Geotechnical engineering multi-mode simulation design method and model test loading device thereof

Abstract

The invention discloses a geotechnical engineering multi-mode simulation design method and a model test loading device, which solve the problems of single loading mode, low control precision and poor adaptability of the existing device, and the method comprises the following steps: establishing a pile-soil system wave equation, setting boundary initial conditions, correcting a vibration equation, deriving a displacement response curve, carrying out PID feedback regulation, and carrying out multi-mode simulation design on the basis of the parameters of Kp = 1.8, Ki = 0.4 and Kd = 0.02. A steady state is reached within 2s, the loading error is less than 3%, a complete mathematical model is constructed, the device comprises a base, a driving device and the like, and the base is adaptive to a multi-specification model box; the driving device ensures stable precision; the loading assembly uses an adjustable coupling and a modularized end, each part is modularized, and an upper computer is supported to control parameters and memories. Compared with the prior art, the invention has the advantages of multi-mode loading, high-precision control, strong adaptability and efficient operation, meets the requirements of complex rock and soil tests, and provides support for related mechanism research.

Description

Technical Field

[0001] This invention relates to the field of geotechnical engineering foundation structure model testing technology, specifically a multi-mode simulation design method for geotechnical engineering and its model test loading device. Background Technology

[0002] In geotechnical engineering similarity model tests, the loading system is a key component for studying the interaction mechanism between soil and structure. With the continuous expansion of research needs, as illustrated in the visualized three-dimensional loading pull-out test chamber disclosed in announcement number CN109283059A, traditional static pull-out tests are no longer sufficient to meet the requirements for simulating complex working conditions. Especially in the study of static pressure pile driving, dynamic pile driving, and cyclic pull-out problems, there is an urgent need for a composite loading device capable of precisely adjusting parameters such as loading force, displacement, and velocity under different test conditions.

[0003] Most existing loading devices employ a single loading mode, such as simple electric screws or weights. These methods suffer from limitations in loading paths and lag in control system response, and cannot simulate complex engineering conditions like vibration, impact, or intermittent loading. Furthermore, existing devices generally suffer from poor integration with experimental data acquisition systems, limiting the real-time and accurate acquisition and feedback of key variables such as displacement and load. Moreover, existing devices typically lack a theoretical modeling and closed-loop control algorithm based on pile-soil dynamic interaction, making it difficult to accurately predict and correct complex physical phenomena such as stress wave propagation and nonlinear vibration during the loading process. These shortcomings are the fundamental reasons limiting loading accuracy and dynamic simulation effectiveness.

[0004] Furthermore, existing loading devices also have significant shortcomings in terms of connection adaptability. On the one hand, the coupling structure is of fixed size, making it difficult to connect to connecting rods of different diameters; on the other hand, the end type connected to the foundation structure is uniform and lacks modular design, making it impossible to quickly change the end type according to different test requirements, which directly affects the test adaptability and operational efficiency of the loading device.

[0005] In summary, existing loading devices have limitations in loading modes, control accuracy, and connection adaptability, making it difficult to meet the diverse needs of complex geotechnical engineering tests for static and dynamic loading. Therefore, there is an urgent need to develop a composite vertical loading device that combines high-precision control, multi-mode loading, and good adaptability. This device incorporates an adjustable-diameter coupling to accommodate connecting rods of different sizes, and features quickly replaceable loading ends that can be switched according to test requirements and foundation structure. Furthermore, by integrating servo drives and a programmable control unit, it achieves high-precision loading control under various working conditions, significantly improving the device's versatility, flexibility, and testing efficiency. Summary of the Invention

[0006] The technical problem to be solved by this invention is to overcome the above-mentioned technical defects and provide a multi-mode simulation design method for geotechnical engineering and a model test loading device thereof.

[0007] To solve the above problems, the technical solution of the present invention is: a multi-mode simulation design method for geotechnical engineering, characterized by comprising the following steps: S1 Pile-Soil System Wave Equation Establishment: Assuming the soil is a homogeneous, isotropic elastic medium, and the pile is loaded vertically, according to Newton's second law, the small element of the soil at depth x satisfies the following under the condition of force equilibrium: Equation (1) In the formula, ρ is the soil density, A is the cross-sectional area of ​​the soil micro-unit, and f(x,t) is the external load density. After further simplification, we get: Formula (2). In a one-dimensional elastic body, we have: Equation (3) Substituting equation (3) into equation (2) yields equation (4). If external forces are ignored, that is, when f(x,t)=0, equation (4) can be simplified to: equation (5) In the formula The essence of this equation is: when the pile sinks into the soil, the disturbance of the pile to the soil propagates in the soil in the form of waves. That is, when the pile hammer hits or servo loads, the force is not transmitted to the entire bottom of the pile instantaneously and uniformly, but gradually propagates as "stress waves". The wave velocity c determines the speed of stress transmission in the soil. S2 Boundary and Initial Condition Settings: Considering that the pile top is loaded by a servo motor or impacted by a pile hammer, its displacement changes with time as follows: Equation (6) In the formula, The frequency of pile top vibration is used here, which is simplified to frequency. The input is in the form of a simple harmonic wave. The bottom of the pile is usually a free end, that is, there is no external force constraint at the bottom of the soil. The stress at the bottom of the pile is 0, that is: Equation (7). The general solution of the one-dimensional wave equation is: Equation (8) In equation (8), it is generally assumed that there is a wave propagating in the +x direction and a wave propagating in the -x direction in the system at the same time. Under the condition of pile top loading and pile bottom free, the main propagation direction is the downward wave (+x direction), so we can get: equation (9). ,in, , where is the wave speed, and represents the rate of change of the wave in space. Substituting equation (9) into equation (2), we get: equation (10). In actual monitoring, the stress response at a certain point in the soil changes with time as approximated by: Equation (11) The function yields a sinusoidal response curve of stress over time, with its phase lag increasing linearly with depth, reflecting the hysteresis effect of the soil on loading. S3 Vibration Equation Nonlinear Correction: Under actual dynamic loading, the pile not only vibrates up and down, but is also affected by soil damping, restoring force and nonlinear deformation. Starting from the mass-damping-stiffness system, the general form of the vibration equation is: Equation (12). In the formula, m is the equivalent mass, i.e., the mass of the pile and its adjacent soil participating in the vibration; c is the pile-soil damping coefficient; k0 is the linear stiffness; and γ is the nonlinear correction coefficient. Given an external periodic load, under steady-state conditions, the solution is assumed to be... Substituting into equation (12) and separating the real and imaginary parts, we obtain the amplitude equation: equation (13). Furthermore, the amplitude-frequency curve is obtained: Equation (14) ; S4 Soil Displacement Reaction Force and Displacement Response Curve: To describe the influence of the pile sinking velocity vpile on the reaction force, an empirical nonlinear relationship is introduced, Equation (15). Assuming Substituting into the vibration equation: Equation (16) By linearizing it and finding the steady-state solution, the time history curve of the pile displacement can be obtained: Equation (17) In the formula, , is the damping ratio. , is the system's inherent frequency. The damping vibration frequency is represented by this curve, which describes the displacement decay trend of the pile body over time during the initial loading stage. By fitting it with experimental data, the system damping and equivalent stiffness can be deduced. In servo system control, this curve is used to calculate the reference trajectory of the target displacement, providing the target path input for the PID controller. S5PID feedback regulation and error convergence curve: In actual control, in order to eliminate external disturbances and nonlinear deviations, this device adopts PID feedback control law: Equation (18) The system closed-loop error transfer function is: Equation (19) In the formula, G(s) is the transfer function of the servo loading system, and H(s) is the transfer function of the PID controller. In the time domain, its error convergence curve is: S6 This indicates that the system error decays exponentially with time, and the convergence speed is proportional to the proportional gain Kp and negatively correlated with the damping ratio ξ. Actual tests show that when Kp=1.8, Ki=0.4, and Kd=0.02, the system reaches steady state within 2 seconds, with a loading error of less than 3%. The above model, from wave propagation to nonlinear vibration response and then to servo closed-loop control, constitutes a complete mathematical description of the pile-soil-control system. By characterizing the stress propagation law through the wave equation and capturing the nonlinear dynamic characteristics through the vibration equation, combined with the PID algorithm, adaptive adjustment of loading accuracy and stability is achieved, thus realizing multi-mode, high-precision vertical loading control.

[0008] A loading device for multi-mode model tests in geotechnical engineering, characterized in that it comprises: The base is used to support the entire loading device and has multiple sets of holes reserved on it, which can be connected to model box platforms of different specifications through quick-release bolts. The drive device includes a servo motor, a reducer, an output shaft, and an integrated end cover. The servo motor drives a gear set to rotate sequentially through the reducer and the output shaft. The gear set is meshed with a sprocket. The integrated end cover integrates an encoder interface and a fan cooling system. The encoder interface is used to monitor displacement accuracy and ensure that the displacement monitoring data can be used for parameter calibration of the wave equation and vibration equation. The guiding mechanism includes linear guide rails and sliders on both sides of the loading plate. The guide rails are symmetrically arranged on both sides of the loading plate. The preload between the guide rails and the sliders is adjustable to restrict the loading plate to move only in the vertical direction, ensuring that the displacement data during loading conforms to the vertical displacement assumptions of ux,t. The loading assembly includes a force gauge, an adjustable diameter coupling, a sleeve-type connecting rod, and a modular loading end. One end of the force gauge is connected to the loading plate, and the other end is connected to the connecting rod via the adjustable diameter coupling. The adjustable diameter coupling has internal opening and closing claws and clamping screws, and the clamping diameter can be adjusted with an Allen wrench to adapt to connecting rods with different outer diameters. At the same time, the loading force stable transmission end has a foundation structure to meet the force transmission conditions required for stress wave propagation. The connecting rod is a telescopic structure with an internal positioning pin and a rotating locking device. Its lower end is connected to the loading end via a thread, and the length can be adjusted according to the model height to ensure effective docking between the loading end and the foundation structure when the lower end of the foundation structure is placed in the test filling material. The loading end can be selectively replaced with a pressure plate type, an anchor clamp type, or a pile cap sleeve type to adapt to different types of foundation structures and ensure the diversity of pile-soil interaction tests. The system includes a force acquisition module and a limit protection mechanism. The force acquisition module comprises a force gauge and a displacement sensor for real-time acquisition of loading force and axial displacement data. A control cabinet is provided for data transmission. The acquired data can be directly used for the calculation of σ(x,t) and u(t) and error analysis of PID feedback control. The limit protection mechanism includes a guide rail with photoelectric sensors and rubber buffer pads at both ends of its travel. When the loading component approaches its limit travel, the photoelectric sensor triggers a stop command to prevent displacement from exceeding the effective calculation range of the wave equation and vibration equation during loading, thus ensuring experimental safety and data validity. Furthermore, the power transmission path of the drive device includes a servo motor, a reducer, an output shaft, a gear set, a sprocket, a closed-loop chain, a transmission block, and a loading plate. The closed-loop chain is wound between the upper and lower sets of sprockets, and the transmission block is fixed to both ends of the chain and connected to the loading plate.

[0009] Furthermore, the force transmission path of the loading component includes a loading plate, a force gauge, an adjustable diameter coupling, a connecting rod, a loading end, and a base structure. The lower end of the base structure is placed in the test packing, and the loading force data collected by the force gauge is used as the feedback input for PID closed-loop control.

[0010] Furthermore, the modular loading end is threadedly connected to the connecting rod, and the replacement time is no more than a few minutes. The adaptable foundation structures include model piles, model anchors, and underground pipe gallery models. Different end forms can simulate the stress state of foundation structures such as piles and anchors, ensuring the applicability of the wave equation and vibration equation of the pile-soil system under different test objects.

[0011] Furthermore, the photoelectric sensor of the limit protection mechanism is electrically connected to the control cabinet. When the loading component triggers the photoelectric sensor, the control cabinet immediately cuts off the servo motor drive signal. At the same time, the rubber buffer pad is used to absorb the impact energy and avoid structural damage.

[0012] Furthermore, the drive device, guide mechanism, and loading components all adopt a modular design. Each component is connected by bolts and can be disassembled and maintained independently. The replacement time for a single component is no more than a few minutes. The modular design facilitates equipment calibration, ensures the measurement accuracy of parameters such as the required loading force, displacement, and speed, and guarantees the repeatability of test data.

[0013] Furthermore, the control cabinet is connected to a host computer, which supports setting loading parameters, displaying loading curves in real time, and saving test data through the host computer. The loading parameters include loading mode, loading amplitude, loading frequency, and loading duration.

[0014] The advantages of this invention compared to existing technologies are: This multi-mode model test loading device and design method for geotechnical engineering breaks through the limitations of traditional loading devices with a single loading mode. By combining servo motor drive and PID feedback control algorithm, it can realize multiple loading modes such as static loading, dynamic loading, and cyclic loading, which can meet the simulation requirements of different complex working conditions such as static pressure pile driving, dynamic pile driving, and cyclic pull-out. At the same time, by establishing the wave equation and vibration equation of the pile-soil system and performing nonlinear correction, combined with real-time data acquisition and closed-loop control, the system can reach steady state within 2 seconds with a loading error of less than 3%, significantly improving the loading accuracy and providing precise loading conditions for complex geotechnical engineering tests.

[0015] In terms of connection and adaptation, the device innovatively adopts an adjustable diameter coupling, which can adapt to sleeve-type connecting rods with different outer diameters by adjusting the clamping diameter, thus solving the problem of poor compatibility of traditional couplings. The modular loading end supports quick replacement, with a replacement time of no more than 5 minutes, and can be adapted to various foundation structures such as model piles, model anchors, and underground pipe gallery models, greatly improving the experimental adaptability of the device. In addition, the modular design of each component of the device allows for the replacement of a single component to be no more than 30 minutes, making maintenance convenient and efficient. At the same time, the coordinated control between the host computer and the control cabinet simplifies the experimental operation process and improves experimental efficiency. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the working principle and structure of the vertical loading device of the present invention.

[0017] Figure 2 This is a structural diagram of the vertical loading device of the present invention.

[0018] Figure 3 This is a structural diagram of the driving device of the present invention.

[0019] Figure 4 This is a structural diagram of the replacement pile head of the present invention.

[0020] Figure 5 This is a roadmap of the theoretical method and loading test technology of the present invention.

[0021] As shown in the figure: 1. Host computer; 2. Control cabinet; 3. Force gauge; 4. Coupling; 5. Connecting rod; 6. Loading end; 7. Basic structure; 8. Drive device; 9. Base; 10. Gear set; 11. Sprocket; 12. Closed-loop chain; 13. Guide rail; 14. Slider; 15. Transmission block; 16. Loading plate; 17. Loading connection seat; 18. Photoelectric sensor; 19. Servo motor; 20. Reducer; 21. Output shaft; 22. Integrated end cover. Detailed Implementation

[0022] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings. Identical components are indicated by the same reference numerals.

[0023] It should be noted that the terms “front,” “back,” “left,” “right,” “up,” and “down” used in the following description refer to the directions shown in the attached diagram, while the terms “inside” and “outside” refer to the directions toward or away from the geometric center of a specific component, respectively.

[0024] To make the content of this invention easier to understand, the technical solutions in the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings.

[0025] like Figures 1 to 5As shown, a multi-mode simulation design method for geotechnical engineering first establishes the wave equation of the pile-soil system before conducting multi-mode simulation tests. It is assumed that the soil used in the test is a homogeneous, isotropic elastic medium, and the pile is subjected to vertical loading forces. Based on Newton's second law, the force equilibrium state of the small soil element at depth x is analyzed, and this small element satisfies equation (1). , where ρ is the soil density, A is the cross-sectional area of ​​the soil micro-unit, and f(x,t) is the external load density. Further simplification of equation (1) yields equation (2). Within the framework of the physical properties of a one-dimensional elastic body, equation (3) exists. By substituting equation (3) into equation (2) based on the relationship shown, equation (4) can be derived. When the external force is ignored, i.e., f(x,t)=0, equation (4) can be simplified to equation (5). ; This equation clearly reveals the physical essence of the pile sinking process: the disturbance generated by the pile on the soil will propagate in the soil in the form of waves. Whether the pile is struck by a pile hammer or loaded by a servo motor, the loading force will not be transmitted to the entire bottom of the pile instantaneously and uniformly, but will propagate gradually in the form of "stress waves". The stress wave velocity c directly determines the speed of stress transmission in the soil, providing a theoretical basis for stress propagation analysis in subsequent loading tests. After establishing the wave equation, we proceed to the boundary and initial condition setting stage. Considering that the pile top may be subjected to two common loading methods in the experiment, namely servo motor loading or pile hammer impact, we set the change law of pile top displacement with time to conform to equation (6). In the formula, ω is the vibration frequency of the pile top. Here, the vibration of the pile top is simplified to be input in the form of a simple harmonic wave with frequency ω. For the pile bottom, it is usually regarded as a free end, that is, there is no external force constraint at the bottom of the soil and the stress at the bottom of the pile is 0, which satisfies formula (7). ; The general solution of the one-dimensional wave equation is given by equation (8). In this formula, waves usually exist simultaneously in the system along the +x direction and the -x direction. Considering the specific working conditions of pile top loading and pile bottom free in this experiment, the main propagation direction of the stress wave is the downward +x direction, from which we can obtain formula (9). , where c is the wave speed, representing the rate of change of the wave in space. Substituting equation (9) into equation (2), equation (10) can be derived. In actual experimental monitoring, the stress response at a certain point in the soil over time can be approximated by equation (11). The function can be used to plot a sinusoidal response curve of stress over time. The phase lag in the curve increases linearly with depth, which intuitively reflects the hysteresis effect of the soil on the loading force and provides a reference for the analysis and verification of experimental data. In actual dynamic loading environments, the motion state of piles is quite complex. They not only vibrate up and down, but are also affected by soil damping, restoring force and nonlinear deformation. Based on the mechanical model of the mass, damping and stiffness system, a general form of vibration equation is established as shown in equation (12). In the formula, m is the equivalent mass, that is, the mass of the pile and its adjacent soil that participate in the vibration, c is the pile-soil damping coefficient, k0 is the linear stiffness, γ is the nonlinear correction coefficient, and F0sin(ωt) is the external periodic load. Under steady-state conditions, assuming the solution to the vibration equation is u(t) = Usin(ωt-φ), substituting it into equation (12) and separating the real and imaginary parts, we can obtain the amplitude equation as shown in equation (13). Further derivation yields equation (14) corresponding to the amplitude-frequency curve. By nonlinearly correcting the vibration equation, the dynamic characteristics of the pile body during actual loading can be captured more accurately, improving the simulation test's fidelity to the real engineering scenario and providing theoretical support for the subsequent optimization of loading parameters. To accurately describe the pile sinking speed v pile The influence of soil displacement reaction force is determined by an empirical nonlinear relationship, as shown in equation (15). Assuming that the relevant parameters meet certain conditions, we substitute them into the vibration equation to obtain equation (16). By linearizing equation (16) and solving for the steady-state solution, equation (17) corresponding to the pile displacement time history curve can be obtained. In the formula, ζ is the damping ratio, and ω n ω is the system's natural frequency, and ω_d is the damped vibration frequency; The displacement-time history curve clearly shows the decay trend of the pile displacement over time in the initial stage of loading. By fitting the curve with the actual data collected during the test, the damping coefficient and equivalent stiffness of the system can be deduced. In the servo system control process, this curve can serve as an important basis for calculating the target displacement reference trajectory, providing the PID controller with accurate target path input, and ensuring the stability and accuracy of the loading process. In the actual test control process, in order to effectively eliminate the deviation caused by external disturbances and system nonlinear factors, this simulation test device adopts PID feedback control law, the expression of which is equation (18). The system closed-loop error transfer function is shown in equation (19). In the formula, G(s) is the transfer function of the servo loading system and H(s) is the transfer function of the PID controller. Within the time domain, the system error convergence curve conforms to a specific law, indicating that the system error will decrease exponentially with time, and the convergence speed is proportional to the proportional gain Kp and negatively correlated with the damping ratio ξ. Through actual testing, it was verified that when the PID controller parameters were set to Kp=1.8, Ki=0.4, and Kd=0.02, the system could reach steady state within 2 seconds, and the loading error was controlled within 3%, meeting the experimental requirements for loading accuracy. The above complete model, from the establishment of the wave equation to the analysis of nonlinear vibration response and then to the servo closed-loop control, constructed a comprehensive mathematical description of the pile-soil-control system, providing a complete theoretical system for multi-mode, high-precision vertical loading control.

[0026] A loading device for multi-mode model tests in geotechnical engineering includes: The base 9 serves as the supporting foundation for the entire loading device, and its structural design directly affects the stability of the device and the reliability of the test. Multiple sets of standardized holes are pre-drilled on the base 9, allowing for quick connection with model box platforms of different specifications via quick-release bolts during the test installation phase. During installation, it is crucial to ensure a secure connection between the base 9 and the model box platform to prevent additional vibrations during loading due to loose connections, which could affect the accuracy of the test data. Simultaneously, the tightening torque of the quick-release bolts should be adjusted appropriately according to the specific dimensions of the model box platform to ensure uniform stress on the base 9, laying a solid foundation for the smooth installation of subsequent components and the successful conduct of the test. The drive unit 8 is the power core of the loading device, mainly composed of a servo motor 19, a reducer 20, an output shaft 21, an integrated end cover 22, a gear set 10, a sprocket 11, a closed-loop chain 12, and a transmission block 15. Its power transmission path is as follows: After the servo motor 19 starts, the output power is reduced and amplified by the reducer 20, and then transmitted to the gear set 10 through the output shaft 21. The gear set 10 meshes with the sprocket 11, driving the sprocket 11 to rotate. The closed-loop chain 12 is wound between the upper and lower sets of sprockets 11. As the sprockets 11 rotate, the closed-loop chain 12 moves synchronously, thereby driving the transmission blocks 15 fixed at both ends of the chain to move. The transmission blocks 15 are connected to the loading plate 16, ultimately driving the loading plate 16. The integrated end cover 22 integrates an encoder interface and a fan cooling system. The encoder interface is used to monitor the speed and rotation angle of the servo motor 19 in real time, and then calculate the displacement data of the loading plate 16 to ensure the accuracy of the displacement monitoring data. This data can be directly used for parameter calibration of wave equation and vibration equation. The fan cooling system can continuously dissipate heat during the operation of the servo motor 19, avoid the motor from being affected by excessively high operating temperature for a long time, and ensure the stable operation of the drive device 8. The guiding mechanism mainly consists of linear guide rails 13 on both sides of the loading plate 16 and sliders 14. Its core function is to ensure that the loading plate 16 moves only in the vertical direction, ensuring that the displacement data during loading conforms to the vertical displacement assumption of u(x,t). The linear guide rails 13 are symmetrically arranged on both sides of the loading plate 16, and the preload between the guide rails 13 and the sliders 14 can be adjusted according to the test requirements. During installation, the parallelism and perpendicularity of the guide rails 13 on both sides must be ensured to avoid jamming or offset of the loading plate 16 during movement due to guide rail installation deviation. When the driving device 8 drives the loading plate 16 to move, the sliders 14 move linearly along the guide rails 13, accurately guiding the movement direction of the loading plate 16, effectively limiting the horizontal displacement of the loading plate 16, ensuring that the loading force can be completely transmitted vertically to the loading component, and improving the accuracy and reliability of the loading test. The loading assembly is a key component for realizing the transmission of loading force and the switching of loading modes. It consists of a force gauge 3, an adjustable diameter coupling 4, a sleeve-type connecting rod 5, and a modular loading end 6. Its force transmission path is as follows: after receiving the power transmitted by the driving device 8, the loading plate 16 transmits the loading force to the force gauge 3. The force gauge 3 collects the loading force in real time. Then, the loading force is transmitted to the sleeve-type connecting rod 5 through the adjustable diameter coupling 4. The connecting rod 5 transmits the loading force to the modular loading end 6. Finally, the loading end 6 acts on the foundation structure 7. The lower end of the foundation structure 7 is placed in the test packing to realize the loading of the test object. The adjustable diameter coupling 4 has internally adjustable jaws and clamping screws. Test personnel can adjust the opening and closing degree of the jaws using an Allen wrench, thereby adjusting the clamping diameter to accommodate sleeve-type connecting rods 5 with different outer diameters. This solves the problems of fixed dimensions and poor adaptability in traditional coupling structures. Simultaneously, a foundation structure 7 is provided at the stable force transmission end to meet the force transmission conditions required for stress wave propagation. The sleeve-type connecting rod 5 adopts a telescopic structure design, with internal positioning pins and a rotating locking device. Test personnel can adjust the length of the connecting rod 5 according to the model height, ensuring that when the lower end of the foundation structure 7 is placed in the test packing, the loading end 6 can effectively connect with the foundation structure 7. The modular loading end 6 is connected to the connecting rod 5 by a thread, and the replacement time is no more than 5 minutes, making the operation convenient and efficient. The loading end 6 can be selectively replaced with a pressure plate type, anchor clamp type, or pile cap sleeve type according to the test requirements. The compatible foundation structures 7 include model piles, model anchors, and underground pipe gallery models. Different end forms can simulate the stress state of foundation structures 7 such as piles and anchors, ensuring the applicability of the wave equation and vibration equation of the pile-soil system under different test objects, and significantly improving the test adaptability and operation efficiency of the loading device. The mechanical data acquisition module mainly consists of a force gauge 3 and a displacement sensor. Its core function is to acquire loading force and axial displacement data in real time during the loading process. The force gauge 3 is connected to the loading plate 16 and the adjustable diameter coupling 4. During the loading force transmission process, it monitors the magnitude of the loading force in real time and transmits the data to the control cabinet 2. The displacement sensor is installed on the guide mechanism or loading assembly and acquires the axial displacement data of the loading plate 16 and the foundation structure 7 in real time, which is also transmitted to the control cabinet 2. The acquired data can be directly used to calculate σ(x,t) and u(t), providing measured data support for the verification and correction of wave equations and vibration equations. It also provides a basis for error analysis of PID feedback control, ensuring that the loading process can be adjusted in real time according to actual data and guaranteeing loading accuracy. The limit protection mechanism is based on the linear guide rail 13, with photoelectric sensors 18 and rubber buffer pads installed at both ends of the guide rail 13's travel. The photoelectric sensors 18 are electrically connected to the control cabinet 2. When the loading component approaches the limit travel of the guide rail 13 during movement, the photoelectric sensors 18 will trigger a stop command and transmit the command to the control cabinet 2. The control cabinet 2 will immediately cut off the drive signal of the servo motor 19, causing the loading component to stop moving. This prevents the displacement from exceeding the effective calculation range of the wave equation and vibration equation during loading, ensuring the validity of the test data. At the same time, the rubber buffer pads can absorb impact energy when the loading component accidentally touches the guide rail 13, preventing rigid collisions between the loading component and the end of the guide rail 13, protecting the device structure from damage, and improving the safety and service life of the loading device. Control cabinet 2 is the core of the loading device. On one hand, it receives data such as loading force and displacement transmitted from the mechanical acquisition module, analyzes and processes the data through its built-in control program, and generates control commands using a PID feedback control algorithm, sending them to the drive device 8 to achieve real-time closed-loop control of the loading process. On the other hand, control cabinet 2 establishes a communication connection with the host computer 1. Test personnel can set loading parameters through the host computer 1, including loading mode, loading amplitude, loading frequency, and loading duration. The host computer 1 also has a real-time loading curve display function, allowing test personnel to intuitively understand the force-displacement relationship during the loading process, promptly detect abnormalities, and intervene. After the test, the host computer 1 automatically saves the test data, including loading and displacement curves and system operation data, providing complete data support for the generation of subsequent test reports and the analysis of test results. The drive unit 8, guide mechanism, and loading components all adopt a modular design. The components are connected by standardized bolts, enabling independent disassembly and maintenance. When a component malfunctions or needs to be replaced, the test personnel can disassemble the component for repair or replacement without disassembling the entire device. The replacement time for a single component does not exceed 30 minutes, which significantly improves the maintenance efficiency of the device and reduces maintenance costs. At the same time, the modular design also facilitates the calibration of the equipment. Each module can be calibrated separately before the test to ensure the measurement accuracy of parameters such as loading force, displacement, and velocity, ensuring the repeatability of data from different test batches and improving the reliability and credibility of the test results.

[0027] The present invention and its embodiments have been described above. This description is not restrictive, and the accompanying drawings are only one embodiment of the present invention; the actual structure is not limited thereto. In conclusion, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the invention, such designs should fall within the protection scope of the present invention.

Claims

1. A multi-mode simulation design method for geotechnical engineering, characterized in that, Includes the following steps: S1 Pile-Soil System Wave Equation Establishment: Assuming the soil is a homogeneous, isotropic elastic medium, and the pile is loaded vertically, according to Newton's second law, the small element of the soil at depth x satisfies the following under the condition of force equilibrium: Equation (1) In the formula, ρ is the soil density, A is the cross-sectional area of ​​the soil micro-unit, and f(x,t) is the external load density. After further simplification, we get: Formula (2). In a one-dimensional elastic body, we have: Equation (3) Substituting equation (3) into equation (2) yields equation (4). If external forces are ignored, that is, when f(x,t)=0, equation (4) can be simplified to: equation (5) In the formula The essence of this equation is: when the pile sinks into the soil, the disturbance of the pile to the soil propagates in the soil in the form of waves. That is, when the pile hammer hits or servo loads, the force is not transmitted to the entire bottom of the pile instantaneously and uniformly, but gradually propagates as "stress waves". The wave velocity c determines the speed of stress transmission in the soil. S2 Boundary and Initial Condition Settings: Considering that the pile top is loaded by a servo motor or impacted by a pile hammer, its displacement changes with time as follows: Equation (6) In the formula, The frequency of pile top vibration is used here, which is simplified to frequency. The input is in the form of a simple harmonic wave. The bottom of the pile is usually a free end, that is, there is no external force constraint at the bottom of the soil. The stress at the bottom of the pile is 0, that is: Equation (7). The general solution of the one-dimensional wave equation is: Equation (8) In equation (8), it is generally assumed that there is a wave propagating in the +x direction and a wave propagating in the -x direction in the system at the same time. Under the condition of pile top loading and pile bottom free, the main propagation direction is the downward wave (+x direction), so we can get: equation (9). ,in, , where is the wave speed, and represents the rate of change of the wave in space. Substituting equation (9) into equation (2), we get: equation (10). In actual monitoring, the stress response at a certain point in the soil changes with time as approximated by: Equation (11) The function yields a sinusoidal response curve of stress over time, with its phase lag increasing linearly with depth, reflecting the hysteresis effect of the soil on loading. S3 Vibration Equation Nonlinear Correction: Under actual dynamic loading, the pile not only vibrates up and down, but is also affected by soil damping, restoring force and nonlinear deformation. Starting from the mass-damping-stiffness system, the general form of the vibration equation is: Equation (12). In the formula, m is the equivalent mass, i.e., the mass of the pile and its adjacent soil participating in the vibration; c is the pile-soil damping coefficient; k0 is the linear stiffness; and γ is the nonlinear correction coefficient. Given an external periodic load, under steady-state conditions, the solution is assumed to be... Substituting into equation (12) and separating the real and imaginary parts, we obtain the amplitude equation: equation (13). Furthermore, the amplitude-frequency curve is obtained: Equation (14) ; S4 Soil Displacement Reaction Force and Displacement Response Curve: To describe the influence of the pile sinking velocity vpile on the reaction force, an empirical nonlinear relationship is introduced, Equation (15). Assuming Substituting into the vibration equation: Equation (16) By linearizing it and finding the steady-state solution, the time history curve of the pile displacement can be obtained: Equation (17) In the formula, , is the damping ratio. , is the system's inherent frequency. The damping vibration frequency is represented by this curve, which describes the displacement decay trend of the pile body over time during the initial loading stage. By fitting it with experimental data, the system damping and equivalent stiffness can be deduced. In servo system control, this curve is used to calculate the reference trajectory of the target displacement, providing the target path input for the PID controller. S5PID feedback regulation and error convergence curve: In actual control, in order to eliminate external disturbances and nonlinear deviations, this device adopts PID feedback control law: Equation (18) The system closed-loop error transfer function is: Equation (19) In the formula, G(s) is the transfer function of the servo loading system, and H(s) is the transfer function of the PID controller. In the time domain, its error convergence curve is: S6 This indicates that the system error decays exponentially with time, and the convergence speed is proportional to the proportional gain Kp and negatively correlated with the damping ratio ξ. Actual tests show that when Kp=1.8, Ki=0.4, and Kd=0.02, the system reaches steady state within 2 seconds, with a loading error of less than 3%. The above model, from wave propagation to nonlinear vibration response and then to servo closed-loop control, constitutes a complete mathematical description of the pile-soil-control system. By characterizing the stress propagation law through the wave equation and capturing the nonlinear dynamic characteristics through the vibration equation, combined with the PID algorithm, adaptive adjustment of loading accuracy and stability is achieved, thus realizing multi-mode, high-precision vertical loading control.

2. A loading device for multi-mode model tests in geotechnical engineering, characterized in that, include: The base (9) is used to support the entire loading device. It has multiple sets of holes that can be connected to model box platforms of different specifications by quick-release bolts. The drive device (8) includes a servo motor (19), a reducer (20), an output shaft (21), and an integrated end cover (22). The servo motor (19) drives the gear set (10) to rotate sequentially through the reducer (20) and the output shaft (21). The gear set (10) is meshed with a sprocket (11). The integrated end cover (22) integrates an encoder interface and a fan cooling system. The encoder interface is used to monitor displacement accuracy and ensure that the displacement monitoring data can be used for parameter calibration of the wave equation and vibration equation. The guiding mechanism includes linear guide rails (13) and sliders (14) on both sides of the loading plate (16). The guide rails (13) are symmetrically arranged on both sides of the loading plate (16). The preload between the guide rails (13) and the sliders (14) is adjustable to restrict the loading plate (16) to move only in the vertical direction, ensuring that the displacement data during loading conforms to the vertical displacement assumption of u(x,t). The loading assembly includes a force gauge (3), an adjustable diameter coupling (4), a sleeve-type connecting rod (5), and a modular loading end (6). One end of the force gauge (3) is connected to the loading plate (16), and the other end is connected to the connecting rod (5) through the adjustable diameter coupling (4). The adjustable diameter coupling (4) is equipped with a hinged jaw and a clamping screw. The clamping diameter can be adjusted by an Allen wrench to adapt to connecting rods (5) with different outer diameters. At the same time, the loading force stable transmission end is equipped with a foundation structure (7) to fully load the load. The force transmission conditions required for stress wave propagation are met. The connecting rod (5) is a telescopic structure with a positioning pin and a rotating locking device inside. Its lower end is connected to the loading end (6) by a thread. The length can be adjusted according to the model height to ensure effective docking between the loading end (6) and the foundation structure (7) when the lower end of the foundation structure (7) is placed in the test filling material. The loading end (6) can be selectively replaced with a pressure plate type, an anchor clamp type or a pile cap sleeve type to adapt to different types of foundation structures (7) and ensure the diversity of pile-soil interaction tests. The mechanical acquisition module includes a force gauge (3) and a displacement sensor, which are used to collect loading force and axial displacement data in real time. The data transmission is set in a control cabinet (2). The collected data can be directly used for the calculation of σ(x,t) and u(t) and error analysis of PID feedback control. The limit protection mechanism includes a guide rail (13). The guide rail (13) is equipped with photoelectric sensors (18) and rubber buffer pads at both ends of its stroke. When the loading component approaches the limit stroke, the photoelectric sensor (18) triggers a stop command to prevent the displacement from exceeding the effective calculation range of the wave equation and vibration equation during the loading process, thus ensuring the safety of the test and the validity of the data.

3. The loading device for multi-mode model tests in geotechnical engineering according to claim 2, characterized in that, The power transmission path of the drive device (8) includes a servo motor (19), a reducer (20), an output shaft (21), a gear set (10), a sprocket (11), a closed-loop chain (12), a transmission block (15), and a loading plate (16). The closed-loop chain (12) is wound between the upper and lower sets of sprockets (11), and the transmission block (15) is fixed at both ends of the chain and connected to the loading plate (16).

4. The loading device for multi-mode model tests in geotechnical engineering according to claim 3, characterized in that, The force transmission path of the loading component includes a loading plate (16), a force gauge (3), an adjustable diameter coupling (4), a connecting rod (5), a loading end (6), and a base structure (7). The lower end of the base structure (7) is placed in the test packing. The loading force data collected by the force gauge (3) is used as the feedback input for PID closed-loop control.

5. The loading device for multi-mode model tests in geotechnical engineering according to claim 4, characterized in that, The modular loading end (6) is threadedly connected to the connecting rod (5), and the replacement time is no more than 5 minutes. The adapted foundation structure (7) includes model piles, model anchors and underground pipe gallery models. Different end forms can simulate the stress state of foundation structures (7) such as piles and anchors respectively, ensuring the applicability of the wave equation and vibration equation of the pile-soil system under different test objects.

6. The loading device for multi-mode model tests in geotechnical engineering according to claim 2, characterized in that, The photoelectric sensor (18) of the limit protection mechanism is electrically connected to the control cabinet (2). When the loading component triggers the photoelectric sensor (18), the control cabinet (2) immediately cuts off the drive signal of the servo motor (19). At the same time, the rubber buffer pad is used to absorb the impact energy to avoid structural damage.

7. The loading device for multi-mode model tests in geotechnical engineering according to claim 2, characterized in that, The drive device (8), guide mechanism and loading components are all modularly designed. Each component is connected by bolts and can be disassembled and maintained independently. The replacement time for a single component does not exceed 30 minutes. The modular design facilitates equipment calibration, ensures the measurement accuracy of the required loading force, displacement, speed and other parameters, and guarantees the repeatability of test data.

8. The loading device for multi-mode model tests in geotechnical engineering according to claim 6, characterized in that, The control cabinet (2) is connected to a host computer (1) for communication. The host computer (1) can set loading parameters, display loading curves in real time, and save test data. The loading parameters include loading mode, loading amplitude, loading frequency, and loading duration.

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