bearing characteristic model test system and method

Abstract

The invention relates to a three-dimensional automatic control pile foundation vertical bearing characteristic model test system and method, and the system comprises a model box which is filled with model soil and is provided with a first sensor installation position; the model pile is inserted into the model soil, and a second sensor mounting position is arranged on the model pile; the loading device is mounted through a test reaction frame and is used for providing an axial load for the model pile; the loading control system is connected with the loading device to automatically adjust the position of the loading device so as to carry out pile sinking penetration and load test on the model pile at any position of the model box; the data acquisition system comprises a plurality of different types of sensors which are respectively arranged in the sensor mounting positions; and the vacuum accelerated consolidation system is used for accelerating seepage consolidation of the model soil in the model box. Compared with the prior art, pile sinking and load tests at any position of the model box can be achieved, and the stability of the tests is improved.

Description

Technical Field

[0001] The invention relates to the technical field of geotechnical engineering constant gravity model testing, and in particular to a three-dimensional automatic controlled pile foundation vertical bearing characteristic model testing system and method. Background Art

[0002] Pile foundations have been widely used in large-scale engineering foundation construction, especially in soft soil foundations, due to their high bearing capacity, good stability, and small settlement. Usually, pile foundations are subject to vertical loads transmitted by upper structures during their service. In the design, calculation, and research of pile foundations, people are often very concerned about the vertical bearing and deformation characteristics of pile foundations, such as pile bearing capacity and settlement, under specific foundation conditions. Therefore, model test research on the vertical bearing characteristics of pile foundations under corresponding foundation conditions has become an indispensable technical means.

[0003] Up to now, the existing pile foundation bearing characteristic model test device still has the disadvantages that the pile foundation boundary conditions are difficult to control, the model test device cannot realize the three-dimensional automatic control of the loading mechanism, and it is still unable to achieve remote automatic control of the pile sinking and load test at any position of the model box, and its degree of automation control needs to be further improved, etc., which leads to inconvenience in test operation, often requires multiple people to cooperate with each other, and has the inconvenience of more test personnel and higher cooperation requirements. For example, the pile foundation bearing characteristic model test device and test method under complex loads disclosed in Chinese patent CN 104631519A uses a jack for vertical loading, and its reaction beam is fixed on the model groove through a vertical channel steel. The jack moves on the reaction beam through a linear sliding guide rail, and can only realize the manual movement of the loading mechanism in the Y (left and right) and Z (up and down) directions. Chinese patent CN 107012896A discloses a multifunctional pile foundation model test system and its assembly and test method. Although its vertical loading device can realize the free sliding of the secondary beam and the free sliding of the vertical jack on the secondary beam manually, it does not involve the automatic control of the three degrees of freedom of the loading mechanism X (front and back), Y (left and right), and Z (up and down), and it is also impossible to achieve remote automatic control of pile sinking and load tests. Both will lead to more participation of test personnel, resulting in a waste of manpower, and the stability of test data is easily affected by human errors.

[0004] Therefore, in view of the above-mentioned shortcomings of the existing pile foundation bearing characteristic model test device, a pile foundation vertical bearing characteristic model test system that can be directly controlled in three dimensions is designed, and a corresponding model test operation method is proposed to realize remote automatic control of pile sinking and load tests at any position of the model box. It is very necessary to simplify and facilitate the vertical bearing characteristic model test operation of single piles and pile groups under different foundation conditions, save labor costs in the test process of model box filling, pile sinking and loading, and improve the stability of the test. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and to provide a three-dimensional automatically controlled pile foundation vertical bearing characteristic model test system and method, so as to realize remote automatic control of pile foundation penetration and load test in X, Y and Z three-dimensional directions, and to realize remote real-time monitoring, analysis and visual display of parameter indicators such as pile foundation settlement characteristics, bearing characteristics, hydraulic characteristics of soil around piles during pile sinking and load tests.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] A three-dimensional automatic control pile foundation vertical bearing characteristic model test system, comprising:

[0008] The model box is filled with model soil and provided with a first sensor installation position;

[0009] A model pile is inserted into the model soil, and a second sensor installation position is arranged on the model pile;

[0010] A loading device, installed through the test reaction frame, is used to provide axial load to the model pile;

[0011] A loading control system connected to the loading device to automatically adjust the position of the loading device to perform pile penetration and load tests on the model piles at any position of the model box;

[0012] The data acquisition system includes a plurality of different types of sensors, which are respectively arranged in each sensor installation position;

[0013] Vacuum accelerated consolidation system, used to accelerate the seepage consolidation of the model soil in the model box;

[0014] Wherein: the loading control system includes an X-direction moving component, a Y-direction moving component, a Z-direction moving component, a pile pressing component and an electronic control component, the electronic control component is respectively connected to a data acquisition system and all moving components, the X-direction moving component and the Y-direction moving component are both installed on a test reaction frame, and the Z-direction moving component is installed on a loading device, and is used to drive the loading device to move in the X, Y and Z directions.

[0015] The test reaction frame includes a reaction beam, a reaction column, an upper frame, a connecting cross piece, a frame base and a frame bottom plate. The model box is placed on the frame bottom plate. The column feet of the reaction columns are detachably connected to the frame bottom plate and the frame base. The upper frame is detachably installed above the column tops of the reaction columns. The reaction beam is installed above the upper frame along the Y direction. The loading device is installed on the reaction beam. The connecting cross piece is detachably installed between the reaction columns to increase the lateral stiffness of each column.

[0016] The X-direction moving assembly is used to realize the uniform movement of the reaction beam in the X-direction, and includes an X-direction moving servo motor, an X-direction precision planetary reducer, an X-direction single spring coupling, an X-direction shaft end trapezoidal lead screw, an X-direction linear guide, an X-direction proximity switch, a cable drag chain, an X-direction motor mounting bracket, an X-direction lead screw support seat, a moving leg, an X-direction proximity switch fixing plate and a cable drag chain support U-shaped plate;

[0017] The X-direction moving servo motor and the X-direction motor mounting bracket are mounted on the front beam or the rear beam of the upper frame, the X-direction linear guide provides linear motion support for the reaction beam, the moving legs are mounted on both ends of the reaction beam along the Y direction, the cable drag chain support U-shaped plate is located at the bottom of the cable drag chain, the cable drag chain is mounted on the side of the X-direction linear guide, the X-direction shaft end trapezoidal lead screw is arranged along the X direction, and its two ends are respectively mounted on the front and rear beams of the upper frame through the X-direction lead screw support seat, the X-direction proximity switch is mounted on the two ends below the X-direction shaft end trapezoidal lead screw, and is mounted on the front and rear beams of the upper frame through the X-direction proximity switch fixing plate.

[0018] The Y-direction moving assembly is used to realize the uniform movement of the loading device along the Y-direction on the reaction beam, and includes a Y-direction moving servo motor, a Y-direction precision planetary reducer, a Y-direction single spring coupling, a Y-direction shaft end trapezoidal lead screw, a Y-direction linear guide, a Y-direction proximity switch, a Y-direction motor mounting bracket, a Y-direction lead screw support seat and a Y-direction proximity switch fixing plate;

[0019] The Y-axis moving servo motor and the Y-axis motor mounting bracket are installed on one side of the reaction beam, the Y-axis shaft end trapezoidal screw is arranged above the reaction beam along the Y direction, and Y-axis screw support seats are installed at both ends thereof, the Y-axis linear guide is installed on the front side of the reaction beam, the Y-axis proximity switch is installed at both ends below the Y-axis shaft end trapezoidal screw, and is installed on the reaction beam through the Y-axis proximity switch fixing plate, and the back of the loading device is respectively installed with a moving connection block and a moving slider that can move along the Y-axis shaft end trapezoidal screw and the Y-axis linear guide.

[0020] The Z-direction moving assembly is used to realize the uniform speed movement of the loading device along the Z-direction, and includes a Z-direction moving servo motor, a Z-direction precision planetary reducer and a Z-direction linear module;

[0021] The Z-direction moving servo motor is connected to the Z-direction linear module through a Z-direction precision planetary reducer, the pile pressure assembly is installed at the front of the Z-direction linear module, the rear of the Z-direction linear module is equipped with a linear module fixed aluminum plate assembly, the linear module fixed aluminum plate assembly is connected to the moving connecting block, Z-direction module position switches are equipped near both ends of the Z-direction linear module, and an electronic ruler is provided on the Z-direction linear module.

[0022] The pile driving assembly is used for pile penetration and load testing of model piles, and includes a slide, a slide connecting bracket, a force transmission column, a pile cap, a displacement meter and a tension and compression sensor;

[0023] The slide is located on the Z-axis linear module, the slide connecting bracket is installed on the slide, and is detachably connected to the top of the force transfer column through a reserved bolt hole, the bottom end of the force transfer column is connected to the pile cap through a displacement meter and a tension and compression sensor, the pile cap is connected to the top of the model pile, and multiple force transfer columns can be spliced ​​and disassembled to meet the requirements of different lengths of force transfer columns during pile sinking and load tests. The displacement meter and tension and compression sensor are connected to the data acquisition system and provide real-time remote feedback to the data acquisition system on the pile top load and vertical displacement during the pile sinking and penetration and load tests of the model pile.

[0024] The electric control component includes a control cabinet, a remote computer host, and a wireless transmission module. A servo controller and a PLC controller are installed inside the control cabinet. The servo controller is respectively connected to all servo motors and proximity switches. The control cabinet is connected to the remote computer host. The remote computer host is installed with loading control software, and remote control is achieved through the wireless transmission module.

[0025] The data acquisition system also includes an earth pressure gauge, a pore pressure gauge, a moisture sensor, a strain gauge, an end resistance sensor and a multi-channel data acquisition instrument;

[0026] The multi-channel data acquisition instrument is connected to each soil pressure gauge, pore pressure gauge, moisture sensor, strain gauge, end resistance sensor, tension and compression sensor and displacement meter respectively, and has a built-in signal amplifier and is connected to a remote computer host. The remote computer host is installed with data acquisition software, and realizes remote real-time monitoring, analysis and visual display of pile driving and load test data through a wireless transmission module.

[0027] The model box adopts a cylindrical design, including a circular bottom plate, a cylinder and a circular upper vacuum cover plate. The vacuum accelerated consolidation system includes a vacuum pump, a vacuum hose and a circular upper vacuum cover plate. One side of the vacuum pump is connected to the quick-connect connector of the circular upper vacuum cover plate through the vacuum hose, and the other side is connected to a power supply. A vacuum pressure regulating valve is installed on the vacuum pump to adjust the negative pressure of the model box during vacuuming.

[0028] A stainless steel ball valve, a vacuum pressure gauge and a pair of handles are installed on the circular air extraction cover plate. A quick-connect connector is installed at one end of the stainless steel ball valve to quickly connect with the air extraction hose, and the other end is installed on the circular air extraction cover plate through a stainless steel connector. The vacuum pressure gauge is used to monitor the pressure value in the model box during vacuum accelerated soil consolidation.

[0029] A test method for the test system as described above comprises:

[0030] Step S1: making a model pile, including: chiseling marks on the surface of different sections of the model pile body, embedding an earth pressure gauge and a pore pressure gauge respectively, splitting the model pile in half, pasting strain gauges at different sections of the inner wall of the pile body, welding and fixing the pile body, and embedding an end resistance sensor at the pile end shoe position;

[0031] Step S2: preparing the model soil, including: air-drying and crushing the soil sample taken from the site, adding water and stirring according to the saturation of the experimental design to prepare the model soil;

[0032] Step S3: filling the model box, including: laying a pebble layer at the bottom of the model box, laying a geotextile on top, filling the model box with the prepared model soil in layers, and burying a number of soil pressure gauges, piezometers and moisture sensors;

[0033] Step S4: vacuum accelerated soil consolidation, including: using a vacuum accelerated consolidation system to accelerate the consolidation of the model soil, so that it reaches the test design moisture content and then stands for a certain period of time;

[0034] Step S5: pile sinking, including: pile position positioning, starting the control cabinet, adjusting the loading mode, using the remote computer host to operate the loading control software, remotely moving the loading device and the pile pressing component to perform pile sinking operations, and operating the data acquisition software to collect data measured by the sensor in real time. After the pile sinking is completed, it is left to stand for a period of time to rebalance the pile-soil stress;

[0035] Step S6: load test, including: operating the loading control software, controlling the loading device to apply a preload on the pile top, and then performing graded loading, maintaining the load for a period of time after each loading, observing whether the settlement of the pile top is stable, until the settlement of the pile top reaches a stable or predetermined deformation limit, collecting the data measured by the sensor during the load test in real time, drawing a load-settlement curve, and analyzing the bearing capacity, settlement characteristics and ultimate bearing capacity of the pile foundation.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] 1. It realizes remote automatic control of pile foundation penetration and load test in X, Y and Z directions, and realizes remote real-time monitoring, analysis and visualization of parameter indicators such as pile foundation settlement characteristics, bearing characteristics, hydraulic characteristics of soil around piles, etc. during pile sinking and load test.

[0038] 2. It can simulate the vertical bearing and deformation of pile foundation under different foundation soil conditions, and realize the analysis of pile foundation's sinking characteristics, load-settlement characteristics, bearing characteristics and their evolution laws.

[0039] 3. It is also equipped with a vacuum accelerated consolidation system to accelerate the seepage consolidation of the model soil.

[0040] 4. It can realize remote automatic control of pile driving and load tests at any position of the model box, simplify and facilitate test operations, save labor costs, effectively reduce errors caused by manpower, and improve the accuracy and stability of the test. It is particularly suitable for vertical bearing characteristic model tests such as static and dynamic loads of single piles and pile groups under various foundation conditions, and has good use and promotion value.

[0041] 5. On the moving component, a shaft-end trapezoidal lead screw is set in the X and Y directions, a linear module is set in the Z direction, and a moving component proximity switch and a module position switch are installed respectively. The servo controller of the electronic control component and the PLC system developed and compiled specifically are used to respectively locate and limit the automatic movement positions of the reaction beam, loading device, and pile pressing component in the X, Y, and Z three-dimensional directions. In order to ensure the accuracy and stability of the servo motor operation, the servo motors in the X, Y, and Z directions are equipped with precision planetary reducers to adjust the rotational motion output by the servo motor to linear motion in a specific direction to meet the working needs of high-precision linear motion control of the moving component.

[0042] 6. The trapezoidal screw at the X-axis end passes through the reaction beam downward along the X direction, and cooperates with the X-axis moving servo motor to drive the reaction beam to move along the X (front and back) direction on the trapezoidal screw at the X-axis end, driving the moving legs at both ends of the reaction beam to move synchronously on the X-axis linear guide rails on the left and right side beams of the upper frame. The trapezoidal screw at the Y-axis end is arranged above the reaction beam along the Y direction; the Z-axis linear module is equipped with a pile pressure assembly at the front, and a linear module fixed aluminum plate assembly at the rear, and is installed on the Y-axis end trapezoidal screw through a mobile connecting block to support and fix the linear module and the Z-axis moving assembly. The Y-axis linear guide rail is installed on the front side of the reaction beam, and the back of the loading device is respectively equipped with a mobile connecting block and a mobile slider that can move along the Y-axis end trapezoidal screw and the Y-axis linear guide rail. The loading device, together with the Z-axis moving component and the pile pressing component, is installed on the trapezoidal screw at the Y-axis end through the upper moving connecting block, and the loading device is driven by the Y-axis moving servo motor to move along the Y (left and right) direction on the trapezoidal screw at the Y-axis end, and at the same time, the loading device is driven to move synchronously on the Y-axis linear guide rail of the reaction beam through the lower moving slider.

[0043] 7. In three-dimensional movement, in order to drive the reaction beam to move along the X direction on the trapezoidal lead screw at the shaft end driven by the servo motor, mobile legs are designed at both ends of the reaction beam, and a cable drag chain is used to move on the linear guide. In addition, unlike the traditional linear guide arranged on the top surface of the reaction beam, the Y-axis linear guide is arranged on the front side of the reaction beam, and a mobile connection block and a mobile slider are designed on the back of the loading device, respectively, to drive the loading device to carry the Z-axis moving component and the pile pressing component on the Y-axis trapezoidal lead screw at the upper part of the reaction beam and the Y-axis linear guide on the front side of the reaction beam. In addition, a slide connection bracket is specially designed at the front of the Z-axis linear module for installing the pile pressing component, and a linear module fixing aluminum plate assembly is specially designed at its back (rear), which is installed on the trapezoidal lead screw at the Y-axis end through a mobile connection block to support and fix the linear module and the Z-axis moving component. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a structural schematic diagram of a three-dimensional automatic controlled pile foundation vertical bearing characteristic model test system according to the present invention;

[0045] Figure 2 It is a three-dimensional schematic diagram of the model box of the present invention;

[0046] Figure 3 for Figure 2 Multiple directional views of the model box (excluding the circular upper air extraction cover);

[0047] Figure 4 for Figure 2 A schematic cross-sectional view of the model box (excluding the circular upper air extraction cover);

[0048] Figure 5 for Figure 2 A schematic diagram of the installation positions of the circular air extraction upper cover plate of the model box;

[0049] Figure 6 for Figure 2 A schematic diagram of the structure of the silicone sealing pad of the model box;

[0050] Figure 7 This is a schematic diagram of the arrangement of the model piles of the present invention;

[0051] Figure 8 It is a front view schematic diagram of the test reaction frame and the loading device of the present invention;

[0052] Fig. 9 It is a side view schematic diagram of the test reaction frame and the loading device of the present invention;

[0053] Fig.10 It is a top view schematic diagram of the test reaction frame and the loading device of the present invention;

[0054] Fig.11 It is a front view schematic diagram of the moving components of the loading control system of the present invention;

[0055] Fig.12 It is a right side schematic diagram of the moving component of the loading control system of the present invention;

[0056] Fig.13 It is a left side schematic diagram of the moving component of the loading control system of the present invention;

[0057] Fig.14 It is a schematic diagram of the connection arrangement of the loading control system according to the present invention;

[0058] Fig.15 It is a schematic diagram of the connection arrangement of the data acquisition system of the present invention;

[0059] Fig.16 It is a schematic diagram of the connection arrangement of the vacuum accelerated consolidation system of the present invention;

[0060] Among them: 1. Model box, 11. Round bottom plate, 111. Bottom plate bolt hole, 12. Cylinder, 121. Cylinder top flange, 122. Flange bolt hole, 13. Round exhaust cover plate, 131. Stainless steel ball valve, 132. Vacuum pressure gauge, 133. Handle, 134. Quick connector, 135. Stainless steel connector, 136. Handle fixing plate, 137. Stainless steel screw fastener, 138. Exhaust cover plate bolt fastener, 14. Model soil, 15. Geotextile, 16. Pebble layer, 17. Acrylic reinforcing rib, 18. Drain, 181. Drain valve, 182. Plug, 19. Silicone sealing pad, 2. Model pile, 21. Pile shoe, 3. Test reaction frame, 31. Reaction beam, 32. Reaction stand Column, 33, upper frame, 34, connecting crossbar, 35, rack base, 36, rack bottom plate, 37, steel reinforcing ribs, 4, loading control system, 41, X-axis moving assembly, 411, X-axis moving servo motor, 412, X-axis linear guide, 413, X-axis motor mounting bracket, 414, X-axis moving legs, 415, X-axis drag chain support U-shaped plate, 416, X-axis motor mounting bracket bolt fasteners, 417, X-axis cable drag chain, 418, X-axis precision planetary reducer, 419, X-axis single spring coupling, 4110, X-axis shaft end trapezoidal screw, 4111, X-axis shaft end trapezoidal screw support seat, 4112, X-axis proximity switch, 4113, X-axis proximity switch fixing plate, 42, Y-axis moving Moving components, 421, Y-axis moving servo motor, 422, Y-axis precision planetary reducer, 423, Y-axis single spring coupling, 424, Y-axis shaft end trapezoidal screw, 425, Y-axis linear guide, 426, Y-axis proximity switch, 427, Y-axis motor mounting bracket, 428, Y-axis shaft end trapezoidal screw support seat, 429, Y-axis proximity switch fixing plate, 4210, moving connection block, 4211, moving slider, 43, loading device, 44, Z-axis moving component, 441, Z-axis moving servo motor, 442, linear module, 443, linear module fixed aluminum plate component, 444, module position switch, 445, electronic ruler, 45, pile pressing component, 451, slide, 452, slide connecting bracket, 45 3. Force transfer column, 454. Pile cap, 455. Force transfer column joint component, 46. Electronic control component, 461. Control cabinet, 462. Servo controller, 463. PLC controller, 464. Remote computer host, 465. Wireless transmission module, 5. Data acquisition system, 51. Tension and compression sensor, 52. Displacement meter, 53. Soil pressure gauge, 54. Pore pressure gauge, 55. Moisture sensor, 56. Strain gauge, 57. End resistance sensor, 58. Multi-channel data acquisition instrument, 6. Vacuum accelerated consolidation system, 61. Vacuum pump, 611. Vacuum pressure regulating valve, 612. Pressure regulating valve pressure gauge, 613. Pressure relief valve, 62. Exhaust hose, 63. Vacuum accelerated consolidation system distribution box, 7. Main distribution box, 8. Electrical wire. DETAILED DESCRIPTION

[0061] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0062] The present invention provides a three-dimensional automatic control pile foundation vertical bearing characteristic model test system, the structural schematic diagram of which is shown in FIG. Figure 1 As shown, it includes a model box 1, a model pile 2, a test reaction frame 3, a loading control system 4, a data acquisition system 5, a vacuum accelerated consolidation system 6 and related supporting electrical wires. The model box 1 is placed on the bottom plate of the test reaction frame 3, the model box 1 is filled with model soil 14, and a sensor is buried; the model pile 2 is inserted into the model soil 14 in the model box 1, and the pile end is ensured to be located in the model soil 14 and not in contact with the geotextile 15. The model pile 2 is provided with sensors, and the pile top can be connected to the loading control system 4; a linear guide is provided on the top of the test reaction frame 3, and a loading device 43 is installed on its upper reaction beam 31 for providing an axial load for the model pile 2; the loading control system 4 can remotely and automatically control the movement of the pile driving assembly 45 in the three degrees of freedom directions of X (front and back), Y (left and right), and Z (up and down), and is used for pile penetration and load testing of the model pile 2 at any position in the model box 1; the data acquisition system 5 is used for remote real-time collection, storage and visual display of sensor monitoring data in the model soil 14 and the model pile 2; the vacuum accelerated consolidation system 6 is used to accelerate the seepage consolidation of the model soil 14 in the model box 1, and facilitate the compaction of the model soil 14 during the layered filling process of the model box 1 and the consolidation of the model soil 14 after the filling is completed.

[0063] In this embodiment, the model box 1 adopts a cylindrical design to reduce the influence of the boundary effect and better simulate the stress and deformation distribution of the soil under stress. Figure 2As shown, the cylindrical model box 1 includes a circular bottom plate 11, a cylinder 12 and a circular air-extraction upper cover plate 13, all of which are made of transparent acrylic material to facilitate observation of the test process and results, and can be combined with the vacuum accelerated consolidation system 6 to accelerate the seepage consolidation of the soil in the model box 1 by vacuuming. The upper part of the circular bottom plate 11 is bonded to the cylinder 12, and the top of the cylinder 12 is in the form of a flange, and bolt holes are reserved on its outer edge, which can be connected to the circular air-extraction upper cover plate 13 through bolt fasteners 138, and a silicone sealing pad 19 is arranged between the two to ensure the sealing during the vacuum accelerated soil consolidation process. A stainless steel ball valve 131, a vacuum pressure gauge 132 and a pair of handles 133 are installed on the circular air-extraction upper cover plate 13. A quick-plug connector 134 is installed at one end of the stainless steel ball valve 131, which can be quickly connected to the air extraction hose 62 of the vacuum accelerated consolidation system 6; the other end is installed on the circular air-extraction upper cover plate 13 through a stainless steel connector 135. The vacuum pressure gauge 132 is used to monitor the pressure value in the model box 1 during the vacuum accelerated soil consolidation process. The handle 133 is installed on the handle fixing plate 136 by a stainless steel screw fastener 137, and the handle fixing plate 136 is bonded to the circular air extraction upper cover plate 13. Acrylic reinforcing ribs 17 are evenly and symmetrically arranged at the contact part between the bottom of the cylinder 12 and the circular bottom plate 11 and the position of the top flange 121 of the cylinder for reinforcement to prevent the deformation of the model box cylinder 12. In addition, bolt holes are reserved on the outer edge of the circular bottom plate 11 to facilitate the fixation of the model box 1. Further, the bonding between the acrylic plates such as the model box cylinder 12, the circular bottom plate 11, the acrylic reinforcing ribs 17, the handle fixing plate 136, and the circular air extraction upper cover plate 13 of this embodiment is firm and reliable to ensure sealing. In addition, the bottom of the cylinder 12 is symmetrically provided with a drain port 18, corresponding to the bottom of the pebble layer 16 in the model box 1, as a soil drainage channel. Each drain port 18 has a drain filter screen inside and a drain valve 181 installed outside. The drain valve 181 is equipped with a plug 182.

[0064] Further, the AA, A1-A1, BB, B1-B1, CC and C1-C1 views and cross-sectional schematic diagrams of the model box 1 (excluding the circular air extraction upper cover plate 13) in this embodiment are respectively as shown in FIG. Figure 3 and 4As shown. The outer diameter and thickness of the circular bottom plate 11 and the top flange 121 of the model box 1 are the same, and the diameter is d1 = 900mm, wherein the thickness t3 of the top flange 121 of the cylinder is 20mm; the thickness t4 of the circular bottom plate 11 is also 20mm. The outer diameter d7 of the cylinder 12 is 800mm, the wall thickness t2 is 20mm, the inner diameter d2 is 760mm, and the height h2 is 880mm. Among them, there are 12 flange bolt holes 122 evenly distributed along the circumference of the outer edge of the top flange 121 of the cylinder, and the hole diameter d4 is 10mm, the distance d3 between the opposite bolt holes is 830mm, and the angle θ1 between adjacent flange bolt holes 122 is 30°. In addition, 12 acrylic reinforcing ribs 17 are evenly arranged along the circumference of the connection between the top flange 121 of the cylinder and the cylinder 12 for reinforcement. The cross section of each reinforcing rib is a pentagon, wherein the right angle side a1 is 25mm, a2 is 50mm, a3 is 25mm, the height h3 is 95mm, and the plate thickness b1 is 20mm. Similarly, two adjacent reinforcing ribs are arranged at an interval of 30° along the circumference of the top flange 121 of the cylinder. There are 8 bottom plate bolt holes 111 evenly distributed along the circumference of the outer edge of the circular bottom plate 11, and the hole diameter d5 is also 10mm, the distance d6 between the opposite bolt holes is 850mm, and the angle θ3 between adjacent bottom plate bolt holes 111 is 45°. Eight acrylic reinforcing ribs 17 are evenly arranged along the circumference of the contact part between the circular bottom plate 11 and the bottom of the cylinder 12 for reinforcement. The cross section of each reinforcing rib is also pentagonal, wherein the right angle side a4 is 25mm, a5 is 50mm, a6 is 25mm, the height h4 is 125mm, and the plate thickness b2 is 20mm. The interval angle θ4 between two adjacent reinforcing ribs along the circumference of the circular bottom plate 11 is also 45°, and the interval angle θ2 between adjacent reinforcing ribs and the bottom plate bolt holes 111 along the circumference of the circular bottom plate 11 is 22.5°. In addition, four drain outlets 18 are symmetrically arranged along the circumference at the bottom of the model box cylinder 12, and the height h1 of each drain outlet 18 from the top surface of the circular bottom plate 11 is 40 mm, the thread depth t1 of the drain outlet 18 is 15 mm, and the angle θ5 between the drain outlet 18 and the symmetry axis along the circumference is 30° or 60°, then the circumferential spacing angle 2θ5 between two adjacent drain outlets 18 is 60° or 120°.

[0065] The schematic diagram of the installation position of the circular air extraction upper cover plate 13 of the model box 1 in this embodiment and the schematic diagram of the structure of the silicone sealing pad 19 are shown in FIG. Figure 5-6As shown. The outer diameter of the circular upper exhaust cover plate 13 is the same as that of the top flange 121 of the cylinder, and its diameter is also d1=900mm. The thickness of the circular upper exhaust cover plate 13 is 15mm. In one-to-one correspondence with the bolt holes 122 of the top flange of the cylinder, there are 12 threaded holes evenly distributed along the circumference of the outer edge of the circular upper exhaust cover plate 13, and the hole diameter d4 is also 10mm. The distance d3 between the threaded holes is 830mm, and the angle θ1 between adjacent threaded holes is 30°. The depth of the threaded holes runs through the entire thickness of the circular upper exhaust cover plate 13, and the circular upper exhaust cover plate 13 can be installed together with the top flange 121 of the cylinder through the upper exhaust cover plate bolt fasteners 138. Threaded holes for installing a stainless steel ball valve 131 and a vacuum pressure gauge 132 are reserved on both sides of the center of the circular exhaust cover 13, wherein the distance c1 between the center of the threaded hole of the stainless steel ball valve 131 and the center of the circle is 350 mm, and the depth t7 of the threaded hole is 15 mm, so that it penetrates the thickness of the circular exhaust cover 13; the distance c2 between the center of the threaded hole of the vacuum pressure gauge 132 and the center of the circle is also 350 mm, and the depth t6 of the threaded hole is 15 mm, so that it penetrates the thickness of the circular exhaust cover 13. In addition, in the orthogonal direction, two threaded holes for handles 133 are reserved at equal intervals on both sides of the center of the circle, and the distance c4 between the two threaded holes on the same side is 120 mm, wherein the depth t5 of the threaded hole is also 15 mm, so that it penetrates the thickness of the circular exhaust cover 13, and the handle 133 can be fixed on the handle fixing plate 136 by stainless steel screw fasteners 137. The length c3 of the handle fixing plates 136 on both sides is 200mm, the width m2 is 60mm, the thickness is 15mm, and the distance m1 between the handle fixing plates 136 on both sides and the center of the upper exhaust cover plate is 320mm. In addition, the silicone seal 19 has the same outer diameter as the circular upper exhaust cover plate 13 and the flange 121 on the top of the cylinder, and its diameter is also d1=900mm, and its thickness is 5mm, which corresponds to the threaded holes of the circular upper exhaust cover plate 13 and the bolt holes 122 on the flange on the top of the cylinder. There are 12 circular holes evenly distributed along the circumference of the outer edge of the silicone seal 19, and the hole diameter d8 is 12mm, the hole distance d3 of the opposite holes is 830mm, and the angle θ1 between adjacent circular holes is also 30°. When the circular upper exhaust cover plate 13 and the top flange 121 of the cylinder are installed together by using the upper exhaust cover plate bolt fasteners 138 , the silicone sealing pad 19 is placed between the two to ensure the sealing of the model box 1 .

[0066] Furthermore, the model box 1 is filled with model soil 14, geotextile 15, and pebble layer 16. The pebble layer 16 is covered with geotextile 15, and the model soil 14 is filled on the top of the geotextile 15. In the model soil 14, two soil pressure gauges 53 and two pore pressure gauges 54 are buried in the horizontal direction at four soil layer depths on both sides of the pile. A total of eight soil pressure gauges 53 and eight pore pressure gauges 54 are buried to monitor the soil pressure and pore water pressure of the soil around the pile during the test. At the same time, three moisture sensors 55 are buried in the model soil 14 along different soil layer depths to monitor the moisture content distribution in the soil.

[0067] The schematic diagram of the arrangement of the model pile 2 in this embodiment is as follows Figure 7 As shown, the model pile 2 is designed as a tubular pile with a pile shoe 21 and is made of aluminum alloy. The design parameters of the model pile 2, such as the size and elastic modulus, are determined based on the dimensional design principle and the model scale. The model pile 2 selects 8 pile sections at equal intervals along both sides of the pile body, and a strain gauge 56 is posted on its inner wall respectively. Four cross-sectional positions are selected at equal intervals along both sides of the pile body, and a micro soil pressure gauge 53 is embedded on one side and a pore pressure gauge 54 is embedded on the other side. In addition, an end resistance sensor 57 is installed at the pile shoe 21 position at the pile end, which is used to monitor the strain distribution, pile end resistance, and pile side soil pressure and pore pressure of different pile sections of the model pile 2 during loading. Furthermore, the top of the model pile 2 is connected to the loading control system 4 through components such as a tension and compression sensor 51, a displacement meter 52, and a force transmission column 453.

[0068] The structural diagram of the test reaction frame 3 and the loading control system 4 in this embodiment is as follows Figure 8-14As shown, the test reaction frame 3 is made of steel, including reaction beams 31, reaction columns 32, upper frames 33, connecting crosspieces 34, frame bases 35 and frame bottom plates 36. The model box 1 is placed on the frame bottom plate 36 of the test reaction frame 3. The column feet and column tops of the reaction columns 32 are made of steel gaskets, wherein the column feet are connected to the frame bottom plate 36 and the frame base 35 by bolts, and the upper frame 33 is installed above the column tops of the reaction columns 32 by bolts. The reaction beam 31 of the test reaction frame 3 is installed above the upper frame 33 along the Y direction (left and right direction), wherein a loading device 43 is installed on the reaction beam 31. Connecting crosspieces 34 are installed between the reaction columns 32 by bolts to increase the lateral stiffness of each column. Further, the reaction beam 31 is respectively provided with a movable leg 414 at both ends along the Y direction (left-right direction), and the connection portion between the movable leg 414 and the reaction beam 31 is symmetrically arranged with a steel reinforcing rib 37 to ensure the stability of the movement of the reaction beam 31. The upper portions of the left and right side beams of the upper frame 33 are respectively provided with a linear guide rail along the X direction (front-back direction) to ensure that the upper reaction beam 31 can move along the X direction (front-back direction) on the linear guide rail through the movable leg 414. The front side of the reaction beam 31 itself is provided with a linear guide rail along the Y direction (left-right direction) to ensure that the loading device 43 can move along the Y direction (left-right direction). The pile pressing assembly 45 of the loading device 43 can be moved along the Z direction (up-down direction) through the linear module 442. In addition, the connection portion between the column foot of the reaction column 32 and the frame bottom plate 36, and the connection portion between the column top of the reaction column 32 and the upper frame 33 are symmetrically fixed with a steel reinforcing rib 37 for reinforcement. Bolt holes are reserved along the height direction of the column body of the reaction force column 32 to facilitate adjusting the height of the upper frame 33 and the connecting cross piece 34 according to the height of the model box 1.

[0069] In this embodiment, the loading control system 4 includes an X-direction moving component 41, a Y-direction moving component 42, a Z-direction moving component 44, a pile pressing component 45 and an electric control component 46, so as to realize remote automatic control of the loading device 43 to move at a uniform speed in three degrees of freedom directions, namely, the X-direction (front and back), the Y-direction (left and right), and the Z-direction (up and down). Figure 11-13The X-direction moving assembly 41 is installed on the upper frame 33 of the test reaction frame 3, and includes an X-direction moving servo motor 411, an X-direction precision planetary reducer 418, an X-direction single spring coupling 419, an X-direction shaft end trapezoidal lead screw 4110, an X-direction linear guide 412, an X-direction proximity switch 4112, an X-direction cable drag chain 417 and its matching X-direction motor mounting bracket 413, an X-direction lead screw support seat 4111, a moving leg 414, an X-direction proximity switch fixing plate 4113, an X-direction drag chain support U-shaped plate 415 and related bolt fasteners 416 and other components, so as to realize the uniform speed movement of the reaction beam 31 in the X (front and rear) direction. The Y-direction moving assembly 42 is installed on the reaction beam 31 of the test reaction frame 3, and includes a Y-direction moving servo motor 421, a Y-direction precision planetary reducer 422, a Y-direction single spring coupling 423, a Y-direction shaft end trapezoidal screw 424, a Y-direction linear guide 425, a Y-direction proximity switch 426 and its matching Y-direction motor mounting bracket 427, a Y-direction screw support seat 428, a moving slider 4211, a Y-direction proximity switch fixing plate 429, a moving connecting block 4210 and related bolt fasteners and other components, so as to realize the uniform movement of the loading device 43 in the Y (left and right) direction on the reaction beam 31. The Z-direction moving assembly 44 is installed on the loading device 43, and includes a Z-direction moving servo motor 441, a precision planetary reducer, a linear module 442, a Z-direction module position switch 444 and its matching linear module fixing aluminum plate assembly 443 and other components, so as to realize the uniform movement of the pile pressing assembly 45 of the loading device 43 in the Z (up and down) direction.

[0070] Furthermore, the X-direction, Y-direction and Z-direction moving servo motors are all equipped with precision planetary reducers, and the rotary motion output by the servo motor is adjusted to linear motion in a specific direction by combining the shaft end trapezoidal screw of the X-direction and Y-direction moving components or the linear module of the Z-direction moving component. The X-direction and Y-direction moving servo motors are both equipped with motor mounting brackets for fixing and supporting the servo motors. Among them, the X-direction moving servo motor 411 and its X-direction motor mounting bracket 413 are installed on the front beam or rear beam of the upper frame 33 of the test reaction frame 3; the Y-direction moving servo motor 421 and its Y-direction motor mounting bracket 427 are installed on one side of the reaction beam 31. At the same time, a single spring coupling is installed behind the X-direction and Y-direction moving servo motors to transmit power, compensate for the slight displacement and deviation between the shafts, and improve the service life and operation stability of the equipment. The shaft end trapezoidal screws of the X-direction and Y-direction moving components are used as transmission devices, and are connected to the servo motors through single spring couplings and precision planetary reducers to achieve high-precision linear motion control in a specific direction. The linear guide rails of the X-axis and Y-axis moving components provide linear motion support for the reaction beam 31 and the loading device 43 respectively.

[0071] Furthermore, the X-axis end trapezoidal screw rod 4110 of the X-axis moving assembly 41 is arranged along the X-direction, and its two ends are respectively mounted on the front and rear beams of the upper frame 33 of the test reaction frame 3 through the X-axis screw rod support seat 4111, which is used to support the X-axis end trapezoidal screw rod 4110. The X-axis end trapezoidal screw rod 4110 of the X-axis moving assembly 41 passes through the reaction beam 31, and cooperates with the servo motor 411 to drive the reaction beam 31 to move along the X (front and back) direction on the X-axis end trapezoidal screw rod 4110, driving the moving legs 414 at both ends of the reaction beam 31 to move synchronously on the X-axis linear guide rails 412 on the left and right side beams of the upper frame 33. Below the trapezoidal lead screw 4110 at the X-axis end of the X-axis moving assembly 41, an X-axis proximity switch 4112 is installed near both ends, and is installed on the front and rear beams of the upper frame 33 of the test reaction frame 3 through the X-axis proximity switch fixing plate 4113, which is used for positioning control and limit control of the position of the reaction beam 31 moving along the X direction on the trapezoidal lead screw 4110 at the X-axis end. In addition, an X-axis cable drag chain 417 is installed on the side of the X-axis linear guide 412, which is used to carry, protect and support related cables and realize their follow-up movement, so that when the reaction beam 31 moves back and forth on the X-axis linear guide 412 on the upper part of the left and right side beams of the upper frame 33, it is ensured that the related cables move synchronously with the reaction beam 31 to avoid entanglement. An X-axis drag chain support U-shaped plate 415 is fixed at the bottom of the X-axis cable drag chain 417 to fix and support the X-axis cable drag chain 417 to ensure that the drag chain will not deviate or fall off during movement. The X-direction drag chain supporting U-shaped plate 415 is fixedly mounted on the left and right side beams of the upper frame 33 by means of bolts.

[0072] The Y-axis end trapezoidal screw rod 424 of the Y-axis moving assembly 42 is arranged above the reaction beam 31 along the Y direction, and Y-axis screw rod support seats 428 are respectively installed at both ends thereof to support the Y-axis end trapezoidal screw rod 424. The Y-axis linear guide rail 425 of the Y-axis moving assembly 42 is installed on the front side of the reaction beam 31, and the back of the loading device 43 is respectively installed with a moving connection block 4210 and a moving slider 4211 that can move along the Y-axis end trapezoidal screw rod 424 and the Y-axis linear guide rail 425 of the Y-axis moving assembly 42. The loading device 43, together with the Z-axis moving assembly 44 and the pile pressing assembly 45, is installed on the Y-axis shaft end trapezoidal screw 424 of the Y-axis moving assembly 42 through the upper moving connecting block 4210, and the loading device 43 is driven to move along the Y (left and right) direction on the Y-axis shaft end trapezoidal screw 424 through the Y-axis moving servo motor 421, and at the same time, the loading device 43 is driven to move synchronously on the Y-axis linear guide 425 of the reaction beam 31 through the lower moving slider 4211. Below the Y-axis shaft end trapezoidal screw 424 of the Y-axis moving assembly 42, Y-axis proximity switches 426 are respectively installed near both ends, and are installed on the reaction beam 31 through the Y-axis proximity switch fixing plate 429, so as to position and limit the position of the loading device 43 moving along the Y direction on the Y-axis shaft end trapezoidal screw 424.

[0073] The Z-direction moving servo motor 441 is connected to the Z-direction linear module 442 through the Z-direction precision planetary reducer; the Z-direction linear module 442 is equipped with a pile pressing assembly 45 at the front and a linear module fixed aluminum plate assembly 443 at the rear. The linear module fixed aluminum plate assembly 443 is made of a plurality of aluminum plates, and is installed on the Y-direction shaft end trapezoidal screw 424 of the Y-direction moving assembly 42 through a movable connecting block 4210, and is used to support and fix the Z-direction linear module 442 and the Z-direction moving assembly 44 and even the entire loading device 43. The Z-direction linear module 442 can achieve high-precision linear motion under high load conditions, ensuring that the pile pressing assembly 45 of the loading device 43 can move along the Z direction through the Z-direction linear module 442. At the same time, Z-direction module position switches 444 are also provided near both ends of the Z-direction linear module 442, which are used to position and limit the position of the pile pressing assembly 45 moving along the Z direction on the Z-direction linear module 442. In addition, the Z-direction linear module 442 is equipped with an electronic ruler 445, which can accurately measure the moving distance of the pile pressing assembly 45 in the Z direction.

[0074] The connection arrangement diagram of the loading control system 4 in this embodiment is as follows Fig.14As shown. The pile pressing assembly 45 of the loading control system 4 includes components such as a slide connecting bracket 452, a force transmission column 453, and a pile cap 454, and is equipped with sensors such as a displacement meter 52 and a tension and compression sensor 51, which together realize the pile penetration and load test of the pile foundation. Among them, the slide connecting bracket 452 is installed on the slide 451 of the Z-axis linear module 442, and the slide connecting bracket 452 has a force transmission column joint component 455, which is installed together with the top of the force transmission column 453 through a reserved bolt hole. The bottom end of the force transmission column 453 is connected to the pile cap 454 through the displacement meter 52 and the tension and compression sensor 51, and the pile cap 454 is connected to the top of the model pile 2. Furthermore, a bolt is reserved at one end of the force transmission column 453, and a screw hole is reserved at the other end. Several force transmission columns 453 can be spliced ​​and disassembled to meet the requirements of different lengths of the force transmission columns 453 during the pile sinking and loading tests. The tension and compression sensor 51 and the displacement meter 52 are connected to the data acquisition system 5 for real-time remote monitoring of the pile top load and vertical displacement during the pile penetration and load test of the model pile 2.

[0075] The electric control component 46 of the loading control system 4 includes a control cabinet 461, a servo controller 462, a PLC 463, a remote computer host 464, loading control software, a wireless transmission module 465, and related supporting electrical wires 8, auxiliary devices and other components. The servo controller 462 and PLC 463 and related supporting electrical wires 8 and auxiliary devices are installed inside the control cabinet 461. The servo motors and proximity switches of the X-direction, Y-direction, and Z-direction moving components are all connected to the servo controller 462 and PLC 463 system in the control cabinet 461. One end of the control cabinet 461 is connected to the main distribution box 7, which is powered by the main distribution box 7 through the main power supply, and one end is connected to the remote computer host 464. The remote computer host 464 is installed with the loading control software, and can be remotely controlled by another remote computer host 464 through the wireless transmission module 465. By operating the loading control software, the automatic movement of the loading device 43 in three degrees of freedom directions, namely, X, Y and Z, can be remotely controlled on the computer, and finally remote automatic control of the pile penetration and load test of the model pile 2 at any position in the model box 1 can be achieved.

[0076] The connection arrangement diagram of the data acquisition system 5 in this embodiment is as follows Fig.15As shown. The data acquisition system 5 includes tension and compression sensors 51, displacement meters 52, soil pressure gauges 53, pore pressure gauges 54, moisture sensors 55, strain gauges 56, end resistance sensors 57 and other sensors, multi-channel data acquisition instruments 58, signal amplifiers, remote computer hosts 464, data acquisition software, wireless transmission modules 465 and other equipment components. The tension and compression sensors 51 and displacement meters 52 are installed between the force transmission column 453 and the pile cap 454 of the loading device 43, and are used to monitor the pile top load and vertical displacement of the model pile 2 during the pile sinking and load test in real time. Several soil pressure gauges 53, pore pressure gauges 54 and moisture sensors 55 are buried at different depths in the model soil 14, which are used to monitor the soil pressure at different depths of the model soil, the changes in pore water pressure and the changes in water content in real time during the pile sinking and load test. Strain gauges 56, soil pressure gauges 53, and pore pressure gauges 54 are installed at equal intervals at symmetrical positions on both sides of different pile sections of the model pile 2 to monitor the strain distribution law of different pile sections and the distribution law of mechanical properties such as soil pressure and pore water pressure of the soil around the pile in real time during the pile sinking and load test of the model pile 2. An end resistance sensor 57 is installed at the position of the pile shoe 21 at the end of the model pile 2 to monitor the pile end resistance of the model pile 2 in real time during the pile sinking and load test. Further, each sensor is connected to a multi-channel data acquisition instrument 58, and a signal amplifier is installed in the multi-channel data acquisition instrument 58 to amplify the data signals collected by each sensor. One end of the multi-channel data acquisition instrument 58 is connected to the main distribution box 7, and the other end is connected to a remote computer host 464. The remote computer host 464 is installed with data acquisition software, and can be remotely controlled by another remote computer host 464 through a wireless transmission module 465. Through the data acquisition software, remote real-time acquisition, storage and visual display of all sensor monitoring data can be realized on the computer.

[0077] In this embodiment, the vacuum accelerated consolidation system 6 is connected and arranged as follows: Fig.16As shown. The vacuum accelerated consolidation system 6 includes a vacuum pump 61, an exhaust hose 62 and a circular exhaust cover plate 13 of the model box 1, which are used for compacting the model soil 14 during the layered filling process of the model box 1 and for accelerating the consolidation of the model soil 14 before the pile penetration of the model pile 2 and the load test after the filling is completed. One side of the vacuum pump 61 is connected to the quick-connect connector 134 of the circular exhaust cover plate 13 of the model box 1 through the exhaust hose 62, and one side is connected to the main distribution box 7 for power supply through the vacuum accelerated consolidation system distribution box 63. A vacuum pressure regulating valve 611 is installed on the vacuum pump 61 to adjust the negative pressure of the vacuum box 1. The pressure regulating valve pressure gauge 612 is used to display the negative pressure to be adjusted. A pressure relief valve 613 is installed at the bottom of the vacuum pump 61 to assist in pressure relief. Furthermore, a safety valve is installed in the vacuum pump 61. When the vacuum pump 61 operates normally, the safety valve is in a closed state. When the internal pressure of the vacuum pump 61 exceeds a preset safety value, the safety valve will automatically open to prevent vacuum leakage and overpressure damage.

[0078] In this embodiment, the electrical wires 8 in the model test system include weak current wires and strong current cables. The data and signal collection power supply of each sensor adopts weak current wires; the power supply of each distribution box, each servo motor, control cabinet 461, remote computer host 464, vacuum pump 61 and other instruments and equipment adopts strong current cables.

[0079] Based on the above model test system, a three-dimensional automatic control pile foundation vertical bearing characteristic model test method involved in this embodiment mainly includes the following steps:

[0080] S1: Make a model pile 2. Chisel marks are made on the surface of different cross-sections of the pile body of the model pile 2, and four cross-sections are selected at equal intervals. A micro soil pressure gauge 53 and a pore pressure gauge 54 are respectively embedded on both sides of the pile body. The model pile 2 is cut in half, and eight cross-sections are selected at equal intervals at different cross-sections of the inner wall of the pile body, and strain gauges 56 are pasted and fixed by welding. In addition, an end resistance sensor 57 is built-in at the position of the pile shoe 21 at the pile end.

[0081] S2: Preparation of model soil 14. The soil samples collected on site were air-dried and crushed into powder using a geocrusher. Then, the soil samples were put into a mixer and different amounts of water were added according to the experimental design saturation and stirred for about 4 hours to ensure that the soil was evenly mixed for the preparation of model soil.

[0082] S3: Fill the model box 1. A 5 cm thick pebble layer 16 is laid at the bottom of the model box 1, and a geotextile 15 is laid on it. At the same time, vaseline is applied to the wall of the model box 1 to reduce the influence of the boundary effect. The prepared model soil 14 is layered to fill the model box 1, and the vacuum accelerated consolidation system 6 is used to accelerate the seepage consolidation of the model soil 14. The filled model soil 14 reaches the test design moisture content by combining the loading device 43 loading and other methods, and it is left to stand for more than about 48 hours to make the moisture content in the soil sample uniformly distributed. During the layered filling of the soil body, 2 soil pressure gauges 53 and 2 pore pressure gauges 54 are buried in the horizontal direction at the 4 soil layer depths of the soil body on both sides of the pile. A total of 8 soil pressure gauges 53 and 8 pore pressure gauges 54 are buried to monitor the soil pressure and pore water pressure of the soil body around the pile during the test. At the same time, 3 moisture sensors 55 are buried in the model soil 14 along different soil layer depths to monitor the moisture content distribution in the soil body.

[0083] S4: Vacuum accelerated soil consolidation. When the vacuum accelerated consolidation system 6 is used to accelerate soil consolidation, the circular upper vacuum cover 13 of the model box 1 must first be connected to the model box cylinder 12 through bolt fasteners 138, and a silicone seal 19 is set between the two. If necessary, a fastening clamp is used to reinforce to ensure the sealing during the vacuum accelerated soil consolidation process. Then, the vacuum pump 61 is connected to the quick-connect connector 134 of the upper vacuum cover 13 of the model box 1 using a vacuum hose 62. When accelerating soil consolidation, start the vacuum pump 61, adjust the vacuum pressure regulating valve 611 to the specified pressure, open the stainless steel ball valve 131 of the circular air suction upper cover plate 13, and when the vacuum pressure gauge 132 of the circular air suction upper cover plate 13 shows the specified pressure, close the stainless steel ball valve 131 of the circular air suction upper cover plate 13, turn off the vacuum pump 61, reset the parameters of the pressure regulating valve 611 of the vacuum pump 61 to zero, and open the lower pressure relief valve 613 of the vacuum pump 61 for auxiliary pressure relief. After the pressure relief is stable, close the valve of the vacuum pump 61, unplug the air suction hose 62 on the circular air suction upper cover plate 13, and remove the circular air suction upper cover plate 13.

[0084] S5: pile sinking. The prepared model pile 2 is subjected to pile sinking operation using the loading device 43. The force transmission column 453, displacement meter 52, tension and compression sensor 51 and pile cap 454 are sequentially installed on the loading device 43; the loading control system 4 and the data acquisition system 5 are respectively connected to the circuit for subsequent loading control and sensor data acquisition. The pile position is positioned, the center position of the pile is determined in the model test area, and the positioning accuracy of the pile is ensured by using measuring instruments. The control cabinet 461 is started, the loading mode is adjusted, and the loading control software is operated by the remote computer host 464 to adjust the X-direction, Y-direction, and Z-direction moving components of the loading control system so that the position of the pile pressing component 45 is adjusted to above the pile sinking point, so that the pile cap 454 is in contact with the top of the model pile 2. Then the loading control software is operated, and the pile pressing component 45 of the loading device 43 is used to perform the pile sinking operation, and the model pile 2 is slowly pressed into the soil, the pile sinking speed is controlled, and the pile sinking resistance corresponding to each unit settlement is recorded. During the pile sinking process, the soil penetration depth of the model pile 2 is monitored to ensure that the pile is sunk according to the designed depth. If necessary, the pile load can be gradually increased until the pile end reaches the designed depth. At the same time, the data acquisition software is operated to collect the data measured by the sensors during the pile sinking process in real time to analyze the changes in the soil moisture content, pore water pressure and soil pressure distribution, pile axial force, pile end resistance, pile top load and settlement, etc. After the pile is sunk, it needs to be left still for at least 24 hours to facilitate the rebalancing of pile-soil stress.

[0085] S6: Load test. Operate the loading control software to control the loading device 43 to first apply a certain preload on the pile top to eliminate the gap between the pile pressing assembly 45 and the pile top to ensure the accuracy of subsequent loading. Then carry out graded loading. According to the loading level of the test design, increase the load step by step at a uniform rate. Keep the load for 10-30 minutes after each loading. Observe whether the settlement of the pile top is stable so that the soil and the pile can reach deformation stability, and record the settlement of the pile top under each level of load. In the process of step-by-step loading, the settlement of the pile top reaches a stable or predetermined deformation limit to determine the ultimate bearing capacity of the pile. After completing the loading test, unload step by step and record the settlement recovery amount under each level of unloading to analyze the elastic recovery capacity of the pile. The data measured by the sensor during the load test is collected in real time by the data acquisition software, which is used to analyze the change rules of the moisture content of the soil on the pile side and around the pile, the distribution of pore water pressure and earth pressure, the pile body strain, the pile body bending moment, the pile body axial force, the side friction resistance, the pile end resistance, and the pile top load and settlement during the load test. Through the data collected during the test, the load-settlement curve is drawn to analyze the bearing capacity, settlement characteristics and ultimate bearing capacity of the pile foundation. Furthermore, the time condition can be set to carry out load tests at different times after the pile driving is completed to analyze the evolution law of the time-varying ultimate bearing capacity, load-settlement characteristics and bearing characteristics of the pile foundation. For the pile driving and load test of the pile group, the loading control system 4 can be remotely controlled to move the pile driving assembly 45 and repeat S5 and S6.

[0086] The present embodiment involves a three-dimensional automatic control model test system for the vertical bearing characteristics of pile foundations, which realizes the remote automatic control of the loading device in the three-dimensional directions of X (front and back), Y (left and right), and Z (up and down), as well as the remote real-time monitoring of the pile foundation settlement characteristics, bearing characteristics, hydraulic characteristics of the soil around the pile and other parameter indicators during the pile sinking and load test, overcomes the defects and deficiencies of the existing pile foundation bearing characteristics model test device, and improves the automation level of the test. At the same time, the model test system simplifies and facilitates the test operation, saves labor costs, effectively reduces the errors caused by manpower, and improves the accuracy and stability of the test. It is particularly suitable for vertical bearing characteristics model tests such as static and dynamic loads of single piles and pile groups under various foundation conditions, and has a good use and promotion value.

Claims

1. A three-dimensional automatic control pile foundation vertical bearing characteristic model test system, characterized in that: include: A model box (1) is filled with model soil (14) and is provided with a first sensor installation position; A model pile (2) is inserted into the model soil (14), and a second sensor installation position is arranged on the model pile (2); A loading device (43) is installed through the test reaction frame (3) and is used to provide an axial load for the model pile (2); A loading control system (4) connected to the loading device (43) to automatically adjust the position of the loading device (43) to perform pile penetration and load tests on model piles at any position of the model box; A data acquisition system (5) includes a plurality of different types of sensors, each of which is disposed in each sensor installation position; A vacuum accelerated consolidation system (6) for accelerating the seepage consolidation of the model soil (14) in the model box (1); The loading control system (4) comprises an X-direction moving component (41), a Y-direction moving component (42), a Z-direction moving component (44), a pile pressing component (45) and an electric control component (46); the electric control component (46) is respectively connected to a data acquisition system (5) and all moving components; the X-direction moving component (41) and the Y-direction moving component (42) are both mounted on a test reaction frame (3); the Z-direction moving component (44) is mounted on a loading device (43) and is used to drive the loading device (43) to move in the X, Y and Z directions.

2. A three-dimensional automatic control pile foundation vertical bearing characteristic model test system according to claim 1, characterized in that: The test reaction frame (3) comprises a reaction beam (31), a reaction column (32), an upper frame (33), a connecting cross piece (34), a frame base (35) and a frame bottom plate (36); the model box (1) is placed on the frame bottom plate (36); the column foot of the reaction column (32) is detachably connected to the frame bottom plate (36) and the frame base (35); the upper frame (33) is detachably mounted above the column top of the reaction column (32); the reaction beam (31) is mounted above the upper frame (33) along the Y direction; the loading device (43) is mounted on the reaction beam (31); the connecting cross piece (34) is detachably mounted between the reaction columns (32) to increase the lateral stiffness of each column.

3. A three-dimensional automatic control pile foundation vertical bearing characteristic model test system according to claim 2, characterized in that: The X-direction moving assembly (41) is used to realize the uniform speed movement of the reaction beam (31) in the X-direction, and comprises an X-direction moving servo motor (411), an X-direction precision planetary reducer (418), an X-direction single spring coupling (419), an X-direction shaft end trapezoidal screw (4110), an X-direction linear guide rail (412), an X-direction proximity switch (4112), a cable drag chain (417), an X-direction motor mounting bracket (413), an X-direction screw support seat (4111), a moving leg (414), an X-direction proximity switch fixing plate (4113) and a cable drag chain supporting U-shaped plate (415); The X-direction moving servo motor (411) and the X-direction motor mounting bracket (413) are mounted on the front beam or the rear beam of the upper frame (33); the X-direction linear guide rail (412) provides linear motion support for the reaction beam (31); the moving legs (414) are mounted on both ends of the reaction beam (31) along the Y direction; the cable drag chain support U-shaped plate (415) is located at the bottom of the cable drag chain (417); and the cable drag chain (417) is installed Installed on the side of the X-direction linear guide rail (412), the X-direction shaft end trapezoidal screw rod (4110) is arranged along the X direction, and its two ends are respectively installed on the front and rear beams of the upper frame (33) through the X-direction screw rod support seat (4111), and the X-direction proximity switch (4112) is installed at the two ends below the X-direction shaft end trapezoidal screw rod (4110), and is installed on the front and rear beams of the upper frame (33) through the X-direction proximity switch fixing plate (4113).

4. A three-dimensional automatic control pile foundation vertical bearing characteristic model test system according to claim 2, characterized in that: The Y-direction moving assembly (42) is used to realize the uniform movement of the loading device (43) along the Y-direction on the reaction beam (31), and comprises a Y-direction moving servo motor (421), a Y-direction precision planetary reducer (422), a Y-direction single spring coupling (423), a Y-direction shaft end trapezoidal screw (424), a Y-direction linear guide (425), a Y-direction proximity switch (426), a Y-direction motor mounting bracket (427), a Y-direction screw support seat (428) and a Y-direction proximity switch fixing plate (429); The Y-direction moving servo motor (421) and the Y-direction motor mounting bracket (427) are mounted on one side of the reaction beam (31); the Y-direction shaft end trapezoidal screw rod (424) is arranged above the reaction beam (31) along the Y direction, and its two ends are respectively mounted with Y-direction screw rod support seats (428); the Y-direction linear guide rail (425) is mounted on the front side of the reaction beam (31); the Y-direction proximity switch (426) is mounted on the two ends below the Y-direction shaft end trapezoidal screw rod (424), and is mounted on the reaction beam (31) through the Y-direction proximity switch fixing plate (429); and the back side of the loading device (43) is respectively mounted with a movable connecting block (4210) and a movable sliding block (4211) capable of moving along the Y-direction shaft end trapezoidal screw rod (424) and the Y-direction linear guide rail (425).

5. A three-dimensional automatic control pile foundation vertical bearing characteristic model test system according to claim 4, characterized in that: The Z-direction moving assembly (44) is used to realize the uniform speed movement of the loading device (43) along the Z-direction, and comprises a Z-direction moving servo motor (441), a Z-direction precision planetary reducer and a Z-direction linear module (442); The Z-direction moving servo motor (441) is connected to the Z-direction linear module (442) via a Z-direction precision planetary reducer; the pile pressing assembly (45) is installed at the front of the Z-direction linear module (442); the rear of the Z-direction linear module (442) is equipped with a linear module fixed aluminum plate assembly (443); the linear module fixed aluminum plate assembly (443) is connected to the moving connection block (4210); Z-direction module position switches (444) are provided near both ends of the Z-direction linear module (442); and an electronic ruler (445) is provided on the Z-direction linear module (442).

6. A three-dimensional automatic control pile foundation vertical bearing characteristic model test system according to claim 5, characterized in that: The pile driving assembly (45) is used for pile penetration and load testing of the model pile (2), and comprises a slide (451), a slide connecting bracket (452), a force transmission column (453), a pile cap (454), a displacement meter (52) and a tension and compression sensor (51); The slide (451) is located on the Z-direction linear module (442); the slide connection bracket (452) is installed on the slide (451) and is detachably connected to the top of the force transmission column (453) through a reserved bolt hole; the bottom end of the force transmission column (453) is connected to the pile cap (454) through a displacement meter (52) and a tension and compression sensor (51); the pile cap (454) is connected to the top of the model pile (2); a plurality of force transmission columns (453) can be spliced ​​and disassembled to meet the requirements of different lengths of the force transmission columns (453) during pile sinking and load tests; the displacement meter (52) and the tension and compression sensor (51) are connected to the data acquisition system (5) and provide real-time remote feedback to the data acquisition system (5) of the pile top load and vertical displacement during the pile sinking and load test of the model pile (2).

7. A three-dimensional automatic control pile foundation vertical bearing characteristic model test system according to claim 5, characterized in that: The electric control assembly (46) comprises a control cabinet (461), a remote computer host (464), and a wireless transmission module (465). A servo controller (462) and a PLC controller (463) are installed inside the control cabinet (461). The servo controller (462) is connected to all servo motors and proximity switches respectively. The control cabinet (461) is connected to the remote computer host (464). The remote computer host (464) is installed with loading control software, and remote control is achieved through the wireless transmission module (465).

8. A three-dimensional automatic control pile foundation vertical bearing characteristic model test system according to claim 7, characterized in that: The data acquisition system (5) further comprises an earth pressure gauge (53), a pore pressure gauge (54), a moisture sensor (55), a strain gauge (56), an end resistance sensor (57) and a multi-channel data acquisition instrument (58); The multi-channel data acquisition instrument (58) is respectively connected to each soil pressure gauge (53), pore pressure gauge (54), moisture sensor (55), strain gauge (56), end resistance sensor (57), tension and compression sensor (51) and displacement meter (52). The multi-channel data acquisition instrument (58) has a built-in signal amplifier and is connected to a remote computer host (464). The remote computer host (464) is installed with data acquisition software, and remote real-time monitoring, analysis and visual display of pile driving and load test data are realized through a wireless transmission module (465).

9. A three-dimensional automatic control pile foundation vertical bearing characteristic model test system according to claim 1, characterized in that: The model box (1) is cylindrical in design and comprises a circular bottom plate (11), a cylinder (12) and a circular upper vacuum cover plate (13); the vacuum accelerated consolidation system (6) comprises a vacuum pump (61), an air suction hose (62) and a circular upper vacuum cover plate (13); one side of the vacuum pump (61) is connected to a quick-connect connector (134) of the circular upper vacuum cover plate (13) via the air suction hose (62), and the other side is connected to a power supply; a vacuum pressure regulating valve (611) is installed on the vacuum pump (61) for regulating the negative pressure of the model box during vacuuming; A stainless steel ball valve (131), a vacuum pressure gauge (132) and a pair of handles (133) are installed on the circular air extraction upper cover plate (13); one end of the stainless steel ball valve (131) is installed with a quick-connect connector (134) for quick connection with an air extraction hose (62); the other end is installed on the circular air extraction upper cover plate (13) via a stainless steel connector (135); the vacuum pressure gauge (132) is used to monitor the pressure value in the model box during vacuum accelerated soil consolidation.

10. A test method of the test system according to any one of claims 1 to 9, characterized in that: include: Step S1: making a model pile (2), including: chiseling marks on the surface of different cross-sections of the pile body of the model pile (2), respectively embedding an earth pressure gauge (53) and a pore pressure gauge (54), and splitting the model pile (2) in half, pasting strain gauges (56) at different cross-sections of the inner wall of the pile body, welding and fixing the pile body, and embedding an end resistance sensor (57) at the position of the pile end shoe; Step S2: preparing the model soil (14), including: air-drying and crushing the soil sample collected on site, adding water and stirring according to the saturation of the experimental design, and using the mixture to prepare the model soil (14); Step S3: filling the model box (1), including: laying a pebble layer (16) at the bottom of the model box (1), laying a geotextile (15) on top, filling the model box (1) with the prepared model soil (14) in layers, and burying a plurality of soil pressure gauges (53), pore pressure gauges (54) and moisture sensors (55); Step S4: vacuum accelerated soil consolidation, including: using a vacuum accelerated consolidation system (6) to accelerate the consolidation of the model soil (14), so that the model soil (14) reaches the test design moisture content and then stands for a certain period of time; Step S5: pile driving, including: pile position positioning, starting the control cabinet (461), adjusting the loading mode, using the remote computer host (464) to operate the loading control software, remotely moving the loading device (43) and the pile driving assembly (45) to perform pile driving operations, and operating the data acquisition software to collect data measured by the sensor in real time. After the pile driving is completed, it is left to stand for a period of time to rebalance the pile-soil stress; Step S6: load test, including: operating the loading control software to control the loading device (43) to apply a preload on the pile top, and then performing graded loading, maintaining the load for a period of time after each loading, observing whether the settlement of the pile top is stable, until the settlement of the pile top reaches a stable or predetermined deformation limit, collecting data measured by the sensor during the load test in real time, drawing a load-settlement curve, and analyzing the bearing capacity, settlement characteristics and ultimate bearing capacity of the pile foundation.

Images