A fixed-rope length stepless direction-changing foundation pile anti-pulling model test device and method

Abstract

The application provides a foundation pile anti-pulling model test device and method with constant rope length and stepless direction change, relates to the technical field of foundation structure test, and comprises a model box, a model pile, a first support, a second support, a guide rail, a fixed pulley, a movable pulley, a steel wire rope and a loading and detection assembly. The first support and the second support are arranged on the two sides of the model box, and the heights of the first support and the second support can be adjusted. The two ends of the guide rail are installed on the first support and the second support, and the guide rail is provided with an arc-shaped groove with a hollow middle part. The fixed pulley is installed on the first support. The movable pulley is slidingly installed in the arc-shaped groove. The steel wire rope is connected to the top of the model pile and the loading and detection assembly, and is wound around the movable pulley and the fixed pulley. The design of the arc-shaped groove can ensure the consistency of the stress conditions under different loading directions under the premise that the total length of the steel wire rope is constant, without the need to replace components and adjust the rope length, and can ensure the constant static load in each direction and the stability of the cyclic load.

Description

Technical Field

[0001] This invention relates to the field of basic structure testing technology, and in particular to a test device and method for a pile pull-out model with a fixed rope length and stepless direction change. Background Technology

[0002] As a core foundation type for various structures in civil engineering, pile foundations are widely used in engineering scenarios such as transmission towers, offshore wind power foundations, photovoltaic support anchor pile foundations, and underground anti-buoyancy structures. During actual service, pile foundations face various complex working conditions that easily generate pull-out loads. These pull-out loads, especially the long-term effects of oblique cyclic pull-out loads, significantly affect the pull-out bearing capacity and deformation characteristics of the pile foundation. They are key factors determining the rationality and safety of engineering design and are also important reference bases for pile foundation design.

[0003] Traditional testing devices can achieve static pull-out in all directions, but it is difficult to ensure the constant static load during the change of direction. The limitations are even more obvious in terms of cyclic load application. Most devices can only achieve cyclic loading in a single vertical or horizontal direction. Not only is the stability and accuracy of cyclic load in each direction insufficient, but it is also impossible to achieve continuous stepless adjustment of constant amplitude cyclic load in each direction, which makes it difficult to meet the requirements of fine simulation of oblique dynamic cyclic load.

[0004] To address these issues, some researchers have proposed using pulley assemblies to guide the wire rope to apply oblique loads. However, existing devices often rely on linear or ordinary curved guide rails for their pulleys. Since the center of curvature of the pulley's trajectory does not coincide with the anchor point at the top of the pile, the straight-line distance from the anchor point to the pulley's tangent point and the wire rope's wrap angle change when the pulley is moved. This alters the working length of the wire rope. Because the wire rope is elastic, this change in length directly affects the overall stiffness of the loading system, leading to inconsistent test data benchmarks at different loading angles and severely impacting the lateral comparability of test results. More importantly, manually adjusting the wire rope length to match the pulley position during the test requires interrupting the loading process, making a continuous and smooth transition of the stress path impossible. This not only fails to meet the high-precision requirements of oblique cyclic pull-out tests but also fails to fundamentally solve the challenges of achieving constant static load, stable cyclic load, and constant amplitude loading. Furthermore, the existing devices have particularly prominent shortcomings in dynamic cyclic loading. They not only have difficulty in reproducing the effects of real dynamic loads such as wind loads and wave loads, but also cannot explore the attenuation law of the pull-out performance of pile foundations under fatigue loads, which greatly limits the in-depth study of the mechanical behavior of pile foundations under complex working conditions. Summary of the Invention

[0005] In view of this, the present invention proposes a test device and method for a pile pull-out model with a fixed rope length and stepless direction change, in order to solve the technical problems mentioned in the background art, where the change in the working length of the steel wire rope directly leads to the change in the overall stiffness of the loading system, resulting in inconsistent test data benchmarks under different loading angles and seriously affecting the lateral comparability of test results; and the technical problem that manually adjusting the length of the steel wire rope to adapt to the pulley position cannot fundamentally solve the difficulties in achieving constant static load, stable cyclic load, and constant amplitude loading.

[0006] The technical solution of this invention is implemented as follows: In a first aspect, the present invention provides a pile pull-out model test device with a fixed rope length and continuously variable direction, comprising a model box, a model pile, a first support, a second support, a guide rail, a fixed pulley, a movable pulley, a wire rope, and a loading detection component, wherein: The model box is filled with soil in layers; The model pile was made according to the experimental scale and was inserted into the soil. The first bracket and the second bracket are respectively located on both sides of the model box, and their heights are adjustable. The two ends of the guide rail are respectively mounted on the first bracket and the second bracket, and the guide rail is provided with an arc-shaped groove with a hollow center; The fixed pulley is mounted on the first bracket; The movable pulley is slidably installed in the arc-shaped groove and can be snapped and fixed at a designated position in the arc-shaped groove; One end of the steel wire rope is connected to the top of the model pile, and is wound around the movable pulley and the fixed pulley in sequence. The other end is connected to the loading detection component, and the total length remains unchanged. The loading detection component is used to provide a constant tensile force or a dynamic cyclic load within a preset frequency range, and to collect the pile strain data of the model pile.

[0007] In some optional embodiments, preferably, the guide rail is provided with uniformly distributed positioning slots, and the movable pulley includes a pulley body and a central rotating shaft. The pulley body is rotatably mounted on the central rotating shaft, and the two ends of the central rotating shaft are used to be engaged in the positioning slots.

[0008] In some alternative implementations, preferably, the trajectory of the arc-shaped groove is designed based on the condition of a constant total working length of the wire rope, and is jointly determined by the rope length constraints between the center of the fixed pulley, the center of the movable pulley, and the fixed point at the top of the model pile.

[0009] In some alternative embodiments, preferably, the first support includes a first base and a first connecting rod, the first base being anchored to the test bench foundation, the bottom of the first connecting rod being detachably connected to the first base, and the top of the first connecting rod being connected to one end of the guide rail; the second support includes a second base and a second connecting rod, the second base being anchored to the test bench foundation, the bottom of the second connecting rod being detachably connected to the second base, and the top of the second connecting rod being connected to one end of the guide rail.

[0010] In some alternative implementations, preferably, the loading detection component includes an electro-hydraulic servo loading device, which is fixedly mounted above the first bracket, and the axis of its output end is tangent to the outer edge of the fixed pulley.

[0011] In some optional embodiments, preferably, the loading detection component further includes a force sensor and a strain gauge. The force sensor is connected in series on the wire rope between the electro-hydraulic servo loading device and the fixed pulley to collect the tensile force data applied to the model pile in real time. The strain gauge is attached to the pile body of the model pile to collect the pile body strain data.

[0012] In some optional embodiments, preferably, the loading detection component further includes a data acquisition device, which is electrically connected to the force sensor and the strain gauge to synchronously acquire the tensile force data of the force sensor and the pile strain data of the strain gauge, so as to realize the real-time storage and analysis of the test data.

[0013] In some alternative embodiments, preferably, the model box includes a frame, a base plate, and glass side panels. The frame is a rectangular hollow frame welded from structural steel. The base plate is welded to the bottom of the frame, and the glass side panels are sealed and installed on the four sides of the frame.

[0014] In some alternative implementations, preferably, the bottom of the base plate is equipped with swivel casters with brakes.

[0015] Secondly, the present invention provides a method for testing the pull-out resistance model of a foundation pile with a fixed rope length and continuously variable direction, using the foundation pile pull-out resistance model testing device with a fixed rope length and continuously variable direction described in the first aspect. The testing method includes: According to the soil sample type and compaction requirements of the test design, the soil was filled in layers in the model box, and the model piles were precisely pre-embedded in the soil at the designed position. The soil was left to cure for the set time, and the compaction of the soil and the embedment status of the model piles were observed to ensure that the model preparation met the standards. Assemble the test apparatus and conduct preliminary debugging to ensure that the entire apparatus is subjected to force smoothly and is sensitive to detection. Take images of the initial state of the soil and retain the original benchmark data of the test. The loading and detection components apply graded constant tensile forces. After each load is held until the pile top displacement stabilizes, tensile force data and pile strain data under that load are collected. By adjusting the position of the movable pulley while keeping the total length of the wire rope constant, the loading direction is switched, and graded constant tensile forces are applied to complete the horizontal, oblique, and vertical pull-out tests in sequence. The deformation, crack development, and relative displacement characteristics of the soil around the model pile are observed and recorded. Debug the loading detection component to the dynamic cyclic loading mode, set the loading parameters including cyclic load amplitude, frequency and number of cycles, repeat the above steps of switching loading direction, apply cyclic tension at the horizontal, oblique and vertical positions respectively to simulate reciprocating dynamic load, and synchronously collect the pile strain data under cyclic load until the set number of cycles is reached or the pile enters the fatigue failure state. After the test, the device was reset, the test data and visualization observation results were sorted out, and the tensile bearing characteristics and failure modes of the foundation piles were analyzed.

[0016] The fixed-rope-length, stepless directional change model test device and method for pile pull-out resistance of the present invention have the following advantages over the prior art: (1) The guide rail is provided with an arc-shaped groove with a hollow center. The movable pulley is slidably installed in the arc-shaped groove and can be locked and fixed in the designated position of the arc-shaped groove. The arc-shaped groove accurately corresponds to the moving trajectory of the movable pulley. Under the premise of keeping the total length of the wire rope constant, it can achieve precise switching of horizontal, oblique and vertical pull-out force without replacing components or adjusting the rope length. It can also ensure constant static load and stable cyclic load in each direction, effectively eliminate mechanical test errors caused by rope length changes, ensure the consistency of force conditions under different loading directions, and greatly reduce the impact on the lateral comparability of test results. (2) The guide rail is evenly provided with positioning slots. The movable pulley includes a pulley body and a central rotating shaft. The pulley body is rotatably mounted on the central rotating shaft. The two ends of the central rotating shaft are used to be locked in the positioning slots to ensure that the movable pulley can be accurately fixed in different positions. (3) The trajectory of the arc groove is designed based on the constant condition of the total working length of the wire rope, and is jointly determined by the rope length constraints between the fixed pulley center, the movable pulley center and the fixed point at the top of the model pile. By substituting the fixed pulley radius, the movable pulley radius, the coordinates of each fixed point and the initial rope length constant into the design stage, the continuous trajectory of the movable pulley center can be solved, thereby forming a guide rail curve that satisfies the constant rope length condition. This ensures that the total length of the wire rope remains absolutely constant throughout the process of the movable pulley changing direction steplessly along the guide rail and continuously adjusting the pulling angle, thereby eliminating the system stiffness error caused by the change in rope length. (4) The test is equipped with an electro-hydraulic servo loading device, which supports the application of constant static load and dynamic cyclic load. It can accurately simulate complex reciprocating load conditions such as wind and waves, overcome the limitations of traditional loading devices, and fill the technical gap in pile pull-out test under complex conditions. The model box adopts a high-transmittance glass side plate, which can capture key processes such as soil deformation around the pile, crack development, and relative displacement of the pile and soil in real time. With the help of a multi-dimensional detection system, mechanical data and soil deformation characteristics can be collected synchronously, making the mechanism analysis more intuitive.

[0017] (5) The bottom of the first connecting rod is detachably connected to the first base, and the top of the first connecting rod is connected to one end of the guide rail; the bottom of the second connecting rod is detachably connected to the second base, and the top of the second connecting rod is connected to one end of the guide rail, so as to realize the height adjustment of both ends of the guide rail, meet the test conditions of model piles of different heights, and be applicable to various geotechnical engineering foundation pile multi-directional pull-out model test scenarios. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a front view of the pile pull-out model test device with constant rope length and stepless direction change in an embodiment of the present invention; Figure 2 This is a structural schematic diagram illustrating the principle of fixed wire rope length in an embodiment of the present invention; Figure 3 This is a side view of the pile pull-out model test device with constant rope length and stepless direction change in an embodiment of the present invention; Figure 4 This is a top view of the pile pull-out model test device with constant rope length and stepless direction change in an embodiment of the present invention; Figure 5 This is a schematic diagram of the guide rail structure in an embodiment of the present invention; Figure 6 This is a flowchart illustrating the test method for the pull-out resistance model of a foundation pile with a fixed rope length and continuously changing direction, as described in an embodiment of the present invention.

[0020] Explanation of reference numerals in the attached figures: 1-Model box, 2-Model pile, 3-First support, 4-Second support, 5-Guide rail, 6-Fixed pulley, 7-Modible pulley, 8-Wire rope, 9-Loading detection component, 10-Soil; 11-Frame, 12-Base plate, 13-Glass side panel, 14-Swivel casters; 21-Hanging rings; 31-First base, 32-First connecting rod; 41-Second base, 42-Second connecting rod; 51-Arc-shaped groove, 52-Support flange, 53-Positioning slot; 71-Pulley body, 72-Central pivot; 91-Electro-hydraulic servo loading device, 92-Force sensor, 93-Strain gauge, 94-Data acquisition device. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0022] In the description of the embodiments of the present invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of the present invention based on the specific circumstances.

[0023] In the description of the embodiments of the present invention, it should be noted that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of the present invention.

[0024] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0025] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0026] The following disclosure provides numerous different embodiments or examples for implementing various structures of the invention. To simplify the disclosure, specific examples of components and arrangements are described below. These are merely examples and are not intended to limit the invention. Furthermore, reference numerals and / or letters may be repeated in different examples. Such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. Additionally, examples of various specific processes and materials are provided in this invention; however, those skilled in the art will recognize the applicability of other processes and / or the use of other materials.

[0027] The technical solution will now be explained in detail: Reference Figures 1-5 As shown, in a first aspect embodiment of the present invention, a pile pull-out model test device with a fixed rope length and continuously variable direction is proposed, comprising a model box 1, a model pile 2, a first support 3, a second support 4, a guide rail 5, a fixed pulley 6, a movable pulley 7, a wire rope 8, and a loading detection component 9, wherein: The model box 1 is filled with soil 10 in layers. The model box 1 includes a frame 11, a bottom plate 12, and glass side plates 13. The frame 11 is a rectangular hollow frame welded from steel profiles. The bottom plate 12 is welded to the bottom of the frame 11. The glass side plates 13 are high-transmittance acrylic glass (PMMA) side plates, which are sealed and installed on the four sides of the frame 11. The thickness of the glass side plates is 10~20 mm, which ensures both structural rigidity and impermeability, and allows for clear observation of changes in soil 10 displacement, crack development, pile-soil interaction, etc. during the test. The glass side plates 13 are connected to the frame 11 by bolts, and impermeable strips are pasted at the joints to prevent soil 10 from leaking. The model pile 2 is made according to the experimental scale and is inserted into the soil 10. The model pile 2 can be made of PVC pipe, aluminum alloy or thin steel pipe. A lifting ring 21 is reserved at the top of the pile for connecting the steel wire rope 8. The first bracket 3 and the second bracket 4 are respectively located on both sides of the model box 1, and their heights are adjustable. The guide rail 5 is mounted on the first bracket 3 and the second bracket 4 at both ends. The guide rail 5 has an arc-shaped groove 51 with a hollow center. The trajectory of the arc-shaped groove 51 is designed based on the constant total working length of the wire rope 8, and is determined by the rope length constraints between the center of the fixed pulley 6, the center of the movable pulley 7, and the top fixed point of the model pile 2. By substituting the radius of the fixed pulley 6, the radius of the movable pulley 7, the coordinates of each fixed point, and the initial rope length constant during the design stage, the continuous trajectory of the center of the movable pulley 7 can be solved, thus forming the guide rail 5 curve that satisfies the constant rope length condition. This ensures that the total length of the wire rope 8 remains absolutely constant throughout the process of the movable pulley 7 continuously changing direction and adjusting the pulling angle along the guide rail 5, thereby eliminating the system stiffness error caused by the rope length change. The two sides of the arc-shaped groove 51 are support flanges 52, made of 5mm thick hard aluminum alloy plate. The spacing between the two support flanges 52 needs to be designed to match the size of the movable pulley 7, slightly larger than the thickness of the movable pulley 7, with a reserve of 0.1~0.3. A sliding gap of mm is provided to ensure smooth movement. Several positioning slots 53 are evenly opened along the curve of the guide rail 5 on the inner side of the support flange 52. The spacing of the positioning slots 53 is adjusted according to the test loading direction. Each slot is marked with a corresponding number to ensure that the movable pulley 7 can be accurately fixed in different positions. The fixed pulley 6 is installed on the first bracket 3; the fixed pulley 6 can be made of aluminum alloy or cast steel, and its diameter is usually in the range of 400-600 mm. It is equipped with a deep groove ball bearing to ensure flexible rotation and stable load bearing, and is compatible with the steel wire rope 8 used in the test to meet the load force transmission requirements. The movable pulley 7 is slidably installed in the arc-shaped groove 51 and can be locked and fixed in a designated position in the arc-shaped groove 51. The movable pulley 7 includes a pulley body 71 and a central rotating shaft 72. The pulley body 71 is rotatably installed on the central rotating shaft 72, and the two ends of the central rotating shaft 72 are used to be locked in the positioning slots 53. The material of the movable pulley 7 can be nylon or aluminum alloy, and the pulley diameter is usually in the range of 400-600 mm. When it is necessary to change the direction of the loading force, the movable pulley 7 is gently lifted upward to make the central rotating shaft 72 disengage from the current positioning slot 53. After sliding smoothly along the guide rail 5 to the target position, it is released, and the central rotating shaft 72 automatically locks into the corresponding positioning slot 53 to achieve positioning and fixation. One end of the steel wire rope 8 is connected to the top of the model pile 2, and is wound around the movable pulley 7 and the fixed pulley 6 in sequence. The other end is connected to the loading detection component 9, and the total length remains unchanged. The loading detection component 9 is used to provide a constant tensile force or a dynamic cyclic load within a preset frequency range, and to collect the pile strain data of the model pile 2.

[0028] The fixed-length, stepless directional pile pull-out model test device proposed in this embodiment features a centrally hollowed-out arc-shaped groove 51 on the guide rail 5. The movable pulley 7 is slidably installed in the arc-shaped groove 51 and can be locked and fixed at a designated position on the arc-shaped groove 51. The arc-shaped groove 51 precisely corresponds to the movement trajectory of the movable pulley 7. Under the premise of keeping the total length of the wire rope 8 constant, it can achieve precise switching of horizontal, oblique, and vertical pull-out forces without replacing components or adjusting the rope length. It can also ensure constant static load and stable cyclic load in all directions, effectively eliminating mechanical test errors caused by rope length changes, ensuring the consistency of stress conditions under different loading directions, and significantly reducing the impact on the lateral comparability of test results.

[0029] In some embodiments, to achieve the core requirements of fixed rope length and stepless direction change, this invention designs a special guide rail 5 adapted to the pulley's movement trajectory, namely a specially designed curved guide rail 5, which adopts a structure with a centrally hollowed-out arc-shaped groove 51. To achieve continuous adjustment of the loading direction between horizontal, oblique, and vertical directions without changing the length of the wire rope 8, the trajectory of this guide rail 5 needs to be determined by the constant constraint of the wire rope 8 length: the center of the pulley 6 is set as... F 1( x 1, y 1) The radius of the fixed pulley 6 is R 1; The center of the movable pulley 7 is P ( x , y ), radius is R 2; The fixed point of the top of model pile 2 is F 2( x 2, y 2) The wire rope 8 connects to the fixed point at the top of the pile after passing through the fixed pulley 6 and the movable pulley 7 from the fixed end. The rope always wraps around the outer edge of the pulleys. Since there are tangent segments and wrap angle arcs between the fixed pulley 6 and the movable pulley 7, and between the movable pulley 7 and the fixed point at the top of the pile, the trajectory of the center of the movable pulley 7 should satisfy the constraint condition of the fixed rope length: (1); In equation (1), d 1 represents the distance from the center of the movable pulley 7 to the center of the fixed pulley 6. d 2 represents the distance from the center of the movable pulley 7 to the fixed point at the top of the model pile 2. R 1 represents the radius of the fixed pulley 6. R 2 represents the radius of the movable pulley 7. C 0 is a constant determined by both the initial rope length and the fixed wrapping length; Length of the external common tangent segment from fixed pulley 6 to movable pulley 7 L The formula for calculating 1 is as follows: (2); The length of the tangent segment from the movable pulley 7 to the fixed point at the top of the model pile 2 L The formula for calculating 2 is as follows: (3); Arc length corresponding to the 6-angle wrap of the fixed pulley s The formula for calculating 1 is as follows: (4); Arc length corresponding to the 7-angle wrap of the movable pulley s The formula for calculating 2 is as follows: (5); According to formulas (1) to (5), the trajectory points of the movable pulley 7 can be solved according to the actual installation dimensions and initial working conditions, and the fixed rope length stepless direction-changing special curved guide rail 5 can be processed accordingly.

[0030] In some embodiments, the first support 3 includes a first base 31 and a first connecting rod 32. The first base 31 is anchored to the test bench foundation, the bottom of the first connecting rod 32 is detachably connected to the first base 31, and the top of the first connecting rod 32 is connected to one end of the guide rail 5. The second support 4 includes a second base 41 and a second connecting rod 42. The second base 41 is anchored to the test bench foundation, the bottom of the second connecting rod 42 is detachably connected to the second base 41, and the top of the second connecting rod 42 is connected to one end of the guide rail 5. By adjusting the connection position between the bottom of the first connecting rod 32 and the first base 31, and adjusting the connection position between the bottom of the second connecting rod 42 and the second base 41, the height of both ends of the guide rail 5 can be adjusted to meet the test conditions of model piles 2 at different heights, thus improving applicability. The first base 31 and the second base 41 are welded from Q235 steel.

[0031] In some embodiments, the loading detection component 9 includes an electro-hydraulic servo loading device 91, which is fixedly mounted above the first support 3, and the axis of its output end is tangent to the outer edge of the fixed pulley 6. The electro-hydraulic servo loading system can provide constant tension or dynamic cyclic load of 0.1~5Hz, with stable output and high control precision. By ensuring that the axis of its output end is tangent to the outer edge of the fixed pulley 6, the electro-hydraulic servo loading device 91, the fixed pulley 6, the model pile 2, and the guide rail 5 are all on the same force-bearing plane.

[0032] In some embodiments, the loading detection component 9 further includes a force sensor 92 and a strain gauge 93. The force sensor 92 is connected in series on the wire rope 8 between the electro-hydraulic servo loading device 91 and the fixed pulley 6, and is used to collect the tensile force data applied to the model pile 2 in real time. The strain gauge 93 is attached to the pile body of the model pile 2 and is used to collect the pile body strain data of the model pile 2.

[0033] In some embodiments, the loading detection component 9 further includes a data acquisition device 94, which is electrically connected to the force sensor 92 and the strain gauge 93, and is used to synchronously acquire the tensile force data of the force sensor 92 and the pile strain data of the strain gauge 93, so as to realize the real-time storage and analysis of the test data.

[0034] In some embodiments, the bottom of the base plate 12 is equipped with universal casters 14 with brakes. Four to six universal casters 14 with brake locking function are installed at the four corners and the middle of the bottom of the base plate 12 to facilitate the adjustment of the position of the model box 11, site handling and model reset during the test. The load-bearing capacity of the universal casters 14 is not less than 1.5 times the full load weight of the model box 1.

[0035] Based on the same concept, a second aspect of the present invention, combined with... Figure 6 As shown, a method for testing the pull-out resistance of a pile foundation with a fixed rope length and continuously variable direction is provided. This method utilizes the pile foundation pull-out resistance testing apparatus with a fixed rope length and continuously variable direction described in the first aspect. The testing method includes: Step S1: According to the soil sample type and compaction requirements of the test design, fill the soil 10 in layers in the model box 1, and simultaneously embed the model pile 2 precisely in the designed position of the soil 10. Let it stand for curing for the set time, observe the compaction of the soil 10 and the embedding status of the model pile 2 to ensure that the model preparation meets the standards. Step S2: Assemble the test device and perform preliminary debugging to ensure that the entire device is subjected to force smoothly and the detection is sensitive. Take images of the initial state of the soil and retain the original benchmark data of the test. Step S3: Apply graded constant tensile force through the loading detection component 9. After each load is held until the pile top displacement stabilizes, collect the tensile force data and pile strain data under that load. By adjusting the position of the movable pulley 7 and keeping the total length of the wire rope 8 unchanged, switch the loading direction and continue to apply graded constant tensile force. Complete the horizontal, oblique, and vertical pull-out tests in sequence. Observe and record the deformation, crack development, and relative displacement characteristics of the soil 10 around the model pile 2. Step S4: Debug the loading detection component 9 to the dynamic cyclic loading mode, set the loading parameters including cyclic load amplitude, frequency and number of cycles, repeat the above steps of switching loading direction, apply cyclic tension to the horizontal, oblique and vertical positions respectively, simulate reciprocating dynamic load, and synchronously collect the pile strain data under cyclic load until the set number of cycles is reached or the pile enters the fatigue failure state. Step S5: After the test, reset the device, organize the test data and visualization observation results, and analyze the tensile bearing characteristics and failure mode of the foundation pile.

[0036] In step S5, after the test is completed, the device is reset, including: after the test is completed, the device is unloaded to zero step by step, the connection between the moving pulley 7 and the top of the model pile 2 is loosened, and the steel wire rope 8 is removed; the brake of the bottom caster of the model box 1 is unlocked, the model box 1 is pushed to the cleaning area, the model pile 2 is removed and the soil 10 inside the box is cleaned; the loading and detection system is turned off, the test equipment is organized, and the integrity of components such as the guide rail 5, pulley, and force sensor 92 is checked to prepare for the next test.

[0037] The model test and method for pile pull-out resistance with constant rope length and stepless direction change proposed in this embodiment have the following advantages: (1) A special curved guide rail 5 with a positioning slot 53 was developed. The guide rail 5 accurately corresponds to the moving trajectory of the movable pulley 7. Under the premise of keeping the total length of the wire rope 8 constant, it can achieve precise switching of horizontal, oblique and vertical pull-out force without replacing components or adjusting the rope length. It can also ensure constant static load and stable cyclic load in each direction. This design solves the limitations of traditional devices, such as cumbersome adjustment of loading direction, static load can be pulled in each direction but cannot achieve constant load, and cyclic load can only be applied vertically / horizontally and cannot achieve cyclic constant load. It effectively eliminates mechanical test errors caused by rope length changes and ensures the consistency of force conditions under different loading directions. At the same time, by simplifying the rope adjustment process, the device significantly improves the accuracy and repeatability of test data, makes the switching of loading conditions faster, and the test process more stable and continuous. (2) Equipped with an electro-hydraulic servo loading system, it supports the application of constant static load and dynamic cyclic load, and can accurately simulate complex reciprocating load conditions such as wind and waves. It overcomes the limitations of traditional loading devices, significantly expands the research dimensions of the tensile fatigue characteristics of foundation piles, and fills the technical gap in the tensile test of foundation piles under complex conditions. (3) The model box 1 uses a high-transmittance organic glass side plate 13, which can capture key processes such as deformation of the soil around the pile 10, crack development, and relative displacement of the pile and soil in real time. Combined with a multi-dimensional detection system, it can realize the synchronous acquisition of mechanical data and soil deformation characteristics, making the analysis of the test mechanism more intuitive. (4) The base of the model box 1 is equipped with universal casters 14 with brakes, which improves the flexibility of test adjustment and equipment movement. The integrated design of the guide rail 5 and the pulley simplifies the disassembly and assembly process and effectively reduces the difficulty of test preparation and post-cleaning. (5) The device adopts a modular design, integrating a loading detection system and a height-adjustable support, which can be flexibly adapted to various scale models and soil conditions. The system has stable operation performance, high acquisition accuracy, and is suitable for various geotechnical engineering pile multi-directional pull-out model test scenarios.

[0038] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A pile pull-out model test device with a fixed rope length and continuously variable direction, characterized in that, It includes a model box, model piles, first support, second support, guide rails, fixed pulleys, movable pulleys, wire ropes, and a loading detection assembly, among which: The model box is filled with soil in layers; The model pile was made according to the experimental scale and was inserted into the soil. The first bracket and the second bracket are respectively located on both sides of the model box, and their heights are adjustable. The two ends of the guide rail are respectively mounted on the first bracket and the second bracket, and the guide rail is provided with an arc-shaped groove with a hollow center; The fixed pulley is mounted on the first bracket; The movable pulley is slidably installed in the arc-shaped groove and can be snapped and fixed at a designated position in the arc-shaped groove; One end of the steel wire rope is connected to the top of the model pile, and is wound around the movable pulley and the fixed pulley in sequence. The other end is connected to the loading detection component, and the total length remains unchanged. The loading detection component is used to provide a constant tensile force or a dynamic cyclic load within a preset frequency range, and to collect the pile strain data of the model pile.

2. The pile pull-out model test device with stepless direction change of fixed rope length as described in claim 1, characterized in that, The guide rail is provided with evenly spaced positioning slots. The movable pulley includes a pulley body and a central rotating shaft. The pulley body is rotatably mounted on the central rotating shaft, and the two ends of the central rotating shaft are used to be engaged in the positioning slots.

3. The pile pull-out model test device with stepless direction change of fixed rope length as described in claim 1, characterized in that, The trajectory of the arc-shaped groove is designed based on the constant total working length of the wire rope, and is jointly determined by the rope length constraints between the center of the fixed pulley, the center of the movable pulley, and the fixed point at the top of the model pile.

4. The pile pull-out model test device with stepless direction change of fixed rope length as described in claim 1, characterized in that, The first bracket includes a first base and a first connecting rod. The first base is anchored to the foundation of the test bench. The bottom of the first connecting rod is detachably connected to the first base, and the top of the first connecting rod is connected to one end of the guide rail. The second bracket includes a second base and a second connecting rod. The second base is anchored to the foundation of the test bench. The bottom of the second connecting rod is detachably connected to the second base, and the top of the second connecting rod is connected to one end of the guide rail.

5. The pile pull-out model test device with constant rope length and stepless direction change as described in claim 1, characterized in that, The loading detection component includes an electro-hydraulic servo loading device, which is fixedly installed above the first bracket, and the axis of its output end is tangent to the outer edge of the fixed pulley.

6. The pile pull-out model test device with stepless direction change of fixed rope length as described in claim 5, characterized in that, The loading detection component also includes a force sensor and a strain gauge. The force sensor is connected in series on the steel wire rope between the electro-hydraulic servo loading device and the fixed pulley, and is used to collect the tensile force data applied to the model pile in real time. The strain gauge is attached to the pile body of the model pile and is used to collect the pile body strain data of the model pile.

7. The pile pull-out model test device with stepless direction change of fixed rope length as described in claim 6, characterized in that, The loading detection component also includes a data acquisition device, which is electrically connected to the force sensor and the strain gauge to synchronously acquire the tensile force data of the force sensor and the pile strain data of the strain gauge, thereby realizing real-time storage and analysis of the test data.

8. The pile pull-out model test device with stepless direction change of fixed rope length as described in claim 1, characterized in that, The model box includes a frame, a base plate, and glass side panels. The frame is a rectangular hollow frame welded from steel profiles. The base plate is welded to the bottom of the frame, and the glass side panels are sealed and installed on the four sides of the frame.

9. The pile pull-out model test device with stepless direction change of fixed rope length as described in claim 8, characterized in that, The bottom of the base plate is equipped with swivel casters with brakes.

10. A method for a pile pull-out model test with a fixed rope length and continuously changing direction, characterized in that, Using the pile pull-out model test device with constant rope length and stepless direction change as described in any one of claims 1 to 9, the test method includes: According to the soil sample type and compaction requirements of the test design, the soil was filled in layers in the model box, and the model piles were precisely pre-embedded in the soil at the designed position. The soil was left to cure for the set time, and the compaction of the soil and the embedment status of the model piles were observed to ensure that the model preparation met the standards. Assemble the test apparatus and conduct preliminary debugging to ensure that the entire apparatus is subjected to force smoothly and is sensitive to detection. Take images of the initial state of the soil and retain the original benchmark data of the test. The loading and detection components apply graded constant tensile forces. After each load is held until the pile top displacement stabilizes, tensile force data and pile strain data under that load are collected. By adjusting the position of the movable pulley while keeping the total length of the wire rope constant, the loading direction is switched, and graded constant tensile forces are applied to complete the horizontal, oblique, and vertical pull-out tests in sequence. The deformation, crack development, and relative displacement characteristics of the soil around the model pile are observed and recorded. Debug the loading detection component to the dynamic cyclic loading mode, set the loading parameters including cyclic load amplitude, frequency and number of cycles, repeat the above steps of switching loading direction, apply cyclic tension at the horizontal, oblique and vertical positions respectively to simulate reciprocating dynamic load, and synchronously collect the pile strain data under cyclic load until the set number of cycles is reached or the pile enters the fatigue failure state. After the test, the device was reset, the test data and visualization observation results were sorted out, and the tensile bearing characteristics and failure modes of the foundation piles were analyzed.

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