阅读说明：本技术 一种测定土体冻结温度的试验装置 (Test device for measuring freezing temperature of soil body ) 是由 不公告发明人 于 2020-06-16 设计创作，主要内容包括：本发明公开了一种测定土体冻结温度的试验装置,其结构特征在于使用高频激振系统,为试样提供高频脉冲激振条件；使用控温精度超过±0.01℃的协同控温系统,为试样提供降温速率低于-0.1℃/min的缓慢线性降温冻结条件。高频脉冲激振可打破孔隙水冻结过程中的过冷状态,避免土体达到超过冷状态而无法测得有效的冻结温度数据。缓慢线性降温冻结模式可为试样提供均匀降温条件,从而保证整个试样处于相同的热状态,避免不均匀冻结过程对试验结果的影响。该装置解决了冻结温度试验中超过冷状态和试样尺寸效应对试验结果影响突出的问题,可以为研究土体冻结机理提供可靠的试验技术支撑。(The invention discloses a test device for measuring freezing temperature of a soil body, which is structurally characterized in that a high-frequency excitation system is used for providing high-frequency pulse excitation conditions for a sample; and a cooperative temperature control system with the temperature control precision exceeding +/-0.01 ℃ is used for providing a slow linear temperature reduction freezing condition with the temperature reduction rate lower than-0.1 ℃/min for the sample. The supercooling state in the pore water freezing process can be broken through by high-frequency pulse excitation, and the problem that effective freezing temperature data cannot be measured when the soil body exceeds the supercooling state is avoided. The slow linear cooling freezing mode can provide uniform cooling conditions for the sample, so that the whole sample is ensured to be in the same thermal state, and the influence of the non-uniform freezing process on the test result is avoided. The device solves the problem that the effect of exceeding a cold state and the size of a sample in a freezing temperature test has a remarkable influence on a test result, and can provide a reliable test technology support for researching a soil body freezing mechanism.)

1. A test device for measuring freezing temperature of soil body comprises a high-frequency excitation system, a top/bottom cooperative temperature control system, a test box, a heat insulation layer, a test box fixing screw rod, a temperature data acquisition system, a counter-force loading system and a thermostat, and is characterized in that the high-frequency excitation system consists of an excitation exciter, an excitation control module and an excitation plate, the excitation exciter is fixed on the excitation plate and is connected with the excitation control module by using a data line, and the high-frequency excitation system provides pulse excitation conditions with frequency exceeding 35kHz and amplitude lower than 60 mu m for a sample in a negative temperature state.

2. The testing device for measuring the soil body freezing temperature according to claim 1, wherein the top/bottom cooperative temperature control system is composed of a top temperature control plate, a bottom temperature control plate, a temperature sensor and a temperature control module, the top temperature control plate is arranged at the top of the sample, the bottom temperature control plate is arranged at the bottom of the sample, the temperature sensor is arranged in the top temperature control plate and the bottom temperature control plate and is connected with the temperature control module by a data line, the top temperature control plate and the bottom temperature control plate are connected with the temperature control module by a data line, the temperature control precision of the cooperative temperature control system exceeds +/-0.01 ℃, and a slow linear temperature reduction freezing condition with the temperature reduction rate lower than-0.1 ℃/min is provided for the sample.

Technical Field

The invention relates to the field of geotechnical engineering tests, in particular to a test device for measuring freezing temperature of a soil body.

Background

The freezing temperature is the critical temperature for the soil body to be converted from the non-freezing state to the freezing state, and is a key parameter which must be acquired in the construction process of cold regions and the construction process of the artificial freezing method. In the freezing process, the pore water is in an ice-water mixed state within a period of time after the phase change, a curve approximately parallel to a time axis is represented on a temperature curve, the curve is called as a stable freezing platform, and the temperature at the moment is the freezing temperature. The stable freezing platform provides conditions for acquiring freezing temperature data, and common modes comprise that a temperature sensor is used for directly acquiring freezing temperature and a frequency domain reflection method is used for indirectly acquiring freezing temperature.

It is well known that pore water is highlighted by capillary restriction, thereby causing the supercooling of water during freezing to be more prominent. If the supercooling temperature is too low, the amount of latent heat of phase change released is less than the amount of heat transferred from the test system to the sample, resulting in a very short time for the pore water to be in an ice-water mixed state, which appears as the absence of a stable freezing plateau on the freezing curve, a phenomenon known as "over-cooling" which, once present, does not result in an effective freezing temperature (Kozlowski T. Some factors after freezing and the freezing point in water-systems [ J ]. Cold Regions Science and Technology, 2009, 59(1): 25-33.). In addition, the test is carried out in the current geotechnical test method standard (GB/T50123-2019) by adopting a constant-temperature freezing mode, namely, the temperature of cooling liquid is kept constant, and a test sample is immersed into the cooling liquid for freezing and temperature measurement. However, in the freezing process, the surface layer of the sample may be frozen and the interior of the sample is at a normal temperature, so that the whole sample cannot be ensured to be in a uniform cooling and freezing state in the test process. Differential freezing can affect the test result of the freezing temperature, thereby causing the size effect of the test sample to be prominent. The soil body excess cold and size effects are two major factors influencing the quality of test data, and are problems to be solved urgently by current scientific research technicians.

Disclosure of Invention

The invention aims to provide a test device for measuring the freezing temperature of a soil body. The device can effectively solve the problems that the over-cooling phenomenon and the sample size effect widely existing in the current freezing temperature test have prominent influence on the test result.

The technical scheme for solving the technical problems is as follows: a test device for measuring freezing temperature of a soil body comprises a high-frequency excitation system, a top/bottom cooperative temperature control system, a test box, a heat insulation layer, a test box fixing screw rod, a temperature data acquisition system, a counter-force loading system and a constant temperature box. The high-frequency excitation system consists of an exciter, an excitation control module and an excitation plate, wherein the exciter is fixed on the excitation plate and is connected with the excitation control module by using a data line, and the high-frequency excitation system provides a pulse excitation condition with the frequency of more than 35kHz and the amplitude of less than 60 mu m for a sample in a negative temperature state.

The top/bottom cooperative temperature control system is composed of a top temperature control plate, a bottom temperature control plate, a temperature sensor and a temperature control module, wherein the top temperature control plate is arranged at the top of a sample, the bottom temperature control plate is arranged at the bottom of the sample, the temperature sensor is arranged in the top temperature control plate and the bottom temperature control plate and is connected with the temperature control module by a data line, the top temperature control plate and the bottom temperature control plate are connected with the temperature control module by the data line, the temperature control precision of the cooperative temperature control system exceeds +/-0.01 ℃, and a slow linear cooling freezing condition with the cooling rate lower than-0.1 ℃/min is provided for the sample.

The advantages and the beneficial effects of the invention are as follows:

1. the high-frequency pulse excitation is used for avoiding the occurrence of a soil body exceeding a cold state in the freezing process, ensuring that pore water is in an ice-water mixed state for a long time, and obtaining high-quality freezing temperature data.

2. The slow linear cooling freezing mode provided by the cooperative temperature control system provides uniform cooling conditions for the sample, thereby avoiding the condition of differential freezing inside and outside the sample, overcoming the influence of the non-uniform freezing process on the test result, and solving the problem of sample size effect.

Drawings

FIG. 1 is a schematic structural diagram of a soil freezing temperature test device of the present invention

FIG. 2 is a schematic diagram of the high frequency excitation system of the present invention

FIG. 3 is a schematic structural diagram of a top/bottom cooperative temperature control system according to the present invention

FIG. 4 is a schematic structural diagram of the test box, the insulating layer, the test box fixing screw, the temperature data acquisition system, the counter force loading system and the incubator of the invention

FIG. 5 is a comparison of test results with and without high frequency excitation

FIG. 6 is a comparison of test results of linear cooling freezing and cold bath constant temperature freezing

In the figure: 1. a high-frequency excitation system; 2. a top/bottom coordinated temperature control system; 3. a test kit; 4. a heat-insulating layer; 5. the test box is fixed with the screw; 6. a temperature data acquisition system; 7. a counter-force loading system; 8. a thermostat; 11. a vibration exciter; 12. an excitation control module; 13. an excitation plate; 14. a data line; 21. a top temperature control plate; 22. a bottom temperature control plate; 23. a temperature sensor; 24. a temperature control module; 25. a data line; 26. a data line; 31. a temperature sensor; 32. a temperature data acquisition module; 33. a data line; 34. a loading device; 35. loading a control module; 36. a reaction frame; 37. a data line; 38. screw rod

Detailed Description

The technical solutions of the present invention are described by way of embodiments with reference to the accompanying drawings, and the examples are only for explaining the present invention and are not used to limit the scope of the present invention. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

As shown in figure 1, the test device for measuring the freezing temperature of the soil body comprises a high-frequency excitation system 1, a top/bottom cooperative temperature control system 2, a test box 3, a heat insulation layer 4, a test box fixing screw 5, a temperature data acquisition system 6, a counter force loading system 7 and a constant temperature box 8. The high-frequency excitation system 1 consists of an exciter 11, an excitation control module 12 and an excitation plate 13, wherein the exciter 11 is fixed on the excitation plate 13 and is connected with the excitation control module 12 by a data line 14, and the high-frequency excitation system 1 provides a pulse excitation condition with the frequency of more than 35kHz and the amplitude of less than 60 mu m for a sample in a negative temperature state. The top/bottom cooperative temperature control system 2 is composed of a top temperature control plate 21, a bottom temperature control plate 22, a temperature sensor 23 and a temperature control module 24, wherein the top temperature control plate is arranged at the top of a sample, the bottom temperature control plate is arranged at the bottom of the sample, the temperature sensor 23 is arranged in the top temperature control plate 21 and the bottom temperature control plate 22 and is connected with the temperature control module 24 by a data line 25, the top temperature control plate 21 and the bottom temperature control plate 22 are electrically connected with the temperature control module 24 by a data line 26, the temperature control precision of the cooperative temperature control system 2 exceeds +/-0.01 ℃, and a slow linear cooling and freezing condition with the cooling rate lower than-0.1 ℃/min is provided for the sample. The test box 3 is packaged by the heat-insulating layer 4 and is fixed with the excitation plate 13 through the test box fixing screw 5. The temperature data acquisition system 6 is composed of a temperature sensor 31 and a temperature data acquisition module 32, wherein the temperature sensor 31 is connected with the temperature data acquisition module 32 by a data line 33. The reaction force loading system 7 is composed of a loading device 34, a loading control module 35 and a reaction frame 36, wherein the loading device 34 is connected with the loading control module 35 through a data line 37, and the reaction frame 36 is fixed with the vibration exciting plate 13 through a screw 38.

A freezing temperature test is carried out by using kaolin with the water content of 35 percent, 2 groups of tests (sample 1 and sample 2) are arranged according to the vertical pressure of 0MPa and 1MPa, 2 groups of control tests (sample 3 and sample 4) without high-frequency excitation are arranged under the same pressure condition, and in addition, 1 group of control group (sample 5) is arranged according to the freezing temperature test in the geotechnical test method standard (GB/T50123 and 2019). The initial temperature was set to 0.5 ℃ and held for 2 hours, after which a formal freezing test was carried out. The freezing mode adopts linear cooling and freezing, the cooling rate is-0.03 ℃/min, the duration of the freezing process is 5 hours, when the soil body temperature is in a negative temperature state, high-frequency pulse excitation is carried out, the frequency is 40kHz, the amplitude is 40 mu m, and the pulse frequency is 2 seconds/time. Fig. 5 shows temperature time-course curves of the samples 1, 2, 3 and 4 during the test, and fig. 6 shows temperature time-course curves of the samples 1, 3 and 5 during the test. As can be seen from FIG. 5, the high-frequency excitation can effectively break the metastable thermal state of the pore water in the freezing process, ensure the stable proceeding of the ice-water phase change, and represent a stable freezing platform for a long time in the temperature curve. The freezing temperatures obtained for samples 1 and 2 to which high-frequency pulse excitation was applied were-0.48 ℃ and-0.95 ℃, and the freezing temperatures obtained for samples 3 and 4 to which high-frequency pulse excitation was not applied were-0.87 ℃ and-1.41 ℃. Since both the samples 3 and 4 reached a cold state in the test, the measured freezing temperature values were low. As can be seen from fig. 5, according to the test method specified in the standard of geotechnical test methods (GB/T50123-2019), a temperature curve including a stable freezing platform cannot be obtained, and the freezing temperature of kaolin having a water content of 35% cannot be obtained.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.