Unsaturated frozen soil roadbed effective stress simulation test system and method

Abstract

The invention discloses an unsaturated frozen soil roadbed effective stress simulation test system and method, and belongs to the technical field of frozen soil engineering. The system comprises a multi-field coupling environment box, a three-dimensional loading system, a multi-parameter sensing array, a high-frequency pulse ultrasonic imaging module and a data fusion and processing platform. The environment box simulates a temperature-humidity-force-ice crystal coupling environment, the loading system applies various loads, the sensing array monitors multiple parameters of a soil body, the imaging module monitors ice crystals and a soil body structure, and the data platform realizes data processing and model updating. The method comprises the steps of preparing a soil sample embedded sensor, performing multi-field coupling loading, calculating effective stress and inverting related parameters, evaluating damage and predicting the service life based on a specific algorithm and the like. The frozen soil roadbed service environment can be truly reproduced, the ice pressure can be directly measured, the model parameters can be dynamically updated, the service life can be accurately predicted, a reliable basis is provided for cold region engineering research, design and preventive maintenance, and the freezing injury risk is effectively reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of frozen soil engineering, and in particular to a system and method for simulating and testing effective stress of an unsaturated frozen soil roadbed. Background Art

[0002] In cold-region engineering construction, the stability of frozen soil roadbeds is a critical factor in ensuring project safety and long-term operation. The unique properties of frozen soil cause complex changes in mechanical properties due to the coupled effects of multiple factors, including temperature, humidity, load, and ice crystal phase transitions. Traditional testing methods struggle to fully and accurately simulate these multi-field coupled environments, particularly for monitoring the dynamic stresses generated during ice crystal growth. For example, existing ice pressure measurements often rely on indirect inferences, resulting in errors as high as 22%, which cannot meet the requirements of high-precision research and engineering applications. Furthermore, traditional methods suffer from poor data synchronization accuracy, reaching only ±1.2 seconds, making it difficult to capture subtle changes in soil response under multi-field coupling. Furthermore, experimental cycles often last over 72 hours, resulting in low efficiency and difficulty in providing effective and rapid basis for engineering decision-making. Therefore, the development of a system and method that can accurately simulate multi-field coupled environments, achieve high-precision measurements, and conduct rapid testing is urgently needed. Summary of the Invention

[0003] The purpose of the present invention is to provide an effective stress simulation test system and method for unsaturated frozen soil roadbed, which solves the problems of difficulty in synchronously simulating multi-field coupling environments, especially dynamic stress monitoring of ice crystal growth processes; low data synchronization accuracy; and long experimental cycle.

[0004] To achieve the above-mentioned object, the present invention provides an unsaturated frozen soil roadbed effective stress simulation test system, comprising:

[0005] Multi-field coupled environmental chamber, integrating temperature control unit, humidity control module and cavity structure, is used to simulate the temperature-humidity-force-ice crystal coupled environment of frozen soil roadbed;

[0006] Three-dimensional loading system, including axial loading unit, dynamic loading module and lateral restraint unit, used to apply static load, dynamic load and confining pressure;

[0007] A multi-parameter sensing array, including distributed fiber Bragg grating sensors, piezoelectric ice pressure sensors, and dielectric moisture sensors, is used to monitor soil temperature, strain, unfrozen water content, and ice pressure in real time;

[0008] High-frequency pulsed ultrasonic imaging module for non-invasive monitoring of ice crystal distribution and soil structure evolution;

[0009] The data fusion and processing platform realizes the synchronous collection, fusion analysis and dynamic update of multi-source data.

[0010] Preferably, the temperature control unit includes a Peltier semiconductor chip array, a liquid nitrogen-assisted cooling system, and a PID temperature controller, achieving bidirectional temperature control between -30°C and 30°C with an accuracy of ±0.1°C.

[0011] Preferably, the humidity control module realizes 0-500kPa suction control and water supply through microporous ceramic plates, high-precision vacuum pumps and peristaltic pumps, and supports dynamic adjustment of the unfrozen water content of frozen soil.

[0012] Preferably, the three-dimensional loading system includes a drive system of a servo motor and a hydraulic vibrator, which is used to apply a static load of 0 to 15 kN and a dynamic load of 0.1 to 50 Hz, and the lateral constraint is achieved by a flexible latex airbag to achieve 0 to 200 kPa confining pressure control.

[0013] Preferably, the multi-parameter sensing array adopts a spiral fiber Bragg grating arrangement, embedded ice pressure sensors at predicted positions, and regular triangle TDR probe distribution to achieve three-dimensional monitoring of soil parameters.

[0014] Preferably, the high-frequency pulse ultrasonic imaging module includes a 64-channel probe array and a three-dimensional imaging algorithm based on inverse Radon transform, which is used to reconstruct ice crystal distribution tomographic images with a resolution of millimeter level.

[0015] Preferably, the data fusion and processing platform adopts FPGA hardware synchronization mechanism and dynamic time warping algorithm to achieve nanosecond-level alignment of multi-source data, and dynamically updates the constitutive model parameters through particle swarm algorithm.

[0016] The present invention also provides a method for simulating and testing effective stress of an unsaturated frozen soil roadbed, comprising the following steps:

[0017] The following steps are involved:

[0018] S1, prepare unsaturated soil samples and embed sensor arrays;

[0019] S2, freeze-thaw cycle loading is performed using a multi-field coupled environmental chamber, with simultaneous monitoring of temperature, humidity, load, and ice crystal growth;

[0020] S3, using the improved Bishop model to calculate effective stress, combined with ultrasonic imaging to invert ice crystal distribution and ice pressure;

[0021] S4. Damage assessment and life prediction based on LSTM neural network and extended Paris formula.

[0022] Preferably, the effective stress calculation formula is specifically as follows:

[0023] σ′=σ total -u a +χ(u a -u w)+βσ ice ;

[0024] in, β=1-exp(-2.3θ ice ), dynamically update parameters through real-time data.

[0025] Preferably, the life prediction method analyzes the crack length by wavelet energy spectrum and calculates the remaining fatigue life based on the extended Paris formula integral, which is expressed as:

[0026]

[0027] in, D c =0.5 is the critical damage threshold.

[0028] Therefore, the present invention adopts a non-saturated frozen soil roadbed effective stress simulation test system and method of the above structure, which has the following beneficial effects:

[0029] (1) It achieves a true and comprehensive reproduction of the service environment of frozen soil roadbed, providing an extremely reliable testing platform for research and practice in the field of cold region engineering, and helps to gain a deeper understanding of the mechanical behavior and stability change laws of frozen soil roadbed under the action of multi-field coupling.

[0030] (2) The direct ice pressure measurement technology breaks through the limitations of traditional indirect calculations, greatly improving the accuracy of ice pressure measurement in cold region geotechnical research and providing more accurate data support for related theoretical research and engineering design.

[0031] The unique adaptive model engine can dynamically update the constitutive model parameters based on real-time collected data, making the prediction accuracy reach more than 95%, significantly improving the accuracy and reliability of the prediction of changes in the mechanical properties of frozen soil roadbed.

[0032] (3) By integrating LSTM and the Paris formula, the intelligent early warning system realizes the full-cycle life prediction from micro-damage to macro-destruction, providing a powerful tool for preventive maintenance and scientific decision-making of cold region projects. It can effectively reduce the risk of frost damage, extend the service life of engineering facilities, and have significant social and economic benefits.

[0033] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a structural schematic diagram of a system and method for simulating effective stress of unsaturated frozen soil roadbed according to the present invention;

[0035] Figure 2Schematic diagram of a multi-field coupling environmental chamber for a simulation test system and method for effective stress of unsaturated frozen soil roadbed according to the present invention;

[0036] Figure 3 A schematic diagram of a high-frequency pulse ultrasonic imaging module of a system and method for simulating and testing effective stress of an unsaturated frozen soil roadbed according to the present invention;

[0037] Figure 4 The present invention is a structural schematic diagram of an unsaturated frozen soil roadbed effective stress simulation test system and method. DETAILED DESCRIPTION

[0038] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments.

[0039] Unless otherwise defined, the technical or scientific terms used in the present invention shall have the usual meanings understood by persons of ordinary skill in the field to which the present invention belongs. The words "first", "second" and similar terms used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. Words such as "include" or "comprise" mean that the elements or objects preceding the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Words such as "connect" or "connected" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0040] Example

[0041] like Figure 1-4 As shown, the present invention provides an unsaturated frozen soil roadbed effective stress simulation test system, which is specifically as follows:

[0042] The multi-field coupled environmental chamber is highly integrated, utilizing semiconductor temperature control technology and a Peltier semiconductor chip array for bidirectional temperature control within a temperature range of -30°C to 30°C. For extreme low-temperature applications, a liquid nitrogen-assisted cooling system ensures the required low temperature is quickly and stably reached. For humidity control, a microporous ceramic plate with a pore size of 0.1μm covers the bottom of the specimen. Combined with a high-precision vacuum pump, it enables suction control from 0 to 500kPa. A water supply channel is also provided, with a peristaltic pump precisely controlling the water supply rate to simulate soil moisture migration under varying humidity conditions. The chamber features a double-layer stainless steel structure with a 50mm thick outer insulation layer filled with polyurethane foam to effectively reduce heat transfer and maintain a stable temperature within the chamber. A quartz transmission window is also provided to allow ultrasonic probe signals to penetrate, allowing the high-frequency pulsed ultrasonic imaging module to monitor ice crystal distribution and soil structural evolution, enabling in situ monitoring of ice pressure.

[0043] The three-dimensional loading system utilizes a unique hybrid drive design combining a servo motor and a hydraulic vibrator. The servo motor boasts powerful thrust, reaching a maximum of 10kN and a travel range of ±50mm. A ball screw drive mechanism enables high-precision axial loading with a repeatability of ±0.01mm. A force sensor with a range of 0 to 15kN and an accuracy of 0.1% FS provides accurate, real-time measurement of axial loading forces. The hydraulic vibrator generates dynamic loads with a frequency range of 0.1 to 50Hz and an amplitude of ±20mm. Combined with a waveform generator, it can generate a variety of waveforms, including sine, square, and random vibrations, to simulate the complex dynamic loads encountered in actual projects. Lateral restraint is achieved using flexible latex airbags. The inflation pressure ranges from 0 to 200kPa, precisely adjusted by a closed-loop pneumatic control system via a proportional valve to simulate the lateral confining pressure of soil in an actual roadbed. The system enables coordinated loading of static, dynamic, and confining loads, realistically simulating the actual stress conditions of a roadbed.

[0044] The multi-parameter sensing array is composed of a variety of advanced sensors. The distributed fiber Bragg grating sensor offers excellent strain and temperature measurement capabilities. Its fiber wavelength range is 1520 to 1570 nm and supports 16-channel multiplexing. The strain measurement range reaches ±5000 με with a resolution of 1 με; the temperature measurement range is -40°C to 80°C with a resolution of 0.1°C. The piezoelectric ice pressure sensor utilizes a Pb(Zr,Ti)O3 piezoelectric ceramic disc with a diameter of 10 mm and a thickness of 1 mm. It has a measurement range of 0 to 2 MPa, a sensitivity of up to 0.01 MPa, and a frequency response range of 0 to 10 kHz. The surface is gold-plated with electrodes and insulated, making it resistant to temperatures down to -50°C and capable of accurately measuring ice pressure. The TDR moisture probe (dielectric moisture sensor) is 100 mm long and employs a three-pin structure. It has a measurement range of 0 to 100% volume moisture content, a resolution of 0.1%, and an operating frequency of 1 GHz, effectively supporting the detection of unfrozen water content in frozen soil. These sensors work together to monitor key parameters such as soil temperature, strain, unfrozen water content and ice pressure in real time.

[0045] The high-frequency ultrasonic imaging module is equipped with a 64-channel ultrasonic probe array with a center frequency of 1 MHz and a bandwidth of 0.5 to 2 MHz. A high-voltage pulse generator outputs high-voltage pulses with a voltage of ±100 V and a pulse width of 50 ns, stimulating the ultrasonic probe to emit ultrasonic waves. A high-speed data acquisition card then rapidly acquires the reflected signals at a sampling rate of 100 MS / s and 12-bit resolution. The collected signals are processed using a 3D imaging algorithm based on an inverse Radon transform to achieve a 3D reconstruction of the ice crystal distribution, providing a clear and intuitive view of the ice crystal growth and distribution within the soil.

[0046] Data Platform: A synchronous acquisition system is built based on the advanced PXIe architecture. In terms of hardware, it uses the NIPXIe-8861 controller, equipped with a Xeon 8-core processor and FPGA co-processing, and has powerful data processing capabilities. The multi-channel synchronous acquisition card uses a 24-bit ADC with a sampling rate of 1MHz to ensure high-precision data acquisition. The real-time clock module complies with the IEEE1588 protocol, with a synchronization error of less than 1μs, ensuring precise synchronization of data acquisition across modules. On the software level, it supports LabVIEW real-time control programs, which can provide precise real-time control of modules such as temperature control, loading, and suction. It also integrates the Python data analysis framework and incorporates tools such as TensorFlow and COMSOL API to facilitate in-depth data analysis and numerical simulation. It also implements a three-dimensional visualization interface through OpenGL rendering, supports dynamic display of data such as ice crystal distribution, and facilitates intuitive observation and analysis of experimental results.

[0047] Sample preparation: Strictly adhered to the "Permafrost Testing Procedure." Qinghai-Tibet silty clay was selected as the test material, with a particle size distribution of 35% clay, 60% silt, and 5% sand. The soil sample was compacted layer by layer, with each layer controlled to 50 mm thick to achieve a target dry density of 1.75 g / cm³. The initial moisture content was precisely controlled at 18%, and sensors were embedded during the compaction process. Distributed fiber grating sensors were arranged in a spiral pattern, with a grating point every 20 mm along the sample height. Thermally conductive silicone was injected through a pre-embedded 2 mm outer diameter PVC conduit to fill the gaps, ensuring good contact between the sensor and the soil and preventing damage. Piezoelectric ice pressure sensors were embedded horizontally at depths of 30 mm and 60 mm, based on the predicted freezing front position using COMSOL pre-simulation of the temperature field. These sensors were placed horizontally at depths of 30 mm and 60 mm, ensuring direct contact with the soil and accurately measuring ice pressure. Three TDR moisture probes, arranged in an equilateral triangle (50 mm apart), were inserted vertically into the soil to ensure comprehensive and accurate soil moisture measurement.

[0048] Multi-field loading: The entire loading process is divided into two key phases: freezing and thawing. During the freezing phase (lasting from 0 to 24 hours), temperature control is first performed, slowly decreasing from room temperature to -15°C at a rate of 0.5°C / min. During this period, the PID temperature controller parameters are set to Kp = 120, Ki = 0.8, and Kd = 10 to ensure a steady temperature drop. After reaching -15°C, the constant temperature phase begins. During this phase, liquid nitrogen is used to compensate for heat loss and keep temperature fluctuations within <±0.2°C. For humidity control, a high-precision vacuum pump applies a suction force of 100 kPa to the soil sample through a microporous ceramic plate. TDR data is used to record changes in unfrozen water content every 5 minutes to monitor moisture migration. For mechanical loading, a servo motor applies a 50 kPa axial pressure (corresponding to a 10 kN force) to simulate static loading, and a hydraulic vibrator superimposes a 1 Hz sine wave (amplitude ±10 kPa) to simulate dynamic loading. During the melting phase (lasting 24 to 48 hours), the temperature was slowly raised to 5°C at a rate of 0.2°C / min to prevent structural damage to the soil due to thermal shock. The liquid nitrogen system was then shut down, and temperature control relied solely on the Peltier semiconductor chip. To control suction, the vacuum pump was depressurized to 10 kPa to simulate the drop in suction during the melting phase. A peristaltic pump was then activated to replenish water at a rate of 0.1 mL / min to prevent soil desiccation and cracking. Simultaneously, a distributed fiber Bragg grating sensor was used to measure the axial strain εz in real time (with an accuracy of 1 με), and a laser displacement meter was used to monitor surface settlement (with a range of ±20 mm and a resolution of 0.01 mm), comprehensively monitoring soil deformation during the melting process.

[0049] Data processing: During the data acquisition phase, an FPGA generates trigger pulses (rising edge trigger, 1μs pulse width). Each acquisition card uses the PXIe backplane clock as a reference to implement hardware synchronization, with a synchronization error of less than 10ns. Due to differences in response delays among different sensors, a dynamic time warping (DTW) algorithm is used for data alignment. This algorithm dynamically adjusts the data by calculating the similarity between time series.

[0050] Here, d(i, j) is the Euclidean distance between time series data points. This algorithm ensures accurate alignment of multi-source data in the temporal dimension, providing a reliable foundation for subsequent analysis. For effective stress calculation, a modified Bishop model is used.

[0051] In addition, an LSTM neural network is used to predict the probability of critical failure. The network structure uses a two-layer LSTM with a dropout layer in the middle to prevent overfitting. Finally, a fully connected output layer (sigmoid activation) outputs the critical failure probability for the next 30 minutes.

[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. An effective stress simulation test system for unsaturated frozen soil roadbed, characterized by: include: Multi-field coupled environmental chamber, integrating temperature control unit, humidity control module and cavity structure, is used to simulate the temperature-humidity-force-ice crystal coupled environment of frozen soil roadbed; Three-dimensional loading system, including axial loading unit, dynamic loading module and lateral restraint unit, used to apply static load, dynamic load and confining pressure; A multi-parameter sensing array, including distributed fiber Bragg grating sensors, piezoelectric ice pressure sensors, and dielectric moisture sensors, is used to monitor soil temperature, strain, unfrozen water content, and ice pressure in real time; High-frequency pulsed ultrasonic imaging module for non-invasive monitoring of ice crystal distribution and soil structure evolution; The data fusion and processing platform realizes the synchronous collection, fusion analysis and dynamic update of multi-source data.

2. The unsaturated frozen soil roadbed effective stress simulation test system according to claim 1, characterized in that: The temperature control unit includes a Peltier semiconductor chip array, a liquid nitrogen-assisted cooling system, and a PID temperature controller, achieving bidirectional temperature control from -30°C to 30°C with an accuracy of ±0.1°C.

3. The unsaturated frozen soil roadbed effective stress simulation test system according to claim 1, characterized in that: The humidity control module achieves 0-500kPa suction control and water supply through microporous ceramic plates, high-precision vacuum pumps and peristaltic pumps, supporting dynamic adjustment of the unfrozen water content in frozen soil.

4. The unsaturated frozen soil roadbed effective stress simulation test system according to claim 1, characterized in that: The three-dimensional loading system includes a drive system of servo motors and hydraulic vibrators, which is used to apply static loads of 0 to 15 kN and dynamic loads of 0.1 to 50 Hz. The lateral constraint is achieved by flexible latex airbags to achieve 0 to 200 kPa confining pressure control.

5. The unsaturated frozen soil roadbed effective stress simulation test system according to claim 1, characterized in that: The multi-parameter sensing array adopts a spiral fiber Bragg grating arrangement, embedded ice pressure sensors at predicted positions, and equilateral triangle TDR probe distribution to achieve three-dimensional monitoring of soil parameters.

6. The unsaturated frozen soil roadbed effective stress simulation test system according to claim 1, characterized in that: The high-frequency pulsed ultrasonic imaging module includes a 64-channel probe array and a three-dimensional imaging algorithm based on inverse Radon transform, which is used to reconstruct ice crystal distribution tomographic images with a resolution of millimeter level.

7. The unsaturated frozen soil roadbed effective stress simulation test system according to claim 1, characterized in that: The data fusion and processing platform adopts FPGA hardware synchronization mechanism and dynamic time warping algorithm to achieve nanosecond-level alignment of multi-source data, and dynamically updates the constitutive model parameters through particle swarm algorithm.

8. A method for simulating effective stress of an unsaturated frozen soil roadbed, applied to a system for simulating effective stress of an unsaturated frozen soil roadbed according to any one of claims 1 to 7, characterized in that: The following steps are involved: The following steps are involved: S1, prepare unsaturated soil samples and embed sensor arrays; S2, freeze-thaw cycle loading is performed using a multi-field coupled environmental chamber, with simultaneous monitoring of temperature, humidity, load, and ice crystal growth; S3, using the improved Bishop model to calculate effective stress, combined with ultrasonic imaging to invert ice crystal distribution and ice pressure; S4. Damage assessment and life prediction based on LSTM neural network and extended Paris formula.

9. The method for simulating effective stress of unsaturated frozen soil roadbed according to claim 8, characterized in that: The effective stress calculation formula is as follows: σ′=σ total -u a +x(u a -u w )+bs ice ; in, β=1-exp(-2.3θ ice ), dynamically update parameters through real-time data.

10. The unsaturated frozen soil roadbed effective stress simulation test system and method according to claim 8, characterized in that: The life prediction method analyzes the crack length through wavelet energy spectrum and calculates the remaining fatigue life based on the extended Paris formula integral. The expression is: in, D c =0.5 is the critical damage threshold.

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