Model device and test method for supporting on-ground freezing of geotechnical centrifuge

Abstract

This invention relates to a model device and testing method for supporting on-machine freezing in a geotextile centrifuge, comprising: a model test chamber for holding test soil; a measurement system, in conjunction with the model test chamber and the test soil, for measuring soil parameters; a data acquisition system, connected to the measurement system, for acquiring soil parameters; a data analysis system, connected to the data acquisition system, for analyzing soil parameters; and a freezing system, including a semiconductor freezing module positioned above the test soil within the model test chamber. Compared with existing technologies, this invention utilizes the Peltier effect generated by the semiconductor in the freezing system under the action of electric current to cool and freeze the soil in the test chamber. This allows for direct freezing of the soil within the test chamber during centrifuge operation, reducing errors caused by freezing during downtime. Furthermore, by utilizing the equivalence principle between the centrifuge's gravitational field and centrifugal force field, it maximizes the reproduction of the true stress state of frozen or artificially frozen soil.

Description

Technical Field

[0001] This invention relates to the field of geotextile centrifuge applications, and in particular to a model device and testing method for supporting on-machine freezing of a geotextile centrifuge. Background Technology

[0002] Artificial ground freezing is a commonly used green construction method for underground space excavation in soft soil areas along my country's coast. It features good water sealing, strong adaptability, and convenient and environmentally friendly construction, and has been widely applied in subway connecting passages, tunnel boring machine entry and exit, river-crossing and sea-crossing passages, and emergency rescue operations. However, both frozen soil and artificially frozen soil have obvious engineering characteristics such as frost heave, thaw settlement, and rheological properties, which can easily lead to various problems and seriously threaten the safety and stability of buildings and structures.

[0003] Current research on large-scale artificial permafrost or permafrost engineering projects typically utilizes numerical analysis, physical experiments, and physical simulation tests. While full-scale model tests can more closely approximate the engineering prototype, this method suffers from drawbacks such as long development cycles, high costs, and inaccurate data collection. Scale-down model tests, although addressing some of these issues, suffer from the scaling effect, resulting in scale-inaccurate analyses of temperature fields, stress fields, and soil moisture migration.

[0004] To address the shortcomings of full-scale and scaled-down tests, researchers invented the geotextile centrifuge. Correspondingly, geotextile centrifuge simulation tests utilize the high-speed rotation of a centrifuge to create a stress field in the model that matches the stress level of the prototype, thus reproducing the properties of the prototype in the model—a physical simulation method. Therefore, many scholars have used geotextile centrifuges to conduct research on frozen soil or artificial frozen soil engineering.

[0005] Furthermore, conventional freezing methods, such as those using vortex tubes, primarily separate high-speed rotating compressed air into low-temperature and high-temperature gases. The resulting cold air continuously freezes the soil. However, this method requires high-speed rotating compressed air for cooling, and the storage tanks for this compressed air are relatively large, making storage inconvenient. Therefore, to achieve freezing, many researchers use a shutdown method to freeze the soil. However, this indirect freezing method significantly affects the accuracy of the experimental results and is not conducive to observing the freezing evolution of the test soil in the model box under a specific gravity environment and operating time.

[0006] In summary, given the shortcomings of the indirect freezing scheme used in existing geotechnical centrifuge frozen soil research, it is necessary to propose a solution. Summary of the Invention

[0007] The purpose of this invention is to overcome the defects of the prior art by providing a model device and test method for supporting on-machine freezing of a geotextile centrifuge.

[0008] The objective of this invention can be achieved through the following technical solutions:

[0009] According to a first aspect of the present invention, a model-freezing device for supporting on-machine freezing of a geotextile centrifuge is provided, comprising:

[0010] Model test chamber, used to hold test soil;

[0011] The measurement system, used in conjunction with the model test chamber and the test soil, is used to measure soil parameters;

[0012] The data acquisition system, connected to the measurement system, is used to collect soil parameters;

[0013] The data analysis system, connected to the data acquisition system, is used to analyze soil parameters;

[0014] The freezing system includes a semiconductor freezing module, which is positioned above the test soil inside the model test chamber.

[0015] Furthermore, the model test chamber includes an inner chamber and an outer chamber, with a sandwich structure formed between the side walls of the inner and outer chambers. The inner chamber is used to place the test soil, and the inner side wall of the inner chamber is provided with thermal insulation material.

[0016] The freezing system also includes a refrigerant freezing module, which includes a refrigerant medium. The refrigerant medium is placed in the interlayer between the inner and outer boxes. The top of the side wall of the inner box is provided with a refrigerant transmission port, which is located above the top of the test soil. The refrigerant medium enters the inner box through the refrigerant transmission port.

[0017] Furthermore, the semiconductor freezing module includes a heat-conducting aluminum plate, a semiconductor refrigeration chip, a power supply, a heat-conducting copper pipe, and a heat dissipation device. The power supply is connected to each semiconductor refrigeration chip. The semiconductor refrigeration chips are assembled on the heat-conducting aluminum plate, and the cold end of the semiconductor refrigeration chip is connected to the upper surface of the heat-conducting aluminum plate. The hot end of the semiconductor refrigeration chip is connected to the heat dissipation device through the heat-conducting copper pipe.

[0018] Furthermore, the upper surface of the cooling aluminum plate is also covered with a heat-insulating film.

[0019] Furthermore, the heat dissipation device includes a finned heat sink, a cooling fan, and a fan guard. The heat-conducting copper pipe is connected to the finned heat sink, the cooling fan is fixed on the finned heat sink, and the fan guard is disposed outside the cooling fan.

[0020] Furthermore, the freezing system also includes a freezing tube, the end of which is higher than the top of the test soil. The main body of the freezing tube is buried inside the test soil in the model test chamber. The freezing tube is used to transfer the cooling capacity of the semiconductor freezing module and the refrigerant freezing module to the interior of the test soil. The freezing tube is arranged in the upper half of the central plane of the model test chamber in a plane parallel to the side wall of the model test chamber.

[0021] Furthermore, the measurement system includes a pressure measurement system, which includes a soil pressure sensor and a pore pressure sensor. The installation planes are located at different horizontal distances from the freezing pipe, and the soil pressure sensor and the pore pressure sensor are buried at different depths on each installation plane.

[0022] Furthermore, the measurement system includes a temperature measurement system, which includes a transverse thermistor temperature measuring device and a longitudinal thermistor temperature measuring device. The transverse thermistor temperature measuring device is set at different depths on a pre-set frozen curtain boundary plane, with different horizontal distances from the freezing tube as the mounting plane. The longitudinal thermistor temperature measuring device is set at different depths on each mounting plane.

[0023] Furthermore, the measurement system includes a displacement measurement system, which comprises a layered displacement marker and a laser displacement sensor. The installation planes are located at different horizontal distances from the freezing pipe. The lower end plate of the layered displacement marker is set at different depths on each installation plane, and the upper end plate of the layered displacement marker is positioned above the top of the test soil. The laser displacement sensor is installed above the test soil and is used to measure the displacement of the upper end plate of the layered displacement marker.

[0024] According to a second aspect of the present invention, a test method is provided, based on a model apparatus for supporting on-machine freezing of a geotextile centrifuge as described in the first aspect of the present invention, comprising:

[0025] S1. Design a centrifuge test model box, determine the actual research object and the type of soil, and then fill the test soil in layers into the test model box;

[0026] S2. Set up the measurement system in the test model box according to the test plan;

[0027] S3. Install a freezing system on the test model box;

[0028] S4. Place the centrifuge test model box into the centrifuge chamber, turn on the geotechnical centrifuge, and simultaneously start the freezing system to freeze the centrifuge.

[0029] S5. Record the parameter changes of the test soil in the test model box through the measurement system, and transmit the measurement data to the data analysis system through the data acquisition system to perform soil parameter analysis.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) The Peltier effect generated by the semiconductor in the freezing system under the action of current is used to cool and freeze the soil in the test chamber. The soil in the test chamber can be directly frozen during the operation of the centrifuge, which reduces the error caused by freezing when the machine is stopped. The equivalence principle between the gravity field and the centrifugal force field of the centrifuge is used to restore the true stress state of frozen soil or artificial frozen soil to the greatest extent. By gradually freezing during the operation of the centrifuge, the changes in temperature field, stress field and frost heave of frozen soil or artificial frozen soil can be truly reproduced.

[0032] (2) The Peltier effect generated by the semiconductor under the action of electric current is used to cool and freeze the soil in the test chamber. At the same time, the liquid nitrogen and other refrigerants are used to evaporate and generate cold air under the rotation of the centrifuge to cool the soil. Different freezing requirements can be achieved by adjusting the power of the semiconductor freezing module and the amount of cold medium, which effectively ensures the freezing of the soil. The overall operation is simple, the technology is mature and it saves space effectively.

[0033] (3) Throughout the entire test, the temperature, soil pressure, pore water pressure, stratified frost heave, and surface frost heave of the frozen soil can be collected in real time through the data acquisition system. The data analysis system can summarize and analyze the changing patterns of the soil during the continuous freezing process. Attached Figure Description

[0034] Figure 1 This is a longitudinal cross-sectional view of the model test setup;

[0035] Figure 2 This is a partial transverse cross-section and phase transition zone diagram of the model test device;

[0036] Figure 3 This is a schematic diagram of the semiconductor refrigeration system at the top of the model test chamber;

[0037] Figure reference numerals: 1. Model test chamber; 2. Test soil; 3. Cooling medium; 4. Freezing pipe; 5. Insulation material; 6. Soil pressure sensor; 7. Pore pressure sensor; 8. Lateral thermistor temperature sensor; 9. Longitudinal thermistor temperature sensor; 10. Layered displacement gauge; 11. Data acquisition system; 12. Data analysis system; 13. Power switch; 14. Laser displacement sensor; 15. Cooling medium transfer port; 16. Semiconductor refrigeration system; 161. Semiconductor refrigeration chip; 162. Cooling-conducting aluminum plate; 163. Insulation film; 164. Power cord; 165. Thermally conductive copper pipe; 166. Finned radiator; 167. Cooling fan; 168. Fan cover; 169. Fastening screw; 17. Cavity. Detailed Implementation

[0038] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are implemented based on the technical solutions of the present invention, providing detailed implementation methods and specific operating procedures. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them, and the scope of protection of the present invention is not limited to the following embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0039] In the accompanying drawings, components with the same structure are indicated by the same numerical designation, and components with similar structures or functions are indicated by similar numerical designations. The dimensions and thicknesses of each component shown in the drawings are arbitrary, and the present invention does not limit the dimensions and thicknesses of each component. To make the illustrations clearer and show the mating relationships between the components, some parts in the drawings have been appropriately scaled down, and the distances between the components have been increased or decreased.

[0040] In the description of the embodiments of this application, it should be understood that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly placed when the product of this application is used, or the orientation or positional relationship commonly understood by those skilled in the art. They are only for the convenience of describing this application and simplifying the description, and are not intended to indicate or imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0041] In the description of the embodiments of this application, it should also be noted that, unless otherwise expressly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0042] Example 1:

[0043] This invention provides a model freezing device that supports on-machine freezing of a geotextile centrifuge, such as... Figures 1-3 As shown, it includes:

[0044] Model test chamber 1, used to hold test soil 2;

[0045] The measurement system, in conjunction with the model test chamber 1 and the test soil 2, is used to measure soil parameters;

[0046] Data acquisition system 11, connected to the measurement system, is used to collect soil parameters;

[0047] Data analysis system 12, connected to data acquisition system 11, is used to analyze soil parameters;

[0048] The freezing system includes a semiconductor freezing module 16, which is positioned above the test soil 2 inside the model test chamber 1.

[0049] like Figure 3 As shown, the semiconductor cooling module 16 includes a heat-conducting aluminum plate 162, semiconductor cooling chips 161, a power supply, a heat-conducting copper pipe 165, and a heat dissipation device. The power supply is connected to each semiconductor cooling chip 161. Several semiconductor cooling chips 161 are assembled on the heat-conducting aluminum plate 162, with the cold end of the semiconductor cooling chip 161 connected to the upper surface of the heat-conducting aluminum plate 162, and the hot end of the semiconductor cooling chip 161 connected to the heat dissipation device through the heat-conducting copper pipe 165. The upper surface of the heat-conducting aluminum plate 162 is also covered with a heat-insulating film 163 to reduce heat loss. The heat dissipation device includes a finned heat sink 166, a cooling fan 167, and a fan shield 168. The heat-conducting copper pipe 165 connects to the finned heat sink 166, the cooling fan 167 is fixed to the finned heat sink 166, and the fan shield 168 is disposed outside the cooling fan 167.

[0050] Specifically, the dimensions of the cooling aluminum plate 162 can be customized according to the length and width of the designed model box. The cooling aluminum plate 162 is installed on top of the model box, covering the entire interior. Then, semiconductor cooling chips 161, heat-conducting copper pipes 165, and heat dissipation devices are installed on the cooling aluminum plate 162. A battery of suitable size and power can be used as the power source. The various semiconductor cooling chips 161 are interconnected via power lines 164. In practice, the centrifuge is started and the power switch 13 is turned on. When the direct current passes through the thermocouple in the semiconductor cooling chip 161, the Peltier effect is generated at both ends. One side forms a cold junction, absorbing heat from the outside, while the other side forms a hot junction, releasing heat to the outside. Connecting several such thermocouples constitutes a thermopile. The cold junction of the thermopile is placed on the cooling aluminum plate 162, which is placed inside the model box to absorb and cool the model. The heat from the hot junction is conducted through the heat-conducting copper pipes 165, and then quickly dissipated by the finned heat sink 166 and the cooling fan 167. The cooling fan 167 is protected by a fan cover 168, which serves a safety function. The cooling fan 167 can be fixed to the finned heatsink 166 by fastening screws 169.

[0051] The semiconductor freezing module 16 is an independent component that uses the Peltier effect generated by the semiconductor in the freezing system under the action of current to cool and freeze the soil in the model test chamber 1. It can directly freeze the soil in the model test chamber 1 while the centrifuge is running, reducing the error caused by freezing during shutdown. By utilizing the equivalence principle between the centrifuge's gravity field and centrifugal force field, it restores the true stress state of frozen soil or artificially frozen soil to the greatest extent.

[0052] However, considering that the power of semiconductor cooling may not be sufficient to meet the freezing requirements, the freezing system also includes a refrigerant freezing module. Specifically, the model test chamber 1 includes an inner chamber and an outer chamber, with a sandwich structure formed between the side walls of the inner and outer chambers. The inner chamber is used to place the test soil 2, and the inner side wall of the inner chamber is provided with insulation material 5 (such as polystyrene foam board, polyurethane insulation board, etc.). The refrigerant freezing module includes a refrigerant 3 (such as liquid nitrogen, liquid ammonia, dry ice, etc.), which is placed in the sandwich between the inner and outer chambers. The top of the side wall of the inner chamber is provided with a refrigerant transmission port 15, which is located higher than the top of the test soil 2. The refrigerant 3 enters the inner chamber through the refrigerant transmission port 15.

[0053] The model test chamber 1 is made of stainless steel and has a double-layer structure with an inner and outer box. The inner box holds the test soil 2 and various measuring instruments. The model test chamber 1 is filled with insulation material 5, which reduces the loss of cold air inside the model chamber and reduces the heat brought by the outside air through heat conduction with the chamber.

[0054] A refrigerant 3 is placed between the inner and outer walls of the inner and outer boxes. There is a refrigerant transfer port 15 between the inner and outer boxes. The refrigerant 3 enters the inner box through the transfer port. Liquid nitrogen and other refrigerants evaporate under the rotation of the centrifuge to generate cold air, which then continuously cools the surface soil inside the box.

[0055] The freezing system also includes a freezing pipe 4, the end of which is higher than the top of the test soil 2. The main body of the freezing pipe 4 is buried inside the test soil 2 in the model test chamber 1. The freezing pipe 4 is used to transfer the cooling capacity of the semiconductor freezing module 16 and the refrigerant freezing module to the interior of the test soil 2. In particular, the refrigerant 3 evaporates under the rotation of the centrifuge to generate cold air, which can enter the freezing pipe 4 and continuously cool the lower soil through the freezing pipe 4, thus accelerating the entire freezing process.

[0056] It is important to note that the refrigerant transfer port 15 and the freezing tube 4 are not connected by a pipe. Instead, a cavity 17 is reserved to allow the refrigerant to enter the inner chamber from the refrigerant transfer port 15 and then diffuse into the freezing tube 4. There are two reasons for this arrangement. First, the cold air generated by the evaporation of refrigerants such as liquid nitrogen under centrifugal rotation requires a cavity (space). The cold air in the cavity is transferred downwards through the freezing tube 4 for freezing, and also allows the upper surface soil (especially areas far from the freezing tube 4) to begin freezing, thus ensuring uniform freezing of the soil within the test chamber. Second, the cold air generated by the semiconductor cooling chip when the power is turned on relies on the freezing tube 4 for downward transfer. If the pipe is connected or the cavity is not provided, the diffusion efficiency of the cold air generated by the semiconductor cooling chip to the lower soil and other areas is slow, leading to uneven freezing and affecting the overall cooling efficiency. In short, the absence of a connection between the freezing tube and the refrigerant transfer port, and the provision of a cavity, are designed to allow the semiconductor freezing module and the refrigerant freezing module to work together more conveniently and efficiently to achieve uniform freezing and meet the expected requirements.

[0057] The freezing pipe 4 is arranged in a plane parallel to the side wall of the model test chamber 1, on the upper half of the central plane of the chamber 1. The test soil 2 is frozen by the freezing pipe 4 as a planar freezing source. The temperature field of the soil on both sides of the freezing pipe 4 is symmetrical, and the freezing conditions are the same. The direction of the freezing front advances from the freezing pipe 4 to both sides of the model test chamber 1. The freezing pipe 4 is only buried in the upper half of the soil for two reasons. First, considering that the test is conducted on a centrifuge, and taking into account the wear and tear of the equipment and the freezing efficiency of the freezing module, it is not necessary to completely freeze the soil in the test chamber. The existing arrangement of the freezing pipes can form a frozen soil wall, which meets the needs of studying the temperature field, stress field, and frost heave of artificial frozen soil projects. Second, many current artificial freezing projects are constructed under combined strata conditions such as upper soft clay and lower sand, where the upper layer is frozen and the lower layer is not. The arrangement of this invention can meet the needs of various research.

[0058] This invention utilizes the Peltier effect generated by a semiconductor under the influence of an electric current to cool and freeze the soil in the model test chamber 1. Simultaneously, it employs liquid nitrogen or other refrigerants, evaporated under centrifugal rotation to generate cold air, providing dual cooling of the soil. Different freezing requirements can be achieved by adjusting the power of the semiconductor freezing module 16 and the amount of cooling medium 3. This invention can simulate the real state of soil gradually freezing in frozen soil engineering or artificial freezing projects, providing technical support for investigating changes in soil temperature, stress, and displacement during the construction of frozen soil engineering projects and artificial freezing methods for projects such as subway connecting passages and coal mine shafts.

[0059] The measurement system includes a pressure measurement system, a temperature measurement system, and a displacement measurement system. Of course, in practical applications, other measurement devices can be set up according to the parameters to be studied.

[0060] Since the temperature field distribution of the test soil 2 is symmetrical about the freezing pipe 4, and the freezing front advances along the freezing pipe 4 towards both sides of the model test box 1, theoretically, the soil parameters at the same horizontal distance and depth from the freezing pipe 4 are the same. Therefore, taking different horizontal distances from the freezing pipe 4 as the installation plane, each sensor of the measurement system is buried at different depths on each installation plane to complete the overall parameter measurement of the soil.

[0061] The pressure measurement system includes an earth pressure sensor 6 and a pore pressure sensor 7. The earth pressure sensor 6 mainly measures the stress changes of unfrozen and frozen soil during the freezing process; the pore pressure sensor 7 mainly measures the pore water pressure changes of unfrozen and frozen soil during the freezing process.

[0062] The temperature measurement system includes a transverse thermistor temperature measuring device and a longitudinal thermistor temperature measuring device. The longitudinal thermistor temperature measuring device is set at different depths on each mounting plane. In addition, the transverse thermistor temperature measuring device is set at different depths on the pre-set freezing curtain boundary plane. The depths of the thermistor temperature measuring devices set on the freezing curtain boundary plane and the mounting plane can be the same.

[0063] In the temperature measurement system, one set of transverse thermistor temperature sensors 8 and three sets of longitudinal thermistor temperature sensors 9 are configured. Since the soil freezing process involves unfrozen zones, frozen zones, phase transition zones, and the boundary of a freezing curtain (a water-resistant layer formed during freezing, resembling a curtain, also known as a frozen soil wall), the transverse thermistor temperature sensor set is positioned at the assumed freezing curtain boundary during the freezing process of the test soil 2. Four thermistor temperature sensors are horizontally positioned along the depth direction of the model test chamber 1 to monitor the temperature of the frozen soil wall at different depths. The approximate location of the freezing curtain boundary can be determined through pre-experiments or theoretical calculations. Furthermore, as... Figure 2 As shown, during the gradual freezing of the soil, the freezing front continuously evolves from the frozen area to the unfrozen area. Therefore, longitudinal thermistor temperature sensor groups are arranged along the direction of the freezing front's advance, with three groups on each horizontal plane and four groups at the same depth as the transverse thermistor temperature sensor groups, to monitor temperature changes throughout the frozen area. All thermistor temperature sensors are connected to the data acquisition system 11 via data cables, and the data is further analyzed by the data analysis system 12 on the computer.

[0064] The displacement measurement system includes layered displacement markers 10 and laser displacement sensors 14. Layered displacement markers 10 are used in conjunction with laser displacement sensors 14 and other equipment to measure the settlement or heave changes of soil layers at a certain depth. Laser displacement sensors 14 are primarily used to measure the displacement changes of surface soil before and after frost heave. The lower end plate of the layered displacement markers 10 is set at different depths on each installation plane, and the upper end plate of the layered displacement markers 10 is positioned above the top of the test soil mass 2. Laser displacement sensors 14 are installed above the test soil mass 2 to measure the displacement of the upper end plate of the layered displacement markers 10. Three surface displacement measuring points are set up for the horizontal displacement of the model box, located in the center and on both sides of the frozen zone. Vertically, along the displacement measuring point in the center of the frozen zone, a layered displacement marker 10 is buried at different heights and staggered. Since the movement of the upper end plate of the layered displacement marker 10 reflects the displacement of the soil at its lower end plate, the vertical displacement difference can be measured using laser displacement sensors 14. It should be noted that when the layered displacement marker 10 is buried at the designed depth, attention should be paid to the settlement caused by the consolidation of the soil. Therefore, it can be buried at a depth slightly shallower than the designed depth to compensate for the settlement caused by soil consolidation. The specific difference can be determined through preliminary experiments.

[0065] The present invention also provides a test method based on the above-described model device for supporting on-machine freezing of a geotextile centrifuge, comprising:

[0066] S1. Design a centrifuge test model box based on the engineering case, determine the actual research object and the type of soil, and then fill the test soil in two layers into the test model box.

[0067] The scale of the model box is determined based on the engineering case to be studied, then the specific research object is determined, and the physical quantity to be measured is defined, that is, the measurement system is determined.

[0068] To determine the specific research object and soil type, we take the fourth layer of silty clay in Shanghai as an example. This soil layer is frequently encountered during the construction of subway connecting tunnels in Shanghai. The construction of these tunnels typically employs artificial freezing, a special construction technique that uses artificial refrigeration to freeze the water in the strata, transforming the natural rock and soil into frozen soil. This increases the soil's strength and stability, isolates groundwater from underground engineering, and allows for the excavation and lining of shafts or underground structures under the protection of the frozen wall.

[0069] After the samples were obtained on site, the soil was disturbed, so the mud method was used to prepare the reshaped samples. After saturation, the samples were filled into the model test chamber 1 in layers, and the soil was pre-compressed until the settlement reached stability.

[0070] S2. Set up the measurement system in the test model box according to the test plan;

[0071] Before backfilling, insulation material 5 is placed on the inner wall of the model box, and the cooling medium transmission port 15 is covered with an object to prevent it from entering the soil sample. Then, based on the determined physical quantities, the measuring devices are selected and installed. It should be noted that the temperature sensor, earth pressure sensor 6, and stratified displacement marker 10 should be installed slightly shallower than the design depth to offset the soil settlement caused by subsequent soil consolidation. At the same time, based on the estimated freezing curtain boundary, the cooling pipes are also installed at the expected design positions. Then, each measuring device is connected to the data acquisition system 11 via a data cable, and each device is zeroed. After the soil is backfilled, the soil sample is preloaded using the preloading method. After the soil settlement meets the requirements, the next test is conducted.

[0072] S3. Install a freezing system on the test model box;

[0073] Assemble the semiconductor cooling chip 161, the heat-conducting aluminum plate 162, and the cooling fan 167, and perform pre-testing to check for poor contact in the circuitry. Simultaneously, measure the surface temperature of the heat-conducting aluminum plate 162. If the semiconductor freezing module 16 can meet the cooling and freezing power requirements, the refrigerant freezing module does not need to be activated; otherwise, the refrigerant freezing module needs to be activated, as follows:

[0074] After the soil has consolidated, open the refrigerant transfer port 15 and inject a small amount of liquid nitrogen into the space between the inner and outer chambers of the model test. Cover the upper part of the chamber and allow it to stand for a period of time. Then measure the temperature change of the freezing pipe 4. If the temperature at the bottom of the soil shows a decreasing trend compared to when the freezing pipe 4 was not installed, it indicates that the freezing pipe 4 is performing well. Next, inject sufficient liquid nitrogen into the space between the inner and outer chambers of the model test and check for any leaks.

[0075] Then completely cover the top of the model box with the cooling aluminum plate 162.

[0076] S4. Place the centrifuge test model box into the centrifuge chamber, turn on the geotechnical centrifuge, and simultaneously start the freezing system to freeze the centrifuge.

[0077] Set the operating values ​​and operating time of the geotextile centrifuge and start the geotextile centrifuge, while simultaneously turning on the power switch 13 of the semiconductor freezing module.

[0078] S5. The parameter changes of the test soil 2 in the test model box are recorded by the measurement system, and the measurement data is transmitted to the data analysis system 12 through the data acquisition system 11 to perform soil parameter analysis, including data such as temperature, displacement, soil pressure, and pore water pressure.

[0079] Of course, by changing different soil types and measuring devices, the changes in temperature, stress, displacement, and other variables of different soil types under frozen conditions can be obtained. These will not be elaborated here, as those skilled in the art will understand.

[0080] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A model-freezing device for use in a geotextile centrifuge, characterized in that, include: Model test chamber, used to hold test soil; The measurement system, used in conjunction with the model test chamber and the test soil, is used to measure soil parameters; The data acquisition system, connected to the measurement system, is used to collect soil parameters; The data analysis system, connected to the data acquisition system, is used to analyze soil parameters; The freezing system includes a semiconductor freezing module, which is positioned above the test soil inside the model test chamber; The model test chamber includes an inner chamber and an outer chamber, with a sandwich structure formed between the side walls of the inner and outer chambers. The inner chamber is used to hold the test soil, and the inner side wall of the inner chamber is provided with thermal insulation material. The freezing system also includes a refrigerant freezing module, which includes a refrigerant medium. The refrigerant medium is placed in the interlayer between the inner and outer boxes. The top of the side wall of the inner box is provided with a refrigerant transmission port. The refrigerant transmission port is located above the top of the test soil. The refrigerant medium enters the inner box through the refrigerant transmission port. The semiconductor freezing module includes a heat-conducting aluminum plate, a semiconductor refrigeration chip, a power supply, a heat-conducting copper pipe, and a heat dissipation device. The power supply is connected to each semiconductor refrigeration chip. The semiconductor refrigeration chips are assembled on the heat-conducting aluminum plate, and the cold end of the semiconductor refrigeration chip is connected to the upper surface of the heat-conducting aluminum plate. The hot end of the semiconductor refrigeration chip is connected to the heat dissipation device through the heat-conducting copper pipe. The freezing system also includes a freezing tube, the end of which is higher than the top of the test soil. The main body of the freezing tube is buried inside the test soil in the model test chamber. The freezing tube is used to transfer the cooling capacity of the semiconductor freezing module and the refrigerant freezing module to the interior of the test soil. The freezing tube is set in the upper half of the central plane of the model test chamber in a plane parallel to the side wall of the model test chamber.

2. The model device for supporting on-machine freezing of a geotextile centrifuge according to claim 1, characterized in that, The upper surface of the cooling aluminum plate is also covered with a heat-insulating film.

3. The model device for supporting on-machine freezing of a geotextile centrifuge according to claim 1, characterized in that, The heat dissipation device includes a finned heat sink, a cooling fan, and a fan cover. The heat-conducting copper pipe is connected to the finned heat sink, the cooling fan is fixed on the finned heat sink, and the fan cover is installed outside the cooling fan.

4. The model device for supporting on-machine freezing of a geotextile centrifuge according to claim 1, characterized in that, The measurement system includes a pressure measurement system, which includes a soil pressure sensor and a pore pressure sensor. The installation planes are located at different horizontal distances from the freezing pipe, and the soil pressure sensor and the pore pressure sensor are buried at different depths on each installation plane.

5. The model device for supporting on-machine freezing of a geotextile centrifuge according to claim 1, characterized in that, The measurement system includes a temperature measurement system, which includes a transverse thermistor temperature measuring device and a longitudinal thermistor temperature measuring device. The transverse thermistor temperature measuring device is set at different depths on a pre-set frozen curtain boundary plane, with different horizontal distances from the freezing tube as the mounting plane. The longitudinal thermistor temperature measuring device is set at different depths on each mounting plane.

6. The model device for supporting on-machine freezing of a geotextile centrifuge according to claim 1, characterized in that, The measurement system includes a displacement measurement system, which comprises a layered displacement marker and a laser displacement sensor. The installation planes are located at different horizontal distances from the freezing pipe. The lower end plate of the layered displacement marker is set at different depths on each installation plane, and the upper end plate of the layered displacement marker is positioned above the top of the test soil. The laser displacement sensor is installed above the test soil and is used to measure the displacement of the upper end plate of the layered displacement marker.

7. A test method, characterized in that, A model device for supporting on-machine freezing of a geotextile centrifuge as described in any one of claims 1-6, comprising: S1. Design a centrifuge test model box, determine the actual research object and the type of soil, and then fill the test soil in layers into the test model box; S2. Set up the measurement system in the test model box according to the test plan; S3. Install a freezing system on the test model box; S4. Place the centrifuge test model box into the centrifuge chamber, turn on the geotechnical centrifuge, and simultaneously start the freezing system to freeze the centrifuge. S5. Record the parameter changes of the test soil in the test model box through the measurement system, and transmit the measurement data to the data analysis system through the data acquisition system to perform soil parameter analysis.

Images