A freeze-thaw and heavy load coupled large long slope scale model test method

Abstract

This invention provides a method for testing long and narrow slopes under freeze-thaw and heavy load coupling in the field of road engineering testing technology. The method includes the following steps: First, based on the geological data of the target road section, the proportion of similar materials is determined, and then a physical model of the roadbed and pavement on the long and narrow slope is prepared, along with a strain monitoring system. By setting the temperature and time parameters of the freeze-thaw cycle and different longitudinal slope conditions, and by simulating the application of periodic moving loads by simulated vehicles, heavy loads are simulated. During the test, freeze-thaw conditions and moving loads are applied alternately or simultaneously to simulate their coupling effect. Throughout the process, strain data from monitoring points are continuously collected, and the mechanical response and failure process of the model under different conditions are analyzed to obtain experimental results. The advantages of this invention are: it greatly improves the simulation accuracy and test controllability of the structural failure evolution law of long and narrow slope road sections under short-term freeze-thaw and heavy load coupling.

Description

Technical Field

[0001] This invention relates to the field of road engineering testing technology, and in particular to a method for testing a scaled-down model of a long slope coupled with freeze-thaw cycles and heavy loads. Background Technology

[0002] As the expressway network extends deeper into mountainous areas, long and steep slopes have become crucial nodes in mountain highway construction. In some provinces, due to the widespread mountainous terrain, roads are mostly constructed with long and steep slopes. These road sections not only bear significant gravitational loads and vehicle load shear stresses, but also experience short-term freeze-thaw cycles during winter or freezing rain. When heavy vehicles (such as fully loaded 6-axle trucks) travel on long and steep slopes, the continuous gripping force generated uphill and the forces generated downhill both have significant shear failure effects on the pavement and subgrade structure. At the same time, short-term freeze-thaw cycles lead to the deterioration of the engineering properties of the subgrade soil, especially the water-sensitive residual granite soil, further weakening the stability of the pavement structure. Under the coupled effect of heavy vehicle loads and freeze-thaw cycles, long and steep slopes are highly susceptible to cracks, subsidence, and slippage, and their failure modes and mechanisms are significantly more complex than those caused by a single factor.

[0003] Currently, scholars have conducted extensive research on highway freeze-thaw damage and vehicle load issues, but research on typical long and steep slopes in southern regions with short-term freeze-thaw cycles is still insufficient. Existing studies mostly focus on smooth road sections in permafrost or seasonally frozen areas, failing to fully reflect the combined effects of stress redistribution and freeze-thaw cycles caused by slope changes on long and steep slopes. More importantly, existing technologies lack effective experimental methods to systematically study the gradual evolution of road structures from microcrack initiation to macroscopic damage under the coupled effects of short-term freeze-thaw cycles and periodic heavy vehicle loads, using granite residual soil as the subgrade material. Directly conducting full-scale field tests is costly, time-consuming, and difficult to precisely control operating conditions, while conventional numerical simulation analysis has limitations in accurately reproducing complex physical-mechanical coupling processes.

[0004] Therefore, how to provide a scaled-down model test method for long and steep slopes coupled with freeze-thaw cycles and heavy loads, so as to improve the simulation accuracy and test controllability of the structural failure evolution law of long and steep slopes under short-term freeze-thaw cycles and heavy loads, has become an urgent technical problem to be solved. Summary of the Invention

[0005] The technical problem to be solved by this invention is to provide a scaled-down model test method for long and steep slopes coupled with freeze-thaw cycles and heavy loads, so as to improve the simulation accuracy and test controllability of the structural damage evolution law of long and steep slopes under short-term freeze-thaw cycles and heavy loads.

[0006] This invention is implemented as follows: a method for testing a scaled-down model of a long slope coupled with freeze-thaw cycles and heavy loads, comprising the following steps: Step S1: Determine the materials and proportions for the model test: Based on the engineering geological survey report of the target engineering section, calculate and determine the similar materials and their proportions used for model filling; Step S2: Prepare a physical model of a long slope: Determine the size of the model box according to the geometric similarity ratio, and fill and compact the similar subgrade soil in layers in the model box according to the similar materials and their proportions. Then, lay the pavement layer on the surface of the compacted subgrade soil to prepare a physical model of a long slope. Step S3: Deploy the monitoring system: Install resistance strain gauges and high-speed cameras on the physical model of the long slope, and connect the resistance strain gauges to the data acquisition equipment; Step S4: Determine freeze-thaw cycle conditions: Set the freeze-thaw conditions for simulating short-term freeze-thaw cycles, including freezing temperature, thawing temperature, duration of each temperature, and total number of cycles. Step S5: Determine the slope conditions for long slopes: Set at least two different longitudinal road slopes as comparative test conditions; Step S6: Determine the vehicle heavy load simulation scheme: Configure the simulated vehicle and drive system to apply periodic reciprocating moving loads on the physical model of the long slope to simulate the actual vehicle heavy load. Step S7: Perform a coupling test: On the physical model of the long slope, apply the frost heave and thaw settlement conditions and reciprocating moving loads sequentially or alternately to simulate the coupling effect of freeze-thaw and heavy load. Step S8, Data Acquisition and Processing: During the simulation of the coupling effect, strain data of the resistance strain gauge is continuously acquired through the data acquisition device, and video data of the damage formation and development process of the physical model of the long slope is recorded through the high-speed camera. Step S9: Analyze the test results: Based on the strain data and video data, analyze the mechanical response and failure process of the physical model of the long slope under different conditions to obtain the test results.

[0007] Furthermore, in step S1, the similar material is undisturbed residual granite soil with a natural moisture content ranging from 26.50% to 33.80% and a natural density ranging from 1.85 g / cm³ to 1.94 g / cm³.

[0008] Furthermore, in step S2, the paved road layer is a cement concrete road layer, an asphalt concrete road layer, or a composite road layer.

[0009] Furthermore, in step S3, the resistance strain gauges are arranged at the top, middle, and bottom of the slope along the preset trajectory line of the road surface layer in the physical model of the long slope, and each monitoring point includes a resistance strain gauge for measuring longitudinal strain, transverse strain, and vertical strain. The high-speed camera is positioned on one side of the viewing window of the model housing to record and film the entire experimental process, observing the formation and development of damage to the physical model of the long slope.

[0010] Furthermore, in step S4, the freeze-thaw conditions are set by the refrigeration unit, the heating unit, and the temperature controller, and the temperature can be adjusted between -20°C and +20°C for a duration of 0-24 hours.

[0011] Furthermore, in step S5, the longitudinal slope of the road is changed by a support base that supports continuous slope adjustment.

[0012] Furthermore, step S6 specifically includes: Based on the geometric similarity ratio and stress similarity principle, the counterweight mass of the simulated vehicle was calculated. Based on the aforementioned counterweight mass, a simulated vehicle supporting weight adjustment, track width adjustment, wheelbase adjustment, and wheel set number adjustment is configured; A drive system is configured to drive the simulated vehicle to reciprocate on a long slope physical model via a traction device, thereby applying periodic reciprocating moving loads to simulate the heavy load of an actual vehicle.

[0013] Furthermore, the drive system includes a speed-regulating motor and a controller; During the simulated uphill process, the controller controls the output power of the speed-regulating motor to decrease linearly to simulate the vehicle's deceleration during uphill driving.

[0014] Furthermore, step S7 specifically includes: For each type of road longitudinal slope physical model, the total number of freeze-thaw cycles is first performed, and then a set number of reciprocating moving loads are applied to the corresponding long slope physical model to simulate the coupling effect of freeze-thaw and heavy load.

[0015] Furthermore, in step S9, the analysis of the test results includes: The failure process, failure characteristics, and deformation properties of the physical model of the long slope were studied and analyzed. The failure mechanism of the physical model of the long slope under the coupling effect was revealed. The influence weight of each influencing factor was analyzed and determined. Reasonable prevention and control measures for extending the use of the physical model of the long slope under various coupling effects were proposed.

[0016] The advantages of this invention are: 1. By constructing an indoor scaled-down physical model, the original granite residual soil was first precisely selected and its state controlled according to the target engineering geology to simulate real roadbed materials. Then, at least two different longitudinal slopes of the road were set for comparison, and the temperature, time and number of short-term freeze-thaw cycles were precisely controlled. At the same time, a counterweight trolley configured according to the similarity principle and a programmable drive system were used to simulate periodic reciprocating moving loads. In this way, the two key environmental factors of "freeze-thaw" and "heavy load" were accurately, independently and repeatedly applied in the laboratory. By implementing a test sequence of first implementing a complete freeze-thaw cycle and then applying moving loads, the typical coupled failure process of freeze-thaw deterioration followed by heavy load in engineering was simulated. Finally, by using multi-directional strain gauges deployed along the top, middle and bottom of the slope for full-process monitoring, the entire process of stress redistribution, strain development and crack initiation and propagation under coupled action on long slope sections under specific geological conditions was realized through refined observation and pattern analysis, which significantly improved the realism of the simulation and the controllability of the test.

[0017] 2. Constructing a multi-factor coupled test system significantly enhances the engineering relevance and predictive accuracy of the test: Instead of studying the impact of freeze-thaw cycles or vehicle loads on the roadbed in isolation, coupled tests are conducted to apply freeze-thaw settlement conditions and reciprocating moving loads sequentially or alternately on the same long slope physical model. This actively simulates the synergistic and alternating effects of two severe conditions in reality: freeze-thaw cycles and heavy loads. This coupled simulation more realistically reproduces the actual complex stress and environmental conditions faced by the roadbed on long and steep slopes in the short-term frozen soil region of southern China. This allows the test results to more accurately reflect the mechanical response, damage accumulation, and failure process of the roadbed under real complex working conditions, thus providing more valuable experimental data for engineering design and maintenance.

[0018] 3. Employing highly realistic materials and construction methods to enhance the reliability and data validity of model tests: The model construction emphasizes accurate simulation of the prototype, directly using "undisturbed granite residual soil" with specific physical parameter ranges as the similar material, preserving the structural and engineering characteristics of the undisturbed soil to the greatest extent possible; the use of cement mortar to pave the road surface layer and perform curing simulates the actual road surface structure layer; this meticulous design of materials and construction from the subgrade soil to the road surface layer ensures the similarity of the physical model at the material level, making the model's deformation, cracking, and other responses under coupled loads closer to actual engineering, significantly improving the credibility and engineering reference value of the test data.

[0019] 4. Achieving refined, quantifiable control and multi-condition comparison of experimental conditions makes the research conclusions more systematic and scientific: Key experimental variables were precisely and repeatably controlled and designed; the specific temperature, time, and number of freeze-thaw cycles were clarified, making environmental simulation quantifiable and repeatable; at least three different road longitudinal slopes were set as comparative conditions, enabling a systematic study of the influence of slope, a key geometric parameter, on the roadbed coupling response; by calculating counterweights, using the drive system, and simulating uphill deceleration conditions, standardized and programmable application of vehicle loads was achieved; This refined control and multi-level design of the three major elements of freeze-thaw, slope, and load allows the experiment to derive more scientific and universal laws from single-variable comparisons and system combinations.

[0020] 5. Establish a comprehensive, multi-dimensional data acquisition and analysis framework from macroscopic and microscopic mechanical responses to macroscopic failure phenomena, deeply revealing the failure process and mechanism: The monitoring system not only deploys monitoring points at key locations such as the top, middle, and toe of the slope, but also measures the strain in the longitudinal, transverse, and vertical directions simultaneously at each monitoring point, enabling complete acquisition of the stress-strain state of the roadbed in three-dimensional space; the analysis content includes not only the "variation law" of stress and strain in each direction with loading, but also the "initiation and propagation process of pavement layer cracks". This analytical method, which combines the internal continuous mechanical response (strain data) with the external discontinuous failure phenomenon (crack development), can trace from macroscopic phenomena to microscopic mechanical mechanisms, fully revealing the entire chain process of damage accumulation to final failure of long and steep slope roadbeds under the coupling effect of "freeze-thaw-heavy load", providing a solid experimental basis for understanding the nature of failure and proposing prevention and control measures. Attached Figure Description

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0022] Figure 1 This is a flowchart of a long slope scaled-down model test method for freeze-thaw and heavy-load coupling according to the present invention.

[0023] Figure 2 This is a schematic diagram of the experimental apparatus of the present invention.

[0024] Marker explanation: 100-Test apparatus, 1-Model housing, 2-Freeze-thaw cycle system, 3-Slope adjustment system, 4-Vehicle loading simulation system, 5-Data acquisition system, 6-Road model, 21-Refrigeration unit, 22-Heating unit, 211 Nozzle, 41-Simulated vehicle, 42-Drive motor, 43-Traction rope, 51-Resistance strain gauge, 52-High-speed camera. Detailed Implementation

[0025] The technical solution in this application embodiment has the following general idea: Addressing the problem that existing technologies struggle to simulate the damage evolution process of long, steep road sections under the coupled effects of freeze-thaw cycles and heavy loads, an indoor scaled-down model test system is constructed. By using undisturbed granite residual soil and cement mortar to ensure material similarity, different slope conditions are set, freeze-thaw cycle parameters are precisely controlled, and a counterweight trolley is used to simulate periodic moving loads. Freeze-thaw cycles and loads are applied sequentially or alternately to the model to simulate their coupled effect. Finally, multi-directional strain gauges are deployed at the top, middle, and bottom of the slope for full-process monitoring, thereby systematically analyzing the mechanical response and crack development patterns of the roadbed under different slopes to reveal its failure mechanism, significantly improving the realism of the simulation and the controllability of the test, and providing a basis for engineering practice.

[0026] Please refer to Figures 1 to 2 As shown, the test device 100 of the present invention includes a model box 1, a freeze-thaw cycle system 2, a slope adjustment system 3, a vehicle loading simulation system 4, a data acquisition system 5, and a road model (physical model of a long slope) 6.

[0027] The model box 1 is a rectangular box with an open top. Its base plate supports the road model 6. At least one side is made of a transparent material (such as high-strength tempered glass or transparent acrylic sheet) to facilitate observation of the generation and propagation of cracks on the road model surface during the test. To meet the requirement of a geometric similarity ratio of 1:20, the internal net dimensions of the model box 1 are designed to be 1200mm in length, 500mm in width, and 380mm in height.

[0028] The freeze-thaw cycle system 2 is used to create a controllable low-temperature freezing and high-temperature thawing environment within the model chamber to simulate short-term freeze-thaw cycles. Specifically, it includes a refrigeration unit 21, a heating unit 22, and a temperature controller. The refrigeration unit 21 and the heating unit 22 are arranged on the inner wall of the model chamber 1 or connected to the interior of the chamber via air ducts. The temperature controller is electrically connected to the refrigeration unit 21 and the heating unit 22, respectively, and is used to precisely control the freezing temperature (e.g., -10℃), thawing temperature (e.g., +10℃), and the duration of each temperature (e.g., 12 hours each) within the chamber according to preset test conditions. It can also set the total number of cycles (e.g., 10 times). The refrigeration unit 21 is also equipped with spray nozzles 211 for spraying.

[0029] The slope adjustment system 4 supports the road model 6 and establishes a preset test slope in its longitudinal direction (length direction). This system preferably employs a support frame structure with one hinged end and the other end adjustable for height, for example, consisting of a fixed base, a movable platform, and a retractable electric push rod or screw jack. The model housing 1 is fixed to the movable platform. By adjusting the extension length of the electric push rod, the angle between the platform and the horizontal plane can be continuously and precisely changed, thereby setting the longitudinal slope of the road model 6, for example, 1%, 3%, and 7%.

[0030] The vehicle loading simulation system 4 is used to apply periodic reciprocating moving loads to the surface of the pre-formed road model 6 to simulate the heavy load of an actual vehicle. The system includes a simulated vehicle 41, a drive motor 42, and a traction rope 43. The simulated vehicle 41 is a counterweight trolley with rollers mounted on its bottom that can roll freely along the road surface. Its total mass is determined based on similarity principles, for example, 20 kg. The drive motor 42 is fixed to one end (top or bottom of the slope) longitudinally of the model box 1, and its output shaft is connected to a winch via a reducer. One end of the traction rope 43 is wound and fixed to the winch, and the other end is connected to the simulated vehicle 41. The traction rope 43 is electrically connected to the drive motor 42 and is used to control forward and reverse rotation, speed, and output torque. In a preferred embodiment of the invention, during the process of the simulated vehicle climbing a slope, the output power of the drive motor 42 is controlled to decrease linearly over time (e.g., from 80% to 50% of the rated power) to simulate the actual driving condition of a heavy-loaded vehicle gradually decelerating due to increased resistance during the climb.

[0031] The data acquisition system 5 is used to collect data from strain sensors installed inside the road model 6. This system includes a resistance strain gauge 51, a high-speed camera 52, a static strain gauge, and a computer. The resistance strain gauge is connected to the input channel of the static strain gauge via wires, and the data output terminal of the static strain gauge is connected to the computer. Data acquisition software pre-installed in the computer records, displays, and stores strain data from each strain gauge in real time. The high-speed camera 52 is positioned on one side of the viewing window of the model housing 1 to record and film the entire test process, observing the formation and development of damage in the road model 6.

[0032] A preferred embodiment of the present invention provides a method for testing a scaled-down model of a long slope coupled with freeze-thaw cycles and heavy loads, comprising the following steps: Step S1: Determine the materials and proportions for the model test: Based on the engineering geological survey report of the target engineering section, calculate and determine the similar materials and their proportions used for model filling; Step S2: Prepare a physical model of a long slope: Determine the size of the model box according to the geometric similarity ratio, and fill and compact the similar subgrade soil in layers in the model box according to the similar materials and their proportions. Then, lay the pavement layer on the surface of the compacted subgrade soil to prepare a physical model of a long slope. In practice, the size of the model box was determined by taking into account factors such as geometric similarity ratio, boundary effect and test operability. A geometric similarity ratio of 1:20 was adopted. The model box length of 1200mm corresponds to the prototype road length of 24m, and the width of 500mm corresponds to the prototype width of 10m. It basically covers the cross-sectional range of a two-way two-lane road and some road shoulders on both sides. The height of the box is 380mm.

[0033] Based on the engineering geological survey report, the soil mix ratio for the long slope model roadbed was calculated and determined. The roadbed filling adopted a layered compaction method, with the roadbed soil filled in three layers. Each layer had a loose thickness of approximately 60-70mm, and a compacted thickness of approximately 50-55mm. The total roadbed thickness after three compacted layers was 160mm-170mm. During each layer filling, the prepared wet soil was evenly spread in the model box, or after leveling the surface of the previously compacted soil layer, it was compacted with a 1kg tamping hammer 15 times / m². The tamping points were evenly distributed on the soil surface to ensure uniform compaction. After compaction, the soil surface was leveled with a scraper.

[0034] The road surface structure uses cement mortar. The cement used is P·O42.5 grade ordinary Portland cement, and the sand is medium-grade fly ash sand with a particle size range of 0.25-0.5mm. Distilled water is used for mixing. The mix ratio is determined by mass as cement:sand:water = 1:2:0.4, used to simulate the strength of C40 concrete pavement. The specific preparation process of the cement mortar is as follows: First, weigh each component material according to the mix ratio, dry mix the cement and sand evenly, then slowly add the mixing water, and continue stirring for 3-5 minutes until the mortar is uniform and free of lumps. After the mortar is mixed, immediately apply it to the shaped subgrade surface. When applying, use a trowel to spread the mortar evenly, controlling the pavement layer thickness to approximately 15-20mm. Smooth the surface with a scraper to ensure the pavement flatness meets the test requirements. After the pavement layer is applied, allow it to cure naturally at room temperature for 48 hours. Every 6 hours, spray water on the cement mortar pavement and cover the surface with plastic wrap to prevent drying shrinkage cracks caused by excessive moisture evaporation.

[0035] Step S3: Deploy the monitoring system: Install resistance strain gauges and high-speed cameras on the physical model of the long slope, and connect the resistance strain gauges to the data acquisition equipment; this is used to measure the stress and strain of the long slope under the coupled action of freeze-thaw cycles and heavy vehicle loads. Step S4: Determine freeze-thaw cycle conditions: Set the freeze-thaw conditions for simulating short-term freeze-thaw cycles, including freezing temperature, thawing temperature, duration of each temperature, and total number of cycles. Step S5: Determine the slope conditions for long slopes: Set at least two different longitudinal road slopes as comparative test conditions; Step S6: Determine the vehicle heavy load simulation scheme: Configure the simulated vehicle and drive system to apply periodic reciprocating moving loads on the physical model of the long slope to simulate the actual vehicle heavy load. Step S7: Perform a coupling test: On the physical model of the long slope, apply the frost heave and thaw settlement conditions and reciprocating moving loads sequentially or alternately to simulate the coupling effect of freeze-thaw and heavy load. Step S8, Data Acquisition and Processing: During the simulation of the coupling effect, strain data of the resistance strain gauge is continuously acquired through the data acquisition device, and video data of the damage formation and development process of the physical model of the long slope is recorded through the high-speed camera. Step S9: Analyze the test results: Based on the strain data and video data, analyze the mechanical response and failure process of the physical model of the long slope under different conditions to obtain the test results.

[0036] In step S1, the similar material is undisturbed residual granite soil with a natural moisture content ranging from 26.50% to 33.80% and a natural density ranging from 1.85 g / cm³ to 1.94 g / cm³.

[0037] In step S2, the paved road layer is a cement concrete road layer, an asphalt concrete road layer, or a composite road layer.

[0038] In practice, the subgrade soil uses undisturbed soil, and the parameters of the undisturbed soil are as follows:

[0039] In step S3, the resistance strain gauges are arranged at the top, middle and bottom of the slope along the preset trajectory line of the road surface layer in the physical model of the long slope, and each monitoring point contains a resistance strain gauge for measuring longitudinal strain, transverse strain and vertical strain. The high-speed camera is positioned on one side of the viewing window of the model housing to record and film the entire experimental process, observing the formation and development of damage to the physical model of the long slope.

[0040] In practical implementation, a resistance strain gauge of model BF120-3AA can be used, with wire grid dimensions (length × width) of 3 × 2 mm, resistance value of 120 ± 0.1 Ω, and sensitivity coefficient of 2.0 ± 1%. The resistance strain gauge is bonded to the road surface layer with 502 instant adhesive. Before bonding, the bonding area of ​​the road surface should be sanded and cleaned to ensure firm bonding and good contact.

[0041] The strain gauge arrangement is as follows: Along the right-hand wheel line of the road surface, a set of strain gauges is placed at three typical locations: the top, middle, and bottom of the slope. Each set contains three strain gauges, with two strain gauges perpendicular to each other. These perpendicular strain gauges measure the longitudinal strain E11 (along the driving direction) and the transverse strain E33 (in the road width direction), respectively. The remaining strain gauge measures the vertical stress. A total of nine strain gauges are used in the three sets, numbered S1-S9. The strain gauge lead wires extend from the side wall of the model box and connect to the uT7160 static strain gauge for data acquisition.

[0042] In step S4, the freeze-thaw conditions are set by the refrigeration unit, the heating unit, and the temperature controller. The temperature can be adjusted between -20°C and +20°C, and the duration is 0-24h.

[0043] In practice, under the conditions of frost heave and thaw settlement, the refrigeration device is turned on via the control panel to lower and stabilize the ambient temperature of the model to -10℃ as required for the test, and this is maintained for 12 hours to fully freeze the subgrade soil and pavement layer inside the model box. The heating device is then turned on to heat and stabilize the temperature to +10℃, and this is maintained for 12 hours to completely thaw the frozen soil, which constitutes one freeze-thaw cycle. Ten freeze-thaw cycles are repeated between -10℃ and +10℃ to simulate the freeze-thaw cycle environment.

[0044] In step S5, the longitudinal slope of the road is changed by a support base that supports continuous slope adjustment.

[0045] For the long slope, three slope conditions (1%, 3%, and 7%) are designed. After the roadbed filling is completed, the top surface of the roadbed is shaped to improve its slope. First, the roadbed surface is leveled and sloped at a 7% slope, and the slope accuracy is checked using a slope gauge to ensure that the longitudinal slope deviation is controlled within ±0.5%. The subsequent 3% and 1% slope conditions are achieved by surface excavation and adjustment on the original roadbed base. After adjustment, the pavement material is reapplied to ensure consistency of roadbed conditions across different slope conditions.

[0046] Step S6 specifically involves: Based on the geometric similarity ratio and stress similarity principle, the counterweight mass of the simulated vehicle was calculated. Based on the aforementioned counterweight mass, a simulated vehicle supporting weight adjustment, track width adjustment, wheelbase adjustment, and wheel set number adjustment is configured; A drive system is configured to drive the simulated vehicle to reciprocate on a long slope physical model via a traction device, thereby applying periodic reciprocating moving loads to simulate the heavy load of an actual vehicle.

[0047] In practice, a 20 kg simulated vehicle is used to perform reciprocating motion, simulating a 6-axle heavy-duty truck fully loaded with 49 tons. Tests are conducted under three gradient conditions: 1%, 3%, and 7%, with each gradient forming an independent test group. Each test group consists of 100 uphill cyclic loading cycles, with each complete uphill movement of the trolley counting as one loading cycle. A total of 300 cyclic loading tests are completed for the three gradients. Cyclic loading is achieved by the drive system, transmission mechanism, and counterweight trolley. The drive system uses two 25W small variable-speed motors mounted on a retractable gantry at both ends of the model box (top and bottom of the slope), with an output speed of approximately 108-67.5 r / min and an output torque of approximately 14 kg·cm, sufficient to meet the power requirements for traction of the counterweight trolley. An independent speed controller with a forward / reverse switch and speed adjustment knob controls the trolley's uphill and downhill movement. The transmission mechanism consists of a motor pulley and a nylon traction rope, with one end of the nylon rope fixed to the pulley and the other end connected to the counterweight trolley. When the motor rotates forward, the sheave winds the traction rope, driving the trolley upwards along the slope; when the motor rotates in reverse, the sheave releases the traction rope, and the trolley returns to the starting point along the slope. The counterweight trolley adopts a flatbed structure with rollers installed at the bottom, allowing it to roll freely on the road surface model to simulate the load of vehicle tires. The counterweight design is based on the "Highway Engineering Technical Standards" (JTGB01-2014), where a 6-axle heavy-duty truck can have a fully loaded total weight of 49 tons. Using a geometric similarity ratio of 1:20 and the stress similarity principle, the load is calculated using the following formula: ; ; ; in, Represents the geometric similarity ratio; Indicates the area similarity ratio; Indicates the load phase; Indicates the prototype dimensions; Indicates the model dimensions; Represents the area of ​​the prototype; Represents the area of ​​the model; Indicates the prototype load; This represents the model load.

[0048] Calculations show that the model load is approximately 20 kg. To simulate the deceleration characteristics of a vehicle traveling on a slope, the motor power was dynamically adjusted during the experiment. When the vehicle was moving uphill, the motor power linearly decreased from 80% of its rated power to 50% of its rated power to simulate the actual working condition of a vehicle gradually decelerating due to increased driving resistance during the uphill climb. During the downhill process, the controller switched the motor to reverse, and the vehicle returned to the starting position along the slope.

[0049] The drive system includes a speed-regulating motor and a controller; During the simulated uphill process, the controller controls the output power of the speed-regulating motor to decrease linearly to simulate the vehicle's deceleration during uphill driving.

[0050] Step S7 specifically involves: For each type of road longitudinal slope physical model, the total number of freeze-thaw cycles is first performed, and then a set number of reciprocating moving loads are applied to the corresponding long slope physical model to simulate the coupling effect of freeze-thaw and heavy load.

[0051] In step S9, the analysis of the test results includes: The failure process, failure characteristics, and deformation properties of the physical model of the long slope were studied and analyzed. The failure mechanism of the physical model of the long slope under the coupling effect was revealed. The influence weight of each influencing factor was analyzed and determined. Reasonable prevention and control measures for extending the use of the physical model of the long slope under various coupling effects were proposed.

[0052] In summary, the advantages of this invention are as follows: 1. By constructing an indoor scaled-down physical model, the original granite residual soil was first precisely selected and its state controlled according to the target engineering geology to simulate real roadbed materials. Then, at least two different longitudinal slopes of the road were set for comparison, and the temperature, time and number of short-term freeze-thaw cycles were precisely controlled. At the same time, a counterweight trolley configured according to the similarity principle and a programmable drive system were used to simulate periodic reciprocating moving loads. In this way, the two key environmental factors of "freeze-thaw" and "heavy load" were accurately, independently and repeatedly applied in the laboratory. By implementing a test sequence of first implementing a complete freeze-thaw cycle and then applying moving loads, the typical coupled failure process of freeze-thaw deterioration followed by heavy load in engineering was simulated. Finally, by using multi-directional strain gauges deployed along the top, middle and bottom of the slope for full-process monitoring, the entire process of stress redistribution, strain development and crack initiation and propagation under coupled action on long slope sections under specific geological conditions was realized through refined observation and pattern analysis, which significantly improved the realism of the simulation and the controllability of the test.

[0053] 2. Constructing a multi-factor coupled test system significantly enhances the engineering relevance and predictive accuracy of the test: Instead of studying the impact of freeze-thaw cycles or vehicle loads on the roadbed in isolation, coupled tests are conducted to apply freeze-thaw settlement conditions and reciprocating moving loads sequentially or alternately on the same long slope physical model. This actively simulates the synergistic and alternating effects of two severe conditions in reality: freeze-thaw cycles and heavy loads. This coupled simulation more realistically reproduces the actual complex stress and environmental conditions faced by the roadbed on long and steep slopes in the short-term frozen soil region of southern China. This allows the test results to more accurately reflect the mechanical response, damage accumulation, and failure process of the roadbed under real complex working conditions, thus providing more valuable experimental data for engineering design and maintenance.

[0054] 3. Employing highly realistic materials and construction methods to enhance the reliability and data validity of model tests: The model construction emphasizes accurate simulation of the prototype, directly using "undisturbed granite residual soil" with specific physical parameter ranges as the similar material, preserving the structural and engineering characteristics of the undisturbed soil to the greatest extent possible; the use of cement mortar to pave the road surface layer and perform curing simulates the actual road surface structure layer; this meticulous design of materials and construction from the subgrade soil to the road surface layer ensures the similarity of the physical model at the material level, making the model's deformation, cracking, and other responses under coupled loads closer to actual engineering, significantly improving the credibility and engineering reference value of the test data.

[0055] 4. Achieving refined, quantifiable control and multi-condition comparison of experimental conditions makes the research conclusions more systematic and scientific: Key experimental variables were precisely and repeatably controlled and designed; the specific temperature, time, and number of freeze-thaw cycles were clarified, making environmental simulation quantifiable and repeatable; at least three different road longitudinal slopes were set as comparative conditions, enabling a systematic study of the influence of slope, a key geometric parameter, on the roadbed coupling response; by calculating counterweights, using the drive system, and simulating uphill deceleration conditions, standardized and programmable application of vehicle loads was achieved; This refined control and multi-level design of the three major elements of freeze-thaw, slope, and load allows the experiment to derive more scientific and universal laws from single-variable comparisons and system combinations.

[0056] 5. Establish a comprehensive, multi-dimensional data acquisition and analysis framework from macroscopic and microscopic mechanical responses to macroscopic failure phenomena, deeply revealing the failure process and mechanism: The monitoring system not only deploys monitoring points at key locations such as the top, middle, and toe of the slope, but also measures the strain in the longitudinal, transverse, and vertical directions simultaneously at each monitoring point, enabling complete acquisition of the stress-strain state of the roadbed in three-dimensional space; the analysis content includes not only the "variation law" of stress and strain in each direction with loading, but also the "initiation and propagation process of pavement layer cracks". This analytical method, which combines the internal continuous mechanical response (strain data) with the external discontinuous failure phenomenon (crack development), can trace from macroscopic phenomena to microscopic mechanical mechanisms, fully revealing the entire chain process of damage accumulation to final failure of long and steep slope roadbeds under the coupling effect of "freeze-thaw-heavy load", providing a solid experimental basis for understanding the nature of failure and proposing prevention and control measures.

[0057] While specific embodiments of the present invention have been described above, those skilled in the art should understand that the specific embodiments described are merely illustrative and not intended to limit the scope of the present invention. Equivalent modifications and variations made by those skilled in the art in accordance with the spirit of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for a scaled-down model test of a long slope coupled with freeze-thaw cycles and heavy loads, characterized in that: Includes the following steps: Step S1: Determine the materials and proportions for the model test: Based on the engineering geological survey report of the target engineering section, calculate and determine the similar materials and their proportions used for model filling; Step S2: Prepare a physical model of a long slope: Determine the size of the model box according to the geometric similarity ratio, and fill and compact the similar subgrade soil in layers in the model box according to the similar materials and their proportions. Then, lay the pavement layer on the surface of the compacted subgrade soil to prepare a physical model of a long slope. Step S3: Deploy the monitoring system: Install resistance strain gauges and high-speed cameras on the physical model of the long slope, and connect the resistance strain gauges to the data acquisition equipment; Step S4: Determine the freeze-thaw cycle conditions: Set the freeze-thaw conditions for simulating short-term freeze-thaw cycles, including freezing temperature, thawing temperature, duration of each temperature, and total number of cycles. Step S5: Determine the slope conditions for long slopes: Set at least two different longitudinal road slopes as comparative test conditions; Step S6: Determine the vehicle heavy load simulation scheme: Configure the simulated vehicle and drive system to apply periodic reciprocating moving loads on the physical model of the long slope to simulate the actual vehicle heavy load. Step S7: Perform a coupling test: On the physical model of the long slope, apply the frost heave and thaw settlement conditions and reciprocating moving loads sequentially or alternately to simulate the coupling effect of freeze-thaw and heavy load. Step S8, Data Acquisition and Processing: During the simulation of the coupling effect, strain data of the resistance strain gauge is continuously acquired through the data acquisition device, and video data of the damage formation and development process of the physical model of the long slope is recorded through the high-speed camera. Step S9: Analyze the test results: Based on the strain data and video data, analyze the mechanical response and failure process of the physical model of the long slope under different conditions to obtain the test results.

2. The method for a scaled-down model test of a long slope coupled with freeze-thaw and heavy load as described in claim 1, characterized in that: In step S1, the similar material is undisturbed residual granite soil with a natural moisture content ranging from 26.50% to 33.80% and a natural density ranging from 1.85 g / cm³ to 1.94 g / cm³.

3. The method for a scaled-down model test of a long slope coupled with freeze-thaw and heavy load as described in claim 1, characterized in that: In step S2, the paved road layer is a cement concrete road layer, an asphalt concrete road layer, or a composite road layer.

4. The method for a scaled-down model test of a long slope coupled with freeze-thaw and heavy load as described in claim 1, characterized in that: In step S3, the resistance strain gauges are arranged at the top, middle and bottom of the slope along the preset trajectory line of the road surface layer in the physical model of the long slope, and each monitoring point contains a resistance strain gauge for measuring longitudinal strain, transverse strain and vertical strain. The high-speed camera is positioned on one side of the viewing window of the model housing to record and film the entire experimental process, observing the formation and development of damage to the physical model of the long slope.

5. The method for a scaled-down model test of a long slope coupled with freeze-thaw and heavy load as described in claim 1, characterized in that: In step S4, the freeze-thaw conditions are set by the refrigeration unit, the heating unit and the temperature controller. The temperature can be adjusted between -20℃ and +20℃, and the duration is 0-24h.

6. The method for a scaled-down model test of a long slope coupled with freeze-thaw and heavy load as described in claim 1, characterized in that: In step S5, the longitudinal slope of the road is changed by a support base that supports continuous slope adjustment.

7. The method for a scaled-down model test of a long slope coupled with freeze-thaw and heavy load as described in claim 1, characterized in that: Step S6 specifically involves: Based on the geometric similarity ratio and stress similarity principle, the counterweight mass of the simulated vehicle was calculated. Based on the aforementioned counterweight mass, a simulated vehicle supporting weight adjustment, track width adjustment, wheelbase adjustment, and wheel set number adjustment is configured; A drive system is configured to drive the simulated vehicle to reciprocate on a long slope physical model via a traction device, thereby applying periodic reciprocating moving loads to simulate the heavy load of an actual vehicle.

8. The method for a scaled-down model test of a long slope coupled with freeze-thaw and heavy load as described in claim 7, characterized in that: The drive system includes a speed-regulating motor and a controller; During the simulated uphill process, the controller controls the output power of the speed-regulating motor to decrease linearly to simulate the vehicle's deceleration during uphill driving.

9. The method for a scaled-down model test of a long slope coupled with freeze-thaw and heavy load as described in claim 1, characterized in that: Step S7 specifically involves: For each type of road longitudinal slope physical model, the total number of freeze-thaw cycles is first performed, and then a set number of reciprocating moving loads are applied to the corresponding long slope physical model to simulate the coupling effect of freeze-thaw and heavy load.

10. The method for a scaled-down model test of a long slope coupled with freeze-thaw and heavy load as described in claim 1, characterized in that: In step S9, the analysis of the test results includes: The failure process, failure characteristics, and deformation properties of the physical model of the long slope were studied and analyzed. The failure mechanism of the physical model of the long slope under the coupling effect was revealed. The influence weight of each influencing factor was analyzed and determined. Reasonable prevention and control measures for extending the use of the physical model of the long slope under various coupling effects were proposed.

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