An apparatus and a testing method for measuring the thermal conductivity of seepage soil

Abstract

The present invention relates to the technical field of geotechnical construction, and specifically to a device and a testing method for measuring the thermal conductivity of seepage soil. The measuring device includes a test box body, a test sample arranged inside the test box body, a water inlet pipe and a water outlet pipe arranged on the left and right sides of the test box body; it further includes: a thermal conductivity reference material arranged inside the test box body and located above the test sample; a temperature control panel arranged on the upper and lower surfaces of the test box body and in contact with the test sample and the thermal conductivity reference material respectively; a plurality of temperature sensors distributed inside the test box body; and a flowmeter arranged on the water outlet pipe. By obtaining the thermal conductivity of the soil layer under seepage conditions, the present invention can effectively improve the freezing reinforcement effect and the design level of the freezing scheme, can simulate the formation seepage conditions, and test the thermal conductivity of the soil layer under the action of seepage; the present invention can be not affected by factors such as the particle size of the soil sample and the flatness of the test surface, and the test results are reliable and the accuracy is high.

Description

Technical Field

[0001] The present invention relates to the technical field of geotechnical construction, and particularly to a device and a test method for measuring the thermal conductivity of seepage soil mass. Background Technique

[0002] So far, 44 cities in China have opened rail transit, with a total mileage of more than 7,700 kilometers. The length of the subway lines under construction exceeds 2,800 kilometers, and the planned construction lines exceed 2,500 kilometers. Among the cities with opened, under-construction or planned rail transit, about 60% of the cities have the situation of passing through flowing water strata such as under the river bottom or the bottom of the river, for example, the Shanghai Metro passes through the Huangpu River, the Guangzhou Metro passes through the Pearl River, the Wuhan Metro passes through the Yangtze River, the Hangzhou Metro passes under the Qiantang River, the Fuzhou Metro passes under the Wulong River and the Minjiang River, the Lanzhou Metro passes under the Yellow River, the Nanchang Metro passes under the Ganjiang River and the Qingshan Lake, etc., and there are significant seepage phenomena in the strata.

[0003] In the construction of subway tunnels, connection channels and other underground projects in water-rich strata, the artificial freezing method is the most effective method for strengthening the water-rich strata. However, the seepage in the strata will carry away the "cold energy" generated by the freezers, directly affecting the change of the temperature field during the freezing process, resulting in problems such as difficult freezing connection and irregular freezing curtain shape. Considering the thermal conductivity of the soil layer with seepage is a key parameter in the design of the freezing scheme. Accurately obtaining the thermal conductivity of the seepage strata can effectively improve the design level and reinforcement effect of the artificial freezing scheme for the strata.

[0004] The current conventional thermal conductivity measuring instruments only have the function of measuring the thermal conductivity of static specimens and cannot test the thermal conductivity of soil layers under dynamic seepage conditions. In the development of underground space in coastal cities and inland river cities, water-rich and strongly permeable strata are generally encountered. When the freezing method is used for stratum water stop and reinforcement, the seepage effect will have a significant impact on the heat transfer and temperature field distribution in the soil layer. In addition, the current conventional thermal conductivity measuring instruments are significantly affected by the particle size and the flatness of the test surface during the test. In view of this, the present invention proposes a device and a test method for measuring the thermal conductivity of seepage soil mass. Summary of the Invention

[0005] In view of the problem that seepage in the strata affects the freezing connection and the shape of the curtain, the present invention proposes a device and a test method for measuring the thermal conductivity of seepage soil mass.

[0006] The technical problems to be solved by the present invention are realized by adopting the following technical solutions:

[0007] A device for measuring the thermal conductivity of seepage soil mass includes a test box body, a test sample arranged inside the test box body, a water inlet pipe and a water outlet pipe arranged on the left and right sides of the test box body, and the thickness of the test sample is H2;

[0008] It further includes:

[0009] A heat conduction reference material, which is arranged in a layered manner corresponding to the test sample in the test chamber and is located above the test sample, with a thickness of H1;

[0010] A temperature control panel, which is arranged on the upper and lower surfaces of the test chamber and is in contact with the test sample and the heat conduction reference material respectively, for controlling the temperature gradient in the test chamber;

[0011] Temperature sensors, with multiple distributed inside the test chamber, for measuring the temperature inside the test chamber after a stable temperature gradient is formed inside the test chamber;

[0012] A flowmeter, which is arranged on the outlet pipe, for measuring the seepage velocity flowing through the test chamber;

[0013] Based on the temperature values measured by the temperature sensors and the seepage velocity measured by the flowmeter, the temperature gradient of the test sample and the heat conduction reference material and the heat carried out by seepage are calculated, so as to establish an explicit function of the thermal conductivity of the test sample, the thermal conductivity of the reference material, the seepage velocity, and the thicknesses of the test sample layer and the heat conduction reference material layer.

[0014] Preferably, heat insulation materials are provided around the outside of the test chamber.

[0015] Preferably, two layers of gravel buffer layers are correspondingly arranged on the inner sides of the left and right surfaces of the test chamber.

[0016] Preferably, the thickness dimension of the gravel buffer layer is 2 - 5 cm.

[0017] Preferably, the dimension of the thickness H1 of the heat conduction reference material is 3 - 10 cm.

[0018] Preferably, the dimension of the thickness H2 of the test sample is 10 - 30 cm.

[0019] Preferably, the widths of the test sample and the heat conduction reference material are both L, and the dimension of the width L is 10 - 30 cm, and the width L of the heat conduction reference material is equal to the dimension of the thickness H2 of the test sample.

[0020] Preferably, the heat conduction reference material is any one of paraffin, plexiglass, and marble.

[0021] Preferably, multiple temperature sensors are correspondingly distributed on the left and right side walls inside the test chamber, at the contact positions between the temperature control panel and the test sample, between the temperature control panel and the heat conduction reference material, and between the test sample and the heat conduction reference material.

[0022] A test method using the seepage soil thermal conductivity measurement device, the specific steps are as follows:

[0023] (1) Calibrate the thermal conductivity of the thermal reference material: Test the thermal conductivity of the selected thermal reference material to provide calculation parameters for subsequent tests;

[0024] (2) Layer by layer, load the test sample, temperature sensor, and thermal reference material: Load the test sample layer by layer at 5 - 10 cm per layer, fix and place the temperature sensor, and load the thermal reference material;

[0025] (3) Provide a stable water source and control the seepage velocity: Introduce a water source with a stable flow rate into the test chamber, obtain the seepage velocity based on the feedback of the flowmeter, and form a stable seepage in the test sample;

[0026] (4) Set a constant temperature on the upper and lower temperature control panels and measure the stable temperature values at each point: Set the temperatures of the upper and lower two temperature control panels, keep the constant temperature difference greater than 10 °C. After the temperature in the test chamber stabilizes, read the temperature values of each point temperature sensor;

[0027] (5) Calculate the thermal conductivity of the test sample.

[0028] The beneficial effects of the present invention are as follows:

[0029] 1. By obtaining the thermal conductivity of the soil layer under seepage conditions, the present invention can effectively improve the freezing reinforcement effect and the freezing scheme design level, can simulate the formation seepage conditions, and test the thermal conductivity of the soil layer under the action of seepage;

[0030] 2. The present invention can be not affected by factors such as the particle size of the soil sample and the flatness of the test surface, and the test results are reliable and highly accurate;

[0031] 3. The present invention can promote the improvement of the freezing method scheme design level. The formation thermal conductivity is a key thermal parameter in the freezing method design and the prediction and forecast of freezing development. By obtaining the thermal parameters of the seepage formation and quantitatively considering the influence of the seepage velocity in the formation on the thermal performance of the soil body, it has a significant promoting effect on improving the freezing curtain design level and the accuracy of form prediction. Description of the Drawings

[0032] The present invention will be further described below in conjunction with the drawings and embodiments:

[0033] Figure 1 is a schematic structural diagram of the device in the present invention;

[0034] Figure 2 is a schematic diagram of the test principle of the present invention.

[0035] In the figure: 1. Temperature control panel; 2. Test chamber; 3. Thermal insulation material; 4. Water inlet pipe; 5. Water outlet pipe; 6. Flowmeter; 7. Temperature sensor; 8. Gravel sand buffer layer; 9. Test sample; 10. Thermal reference material. Detailed implementation mode

[0036] In order to make the technical means, creative features, achieved purposes and functions of the present invention easy to understand, the present invention will be further described below in conjunction with the attached drawings and embodiments.

[0037] As Figure 1 shown, a device for measuring the thermal conductivity of seepage soil mainly consists of a temperature control panel 1, a test box 2, a heat insulation material 3, a water inlet pipe 4, a water outlet pipe 5, a flow meter 6, a temperature sensor 7, a gravel sand buffer layer 8, a test sample 9, and a thermal conductivity reference material 10. Two temperature control panels 1 are provided, closely attached to the upper and lower surfaces of the test box 2, for controlling the temperature gradient inside the test box 2. The heat insulation material 3 is arranged on the front, back, left, and right sides of the test box 2. The water inlet pipe 4 and the water outlet pipe 5 are arranged on the left and right sides of the test box 2, and the water outlet pipe 5 is connected to the flow meter 6 to measure and control the seepage velocity flowing through the test box 2. Five temperature sensors 7 are provided, corresponding to being distributed on the inner left and right side walls of the test box 2, the contact positions of the temperature control panel 1 with the test sample 9, the contact positions of the temperature control panel 1 with the thermal conductivity reference material 10, and the contact positions of the test sample 9 with the thermal conductivity reference material 10. The test sample 9 and the thermal conductivity reference material 10 are correspondingly arranged in layers inside the test box 2. The thicknesses of the test sample 9 and the thermal conductivity reference material 10 are H2 and H1 respectively. The size of H1 is 3 - 10 cm, and the size of H2 is 10 - 30 cm; the widths of the test sample 9 and the thermal conductivity reference material 10 are both L, and the size of the width L is 10 - 30 cm, and the width L of the thermal conductivity reference material 10 is equal to the size of the thickness H2 of the test sample 9. Two layers of gravel sand buffer layers 8 are provided, correspondingly arranged on the inner sides of the left and right sides of the test box 2, allowing water to flow in and out of the test sample 9 from the left and right sides, and the thickness size of the gravel sand buffer layer 8 is 2 - 5 cm.

[0038] Furthermore, the law of the change of the thermal conductivity of the thermal conductivity reference material 10 with temperature has been obtained in advance and is a known parameter, and materials such as paraffin, plexiglass, and marble can be used.

[0039] The present invention sets the temperature gradient inside the test box 2 through the two temperature control panels 1 on the upper and lower surfaces, and controls the seepage velocity in the test sample 9 by adjusting the water flow rates of the water inlet pipe 4 and the water outlet pipe 5; after the temperature field state is constant during the test, the temperature values at each position are measured, and the temperature gradients in the layers of the test sample 9 and the thermal conductivity reference material 10 and the heat carried away by seepage are calculated, and an explicit function of the thermal conductivity of the test sample, the thermal conductivity of the thermal conductivity parameter material, the seepage velocity, the thickness of each material layer, etc. is established.

[0040] As Figure 2 shown, the principle description of the measuring device in the present invention is specifically as follows:

[0041] Paraffin is used as the heat conduction reference material. The thermal conductivity λ1 is a known quantity, i.e., 0.279 W / (m·°C); the thickness of the paraffin is H1, and the thickness of the test sample is H2; under the action of the upper and lower temperature control panels 1, when the temperatures at each point in the test chamber are stable, the temperature of the top surface of the paraffin is measured as t1, the interface temperature between the paraffin and the test sample 9 is t2, the temperature of the bottom surface of the test sample 9 is t3, the inlet water temperature is t4, and the outlet water temperature is t5; the water flow through the test chamber 2 is uniform and stable, the water flow rate is qw, and the seepage velocity is v = qw / A; in the test chamber, the width L of the top surface of the paraffin is equal to the thickness H2 of the test sample, that is, the top surface area of the paraffin is made equal to the left and right side areas of the test sample, denoted as A. Denote the thermal conductivity of the test sample as λm.

[0042] When the seepage velocity v = 0, the temperatures at each point in the test chamber reach a stable state. According to Fourier's law, the heat flux densities q1 through the paraffin layer and q2 through the test sample layer are:

[0043]

[0044] q1 = q2 (3)

[0045] ΔT1 = t2 - t1 (4)

[0046] ΔT2 = t3 - t2 (5)

[0047] Then the thermal conductivity λ m of the test sample and the thermal conductivity λ1 of the paraffin have the following relationship:

[0048]

[0049] When the seepage velocity v ≠ 0, the water flow rate is qw, and the temperatures at each point in the test chamber 2 reach a stable state. Establish a heat balance equation for the heat in the test chamber 2:

[0050] Q1 = Q 1-2 = Q 2x + Q 2y (7)

[0051] Q1 = Q 1-2 = q1·A y (8)

[0052] Q 2y = q 2y ·A y (9)

[0053] Q 2x = C w ·m w ·△T w (10)

[0054] m w = v·Ax ·ρ w (11)

[0055] △T w = t5 - t4 (12)

[0056] In the above formula, Q1 represents the heat flux flowing through the paraffin layer, Q 1-2 represents the heat flux entering the test sample 9 through the interface between the paraffin layer and the test sample, Q 2x is the heat flux carried away by seepage, Q 2y is the heat flux transferred downward through the test sample 9. A x , A y respectively represent the areas of the left (right) and upper (lower) surfaces of the test surface. Since L = H2, so A x = A y = A. mw represents the mass of water flowing through the test sample 9 per unit time, △T w represents the change in water temperature after passing through the test sample 9, C w represents the specific heat capacity of water, which is 4.2×103 J / (kg·℃), ρ w represents the density of water, which is 1000 kg / m 3 . Then the heat balance equation can be written as:

[0057]

[0058] △T w = t5 - t4 (14)

[0059] v = q w / A x = q w / A (15)

[0060] According to Fourier's law, the heat flux density perpendicular to the paraffin layer and the test soil sample is:

[0061]

[0062] Then the heat balance equation can be written as:

[0063]

[0064] Then the thermal conductivity of the test soil sample considering the influence of seepage is:

[0065]

[0066] The thermal conductivity value of the test soil sample can be obtained. When v = 0, Equation (20) is exactly the same as Equation (6).

[0067] A test method using the device for measuring the thermal conductivity of seepage soil is as follows:

[0068] (1) Calibrate the thermal conductivity of the thermal conductivity reference material 10: Test the thermal conductivity of the selected thermal conductivity reference material 10 to provide calculation parameters for subsequent tests. The selected thermal conductivity reference material 10 has a uniform material overall, without internal cracks or damages.

[0069] (2) Layered loading of the test sample 9, temperature sensor 7, and thermal conductivity reference material 10: Layered load the test sample 9 at 5 - 10 cm per layer, fixedly place the temperature sensor 7, and load the thermal conductivity reference material 10.

[0070] (3) Provide a stable water source and control the seepage rate: Introduce a water source with a stable flow rate into the test box 2, obtain the seepage rate based on the feedback of the flowmeter (6), and form a stable seepage in the test sample 9.

[0071] (4) Set a constant temperature on the upper and lower temperature control panels 1 and measure the stable temperature values at each point: Set the temperatures of the upper and lower temperature control panels 1 to maintain a constant temperature difference greater than 10 °C. After the temperature in the test box 2 stabilizes, read the temperature values of each point of the temperature sensor 7.

[0072] (5) Calculate the thermal conductivity of the test sample 9. Calculate according to formula (20) to obtain the thermal conductivity of the test sample 9.

[0073] The above shows and describes the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification is only the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A device for measuring the thermal conductivity of seepage soil, comprising a test box body (2), a test sample (9) arranged inside the test box body (2), a water inlet pipe (4) and a water outlet pipe (5) arranged on the left and right sides of the test box body (2), characterized in that: The thickness of the test sample (9) is H2; It further includes: A thermal conductivity reference material (10), which is arranged in the test chamber (2) in corresponding layers with the test sample (9) and is located above the test sample (9), and its thickness is H1; A temperature control panel (1), which is arranged on the upper and lower surfaces of the test chamber (2) and is in contact with the test sample (9) and the thermal conductivity reference material (10) respectively, and is used to control the temperature gradient in the test chamber (2); Temperature sensors (7), a plurality of which are distributed inside the test chamber (2), and are correspondingly distributed on the left and right inner side walls of the test chamber (2), the contact positions between the temperature control panel (1) and the test sample (9), the contact positions between the temperature control panel (1) and the thermal conductivity reference material (10), and the contact positions between the test sample (9) and the thermal conductivity reference material (10), and are used to measure the temperature inside the test chamber (2) after a stable temperature gradient is formed inside the test chamber (2); A flowmeter (6), which is arranged on the outlet pipe (5) and is used to measure the seepage velocity flowing through the test chamber (2); Based on the temperature values measured by the temperature sensors (7) and the seepage velocity measured by the flowmeter (6), the temperature gradient of the test sample and the thermal conductivity reference material (10) and the heat carried out by seepage are calculated, so as to establish an explicit function of the thermal conductivity of the test sample, the thermal conductivity of the reference material, the seepage velocity, and the thicknesses of the test sample layer and the thermal conductivity reference material layer.

2. The device for measuring the thermal conductivity of a seepage soil body according to claim 1, characterized in that: Thermal insulation materials (3) are provided around the outside of the test chamber (2).

3. The device for measuring the thermal conductivity of a seepage soil body according to claim 1, wherein: Two layers of gravel sand buffer layers (8) are correspondingly arranged on the inner sides of the left and right surfaces of the test chamber (2).

4. The seepage soil thermal conductivity measuring device according to claim 3, characterized in that: The thickness dimension of the gravel sand buffer layer (8) is 2 - 5 cm.

5. The measuring device for the thermal conductivity of seepage soil according to claim 1, characterized in that: The dimension of the thickness H1 of the thermal conductivity reference material (10) is 3 - 10 cm.

6. The seepage soil thermal conductivity measuring device according to claim 1, wherein: The dimension of the thickness H2 of the test sample (9) is 10 - 30 cm.

7. The measuring device for the thermal conductivity of seepage soil according to claim 1, characterized in that: The widths of the test sample (9) and the thermal conductivity reference material (10) are both L, and the dimension of the width L is 10 - 30 cm, and the width L of the thermal conductivity reference material (10) is equal to the dimension of the thickness H2 of the test sample (9).

8. The device for measuring the thermal conductivity of a seepage soil mass according to claim 1, wherein: The thermal conductivity reference material (10) is any one of paraffin, plexiglass, and marble.

9. The device for measuring the thermal conductivity of a seepage soil body according to claim 1, characterized in that: A plurality of temperature sensors (7) are correspondingly distributed on the left and right inner side walls of the test chamber (2), the contact positions between the temperature control panel (1) and the test sample (9), the contact positions between the temperature control panel (1) and the thermal conductivity reference material (10), and the contact positions between the test sample (9) and the thermal conductivity reference material (10).

10. A testing method using the seepage soil thermal conductivity measuring device according to any one of claims 1 to 9, characterized in that: The specific steps are as follows: (1) Calibrate the thermal conductivity of the thermal conductivity reference material (10): Test the thermal conductivity of the selected thermal conductivity reference material (10) to provide calculation parameters for subsequent tests; (2) Layer by layer load the test sample (9), temperature sensors (7), and thermal conductivity reference material (10): Load the test sample (9) layer by layer at 5 - 10 cm per layer, fix and place the temperature sensors (7) well, and load the thermal conductivity reference material (10); (3) Provide a stable water source and control the seepage velocity: Introduce a water source with a stable flow rate into the test chamber (2), obtain the seepage velocity according to the feedback of the flowmeter (6), and form a stable seepage in the test sample (9); (4) Set a constant temperature on the upper and lower temperature control panels (1), and measure the stable temperature values at each point: Set the temperatures of the upper and lower temperature control panels (1), and keep the constant temperature difference greater than 10 °C. After the temperature in the test chamber (2) stabilizes, read the temperature values of the temperature sensors (7) at each point; (5) Calculate the thermal conductivity of the test sample (9).

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