Device and method for testing thermal-dynamic characteristics of gravel roadbed in permafrost block

Abstract

The invention relates to the technical field of road construction, in particular to a device and a method for testing thermal-dynamic characteristics of a gravel roadbed in a permafrost block. The device comprises a model box, a terminal control system, and a block gravel roadbed model, an irregularity dynamic load simulation system, a pore change intelligent monitoring system, a frozen soil environment simulation system and a thermal-dynamic response monitoring system which are arranged on the inner side of the model box, a terminal control system is arranged on the outer side of the model box; the terminal control system is connected with the irregularity dynamic load simulation system, the pore change intelligent monitoring system, the frozen soil environment simulation system and the thermal-dynamic response monitoring system. According to the invention, the pore change and thermal-dynamic response condition of the block gravel roadbed in a complex operation environment can be well simulated, the obtained observation result is real and reliable, the change condition of complex dynamic load on the real permafrost block gravel roadbed can be simulated indoors, the test period is shortened, and the research cost is reduced; the method is wide in application range and can be popularized and applied.

Description

Technical Field

[0001] The invention relates to the technical field of road construction, and in particular to a thermal-dynamic characteristic test device and method for a gravel roadbed in a permafrost region. Background Art

[0002] my country is the third largest country in the world with permafrost, and the permafrost distribution area accounts for about 22.4% of the country's land area. my country's permafrost not only has the characteristics of high temperature, wide distribution and large thickness, but also faces the problem of degradation caused by the intensification of global warming. As a result, the construction of frozen soil projects represented by the Qinghai-Tibet Railway generally faces very serious frost damage problems. In order to solve these problems, a variety of new roadbed forms using "active cooling" methods have been proposed in recent years. Among them, the block gravel roadbed is the most typical active cooling roadbed engineering measure for the Qinghai-Tibet Railway, accounting for more than 60% of the permafrost sections of the Qinghai-Tibet Railway. The block gravel roadbed can cool the roadbed itself and the underlying foundation by regulating the convective heat exchange between the atmosphere and the roadbed. The actual operation and monitoring of the past 20 years have shown that the block gravel roadbed can solve the frost damage problem faced by the Qinghai-Tibet Railway to a certain extent, but there is still a high disease rate. This is because the block gravel particles will face complex thermal-dynamic coupling effects under repeated dynamic loads, which significantly affects their cooling effect. Therefore, it is necessary to conduct real-time testing of the porosity changes of the block-gravel layer under dynamic loads and to study the evolution of the thermal-mechanical performance degradation of the block-gravel roadbed under complex dynamic loads.

[0003] At present, most of the studies on the porosity change and thermal-dynamic response of the roadbed are conducted by long-term fixed-point observation on site and indoor soil column model test. Among them, the long-term fixed-point observation only gives the approximate deformation of the roadbed from a macroscopic scale, and cannot explain the mechanical deformation mechanism of the block gravel roadbed from a mechanistic perspective. Therefore, it is difficult to reveal the mechanism of the degradation of the cooling effect caused by the porosity change caused by the block gravel roadbed under dynamic loads; and the indoor soil column model test changes the soil parameters due to the difference in specimen size, and the test data obtained are greatly different from the actual situation, so it cannot simulate the real working environment of the roadbed well. In general, the current research methods cannot truly study the porosity change and thermal-dynamic performance evolution process of the block gravel roadbed in permafrost areas under complex dynamic loads. Summary of the invention

[0004] The present invention provides a device and method for testing the thermal-dynamic characteristics of a gravel roadbed in a permafrost region, which overcomes the shortcomings of the above-mentioned prior art and can effectively solve the problem that the existing research methods cannot truly interpret the porosity changes and thermal-dynamic performance evolution process of the gravel roadbed in permafrost regions under complex dynamic loads.

[0005] To solve the above problems, one of the technical solutions of the present invention is realized in the following manner: a thermal-dynamic characteristics test device for block gravel roadbed in permafrost area, comprising a model box, an image acquisition system, a terminal control system, and a block gravel roadbed model arranged inside the model box, an uneven dynamic load simulation system, a pore change intelligent monitoring system, a frozen soil environment simulation system and a thermal-dynamic response monitoring system; a terminal control system is arranged outside the model box;

[0006] The terminal control system is respectively connected to the uneven dynamic load simulation system, the pore change intelligent monitoring system, the frozen soil environment simulation system and the thermal-dynamic response monitoring system. The uneven dynamic load simulation system, the pore change intelligent monitoring system and the thermal-dynamic response monitoring system are all set on the block gravel roadbed model.

[0007] The above-mentioned uneven dynamic load simulation system includes a box top slide rail reaction frame, a servo actuator, a pressure head, an unevenness excitation device, rails and sleepers. A box top slide rail reaction frame is provided on the top of the inner side of the model box, and a servo actuator is slidably connected below the box top slide rail reaction frame. The output end of the servo actuator is connected to the pressure head, and the unevenness excitation device is connected below the pressure head. A sleeper is provided above the block gravel roadbed model, and two rails are provided above the sleeper in a horizontal and vertical direction to the sleeper, and the unevenness excitation device is rollingly connected to the rail.

[0008] The above-mentioned unevenness excitation device includes a main actuating tube, a bolster, a secondary suspension spring group, a side frame, a side wheel hydraulic pipe, a side wheel actuating pressure head, a wheel, and a wheelset axle; a main actuating tube is provided below the pressure head, a bolster is provided at the bottom of the main actuating tube, a group of wheels connected together through the wheelset axle are provided in front and behind the bolster, each wheelset axle close to the wheel position is provided with a side wheel actuating pressure head, and a side wheel hydraulic pipe is provided above each side wheel actuating pressure head; side frames connected to the wheelset axles at corresponding positions at both ends of the bolster are respectively provided, and a secondary suspension spring group is provided at the lower end of the bolster at the outer position of each side frame.

[0009] The above-mentioned block gravel roadbed model includes a block gravel layer, an overlying fill layer, a ballast layer, an insulating base plate, and a detachable waterproof integrated membrane; an insulating base plate is provided at the bottom inner side of the model box, and a block gravel layer, an overlying fill layer and a ballast layer are provided on the upper side of the insulating base plate from bottom to top, and a detachable waterproof integrated membrane is wrapped around the outer side of the block gravel layer.

[0010] The above-mentioned pore change intelligent monitoring system includes an antifreeze pump, a liquid inlet pipe, a liquid outlet pipe, a Martens flask, a Martens flask console and an image acquisition system. An antifreeze pump is arranged on the outside of the model box, which can quantitatively control and inject antifreeze into the gravel layer before the test starts and recover the antifreeze after the test ends. A liquid inlet pipe and a liquid outlet pipe respectively connected to the antifreeze pump are arranged on the left side of the antifreeze pump model box; a Martens flask console is arranged on the outside of the model box, and a Martens flask connected to the model box and provided with a scale is placed on the Martens flask console.

[0011] The above-mentioned image acquisition system includes two high-speed cameras in front and behind the model box and a high-speed camera next to the left side of the Martens flask. The front and rear cameras mainly record the crushing process of the gravel layer under dynamic load, and combine image processing technology to study the performance degradation mechanism of the gravel; the high-speed camera next to the Martens flask on the left side of the model box is mainly responsible for recording the real-time changes in the liquid height in the Martens flask, and converts the liquid height in the image information into porosity data through data terminal processing, so as to study the real-time evolution process of pores caused by the crushing of gravel under different working conditions.

[0012] The above-mentioned frozen soil environment simulation system includes a compressor, a condenser, a connecting pipe, an evaporator, a first loop duct, a second loop duct, a convection simulator, a double potential controller and a slide rail; a compressor is installed on the inside of the model box, the outlet of the compressor is connected to the condenser, the outlet of the condenser is connected to the evaporator through a connecting pipe, the outlet of the evaporator is fixedly connected to the first loop duct, the outlet of the first loop duct is fixedly connected to the second loop duct, and the outlet of the second loop duct is connected to the inlet of the compressor; a slide rail is fixed on the upper edge of the right side wall inside the model box, the convection simulator is slidably connected to the slide rail, and a double potential controller for adjusting the convection simulator is provided on the inside of the model box.

[0013] The above-mentioned thermal-dynamic response monitoring system includes a displacement monitoring device, a velocity monitoring device, an acceleration monitoring device, and a temperature monitoring device;

[0014] The displacement monitoring device includes a vibrating string type multi-point displacement sensor and a first optical fiber conductor. The block gravel roadbed model is provided with a vibrating string type multi-point displacement sensor, and the vibrating string type multi-point displacement sensor is connected to the terminal control system through the first optical fiber conductor.

[0015] The speed monitoring device comprises a speed piezoelectric speedometer and a second optical fiber conductor. The speed piezoelectric speedometer is arranged on the block gravel roadbed model, and the speed piezoelectric speedometer is connected to the terminal control system through the second optical fiber conductor.

[0016] The acceleration monitoring device includes a piezoelectric accelerometer and a third optical fiber conductor. The piezoelectric accelerometer is arranged on the gravel roadbed model, and the piezoelectric accelerometer is connected to the terminal control system through the third optical fiber conductor.

[0017] The temperature monitoring device comprises a thermistor temperature sensor and a fourth optical fiber conductor. The block gravel roadbed model is provided with a thermistor temperature sensor, and the thermistor temperature sensor is connected with the terminal control system through the fourth optical fiber conductor.

[0018] The terminal control system includes an intelligent operation control panel, a data acquisition instrument and a data terminal; the intelligent operation panel is respectively connected to the dual potential controller and the antifreeze pump; the data acquisition instrument is respectively connected to the vibrating string multi-point displacement sensor, the velocity piezoelectric speedometer, the piezoelectric accelerometer, the thermistor temperature sensor and the data terminal; the image acquisition system is connected to the data terminal, and the captured image information is processed in real time through the image processing program.

[0019] The second technical solution of the present invention is achieved by the following method: a method for testing the thermal-dynamic characteristics of a gravel roadbed in a permafrost region, comprising the following steps:

[0020] S1, making a crushed stone roadbed model;

[0021] S2. Install uneven dynamic load simulation system and thermal-dynamic response monitoring system;

[0022] S3. Before the test begins, turn on the antifreeze pump in the pore change intelligent monitoring system, inject antifreeze into the gravel layer, and record the final pumping volume to measure and calculate the initial porosity;

[0023] S4. Adjust the height of the Martens flask through the control console to ensure that the pressure in the Martens flask and the gravel layer is balanced, and turn on the high-speed camera to monitor the pore changes;

[0024] S5. Turn on the frozen soil environment simulation system, simulate the initial temperature and convection conditions, and keep the constant temperature for 12 hours. Then, set the temperature, number of freeze-thaw cycles and wind speed according to the test plan and conduct a formal test.

[0025] S6. Turn on the uneven dynamic load simulation system and perform motion loading through the terminal control system;

[0026] S7. After the test is completed, remove and close the uneven dynamic load simulation system, close the frozen soil environment simulation system, obtain the loaded samples for final porosity test and grading analysis, and process the monitoring data to study the evolution law of dynamic damage of gravel roadbed in permafrost areas.

[0027] The invention has a simple structure and is easy to manufacture. It provides a natural temperature and convection environment through a frozen soil environment simulation system and an uneven dynamic load simulation system, and applies an uneven dynamic load that is more in line with the actual load environment. It tests the real-time changes in the pores of the block gravel layer through a pore change intelligent monitoring system and a thermal-dynamic response monitoring system, and monitors the displacement changes of the top and slope of the block gravel roadbed and the changes in the internal temperature, velocity and acceleration in real time, thereby determining the thermal-dynamic changes of the block gravel roadbed in permafrost areas and the digital laws of the movement of the block gravel layer, and then explains the mechanical deformation mechanism and dynamic damage evolution mechanism of the block gravel roadbed in permafrost areas from a mechanistic point of view, and reveals the interaction between the deformation process of the block gravel roadbed in permafrost areas and the cooling effect. Feedback mechanism; it overcomes the shortcomings of the field long-term fixed-point observation method, that is, the observation period is too long and the mechanical deformation mechanism of the roadbed cannot be explained from a mechanistic point of view; it overcomes the shortcomings of the indoor soil column test observation method, that is, due to the difference in specimen size, the soil parameters change and the thermal-dynamic response of the on-site roadbed morphology and load cannot be well simulated; the present application can not only well simulate the pore changes and thermal-dynamic response of the roadbed in a complex operating environment, and the observation results obtained are true and reliable, but also can simulate the change process of the real permafrost block gravel block gravel roadbed under complex dynamic loads indoors, shortening the test cycle and reducing the research cost; at the same time, the present application has a wide range of application and can be promoted to the relevant scientific research fields of transportation engineering and geotechnical engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The specific implementation modes of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0029] Figure 1 This is a schematic structural diagram of a thermal-dynamic characteristics test device for a block crushed stone roadbed according to Example 1 of the present invention.

[0030] Figure 2 It is a schematic structural diagram of an uneven dynamic load simulation device according to Example 1 of the present invention.

[0031] Figure 3 This is the vertical force excitation diagram of the left and right rails of different wheelsets in Example 1 of the present invention.

[0032] Figure 4 This is a plan view of the pore change intelligent monitoring system of Example 1 of the present invention.

[0033] Figure 5 This is a schematic diagram of monitoring a typical block gravel roadbed model according to Example 1 of the present invention.

[0034] Figure 6 This is a flow chart of the thermal-dynamic characteristics test of Example 2 of the present invention.

[0035] In the figure: 1-box top slide rail reaction frame, 2-servo actuator, 3-pressure head, 4-rail, 5-sleeper, 6-main actuating pipe, 7-rocker, 8-secondary suspension spring group, 9-side frame, 10-side wheel hydraulic pipe, 11-side wheel actuating pressure head, 12-wheel, 13-wheel pair axle, 14-gravel layer, 15-overlying fill layer, 16-ballast bed layer, 17-insulating bottom plate, 18-detachable waterproof integrated membrane, 19-antifreeze pump, 20- Liquid inlet pipe, 21-liquid outlet pipe, 22-Martignano flask, 23-Martignano flask console, 24-image acquisition system, 25-sleeve, 26-compressor, 27-condenser, 28-connecting pipe, 29-evaporator, 30-first loop conduit, 31-second loop conduit, 32-convection simulator, 33-dual potential controller, 34-slide rail, 35-intelligent operation control panel, 36-data acquisition instrument, 37-data terminal, 38-model box. DETAILED DESCRIPTION

[0036] The present invention is not limited by the following embodiments, and specific implementation methods can be determined based on the technical solution of the present invention and actual conditions.

[0037] Example 1: Figure 1-5 As shown, the embodiment of the present invention discloses a thermal-dynamic characteristics test device for block gravel roadbed in permafrost area, including a model box 38, a terminal control system, and a block gravel roadbed model arranged inside the model box 38, an uneven dynamic load simulation system, a pore change intelligent monitoring system, a frozen soil environment simulation system, and a thermal-dynamic response monitoring system; a terminal control system is arranged outside the model box 38;

[0038] The terminal control system is respectively connected to the uneven dynamic load simulation system, the pore change intelligent monitoring system, the frozen soil environment simulation system and the thermal-dynamic response monitoring system. The uneven dynamic load simulation system, the pore change intelligent monitoring system and the thermal-dynamic response monitoring system are all set on the block gravel roadbed model.

[0039] The above-mentioned uneven dynamic load simulation system is used to apply real train dynamic loads; the pore change intelligent monitoring system is used to perform porosity change tests; the frozen soil environment simulation system is used to provide permafrost temperature and convection ventilation conditions for the block gravel roadbed model; the frozen soil environment simulation system and the pore change intelligent monitoring system are both controlled by the terminal control system, which is convenient for performing porosity transformation tests through the circulating water injection method when the freeze-thaw cycle enters a positive temperature state during the test; the thermal-dynamic response monitoring system is used to quantitatively monitor the temperature, deformation, velocity and acceleration response of the block gravel roadbed; the model box 38 is used to accommodate different types of block gravel roadbed models to be tested, and the inner cavity of the model box 38 matches the shape and structure of the block gravel roadbed model.

[0040] During operation, the model box 38 can be fixed on a test bench or the ground, and the block gravel roadbed model is placed in the model box 38. Under the temperature and convection environment conditions provided by the frozen soil environment simulation system, when the uneven dynamic load simulation system applies uneven excitation to the block gravel roadbed model, the block gravel particles in the block gravel roadbed model will undergo friction and collision under the repeated dynamic load, causing a series of degradation processes such as particle sliding, rotational deformation, and pore compression, thereby testing the porosity change between the block gravel particles through the pore change intelligent monitoring system, and through the thermal-dynamic The response monitoring system monitors the displacement changes of the top and slope of the block gravel roadbed model, internal temperature changes, speed changes and acceleration changes in real time, so as to determine the macroscopic relationship between the external deformation, internal temperature, speed, acceleration, block movement of the block gravel roadbed model under different working conditions and complex operating environments such as external temperature, number of freeze-thaw cycles, wind speed changes and uneven train loading, as well as the thermal-dynamic changes at each measuring point and the digital laws of block movement inside the block gravel roadbed model, and then study the thermal-dynamic damage evolution process of the block gravel roadbed model.

[0041] In summary, the present invention has a simple structure and is easy to process and manufacture. It provides a natural temperature and convection environment through a frozen soil environment simulation system and an uneven dynamic load simulation system, and applies an uneven dynamic load that is more in line with the actual load environment. It tests the porosity change of the block gravel through a pore change intelligent monitoring system and a thermal-dynamic response monitoring system, and monitors the displacement changes of the top and slope of the block gravel roadbed and the changes in the internal temperature, velocity and acceleration in real time, thereby determining the thermal-dynamic changes of the block gravel roadbed in permafrost areas and the digital laws of the movement of the block gravel blocks, and then explaining the mechanical deformation mechanism and dynamic damage evolution process of the block gravel roadbed in permafrost areas from a mechanistic point of view, revealing the deformation process and cooling effect of the block gravel roadbed in permafrost areas The feedback mechanism between them is established; it overcomes the shortcomings of the field long-term fixed-point observation method, that is, the observation period is too long and the mechanical deformation mechanism of the roadbed cannot be explained from a mechanistic point of view; it overcomes the shortcomings of the indoor soil column test observation method, that is, due to the difference in specimen size, the soil parameters change and the thermal-dynamic response of the on-site roadbed morphology and load cannot be well simulated; the present application can well simulate the thermal-dynamic response of the roadbed under a complex operating environment, and the observation results obtained are true and reliable, and can simulate the changes of the real permafrost block gravel roadbed under complex dynamic loads indoors, shortening the test period and reducing the research cost; at the same time, the present application has a wide range of application and can be promoted to the relevant scientific research fields of highway engineering and geotechnical engineering.

[0042] like Figure 1As shown, the uneven dynamic load simulation system includes a box top slide rail reaction frame 1, a servo actuator 2, a pressure head 3, an unevenness excitation device, a rail 4 and a sleeper 5. The top of the inner side of the model box 38 is provided with a box top slide rail reaction frame 1, the servo actuator 2 is slidably connected below the box top slide rail reaction frame 1, the output end of the servo actuator 2 is connected to the pressure head 3, and the unevenness excitation device is connected below the pressure head 3; a sleeper 5 is provided above the block gravel roadbed model, two rails 4 are provided above the sleeper 5 in a horizontal and vertical direction to the sleeper 5, and the unevenness excitation device is rollingly connected to the rail 4.

[0043] The sleeper 5 is provided with two, according to Figure 1 The direction of the three-dimensional coordinate axis is shown, wherein two sleepers 5 are laid on the block gravel roadbed model at intervals along the transverse X-axis direction, and the spacing is calculated based on the similarity ratio. The rails 4 are placed on the sleepers 5 along the Y-axis direction, and a one-way driving simulation scheme is adopted. Therefore, two rails 4 can be laid out according to actual engineering conditions such as the Qinghai-Tibet Railway, and fixed to the sleepers 5 through the rail 4 components.

[0044] The above-mentioned box top slide rail reaction frame 1 is made of I-beam material and is welded on the top of the model box 38 along the Y-axis direction. When it is set, the position should be 0.8 meters to 1.2 meters higher than the top of the block gravel roadbed model, and maintained at the same horizontal plane with the rail 4; the lower part of the box top slide rail reaction frame 1 is provided with a slide rail, and the servo actuator 2 is arranged in the groove of the slide rail. The sliding position of the servo actuator 2 can be controlled by the terminal control system to make the servo actuator 2 move on the rail 4, so that the servo actuator 2 applies the simulated train load on the unevenness excitation device through the pressure head 3 to perform full-range train heavy load (including static load and full-cycle dynamic load), and acts on the upper part of the block gravel roadbed model through the rail 4 and the sleeper 5 to simulate the train travel process; during the test, the sliding speed can be set according to the actual working conditions to simulate the uneven dynamic load under various conditions such as uniform speed, acceleration, deceleration, and speed change, so as to more realistically simulate the dynamic load effect of the train during the driving process of the Qinghai-Tibet Railway, and analyze the dynamic characteristics from the perspective of time and space.

[0045] The above-mentioned rail 4 simulates the rail 4 installed on the block gravel roadbed model during service. The main types of rail 4 are 75kg / m, 60kg / m, 50kg / m and 43kg / m. During the test, the model is obtained according to the standard track construction requirements of the required test section. The length of the rail 4 is based on the actual width of the block gravel roadbed model test area.

[0046] The pressure head 3 mainly transmits the full range of train heavy load (including static load and full cycle dynamic load) to the unevenness excitation device; when the static load of the train is transmitted, the input load is set to a constant; when the train heavy load is mainly considered, it can be given by considering the superposition of the exciting force function load composed of static load and geometric unevenness, so as to directly simulate the heavy load generated by the train during driving through the pressure head 3. Among them, when the load amplitude of the servo actuator 2 is 200kN, the maximum stroke is 2cm, and the maximum frequency is 40Hz, the expression of the train load is as follows:

[0047] P(t)=λ0+λ1sin(ω1t)+λ2sin(ω2t)+λ3sin(ω3t) (1)

[0048] Where, λ0 is the static load of wheel 12; λ1, λ2, λ3 are the amplitudes of train vibration loads, and λ i =M0α i ω i 2 , M0 is the unsprung mass of the train, α i is the geometric irregularity height corresponding to the unstable control condition; ω i is the circular vibration frequency of the rail 4 under the unsteady control condition, ω i =2πv / L i ; v is the speed of the train; L i is the typical vibration load length corresponding to the unsteady control condition; t is the load action time.

[0049] like Figure 2 As shown, the unevenness excitation device includes a main actuating tube 6, a bolster 7, a secondary suspension spring group 8, a side frame 9, a side wheel hydraulic pipe 10, a side wheel actuating pressure head 11, a wheel 12, and a wheelset axle 13; a main actuating tube 6 is provided below the pressure head 3, a bolster 7 is provided at the bottom of the main actuating tube 6, a group of wheels 12 connected together through wheelset axles 13 are provided at the front and rear of the bolster 7, each wheelset axle 13 near the wheel 12 is provided with a side wheel actuating pressure head 11, and a side wheel hydraulic pipe 10 is provided above each side wheel actuating pressure head 11; side frames 9 connected to the wheelset axles 13 at corresponding positions at the front and rear are respectively mounted at both ends of the bolster 7, and a secondary suspension spring group 8 is provided at the lower end of the bolster 7 at the outer position of each side frame 9.

[0050] The bolster 7 is connected to the pressure head 3 through the main actuating tube 6, which can transmit the heavy train periodic load output by the servo actuator 2 to the block gravel roadbed model; the side wheel actuating pressure head 11 is set on the wheel pair axle 13 on one side of each wheel 12, and can be driven by servo hydraulics to excite the local uneven dynamic load of each wheel 12. The load amplitude of the side wheel actuating pressure head 11 is 50kN, the maximum stroke is 1cm, and the maximum frequency is 20Hz. The different wheel-rail vertical forces output by each side wheel actuating pressure head 11 are mainly obtained through the Hertz nonlinear elastic contact theory and considering the coupling effect of railway track unevenness, wheel unevenness and track-wheel unevenness.

[0051] When solving the wheel-rail vertical force, the deformation of the wheel-rail system is first calculated through the vehicle system dynamic control equations and the rail 4 vibration equation:

[0052]

[0053] Where, [M] is the mass matrix of the vehicle body, front and rear bogie frames and each wheelset; [C] represents the primary suspension and secondary suspension damping matrix; [k] represents the primary suspension and secondary suspension stiffness matrix; Z c Indicates the floating and sinking deformation of the vehicle body; Indicates the floating and sinking speed of the vehicle body; represents the vehicle body floating acceleration; E represents the elastic modulus of rail 4; I Y represents the moment of inertia of the rail section 4 about the Y axis; Z r (x, t) represents the vibration displacement variable of the rail 4; m r F represents the mass of 4 unit length of rail; rsi (t) represents the reaction force of the five support points of the sleeper; N represents the total number of the five support points of the sleeper within the length l; P i represents the wheel-rail force; x i x is the coordinates of the five support points of each sleeper; wj Indicates the motion coordinates of each wheel 12.

[0054] Then the wheel-rail vertical coupling relationship is obtained:

[0055]

[0056] Where G is the wheel-rail contact constant, δZ(t) is the elastic compression between the wheel and rail at the contact point, which is calculated by subtracting the displacement of the rail 4 from the displacement of the wheel.

[0057] When considering the tapered tread wheel 12, the wheel-rail contact constant is:

[0058] G=4.57R -0.149 ×10 -8 (m / N 2 / 3 ) (5)

[0059] When the wheel-rail contact tread is considered, the wheel-rail contact constant is:

[0060] G=3.86R -0.149 ×10 -8 (m / N 2 / 3 ) (6)

[0061] The elastic compression is calculated by the following formula:

[0062] δZ(t)=Z wj (t)-Z r (x wj ,t) (7)

[0063] The wheel-rail vertical force of each wheel 12 is calculated by equations (2) to (7), and then the vertical force excitation curves of the left and right rails of different wheel pairs can be obtained.

[0064] It should be noted that:

[0065] 1. When the static load of the train is mainly considered, the side wheel actuating pressure head 11 can be kept constant through the control system, and the input load of the servo actuator 2 can be set to a constant;

[0066] 2. When the train heavy load dynamic effect is mainly considered, the side wheel actuating pressure head 11 can be kept constant through the control system, and the input load of the servo actuator 2 is set according to formula (1). The parameter values ​​are selected according to the test design, and the corresponding train heavy load dynamic load data required for the test is calculated. The train heavy load dynamic load generated by the train during driving is simulated by adjusting the loading amplitude and frequency to be applied to the roadbed model;

[0067] 3. If Figure 3 As shown, when the test is mainly considered for the uneven vibration condition of each wheel pair, the wheel-rail vertical force of each wheel 12 can be obtained by equations (2) to (7), and the vertical force excitation curves of the left and right rails of different wheel pairs can be obtained. The corresponding values ​​are combined with the actual engineering situation to obtain the vertical force excitation curves of the left and right rails of different wheel pairs corresponding to the actual engineering operation conditions, and the excitation curves are input into the control terminal to simulate the uneven dynamic load generated by the train during driving to apply it to the roadbed model. Through multiple working conditions, the purpose of uneven dynamic load simulation that is more in line with the actual engineering operation conditions can be finally achieved.

[0068] All the above test schemes can make the servo actuator 2 move on the rail 4 through the lower slide rail of the box top slide rail reaction frame 1 to simulate the actual movement process of the train. Through the above full-condition design scheme, multi-condition, full-range, and full-cycle load environment simulation can be achieved, and the block gravel roadbed model can be provided with a variety of load conditions faced in complex operating environments in a more realistic manner.

[0069] like Figure 1 , 4As shown in , 5 , the block gravel roadbed model includes a block gravel layer 14, an overlying fill layer 15, a ballast layer 16, an insulating bottom plate 17, and a detachable waterproof integrated membrane 18; an insulating bottom plate 17 is provided at the bottom inner side of the model box 38, and a block gravel layer 14, an overlying fill layer 15 and a ballast layer 16 are provided on the upper side of the insulating bottom plate 17 from bottom to top, and the outer side of the block gravel layer 14 is wrapped with a detachable waterproof integrated membrane 18.

[0070] The block gravel layer 14 can be constructed in a sandwich, slope protection or U-shaped structure to simulate different block gravel roadbed forms; the roadbed layer 16 is used to simulate the roadbed structure under the railroad sleeper 5 of the railway roadbed in actual engineering; wherein, in order to quantitatively describe the thermal-dynamic response of the two-way lane of the roadbed, the block gravel roadbed model adopts a single-side roadbed structure, that is, a right-angled trapezoidal structure, and the block gravel roadbed model includes a first side surface, a first right-angled trapezoidal side surface, a second side surface, a second right-angled trapezoidal side surface, and a first side surface, a first right-angled trapezoidal side surface, and a second right-angled trapezoidal side surface that are connected in sequence. The upper base connected to the side surface and the top of the second right-angled trapezoidal side surface and the lower base connected to the first side surface, the first right-angled trapezoidal side surface, the second side surface and the bottom of the second right-angled trapezoidal side surface at the same time; wherein the upper base and the lower base are both rectangular surfaces and are arranged in parallel, the first side surface is a rectangular surface, which is perpendicular to the upper base and the lower base, and the second side surface is a rectangular surface, which has an angle with the first side surface, that is, the second side surface is a roadbed slope; the first right-angled trapezoidal side surface and the second right-angled trapezoidal side surface are directly opposite; when the block gravel roadbed model is in service, the first side surface and the second side surface are arranged in the extension direction of the roadbed.

[0071] The above-mentioned model box 38 includes a second bottom plate in front of the slope, a surrounding plate, a top plate, a fixed steel frame plate, and buckles; the surrounding plate is composed of four parts, front, back, left and right, which are connected end to end in sequence through a fixed steel frame to form a fence, and are connected with the top plate through a fixed steel frame to form a box body; the second bottom plate in front of the slope is arranged on the second side, that is, one side of the roadbed slope, and is connected to the front, rear and right side surrounding plates into a whole through a fixed steel frame; the insulating bottom plate 17, the second bottom plate in front of the slope, and the surrounding plate are all provided with buckles for fixing the detachable waterproof integrated membrane 18; the detachable waterproof integrated membrane 18 is fixed by the buckle, so that when the porosity test of the gravel layer 14 is carried out through the pore change intelligent monitoring system during the test, the detachable waterproof integrated membrane 18 can be completely fixed and ensure that the gravel layer 14 is filled with water and does not leak out.

[0072] It should be noted that the enclosure is perpendicular to the insulating bottom plate 17 and the second bottom plate in front of the slope, two cloths and one membrane are laid on the insulating bottom plate 17, and the block gravel roadbed model is set on the insulating bottom plate 17. A certain width is left on the side of the insulating bottom plate 17 close to the second side, that is, the roadbed slope, so that the block gravel roadbed model can be displaced to the side of the right enclosure slope when subjected to dynamic loads.

[0073] The width of the second bottom plate in front of the slope should be set according to 20%-30% of the bottom width of the block gravel roadbed under study, mainly used to place the frozen soil environment simulation system and ensure a certain convection space. It should be understood that a door is provided on the right side panel so that when assembling the block gravel roadbed model, the test soil sample and equipment can be transported into the model box 38 through the door on one side of the right side panel.

[0074] It should be noted that the insulating bottom plate 17, the second bottom plate in front of the slope and the top plate can all be metal plates or tempered glass plates; a return air duct is provided on the outer side of the left side panel, and the lower part of the left side panel needs to adopt a mesh design so that when simulating an open convection environment, the gravel layer 14 can be connected with the return air duct outside the left side panel, so that the air blown into the gravel layer 14 can circulate back to the model box 38, ensuring the consistency of the model environment and the actual environment, keeping the air inside the gravel layer 14 connected to the outside world, and thus providing conditions for convective heat exchange between the inside and outside air.

[0075] like Figure 1 , 4 As shown, the pore change intelligent monitoring system includes an antifreeze pump 19, a liquid inlet pipe 20, a liquid outlet pipe 21, a Martens flask 22, a Martens flask console 23 and an image acquisition system 24. The left side of the model box 38 is provided with a liquid inlet hole and a liquid outlet hole that are connected inside and outside. The inner sides of the liquid inlet hole and the liquid outlet hole are sealed with a sleeve 25. The sleeve 25 can be sealed in the corresponding liquid inlet hole and liquid outlet hole by a sealant to prevent the antifreeze from leaking from the connection position of the left side panel during the test. The liquid inlet hole is equipped with a liquid inlet pipe 20 whose right end extends to contact with the gravel layer 14, and the liquid outlet hole is equipped with a liquid outlet pipe 21 whose right end extends to contact with the gravel layer 14.

[0076] It should be noted that the liquid inlet pipe 20 and the liquid outlet pipe 20 are arranged on the left side of the model box 38 and are connected to the antifreeze pump 19. The antifreeze pump 19 can be quantitatively controlled and inject antifreeze into the gravel layer 14 through the liquid inlet pipe 20 before the test starts, and the antifreeze is recovered through the liquid outlet pipe 21 after the test.

[0077] Since the crushed stone particles will rub and collide under repeated dynamic loads, causing a series of degradation processes such as particle sliding, crushing, and pore compression, the pore change intelligent monitoring system is mainly used to test the porosity change of the crushed stone layer 14 under uneven dynamic loads through the Marsh flask hydraulic method. Before the test starts, the detachable waterproof integrated membrane 18 is closed (in other cases, the detachable waterproof integrated membrane 18 is in an open state) to ensure that there is no leakage when the antifreeze is injected into the crushed stone layer 14. Then, the water inlet controller 19 is controlled by the terminal control system to uniformly inject the antifreeze into the crushed stone layer 14 at a low speed. After the injection is completed, the injection volume is recorded and the initial porosity is calculated.

[0078] It should be noted that the Marg flask 22 is connected to the bottom left side of the model box and is placed on the Marg flask console 23. The Marg flask console 23 can adjust the height of the Marg flask 22 to ensure the balance of internal and external pressures. The Marg flask 22 is provided with a scale, which can record the liquid height in real time to characterize the change in antifreeze pressure caused by the change in the porosity of the gravel during the test.

[0079] The image acquisition system 24 includes two high-speed cameras at the front and rear of the model box 38 and a high-speed camera next to the left side of the Martens flask 22. The two cameras at the front and rear mainly record the crushing process of the block gravel layer 14 under the action of dynamic load, and combine image processing technology to study the degradation mechanism of block gravel performance. The high-speed camera next to the Martens flask 22 on the left side of the model box 38 is mainly responsible for recording the real-time changes in the liquid height in the Martens flask 22, and converts the liquid height in the image information into porosity data through data terminal processing, so as to study the real-time evolution of pores caused by the crushing of block gravel under different working conditions.

[0080] like Figure 1 As shown, the frozen soil environment simulation system includes a compressor 26, a condenser 27, a connecting pipe 28, an evaporator 29, a first loop conduit 30, a second loop conduit 31, a convection simulator 32, a double potential controller 33 and a slide rail 34; the compressor 26 is installed on the inner side of the model box 38, the outlet of the compressor 26 is connected to the condenser 27, the outlet of the condenser 27 is connected to the evaporator 29 through the connecting pipe 28, the outlet of the evaporator 29 is fixedly connected to the first loop conduit 30, the outlet of the first loop conduit 30 is fixedly connected to the second loop conduit 31, and the outlet of the second loop conduit 31 is connected to the inlet of the compressor 26; a slide rail 34 is fixedly fixed on the upper edge of the right side wall inside the model box 38, the convection simulator 32 is slidably connected to the slide rail 34, and a double potential controller 33 for adjusting the convection simulator 32 is provided on the inner side of the model box 38.

[0081] The first loop conduit 30 is connected to the end of the evaporator 29 as an outlet end, and is fixed on the model box 38 in a symmetrical layout. In order to ensure that the conduit line can effectively cool and not hinder the normal progress of the model test, the first loop conduit 30 needs to be laid at a distance of more than 0.5m from the top of the block gravel roadbed model; the second loop conduit 31 is connected to the first loop conduit 30, and is fixed on the top plate in the model box 38 in a spiral layout, and is connected to the compressor 26 as an air inlet end; the temperature, time, cycle period and other freeze-thaw cycle parameters are set through the terminal control system, and the real-time temperature change process in the model box 38 is recorded.

[0082] The above-mentioned slide rail 34 is mainly used to adjust the working position of the convection simulator 32; the dual potential controller 33 is used to set the wind speed cycle and wind speed gear of the convection simulator 32, and control the position of the convection simulator 32 on the slide rail 34 to change the convection condition, so that the air passes through the block gravel layer 14 and the return air duct outside the left side panel, and forms a circulating air duct in the model box 38, thereby providing conditions for convection heat exchange between the air inside and outside the block gravel layer 14, so as to simulate the natural ventilation environment and provide natural simulation conditions for convection heat exchange for the block gravel roadbed.

[0083] The compressor 26 can generate high-temperature and high-pressure gas after pressurizing the refrigerant, and convert it into high-pressure liquid through the condenser 27, and then convert it into low-pressure liquid through the connecting pipe 28, and then pass through the evaporator 29 for heat absorption and vaporization treatment, and the vaporized refrigerant is sent into the first loop conduit 30 through the outlet end, and finally after passing through the second loop conduit 31, the refrigerant is recovered to the compressor 26 from the inlet end, thereby completing the refrigeration cycle.

[0084] like Figure 1 , 5 As shown, the thermal-dynamic response monitoring system includes a displacement monitoring device, a velocity monitoring device, an acceleration monitoring device, and a temperature monitoring device;

[0085] The displacement monitoring device includes a vibrating string type multi-point displacement sensor and a first optical fiber conductor. The block gravel roadbed model is provided with a vibrating string type multi-point displacement sensor, and the vibrating string type multi-point displacement sensor is connected to the terminal control system through the first optical fiber conductor.

[0086] The speed monitoring device comprises a speed piezoelectric speedometer and a second optical fiber conductor. The speed piezoelectric speedometer is arranged on the block gravel roadbed model, and the speed piezoelectric speedometer is connected to the terminal control system through the second optical fiber conductor.

[0087] The acceleration monitoring device includes a piezoelectric accelerometer and a third optical fiber conductor. The piezoelectric accelerometer is arranged on the gravel roadbed model, and the piezoelectric accelerometer is connected to the terminal control system through the third optical fiber conductor.

[0088] The temperature monitoring device comprises a thermistor temperature sensor and a fourth optical fiber conductor. The block gravel roadbed model is provided with a thermistor temperature sensor, and the thermistor temperature sensor is connected with the terminal control system through the fourth optical fiber conductor.

[0089] The various data monitored by the above-mentioned displacement monitoring device, speed monitoring device, acceleration monitoring device and temperature monitoring device are transmitted to the terminal control system through the first optical fiber wire, the second optical fiber wire, the third optical fiber wire and the fourth optical fiber wire respectively, and the terminal control system performs data processing on external deformation, internal temperature, speed, acceleration and the like to obtain the thermal-dynamic response law of the block gravel roadbed model 14 under the action of uneven dynamic load.

[0090] The above-mentioned vibrating-string multi-point displacement sensor is mainly buried between the overlying fill layer 15 and the roadbed layer 16 on the top of the block gravel roadbed model 14, and is mainly set at points A1 to A3, that is, at the center of the roadbed model, close to the left side panel and close to one side of the roadbed slope. It is mainly used to monitor the vertical displacement of the block gravel roadbed model 14 under dynamic load. In addition, it is also necessary to be arranged on one side of the roadbed slope, and arranged at points A4 to A8 from top to bottom, which is mainly used to monitor the vertical displacement of the block gravel roadbed slope under dynamic load.

[0091] The main monitoring points of the above-mentioned resistive velocity plate, piezoelectric accelerometer and thermistor temperature sensor are B1~B14, among which B1~B4 are located near the left side of the enclosure and arranged in the longitudinal direction (Z direction), B5~B8 are located on the central axis of the roadbed model and arranged in the longitudinal direction (Z direction), B9, B12~B14 are all located on the roadbed slope and arranged in sequence from top to bottom, among which B13 and B3, B7, B10 are all arranged between the block crushed stone layer 14 and the overlying fill layer 15, and the B1, B5, B9 measuring points are buried between the overlying fill layer 15 and the roadbed layer 16 on the top of the block crushed stone roadbed model 14. The measuring points should be arranged according to the lateral (X direction) interval of 0.5m~0.8m and the longitudinal (Z direction) interval of 0.3m~0.6m, and it is ensured that each measuring point is kept on the axial (Y direction) horizontal plane perpendicular to the left light-transmitting plate. In addition, two piezoelectric accelerometers are arranged on the insulation bottom plate 17, one along the excitation direction (X direction) and the other perpendicular to the excitation direction (Y direction) to verify the feedback acceleration obtained by the surface after the input signal.

[0092] like Figure 1 As shown, the terminal control system includes an intelligent operation control panel 35, a data acquisition instrument 36 and a data terminal 37; the intelligent operation panel 35 is respectively connected to the dual potential controller 33 and the antifreeze pump 19; the data acquisition instrument 36 is respectively connected to the vibrating string multi-point displacement sensor, the velocity piezoelectric speedometer, the piezoelectric accelerometer, the thermistor temperature sensor and the data terminal 37; the image acquisition system 24 is connected to the data terminal 37, and the captured image information is processed in real time through the image processing program.

[0093] The intelligent operation control panel 35 is externally arranged on the right side of the enclosure of the model box 38. The frozen soil environment simulation system and the pore change intelligent monitoring system are both controlled by the intelligent operation control panel 35, so that according to the test design, the porosity can be monitored in real time according to the test requirements during the test.

[0094] It should be noted that the high-speed camera on the left side of the model box 38 can extract the liquid height in the Martens flask 22 in real time through image acquisition, and convert the liquid height data through an algorithm in the data terminal 37, and finally obtain the porosity change data at each moment. The high-speed cameras set before and after the model box 38 mainly monitor the changes in the block gravel layer 14 within the area, and extract the porosity change characteristics under dynamic loads through an algorithm in the data terminal 37.

[0095] The data acquisition device 36 is used to collect various data monitored by the displacement monitoring device, the speed monitoring device, the acceleration monitoring device and the temperature monitoring device through the first optical fiber wire, the second optical fiber wire, the third optical fiber wire and the fourth optical fiber wire, and finally reflect them on the data terminal 37, and process the external deformation and internal temperature, speed, acceleration and other data on the data terminal 37 to obtain the thermal-dynamic response law of the block gravel roadbed model under the action of uneven dynamic load.

[0096] Example 2: Figure 6 The embodiment of the present invention discloses a method for testing the thermal-dynamic characteristics of a gravel roadbed in a permafrost region, comprising the following steps:

[0097] S1, making a crushed stone roadbed model;

[0098] S2. Install uneven dynamic load simulation system and thermal-dynamic response monitoring system;

[0099] S3. Before the test begins, turn on the antifreeze pump in the pore change intelligent monitoring system, inject antifreeze into the gravel layer, and record the final pumping volume to measure and calculate the initial porosity;

[0100] S4. Adjust the height of the Martens flask through the control console to ensure that the pressure in the Martens flask and the gravel layer is balanced, and turn on the high-speed camera to monitor the pore changes;

[0101] S5. Turn on the frozen soil environment simulation system, simulate the initial temperature and convection conditions, and keep the constant temperature for 12 hours. Then, set the temperature, number of freeze-thaw cycles and wind speed according to the test plan and conduct a formal test.

[0102] S6. Turn on the uneven dynamic load simulation system and perform motion loading through the terminal control system;

[0103] S7. After the test is completed, remove and close the uneven dynamic load simulation system, close the frozen soil environment simulation system, obtain the loaded samples for final porosity test and grading analysis, and process the monitoring data to study the evolution law of dynamic damage of gravel roadbed in permafrost areas.

[0104] In the above step S1, a block crushed stone roadbed model is made, which specifically includes: preparing test materials, using a standard sieve and a balance to screen according to different apertures, and performing gradation analysis of the block crushed stone material and the fill layer, and the fill layer material by a screening method; laying a block crushed stone layer 14, sealing a detachable waterproof integrated membrane 18, and then laying an overlying fill layer 15 and a ballast layer 16, and laying sleepers 5 and rails 4 according to actual engineering conditions.

[0105] In the above step S2, the thermal-dynamic response monitoring system is installed at the designed measuring points during the process of laying the block gravel roadbed model.

[0106] In the above step S4, the high-speed camera is turned on during the test. When adjusting the height of the Malvern flask 22, the generation speed of the internal bubbles is used as the adjustment target, that is, the bubbles in the flask are generated at a uniform speed, and the height at this time is regarded as the height at which the internal and external pressures are balanced.

[0107] The above step S5 specifically includes: turning on the uneven dynamic load simulation system when starting the formal test, and adjusting the servo actuator 2 to the initial position through the box top slide rail reaction frame 1, generally the position on one side of the rail 4 close to the front and rear panels, and then setting the program through the data terminal 37 to start motion loading.

Claims

1. A thermal-dynamic characteristics test device for gravel roadbed in permafrost areas, characterized in that: It includes a model box, a terminal control system, and a block gravel roadbed model, an uneven dynamic load simulation system, a pore change intelligent monitoring system, a frozen soil environment simulation system, and a thermal-dynamic response monitoring system arranged inside the model box; a terminal control system is arranged outside the model box; The terminal control system is respectively connected to the uneven dynamic load simulation system, the pore change intelligent monitoring system, the frozen soil environment simulation system and the thermal-dynamic response monitoring system. The uneven dynamic load simulation system, the pore change intelligent monitoring system and the thermal-dynamic response monitoring system are all set on the block gravel roadbed model.

2. The thermal-dynamic characteristics test device for permafrost block gravel roadbed according to claim 1, characterized in that: The uneven dynamic load simulation system includes a box top slide rail reaction frame, a servo actuator, a pressure head, an unevenness excitation device, rails and sleepers. A box top slide rail reaction frame is provided on the top of the inner side of the model box, and a servo actuator is slidably connected below the box top slide rail reaction frame. The output end of the servo actuator is connected to the pressure head, and the unevenness excitation device is connected below the pressure head. Sleepers are provided above the block gravel roadbed model, and two rails are provided above the sleepers in a horizontal and vertical direction to the sleepers, and the unevenness excitation device is rollingly connected to the rails.

3. The thermal-dynamic characteristics test device for permafrost block gravel roadbed according to claim 2, characterized in that: The unevenness excitation device includes a main actuating tube, a bolster, a secondary suspension spring group, a side frame, a side wheel hydraulic pipe, a side wheel actuating pressure head, a wheel, and a wheelset axle; a main actuating tube is provided below the pressure head, a bolster is provided at the bottom of the main actuating tube, a group of wheels connected together through the wheelset axle are provided at the front and rear of the bolster, a side wheel actuating pressure head is provided on each wheelset axle close to the wheel position, and a side wheel hydraulic pipe is provided above each side wheel actuating pressure head; side frames connected to the wheelset axles at corresponding positions at the front and rear are respectively provided at both ends of the bolster, and a secondary suspension spring group is provided at the lower end of the bolster at the outer position of each side frame.

4. A thermal-dynamic characteristics test device for permafrost block gravel roadbed according to claim 1, 2 or 3, characterized in that: The block gravel roadbed model includes a block gravel layer, an overlying fill layer, a ballast layer, an insulating base plate, and a removable waterproof integrated membrane; an insulating base plate is provided at the bottom of the inner side of the model box, and a block gravel layer, an overlying fill layer, and a ballast layer are provided on the upper side of the insulating base plate from bottom to top, and a removable waterproof integrated membrane is wrapped around the outer side of the block gravel layer.

5. The thermal-dynamic characteristics test device for permafrost block gravel roadbed according to claim 4, characterized in that: The pore change intelligent monitoring system includes an antifreeze pump, a liquid inlet pipe, a liquid outlet pipe, a Marg flask, a Marg flask console and an image acquisition system. An antifreeze pump is arranged on the outside of the model box, which can quantitatively control the injection of antifreeze into the gravel layer before the test and recover the antifreeze after the test. The antifreeze pump model box is provided with a liquid inlet pipe and a liquid outlet pipe respectively connected to the antifreeze pump, and an antifreeze pump on the left side; a Marg flask console is arranged on the outside of the model box, and a Marg flask connected to the model box and provided with a scale is placed on the Marg flask console.

6. The thermal-dynamic characteristics test device for permafrost block gravel roadbed according to claim 5, characterized in that: The image acquisition system includes two high-speed cameras in front and behind the model box and a high-speed camera next to the left side of the Martens flask. The front and rear cameras mainly record the crushing process of the gravel layer under dynamic load, and combine image processing technology to study the performance degradation mechanism of the gravel; the high-speed camera next to the Martens flask on the left side of the model box is mainly responsible for recording the real-time changes of the liquid height in the Martens flask, and converts the liquid height in the image information into porosity data through data terminal processing, so as to study the real-time evolution of pores caused by the crushing of gravel under different working conditions.

7. A thermal-dynamic characteristics test device for permafrost block gravel roadbed according to claim 1, 2, 3 or 5, characterized in that: The frozen soil environment simulation system includes a compressor, a condenser, a connecting pipe, an evaporator, a first-loop conduit, a second-loop conduit, a convection simulator, a double-potential controller and a slide rail; a compressor is installed inside the model box, the outlet of the compressor is connected to the condenser, the outlet of the condenser is connected to the evaporator through a connecting pipe, the outlet of the evaporator is fixedly connected to the first-loop conduit, the outlet of the first-loop conduit is fixedly connected to the second-loop conduit, and the outlet of the second-loop conduit is connected to the inlet of the compressor; a slide rail is fixed on the upper edge of the right side wall inside the model box, the convection simulator is slidably connected to the slide rail, and a double-potential controller for adjusting the convection simulator is provided inside the model box.

8. The thermal-dynamic characteristics test device for permafrost block gravel roadbed according to claim 6, characterized in that: The thermal-dynamic response monitoring system includes a displacement monitoring device, a velocity monitoring device, an acceleration monitoring device, and a temperature monitoring device; The displacement monitoring device includes a vibrating string type multi-point displacement sensor and a first optical fiber conductor. The block gravel roadbed model is provided with a vibrating string type multi-point displacement sensor, and the vibrating string type multi-point displacement sensor is connected to the terminal control system through the first optical fiber conductor. The speed monitoring device comprises a speed piezoelectric speedometer and a second optical fiber conductor. The speed piezoelectric speedometer is arranged on the block gravel roadbed model, and the speed piezoelectric speedometer is connected to the terminal control system through the second optical fiber conductor. The acceleration monitoring device includes a piezoelectric accelerometer and a third optical fiber conductor. The piezoelectric accelerometer is arranged on the gravel roadbed model, and the piezoelectric accelerometer is connected to the terminal control system through the third optical fiber conductor. The temperature monitoring device comprises a thermistor temperature sensor and a fourth optical fiber conductor. The block gravel roadbed model is provided with a thermistor temperature sensor, and the thermistor temperature sensor is connected with the terminal control system through the fourth optical fiber conductor.

9. The thermal-dynamic characteristics test device for permafrost block gravel roadbed according to claim 7, characterized in that: The terminal control system includes an intelligent operation control panel, a data acquisition instrument and a data terminal; the intelligent operation panel is connected to the dual potential controller and the antifreeze pump respectively; the data acquisition instrument is connected to the vibrating string multi-point displacement sensor, the velocity piezoelectric speedometer, the piezoelectric accelerometer, the thermistor temperature sensor and the data terminal respectively; the image acquisition system is connected to the data terminal, and the captured image information is processed in real time through the image processing program.

10. A method for testing the thermal-dynamic characteristics of gravel roadbed in permafrost areas, characterized in that: The following steps are involved: S1, making a crushed stone roadbed model; S2. Install uneven dynamic load simulation system and thermal-dynamic response monitoring system; S3. Before the test begins, turn on the antifreeze pump in the pore change intelligent monitoring system, inject antifreeze into the gravel layer, and record the final pumping volume to measure and calculate the initial porosity; S4. Adjust the height of the Martens flask through the control console to ensure that the pressure in the Martens flask and the gravel layer is balanced, and turn on the high-speed camera to monitor the pore changes; S5. Turn on the frozen soil environment simulation system, simulate the initial temperature and convection conditions, and keep the constant temperature for 12 hours. Then, set the temperature, number of freeze-thaw cycles and wind speed according to the test plan and conduct a formal test. S6. Turn on the uneven dynamic load simulation system and perform motion loading through the terminal control system; S7. After the test is completed, remove and close the uneven dynamic load simulation system, close the frozen soil environment simulation system, obtain the loaded samples for final porosity test and grading analysis, and process the monitoring data to study the evolution law of dynamic damage of gravel roadbed in permafrost areas.

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