An experimental device and experimental method for simulating the frost heaving of accumulated water inside a tunnel lining

Abstract

The present invention belongs to the technical field of frost heaving experimental equipment, and specifically relates to an experimental device and an experimental method for simulating the frost heaving of accumulated water inside a tunnel lining. The experimental equipment includes a simulated lining and a simulated surrounding rock that are entirely located within a framework. The simulated lining has a trough for accommodating accumulated water, and the simulated surrounding rock seals the trough. A distance measuring device is arranged between the simulated surrounding rock and the simulated lining to reflect the expansion amount of the accumulated water in the trough due to frost heaving. A pressure sensor is arranged at the bottom of the trough to feedback the expansion force of the accumulated water in the trough due to frost heaving. Both the distance measuring device and the pressure sensor are electrically connected to a data acquisition device. The experimental method using this experimental device can better simulate the frost heaving process of the accumulated water in the tunnel lining, and obtain real-time change information. By combining with a processing device for data processing, the formed experimental results are of great reference value to the project quality.

Description

Technical Field

[0001] The present invention relates to the technical field of frost heaving experimental equipment, and more specifically, to an experimental device and an experimental method for simulating the frost heaving of accumulated water inside a tunnel lining. Background Art

[0002] After the accumulated water in the cavity behind the lining of a cold-region tunnel freezes, due to the volume increase of the water body, certain expansion deformation occurs. The existing lining voids cannot meet the demand for volume expansion during the phase change of the water body. Moreover, during the process of volume expansion and deformation of the frozen accumulated water, frost heaving force will be generated due to the constraint of the tunnel surrounding rock, resulting in deformation and even cracking of the tunnel lining. Currently, diseases caused by natural conditions such as cold are widespread in cold-region tunnels.

[0003] The frost heaving of the rock itself can be ignored. Therefore, in cold-region tunnels, the frost heaving pressure of the lining is mainly caused by the frost heaving of the accumulated water body behind the lining. To understand the frost heaving mechanism of tunnels and study the influence of local frost heaving force and expansion rate of accumulated water behind the lining of cold-region tunnels, the existing technologies mainly adopt simulation analysis and engineering measurement methods. The problems existing in the simulation analysis method are mainly that due to the lack of measured data, the pertinence is not strong, and the guiding value for engineering design is not high; the problems existing in the engineering measurement method are mainly that the work cost is high, the experimental results are lagging, and it can only represent a single result of engineering design, and there is no possibility of comparing test schemes; moreover, the existing frost heaving experimental equipment has a complex structure, high use cost, difficult adjustment of experimental parameters, and the data results are disconnected from the actual working conditions, and the engineering reference value is low. Summary of the Invention

[0004] The purpose of the present invention is to provide an experimental device and an experimental method that can affect the local frost heaving force and expansion rate of accumulated water behind the lining of cold-region tunnels by combining various factors such as environmental temperature, surrounding rock stiffness, water accumulation volume, and water quality hardness. It can better simulate the frost heaving process of tunnel lining accumulated water, obtain real-time change information, and form experimental results with great reference value for engineering quality through data processing by combining with a processing device.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] An experimental device for simulating the frost heaving of accumulated water inside a tunnel lining, characterized in that: it includes a simulated lining and a simulated surrounding rock that are both located inside a frame. The simulated lining has a groove for accommodating accumulated water, and the simulated surrounding rock encloses the groove. A distance measuring device is arranged between the simulated surrounding rock and the simulated lining to reflect the expansion amount of the accumulated water frost heaving in the groove; a pressure sensor is arranged at the bottom of the groove to feedback the expansion force of the accumulated water frost heaving in the groove; both the distance measuring device and the pressure sensor are electrically connected to a data acquisition device.

[0007] The additional technical features constituting the above experimental device for simulating the frost heaving of accumulated water inside a tunnel lining further include:

[0008] - The spacing measuring device is a height measuring instrument, which is composed of a reference part arranged outside the simulated lining and a movable part arranged outside the simulated surrounding rock;

[0009] - The pressure sensor includes a resistance strain gauge and a resistance strain indicator connected by a wire. The resistance strain gauge is placed inside the tank body and covered with a sealing partition board. The resistance strain indicator is placed outside the simulated lining and connected to the data acquisition device. The simulated lining has a through hole for the wire to penetrate;

[0010] - The frame includes an upper frame body and a lower frame body made of section steel. The four corners of the upper frame body and the lower frame body have extended ends for setting fastening bolts;

[0011] - A preloading spring is sleeved on the lower part of the nut of the fastening bolt. The compression amount of the preloading spring is not less than the expansion amount after the accumulated water in the simulated lining freezes and heaves;

[0012] - The data acquisition device is a PC or a PLC controller, and the PC or the PLC controller has a processing module for calculating and analyzing the acquired data;

[0013] - The overall shape of the simulated lining is cylindrical. The tank body is located at the center of the upper surface. The simulated surrounding rock is a round plate or disk composed of a front steel plate and a bottom rubber plate, and its size is the same as that of the upper surface of the simulated lining;

[0014] - The front steel plate of the simulated surrounding rock and the simulated lining are both made of Q235 steel. The sealing partition board covering the resistance strain gauge includes a steel backing plate with the same inner diameter as the tank body, and a sealing ring is arranged around the steel backing plate.

[0015] The present invention also provides an experimental method for simulating the frost heaving of accumulated water inside a tunnel lining by using the above experimental device, including the following steps:

[0016] Step 1, assemble the experimental device

[0017] Set a pressure sensor at the bottom of the tank body of the simulated lining, inject water with a set specification into the tank body, seal it with the simulated surrounding rock. The frame makes the simulated surrounding rock and the simulated lining in a relatively free state, or the preloading spring of the frame makes the simulated lining and the simulated surrounding rock in an elastically compressed state as a whole. Install a spacing measuring device between the simulated lining and the simulated surrounding rock. Both the pressure sensor and the spacing measuring device are electrically connected to the data acquisition device;

[0018] Step 2: Simulate the frost heaving process

[0019] Place the experimental device assembled in Step 1 into the refrigeration box and ensure that the accumulated water inside the experimental device is completely frozen within a predetermined time.

[0020] Step 3: Collect experimental data

[0021] During the predetermined time in Step 2, the pressure sensor and the spacing measurer feed back the data of the frost heaving force and the expansion amount to the data acquisition device in real time, and the data acquisition device stores or outputs the experimental results.

[0022] —— Add an experimental parameter adjustment step in Step 1,

[0023] which includes adjusting the thicknesses of the Q235 steel plate and the rubber plate constituting the simulated surrounding rock to obtain different compressive elastic moduli;

[0024] or adjusting the depth of the inner groove of the simulated lining to obtain simulated tunnel internal water accumulation cavities of different sizes;

[0025] or adjusting the water quality injected into the groove to obtain simulated cavity accumulated water of different hardnesses.

[0026] —— Add an experimental parameter adjustment step in Step 2, which includes adjusting the temperature maintained in the refrigeration box to obtain different frost heaving environments for the accumulated water inside the simulated tunnel;

[0027] —— Add an analysis step for the collected data in Step 3, which includes the processing module of the data acquisition device calculating the collected frost heaving force and expansion amount data to form experimental results or other processed data that change with time.

[0028] Compared with the prior art, an experimental device for simulating the frost heaving of accumulated water inside a tunnel lining provided by the present invention has the following advantages: First, since the experimental device includes a simulated lining and a simulated surrounding rock that are entirely located within a frame, the simulated lining has a trough for accommodating accumulated water, and the simulated surrounding rock seals the trough, thereby simulating the water accumulation cavity on the back of the tunnel lining. The overall structure is simple, convenient for processing and manufacturing, with low usage costs, and the structure can be adjusted accordingly for the surrounding rock stiffness, water accumulation volume, etc., improving the application range of the experimental device; Second, since a distance measuring device is provided between the simulated surrounding rock and the simulated lining to reflect the expansion amount of the accumulated water frost heaving in the trough, and a pressure sensor is provided at the bottom of the trough to feedback the expansion force of the accumulated water frost heaving in the trough, both the distance measuring device and the pressure sensor are electrically connected to data acquisition equipment. This experimental device can record the data information of the frost heaving force and the expansion amount in real time, and the obtained experimental data is close to the actual engineering situation. Further, a processing module in the data acquisition equipment that calculates and analyzes the collected data can deeply process the experimental data, and the processing results are more valuable for reference; Third, the experimental method mainly using the above device fully simulates the frost heaving process of water accumulation in the cavity on the back of the tunnel lining. By collecting the data of the frost heaving force and the expansion amount, experimental results close to the actual working conditions of the tunnel are obtained, and various data can be deeply processed according to production needs. This method is simple to operate, the experimental links are clear, the parameters are easy to adjust, the data results are accurate, and the practical value is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a schematic structural diagram of an experimental device for simulating the frost heaving of accumulated water inside a tunnel lining according to the present invention (the part below the dotted line is a three-dimensional view of the experimental device);

[0030] Figure 2 is a schematic structural diagram of the frame including a pre-tightening spring in the experimental device;

[0031] Figure 3 is a schematic diagram of the parameters of three groups of experimental models;

[0032] Figure 4-1 is a frost heaving force - time curve of the first group of experimental models at different temperatures;

[0033] Figure 4-2 is a comparison histogram of the expansion rates of the test models of the first group of experimental models;

[0034] Figure 5-1 is a frost heaving force - time curve of the second group of experimental models under different stiffnesses of the simulated surrounding rock;

[0035] Figure 5-2 is a comparison histogram of the expansion rates of the test models of the second group of experimental models;

[0036] Figure 6-1The frost heaving force - time curve of the third - group experimental model under different water quality conditions;

[0037] Figure 6-2 It is a histogram comparing the expansion rates of the test models of the third - group experimental model. Specific implementation manner

[0038] The following further details the structure and working principle of an experimental device for simulating the frost heaving of accumulated water inside a tunnel lining provided by the present invention with reference to the accompanying drawings.

[0039] See Figure 1 , which is a schematic structural diagram of an experimental device for simulating the frost heaving of accumulated water inside a tunnel lining provided by the present invention. The structure of the experimental device includes a simulated lining 2 and a simulated surrounding rock 3 that are both located inside a frame 1 as a whole. The simulated lining 2 has a trough 21 for accommodating accumulated water, and the simulated surrounding rock 3 encloses the trough 21. A spacing measurer is arranged between the simulated surrounding rock 3 and the simulated lining 2 to reflect the expansion amount of the accumulated water frozen in the trough 21. A pressure sensor is arranged at the bottom of the trough 21 to feedback the expansion force of the accumulated water frozen in the trough 21. Both the spacing measurer and the pressure sensor are electrically connected to a data acquisition device.

[0040] Its working principle is as follows: The trough 21 of the simulated lining 2 of the device is filled with experimental accumulated water, and it is sealed with the simulated surrounding rock 3 on top. The two are placed as a whole inside the frame 1. Inside the frame 1, the simulated surrounding rock 3 and the simulated lining 2 are in a relatively free state. When the water body inside the simulated lining 2 freezes, it pushes the simulated surrounding rock 3 upward, causing the spacing between the simulated surrounding rock 3 and the simulated lining 2 to change. The spacing measurer sends the above - mentioned data to the data acquisition device in real - time. At the same time, due to the pressure sensor arranged inside the trough 21 of the simulated lining 2, during the freezing process of the water body, the pressure sensor sends the frost heaving force data to the data acquisition device in real - time.

[0041] In the structure of the above - mentioned experimental device,

[0042] —— In order to accurately reflect the expansion amount of the accumulated water during the frost heaving process, the above - mentioned spacing measurer is a height measurer 4, which is composed of a reference part 41 arranged outside the simulated lining 2 and a movable part 42 arranged outside the simulated surrounding rock 3. The simulated surrounding rock 3 is pushed by the frozen accumulated water and moves upward, forming a change in the spacing between the simulated surrounding rock 3 and the simulated lining 2. The height measurer 4 is used to detect the change in the relative height of the change state, and this change amount can be used to infer the expansion rate after the accumulated water freezes;

[0043] - Preferably, the above pressure sensor includes a resistance strain gauge 51 and a resistance strain indicator 52 connected by a wire 50. To improve the experimental accuracy, the resistance strain gauge 51 is preferably an ultra-thin type. The ultra-thin resistance strain gauge 51 is adhered to the bottom of the central groove 21 of the simulated lining 2 with a low-temperature-resistant epoxy adhesive. The resistance strain indicator 52 is preferably a dynamic and static resistance strain indicator. The resistance strain gauge 51 is placed inside the groove 21 and covered with a sealed partition to prevent water accumulation from penetrating and damaging the electronic devices. The resistance strain indicator 52 is placed outside the simulated lining 2 and connected to the data acquisition device. The simulated lining 2 has a through hole 53 for the wire 50 to pass through. After the accumulated water freezes, it presses down on the resistance strain gauge 51, and the frost heaving force is converted into electronic data by the resistance strain indicator 52 and sent to the data acquisition device;

[0044] - The above frame 1 includes an upper frame body 11 and a lower frame body 12 made of steel sections. The four corners of the upper frame body 11 and the lower frame body 12 have extended ends for setting fastening bolts 13. In a specific experiment, the theoretical expansion amount after freezing can be deduced based on the injection volume of the experimental accumulated water in the simulated lining 2. At this time, the upper frame body 11 is positioned above this theoretical expansion amount through the fastening bolts 13, so as to satisfy the relatively free movement of the simulated surrounding rock 3, that is, the accumulated water freezes and expands without being restricted by the simulated surrounding rock 3. Such a frame 1 is used to simulate the situation where the surrounding rock 3 does not exert a compressive effect on frost heaving;

[0045] - Further, a pre-tightening spring 15 is sleeved on the fastening bolt 13 below the nut 14 of the above fastening bolt 13. The compression amount of the pre-tightening spring 15 is not less than the expansion amount after the accumulated water in the simulated lining 2 freezes. The frame 1 with the added pre-tightening spring 15 keeps the simulated surrounding rock 3 and the simulated lining 2 in an elastic compression state as a whole. After the accumulated water freezes and expands upward, it is oppressed by the simulated surrounding rock 3, which is closer to the actual distribution of the frost heaving force of the accumulated water in the cavity behind the tunnel lining, and improves the applicable range and data diversity of this experimental device;

[0046] - Preferably, the above data acquisition device is a PLC controller or a PC 6. The PLC controller or the PC 6 has a processing module (including analysis software) for calculating and analyzing the collected data, which can deeply process the collected frost heaving force and expansion amount data. For example, the relative height difference detected by the height measuring instrument 4 is converted into the expansion rate after the accumulated water freezes, and the time change curve of the frost heaving force / expansion rate is plotted and output, making the experimental data visual and diverse, and facilitating construction guidance;

[0047] —— When this experimental device is used to simulate the situation of a tunnel in a cold region, the tunnel can be approximated as a cylindrical container with surrounding constraints, a free top surface, and a rigid bottom surface, which restricts the free expansion of the volume of the local cavity after water accumulation and freezing along the normal direction. Therefore, the above-mentioned simulated lining 2 is overall cylindrical, the groove body 21 is located at the center of the upper surface, and the simulated surrounding rock 3 is a circular sheet or disc composed of a front steel plate 31 and a bottom rubber plate 32, and its size is the same as that of the upper surface of the simulated lining 2;

[0048] —— Preferably, in order to improve the structural strength of the simulated surrounding rock 3, the front steel plate 31 of the above-mentioned simulated surrounding rock 3 and the simulated lining 2 are both made of Q235 steel. After low-temperature freezing, the deformation is small, and compared with the freeze-thaw expansion change of the accumulated water, its deformation amount can be ignored. The sealing partition covering the resistance strain gauge 51 includes a steel backing plate 22 with the same inner diameter as the groove body 21, and a sealing ring 23 is arranged around the steel backing plate 22, ensuring the balanced force of the resistance strain gauge 52 and more accurate detection of the frost heaving force.

[0049] Using the above experimental device to conduct an experiment on the freeze-thaw expansion of accumulated water inside the simulated tunnel lining, a total of 17 simulated tunnel local cavity water accumulation and freezing conditions are involved in the specific embodiments of this patent, which are divided into 3 groups of tests. The specific scheme is as Figure 3 shown:

[0050] Group I includes 3 groups of parallel tests. Each group of parallel tests includes three test models with different simulated cavity depths. During the test, the stiffness of the simulated surrounding rock 3 in each group of parallel tests is the same, but the temperatures are different;

[0051] In Group II, the physical dimensions of the test models are the same, the water level heights are the same, the test temperature environments are the same, and the stiffness of the simulated surrounding rock 3 is different;

[0052] In Group III, the stiffness of the simulated surrounding rock 3 is the same, the physical dimensions of the test models are the same, the test temperatures are the same, and the hardness of the water injected into the simulated cavity is different.

[0053] The specific experimental process is as follows:

[0054] Use a low-temperature-resistant epoxy resin adhesive to paste the resistance strain gauge 51 on the bottom of the groove body 21 of the simulated lining 2, and cover it with a 5-mm-thick steel backing plate 22. A sealing ring is arranged at the edge of the steel backing plate 22 to isolate the water body;

[0055] Inject water to the corresponding height into the tank 21 of each simulated lining 2 according to the experimental plan, seal the tank 21 with the simulated surrounding rock 3, place the two in the frame 1, set the distance (relative height) between the simulated surrounding rock 3 and the simulated lining 2 according to the theoretical expansion amount after the water body in the tank 21 freezes on the upper frame body of the frame 1 and lock it with the fastening bolt 13, or set a pre-tightening spring 15 on the fastening bolt 13 to elastically press the simulated surrounding rock 3 against the simulated lining 2. Both structures can realize the freezing expansion of the experimental accumulated water. The former is not restricted by the simulated surrounding rock 3, or is restricted by the simulated surrounding rock 3. Measure the relative height h1 between the simulated surrounding rock 3 and the simulated lining 2 in the initial state, and place it in a refrigeration box (low-temperature environmental box) at the designed temperature in the experimental plan and freeze for 5 hours to ensure that all the water in the test model freezes;

[0056] Measure the relative height h2 between the simulated surrounding rock 3 and the simulated lining 2 after the experimental accumulated water freezes. Since the expansion volume of the test model due to cooling can be ignored, the relative height difference between the simulated surrounding rock 3 and the simulated lining 2 before and after the water freezes is the expansion amount. Calculate the volume expansion rate of the experimental accumulated water freezing in each test model as (h2 - h1) / tank depth, where the tank depth is the initial depth of the experimental accumulated water. When the reference part 41 of the height measuring instrument 4 is set at the same horizontal position as the bottom of the tank 21 of the simulated lining 2 and the movable part 42 of the height measuring instrument 4 is set at the same horizontal position as the lower edge of the simulated surrounding rock 3, the volume expansion rate of the experimental accumulated water freezing in each test model is (h2 - h1) / h1, and h1 is the initial depth of the experimental accumulated water;

[0057] The resistance strain gauge 52 and the height measuring instrument 4 send the frost heaving stress and expansion amount data received by the test model to the data acquisition device, which is stored or output by the data acquisition device;

[0058] Since the temperature change range is relatively large during the test process, in this patent embodiment, an automatic temperature compensation type resistance strain gauge 51 is selected to monitor the frost heaving force received by the inner wall of the simulated tunnel test model, and a dynamic and static resistance strain gauge 52 is used to measure the strain values at each strain gauge. The data acquisition device collects the strain values at the set sampling frequency and uploads them to the processing module, such as a PC computer 6 or a PLC controller, calculates the frost heaving force and expansion rate received by it, and then draws a strain-time curve;

[0059] Test Results and Analysis

[0060] 1. Different Freezing Temperatures of Experimental Accumulated Water

[0061] In order to explore the influence of temperature on the frost heaving force and expansion rate generated by accumulated water behind the lining of tunnels in cold regions. In the embodiments of this patent, three groups of parallel frost heaving tests are carried out. Each group of parallel tests includes one test model with the depth of the simulated lining 2 groove body 21 (simulated cavity depth) being 10 mm, 20 mm, and 30 mm respectively. In each test model, the simulated surrounding rock 3 is composed of an 8-mm-thick rubber plate + a 12-mm-thick steel plate, the simulated lining 2 is made of Q235 steel plate, and the ultra-thin resistance strain gauge 51 is installed at the bottom of the 5-mm-thick steel backing plate 22 to measure the frost heaving force. According to the depth of the cavity in the simulated lining 2, each test model is filled with water in sequence, and then each group of test models is placed in a low-temperature environmental chamber at -10°C, -15°C, and -20°C for five hours. Set a fixed sampling frequency for the strain value. After the test, the frost heaving force-time curves at different temperatures are plotted as Figure 4-1 shown, and the comparison histogram of the expansion rate of the test models is as Figure 4-2 shown.

[0062] From Figure 4-1 , Figure 4-2 analysis, it can be seen that the trends of the frost heaving force-time curves of each test model are roughly the same and can be divided into three stages: the stage without frost heaving force, the stage with a sharp increase in frost heaving force, and the stage with the frost heaving force tending to be stable. Horizontally comparing the test models with the same depth of the three simulated cavities in the three groups of parallel tests, it can be known that the frost heaving force of the test models with the same physical size is greatly affected by temperature. The lower the temperature and the faster the freezing rate, the greater the final frost heaving force and the smaller the expansion rate.

[0063] Taking the test model with a simulated cavity depth of 30 mm as an example, in the -10°C environment, the holding time of the test model I-3 in the stage without frost heaving force is about 1 hour, the time in the stage with a sharp increase in frost heaving force is about 1.5 hours, and finally its frost heaving force stabilizes at 0.24 MPa; in the -15°C environment, the holding time of the test model I-6 in the stage without frost heaving force is about 45 minutes, the time in the stage with a sharp increase in frost heaving force is about 1 hour and 15 minutes, and after the water completely freezes, its frost heaving force fluctuates around 0.43 MPa; while in the -20°C environment, the holding time of the test model I-9 in the stage without frost heaving force is about 20 minutes, the time in the stage with a sharp increase in frost heaving force is about 1 hour, and finally the frost heaving force it receives is about 0.48 MPa. Under the condition that other conditions are the same, the frost heaving force and the freezing rate increase with the decrease of temperature, and the expansion rate decreases with the decrease of temperature.

[0064] Meanwhile, by vertically comparing the three test models with different simulated cavity depths in each group of parallel tests, it can be seen that: under the same temperature condition, the less the accumulated water volume, the faster the freezing speed. After all the water in the test model is frozen into ice, the frost heaving force generated increases with the increase of the accumulated water volume, while the volume expansion rate tends to be stable and unchanged. Taking the temperature of -10°C as an example, the final frost heaving forces suffered by the test models with simulated cavity depths of 10mm, 20mm, and 30mm are 0.06MPa, 0.12MPa, and 0.24MPa respectively, and the expansion rates of the three are all about 10.7%. Therefore, under the same temperature condition, the expansion rate remains basically unchanged, but the frost heaving force increases with the increase of the accumulated water.

[0065] 2. Different simulated surrounding rock grades

[0066] In the embodiments of this patent, four simulated surrounding rocks 3 with different stiffnesses are used to explore the influence of different surrounding rock grades on the frost heaving force and expansion rate generated by the accumulated water behind the lining of the tunnel in cold regions. The four test models selected in this group of tests have simulated surrounding rocks 3 of 5mm thick rubber plate + 35mm thick steel plate, 4mm thick rubber plate + 36mm thick steel plate, 2mm thick rubber plate + 38mm thick steel plate, and 1mm thick rubber plate + 39mm thick steel plate respectively. The corresponding compression elastic moduli are 200MPa, 400MPa, 800MPa, and 1600MPa in sequence. The simulated cavity depth is 30mm for all. The simulated lining 2 uses Q235 steel plate. The ultra-thin resistance strain gauges 51 are installed at the bottom of the 5mm thick steel backing plate 22 to measure the frost heaving force. Water is filled into the test models in sequence, and then each test model is placed in a low-temperature environmental chamber at -20°C for five hours. Set the sampling frequency of a fixed strain value. After the test, the frost heaving force-time curves under different stiffnesses of the simulated surrounding rock 3 are drawn as Figure 5-1 shown, and the expansion rate comparison histogram of the test models is as Figure 5-2 shown.

[0067] From Figure 5-1 、 Figure 5-2 analysis, it can be seen that the final frost heaving forces suffered by the test models -1、 -2、 -3、 -4 fluctuate around 4.11MPa, 8.80MPa, 13.62MPa, and 24.45MPa respectively; the volume expansion rates are 8.34%, 6.62%, 3.32%, and 1.72% in sequence. From the above data, it can be obtained that the frost heaving force suffered by the simulated tunnel test model increases with the increase of the stiffness of the simulated surrounding rock 3, and is significantly higher than the frost heaving force under the unpressurized state with the same water column height; the volume expansion rate of water freezing decreases with the increase of the stiffness of the simulated surrounding rock 3, and is significantly lower than the volume expansion rate under the unpressurized state with the same water column height.

[0068] The test results show that the surrounding rock grade has a significant impact on the frost heaving force and expansion rate generated by accumulated water. On the premise that other conditions are the same, the greater the stiffness of the surrounding rock, the greater the frost heaving force on the lining of the tunnel in cold regions, and the smaller the expansion rate generated by the freezing of water.

[0069] 3. Different hardness of water

[0070] The types and contents of minerals contained in different geological formations are different. Therefore, the types and contents of minerals contained in the accumulated water under different geological conditions are also not the same. The content of minerals in water directly affects the hardness of water. In engineering projects, it is difficult and time-consuming to measure the frost heaving force of accumulated water, while it is less difficult to detect the hardness of water. Therefore, it is extremely important to clarify the influence of the hardness of water on the frost heaving force and expansion rate of the accumulated water behind the lining of the tunnel in cold regions.

[0071] In order to explore the variation law of the frost heaving force and expansion rate at the same position of the tunnel in cold regions with the hardness of water, four test models with a simulated cavity depth of 30 mm were selected in this patent embodiment. The simulated surrounding rock 3 uses a 1-mm-thick rubber plate + a 39-mm-thick steel plate, and the simulated lining 2 uses Q235 steel plate. The ultra-thin resistance strain gauge 51 is installed at the bottom of the 5-mm-thick steel backing plate 22 to measure the frost heaving force. The test models III-1, III-2, III-3, and III-4 are filled with distilled water, water with calcium carbonate contents of 0.5 mg / L, 1.5 mg / L, and 3.5 mg / L respectively, and finally placed in a low-temperature environmental chamber at -20 °C for freezing for five hours. Set a fixed strain value sampling frequency. After the test, the frost heaving force-time curves under different water quality conditions are plotted as Figure 6-1 shown, and the comparison histogram of the expansion rates of the test models is as Figure 6-2 shown.

[0072] From Figure 6-1 analysis, it can be obtained that the magnitudes of the frost heaving forces finally received by the test models III-1, III-2, III-3, and III-4 are approximately: 24.46 MPa, 23.82 MPa, 23.40 MPa, and 23.08 Mpa in sequence. From Figure 6-2 it can be obtained that the final volume expansion rates of the above four test models are: 1.71%, 1.73%, 1.76%, and 1.78% in sequence. Finally, it can be analyzed that the hardness of the accumulated water has a certain impact on the frost heaving force received by the lining of the tunnel in cold regions and the volume expansion rate of the accumulated water. Since the volume expansion of minerals in water can be ignored under low-temperature conditions, most of the expansion deformation is absorbed during the expansion of water, so the frost heaving force generated by the freezing of the accumulated water is weakened. Therefore, under the condition that other conditions are the same, the greater the hardness of water, the greater the expansion rate and the smaller the frost heaving force.

Claims

1. An experimental device for simulating the frost heaving of accumulated water inside a tunnel lining, Characterized in that: It includes a simulated lining and a simulated surrounding rock that are both located inside a frame. The simulated lining has a tank for accommodating accumulated water, and the simulated surrounding rock encloses the tank. A distance measuring device is arranged between the simulated surrounding rock and the simulated lining to reflect the expansion amount of the accumulated water freezing and swelling in the tank; a pressure sensor is arranged at the bottom of the tank to feedback the expansion force of the accumulated water freezing and swelling in the tank; both the distance measuring device and the pressure sensor are electrically connected to a data acquisition device; The frame includes an upper frame body and a lower frame body composed of steel sections, and the four corners of the upper frame body and the lower frame body have extended ends for setting fastening bolts; The lower part of the nut of the fastening bolt has a pre-tightening spring sleeved on the fastening bolt, and the compression amount of the pre-tightening spring is not less than the expansion amount after the accumulated water in the simulated lining freezes and swells; The simulated lining is integrally cylindrical, the tank is located at the center of the upper surface, and the simulated surrounding rock is a disc or circular plate composed of a front steel plate and a bottom rubber plate and has the same size as the upper surface of the simulated lining.

2. An experimental device for simulating the frost heaving of accumulated water inside a tunnel lining according to claim 1, Characterized in that: The distance measuring device is a height measuring instrument, which is composed of a reference part arranged outside the simulated lining and a movable part arranged outside the simulated surrounding rock.

3. An experimental device for simulating the frost heaving of accumulated water inside a tunnel lining according to claim 1, Characterized in that: The pressure sensor includes a resistance strain gauge and a resistance strain indicator connected by a wire. The resistance strain gauge is placed inside the tank and is covered with a sealing partition plate. The resistance strain indicator is placed outside the simulated lining and is connected to the data acquisition device. The simulated lining has a through hole for the wire to pass through.

4. An experimental device for simulating the frost heaving of accumulated water inside a tunnel lining according to claim 3, Characterized in that: The front steel plate of the simulated surrounding rock and the simulated lining are both made of Q235 steel. The sealing partition plate covering the resistance strain gauge includes a steel backing plate with the same inner diameter as the tank, and a sealing ring is arranged around the steel backing plate.

5. An experimental device for simulating the frost heaving of accumulated water inside a tunnel lining according to claim 1, Characterized in that: The data acquisition device is a PC or a PLC controller, and the PC or the PLC controller has a processing module for calculating and analyzing the collected data.

6. An experimental method for simulating the frost heaving of accumulated water inside a tunnel lining, Characterized in that: Using the experimental device according to any one of claims 1 to 5, including the following steps: Step 1, Assemble the experimental device Set a pressure sensor at the bottom of the tank of the simulated lining, inject water of a set specification into the tank, seal it with the simulated surrounding rock. The frame makes the simulated surrounding rock and the simulated lining in a relatively free state, or the pre-tightening spring of the frame makes the simulated lining and the simulated surrounding rock in an elastically compressed state as a whole. Install a distance measuring device between the simulated lining and the simulated surrounding rock. Both the pressure sensor and the distance measuring device are electrically connected to the data acquisition device; Step 2: Simulate the frost heaving process Place the experimental device assembled in Step 1 into the refrigeration box, and ensure that the accumulated water inside the experimental device is completely frozen within a predetermined time. Step 3: Collect experimental data During the predetermined time in Step 2, the pressure sensor and the spacing measurer feed back the data of frost heaving force and expansion amount to the data acquisition device in real time, and the data acquisition device stores or outputs the experimental results.

7. An experimental method for simulating frost heaving of accumulated water inside a tunnel lining according to claim 6, characterized in that: In Step 1, add an adjustment step for experimental parameters, which includes adjusting the thickness of the Q235 steel plate and the rubber plate constituting the simulated surrounding rock to obtain different compressive elastic moduli; or adjusting the depth of the inner groove body of the simulated lining to obtain simulated tunnel internal water accumulation cavities of different sizes; or adjusting the water quality injected into the groove body to obtain simulated cavity accumulated water of different hardnesses.

8. An experimental method for simulating frost heaving of accumulated water inside a tunnel lining according to claim 6, characterized in that: In Step 2, add an adjustment step for experimental parameters, which includes adjusting the temperature maintained in the refrigeration box to obtain different frost heaving environments of the accumulated water inside the simulated tunnel.

9. An experimental method for simulating frost heaving of accumulated water inside a tunnel lining according to claim 6, characterized in that: In Step 3, add an analysis step for the collected data, which includes the processing module of the data acquisition device calculating the collected data of frost heaving force and expansion amount to form experimental results or other processed data that change with time.

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