WO2021254421A1 - 一种分布式土体导热系数测试方法及其测试系统 - Google Patents

一种分布式土体导热系数测试方法及其测试系统 Download PDF

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WO2021254421A1
WO2021254421A1 PCT/CN2021/100524 CN2021100524W WO2021254421A1 WO 2021254421 A1 WO2021254421 A1 WO 2021254421A1 CN 2021100524 W CN2021100524 W CN 2021100524W WO 2021254421 A1 WO2021254421 A1 WO 2021254421A1
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soil
thermal conductivity
tested
control module
temperature
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PCT/CN2021/100524
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English (en)
French (fr)
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顾凯
施斌
张博
魏广庆
向伏林
魏壮
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南京大学
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Publication of WO2021254421A1 publication Critical patent/WO2021254421A1/zh

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N25/00—Investigating or analyzing materials by the use of thermal means
    • G01N25/20—Investigating or analyzing materials by the use of thermal means by investigating the development of heat, i.e. calorimetry, e.g. by measuring specific heat, by measuring thermal conductivity

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  • the invention relates to the technical field of geological detection, in particular to a distributed soil thermal conductivity test method and a test system thereof.
  • the thermal conductivity of rock and soil is a key parameter reflecting the thermal conductivity of rock and soil.
  • obtaining thermal conductivity can serve for shallow ground temperature energy evaluation, underground engineering, freezing construction or foundation design in freeze-thaw areas, etc.
  • it can also indirectly calculate parameters such as soil moisture content and dry density and evaluate groundwater through thermal conductivity. Seepage and pollutant transfer.
  • Methods of obtaining thermal conductivity include indoor tests and on-site tests.
  • the indoor test includes the flat plate method and the hot wire method, and the field test is the transient hot wire method.
  • the transient hot wire method a metal wire (hot wire) is inserted into the rock and soil during the test, and the hot wire is heated with a constant power.
  • the temperature of the hot wire rises and heat is transferred to the surrounding rock and soil.
  • the speed of the temperature rise of the hot wire is related to the thermal conductivity of the surrounding rock and soil. By measuring the corresponding relationship between the temperature rise of the hot wire and the time, the thermal conductivity of the rock and soil can be obtained.
  • the test method is thermal response test, that is, the thermal conductivity of the surrounding rock and soil is calculated by the temperature change of the hot wire.
  • the calculation formula of the thermal wire method to calculate the thermal conductivity it can be seen that it needs to meet the following two assumptions: the radius of the linear heat source is small enough; the temperature obtained by the test is the temperature of the linear heat source. Therefore, the performance of the line heat source and temperature sensor is very important for the calculation of the thermal conductivity of rock and soil.
  • TRT Thermal Response Test
  • some test methods attach a temperature sensor (such as a traditional thermometer or a temperature measuring optical cable) to the transducer tube to obtain the thermophysical parameters of the formations at different depths.
  • a temperature sensor such as a traditional thermometer or a temperature measuring optical cable
  • the method of combining distributed optical fiber temperature measurement with TRT is called Distributed Thermal Response Test (DTRT).
  • DTRT arranges temperature sensors (such as point sensors or distributed sensors) at different depths of the existing transducer tubes to obtain temperature change data at different depths, and then calculate the thermal conductivity of rock and soil at different depths.
  • some non-aqueous heat source test methods have emerged, such as combining a cable as a heat source and a temperature measuring optical cable.
  • the cable and the temperature measuring optical cable are separately placed in the transducer tube, and the cable and the temperature measuring optical cable are simple After being assembled, it is tied to the transducer tube, and the drill bit is pulled directly buried in the ground.
  • AHFO Actively Heated Fiber Optic method
  • the purpose of the moisture field test is to obtain the moisture content of the unsaturated soil.
  • the application scenario is usually shallow ground (generally less than 10m).
  • the purpose of groundwater seepage test is to obtain the groundwater seepage velocity within a certain depth range, and establish the relationship between temperature rise data and seepage velocity through the convection dispersion equation.
  • Pipeline leakage monitoring generally judges the leakage section based on the abnormal section of the temperature rise data.
  • thermal response test method applied to obtain other parameters is difficult to meet the assumptions of the hot wire method, so it is difficult to meet the thermal conductivity calculation requirements. Therefore, there is an urgent need for a thermal conductivity testing method to solve the above problems, which can obtain the refined thermal conductivity of deep formations in a short time, and is small in size and easy to carry.
  • the purpose of the present invention is to provide an improved distributed soil thermal conductivity test system and a test method for the deficiencies in the prior art.
  • the first object of the present invention is to provide an improved distributed soil thermal conductivity test method, which includes the following steps:
  • Step S1 The composite optical cable is buried in the soil to be tested, the composite optical cable includes an optical fiber and a thermal resistance material layer, and the thermal resistance material layer for heating the soil to be tested covers the optical fiber, so The optical fiber is used to test the temperature of the soil to be tested;
  • Step S2 Use the heating control module to heat the soil to be tested through the thermal resistance material layer, the heating power per unit length of the thermal resistance material layer is q, and the heating time is t;
  • Step S3 the optical signal processing control module according to the formula Calculate and obtain the thermal conductivity ⁇ of the soil to be tested at the depth h:
  • the depth of the soil to be tested includes multiple depths, and the optical signal processing control module simultaneously obtains the thermal conductivity of the soil to be tested at corresponding positions of the multiple depths of the soil to be tested;
  • Step S4 Draw a graph of the thermal conductivity and the depth.
  • the composite optical cable is an internally heated optical cable.
  • the method can be applied to a variety of application scenarios where the thermal conductivity of the soil body needs to be measured, and is particularly suitable for tests that are buried in the soil body to be tested in a vertical manner.
  • the step S2 includes:
  • Step S21 using the heating control module to heat the soil to be tested through the thermal resistance material layer at the preset power P0, the resistance of the thermal resistance material layer is R, and the voltage value V is recorded in real time;
  • Step S22 Calculate the real-time power P according to the voltage value V and the resistance R, and compare the relationship between the real-time power P and the preset power P 0 , if P>(1 ⁇ 0.05) P 0 , end; If P ⁇ (1 ⁇ 0.05)P 0 , go to step S23;
  • Step S23 Record the real-time temperature T i of the soil to be tested, and calculate the k value of the heating time t at different monitoring depths of the soil to be tested, wherein: Perform linear regression on the k value and the heating time t to calculate R 2 , where If R 2 ⁇ 0.95, start to store the real-time temperature Ti as the temperature T of the soil to be tested, repeat step S23, and execute step S3;
  • the method before the step S21, the method further includes:
  • Step S20 Use the optical signal processing control module to collect the initial temperature of the soil to be tested.
  • the collection interval is preferably 0.5 min, and the collection time t 1 ⁇ 30 min; the standard deviation ⁇ of the initial temperature is judged, if the standard The difference ⁇ 0.5°C, store the initial temperature, and execute step S21;
  • step S4 the method further includes:
  • Step S5 Stop the heating control module, the optical signal processing control module collects the cooling temperature of the soil to be tested during the cooling process, the cooling collection time t2 is 30 minutes, and the standard deviation ⁇ of the cooling temperature is judged,
  • step S5 If the standard deviation ⁇ >0.5°C, repeat the step S5; if the standard deviation ⁇ 0.5°C, end. Optionally, if the standard deviation ⁇ >0.3°C, repeat the step S5; if the standard deviation ⁇ 0.3°C, end.
  • the interval between the multiple depths is preferably 0.4 m; in the step S23, the interval between the different monitoring depths is 4-6 m.
  • the composite optical cable is vertically buried in the soil to be tested, and the composite optical cable is arranged in a U-shape, and includes a sinking section and a turn-back section arranged opposite to the sinking section.
  • the second object of the present invention is to provide an improved distributed soil thermal conductivity testing system for testing the thermal conductivity of the soil to be tested, the distributed soil thermal conductivity testing system comprising:
  • a composite optical cable is an internally heated optical cable
  • the composite optical cable includes an optical fiber, a thermal resistance material layer and an optical cable protective layer, the thermal resistance material layer and the optical cable protective layer are arranged concentrically, and the optical fiber is located in the composite In the center of the optical cable, the thermal resistance material layer is located between the optical fiber and the protective layer of the optical cable;
  • a heating control module which is electrically connected to the thermal resistance material layer to form a heating circuit, which is used to heat the soil body to be tested by heating the thermal resistance material layer;
  • the optical signal processing control module is connected with the optical fiber to form an optical path, and the optical signal processing control module is used for collecting the temperature of the soil to be tested and calculating the thermal conductivity of the soil to be tested through the optical fiber.
  • the material of the thermal resistance material layer is copper, stainless steel or carbon fiber.
  • the heating control module includes a control unit, a power supply unit, a voltage transformation unit, and a voltage stabilization unit, and the control unit is used to control the connection, disconnection, and voltage of the heating circuit.
  • the optical signal processing control module includes a storage module, a temperature acquisition module, a signal processing module, and a display module.
  • the temperature acquisition module is used to collect the temperature of the soil to be tested through the optical fiber.
  • the signal processing module is used to calculate the thermal conductivity of the soil to be tested, the storage module is used to store data, and the display module is used to display the result to the user.
  • oil includes rock mass, gravel soil, sand, silt, and the like.
  • composite optical cable includes but is not limited to internally heated optical cables.
  • the present invention has the following advantages compared with the prior art:
  • test system does not require energy conversion equipment based on water circulation, and is small in size and easy to carry;
  • the diameter of the composite optical cable of the test system is small, and the required hole diameter is small, so that the composite optical cable has a good contact relationship with the soil.
  • the temperature of the thermal resistance material layer can be kept highly consistent. Therefore, compared with the transducer tubes used in TRT and DTRT, the composite optical cable satisfies the assumption of the hot wire method and can theoretically improve the test efficiency;
  • the system has a long test distance, which can monitor the temperature changes of rock and soil in a deeper range, and meet the investigation and evaluation of shallow ground temperature energy;
  • the test system has high test efficiency and small error in test results, and can efficiently obtain refined soil thermal conductivity in a short test time;
  • Figure 1 is a schematic diagram of the distributed soil thermal conductivity testing system of the present invention in vertical testing
  • Figure 2 is a schematic diagram of a model using finite element software for proportional modeling
  • Fig. 3 is a T-t curve diagram at a height of 0.75m in Fig. 2;
  • Fig. 4 is a T-lnt curve diagram and a fitting curve diagram at a height of 0.75m in Fig. 2;
  • Fig. 5 is a schematic diagram of the test device of the embodiment and the comparative example
  • Fig. 6 is a data diagram of the test results of the embodiment.
  • Fig. 7 is a comparison data diagram of the test results of the embodiment and the comparative example. Among them: 1. Composite optical cable; 2. Optical signal processing control module; 3. Heating control module; 301, control unit; 302, power supply unit; 303, transformer unit; 304, voltage stabilizing unit; 4. drilling; 5. Transducer tube; 6. Soil to be tested.
  • a distributed soil thermal conductivity test system includes a composite optical cable 1, an optical signal control processing module 2 and a heating control module 3.
  • the resistance material layer and the optical cable protective layer, the thermal resistance material layer and the optical cable protective layer are arranged concentrically, the optical fiber is located in the center of the composite optical cable, and the thermal resistance material layer is located on the optical fiber and the optical cable protective layer between.
  • a metal armor tube may be provided in the conforming optical cable 1 as a metal protective layer, the material of the thermal resistance material layer may be copper, stainless steel or carbon fiber, and the optical cable protective layer is an optical cable sheath.
  • the composite optical cable 1 integrates a coaxially arranged line heat source and a temperature sensor.
  • the thermal resistance material layer is the heat source, and the optical fiber covered by the thermal resistance material layer is the temperature sensor.
  • the overall size of the composite optical cable 1 is similar to that of ordinary The optical cable is consistent.
  • the optical signal control module 2 for collecting the temperature of the soil to be tested and calculating the thermal conductivity of the soil to be tested through the optical fiber is connected with the composite optical cable 1 to form an optical path.
  • the optical signal processing control module includes a storage module, a temperature acquisition module, a signal processing module, and a display module.
  • the temperature acquisition module is used to collect the temperature of the soil body 6 to be tested through the optical fiber
  • the signal processing module is used for To calculate the thermal conductivity of the soil body 6 to be tested
  • the storage module is used to store data
  • the display module is used to display the results to the user.
  • the optical signal control processing module 2 is an optical signal demodulation device and a preprocessing program module, which is developed on the basis of a distributed optical fiber monitoring system.
  • the heating control module 3 is electrically connected with the thermal resistance material layer to form a heating circuit, which is used to heat the soil body to be tested by heating the thermal resistance material layer.
  • the heating control module 3 includes a control unit 301, a power supply unit 302, a voltage transformation unit 303, and a voltage stabilization unit 304.
  • the control unit is used to control the connection, disconnection, and voltage of the heating circuit.
  • the power supply unit 302 may be an alternating current power supply or a direct current power supply.
  • the voltage transformation unit 303 is a portable transformer, and the voltage stabilization unit 304 is a voltage stabilizer.
  • the present invention also provides a distributed soil thermal conductivity test method, which includes the following steps:
  • the composite optical cable is buried in the soil body 6 to be tested.
  • the composite optical cable 1 includes an optical fiber and a thermal resistance material layer, which is used to heat the thermal resistance material layer of the soil body 6 to be tested.
  • Optical fiber, the soil to be tested 6 may be a complex soil composed of multiple layers of different components, and the optical fiber is used to test the temperature of the soil to be tested; methods for burying the composite optical cable 1 include, but are not limited to, drilling and burying methods It is not limited to vertical burying, it can be buried according to specific needs;
  • Step S2 using the heating control module 3 to heat the soil body 6 to be tested through the thermal resistance material layer, the heating power per unit length of the thermal resistance material layer is q, and the heating time is t;
  • the optical signal processing control module is used to collect the temperature T of the soil to be tested at the depth h; further, in step S2, the minimum collection interval for the optical signal processing control module 2 to collect temperature data is 5s ;
  • Step S3 the optical signal processing control module according to the formula Calculate and obtain the thermal conductivity ⁇ of the soil to be tested at the depth h:
  • the depth of the soil to be tested includes multiple depths, and the optical signal processing control module simultaneously obtains the thermal conductivity of the soil to be tested at corresponding positions of the multiple depths of the soil to be tested; Further, the interval between the adjacent multiple depths is 0.4 m;
  • Step S4 Draw a graph of the thermal conductivity and the depth.
  • step S2 it includes:
  • Step S21 using the heating control module to heat the soil to be tested through the thermal resistance material layer at the preset power P0, the resistance of the thermal resistance material layer is R, and the voltage value V is recorded in real time;
  • Step S22 Calculate the real-time power P according to the voltage value V and the resistance R, and compare the relationship between the real-time power P and the preset power P 0 , if P>(1 ⁇ 0.05) P 0 , end; If P ⁇ (1 ⁇ 0.05)P 0 , go to step S23;
  • Step S23 Record the real-time temperature Ti of the soil to be tested, and calculate the k value of the heating time t at different monitoring depths of the soil to be tested, where: Perform linear regression on the k value and the heating time t to calculate R 2 , where, If R 2 ⁇ 0.95, start to store the real-time temperature Ti as the temperature T of the soil to be tested, repeat step S23, and execute step S3;
  • the method further includes:
  • Step S20 Use the optical signal processing control module to periodically collect the initial temperature of the soil to be tested, the interval of timed collection is 0.5 min, and the collection time t 1 ⁇ 30 min; determine the standard deviation ⁇ of the initial temperature, if the standard The difference ⁇ 0.5°C, store the initial temperature, and execute step S21;
  • step S4 it further includes:
  • Step S5 Stop the heating control module, the optical signal processing control module collects the cooling temperature of the soil to be tested during the cooling process, the cooling collection time t2 is 30 minutes, and the standard deviation ⁇ of the cooling temperature is judged,
  • step S23a the interval between different depths of the soil body is 4-6m.
  • the optical signal processing control module 3 collects temperature data at multiple locations of the composite optical cable 1, each location corresponds to a different depth of the soil, and the interval between two adjacent locations is 4-6 m. Taking an interval of 4m as an example, the optical signal processing control module 3 collects temperature data of the composite optical cable 1 at different times at 4m, 8m, 12m,..., 4n m.
  • Step S1 bury the composite optical cable 1 in the soil body 6 to be tested;
  • the composite optical cable 1 is respectively connected with the optical signal processing control module 2 and the heating control module 3 to form an optical path and a heating circuit, and the connectivity of the optical path and the heating circuit are tested respectively.
  • Step S20 Collect the initial temperature of the soil to be tested regularly by using the optical signal processing control module, preferably, the collection interval is 0.5 min, and the collection time t1 is greater than or equal to 30 min;
  • the standard deviation ⁇ of the initial temperature is judged, and if the standard deviation ⁇ >0.5°C, the step S20 is repeated; if the standard deviation ⁇ 0.5°C, the initial temperature is stored, and the step S21 is executed.
  • the unit 304 automatically selects the corresponding voltage connection circuit to heat the composite optical cable 1, the resistance of the thermal resistance material layer is R, and the voltage value V is recorded in real time;
  • Step S22 Calculate the real-time power P according to the voltage value V and the resistance R, and compare the relationship between the real-time power P and the preset power P0, if P>(1 ⁇ 0.05)P0, end; if P ⁇ (1 ⁇ 0.05)P0, go to step S23;
  • Step S23 Test and record the real-time temperature Ti of the soil to be tested every 0.4m, and calculate the k i value of the heating time t of the soil to be tested every 5m, where: Perform linear regression on the k i value and the heating time t to calculate R 2 , where if R 2 ⁇ 0.95, start and continue to store the real-time temperature Ti as the temperature T of the soil to be tested, Repeat step S23, and execute the step S3;
  • Step S3 the optical signal processing control module according to the formula Calculate and obtain the thermal conductivity ⁇ of the soil to be tested for each depth h: specifically, the multiple adjacent depths are separated by 0.4m, the ⁇ T-lnt curve is drawn according to the temperature data, and then the thermal conductivity calculation formula is used Calculate and output the thermal conductivity of the soil at different depths;
  • Step S4 Draw a graph of thermal conductivity and soil depth.
  • Step S5 Stop the heating control module, the optical signal processing control module collects the cooling temperature of the soil to be tested during the cooling process, the cooling collection time t2 is 30 minutes, and the standard deviation ⁇ of the cooling temperature is judged,
  • step S1 a cylinder model with a height of 1.5m is established using finite element COMSOL Multiphysics, where the composite optical cable 1 is located in the center of the cylinder model, and the rest is a hypothetical soil, as shown in Figure 2;
  • the T-t curve is shown in Figure 3, and the T-lnt curve is the scattered point in Figure 4;
  • the thermal conductivity of the soil at different depths can be obtained, and then a graph of the thermal conductivity and the depth of the soil can be drawn.
  • a vertical test example in a specific borehole is taken as an example to illustrate the specific implementation process and test effect of the present invention.
  • the depth of the drilled hole is 95m
  • the radius of the borehole is 153mm
  • the borehole is made of fine sand.
  • Backfill the coupling time is greater than 6 months.
  • Step S1 The composite optical cable 1 is buried in the soil body 6 to be tested by drilling.
  • the composite optical cable 1 is arranged in a U-shape on the wall of the transducer tube 5, which includes a sinking section and a turnback arranged opposite to the sinking section.
  • the interval between the submerged section and the turn-back section is 3-5cm, and the heating power per unit length q is twice the heating power per unit length of a single composite optical cable.
  • the inner diameter of the transducer tube is 30mm, and the outer diameter is 32mm. It is arranged in the center of the drill hole in a double U shape.
  • the material of the transducer tube is PE100.
  • the upper part of the sinking section and the upper part of the turning-back section are respectively connected with the optical signal processing control module 2 and the heating control module 3 to form an optical path and a circuit, and the connectivity of the optical path and the circuit are tested respectively.
  • Step S20 Use the optical signal processing control module 2 to collect the initial temperature data of the soil, and the collection time t1 ⁇ 30min, and determine the standard deviation ⁇ 0.5°C within 30min, if the standard deviation ⁇ >0.5°C, repeat step S20;
  • step S21 If the standard deviation ⁇ 0.5°C, store the initial temperature data for 30 minutes and execute step S21.
  • the unit 304 automatically selects the corresponding voltage connection circuit to heat the composite optical cable 1, the resistance of the thermal resistance material layer is R, and the voltage value V is recorded in real time;
  • Step S22 Calculate the real-time power P according to the voltage value V and the resistance R, and compare the relationship between the real-time power P and the preset power P0, if P>(1 ⁇ 0.05)P0, end; if P ⁇ (1 ⁇ 0.05)P0, go to step S23;
  • Step S23 Test and record the real-time temperature Ti of the soil to be tested every 0.4m, and calculate the k i value of the heating time t of the soil to be tested every 5m, where: Perform linear regression on the k i value and the heating time t to calculate R 2 , where if R 2 ⁇ 0.95, start and continue to store the real-time temperature Ti as the temperature T of the soil to be tested, Step S23 is repeated, and the step S3 is executed; in this embodiment, the heating time corresponding to the value of k i that meets the requirements is 1.6 h.
  • Step S3 the optical signal processing control module according to the formula Calculate and obtain the thermal conductivity ⁇ of the soil to be tested for each depth h: specifically, the multiple adjacent depths are separated by 0.4m, the ⁇ T-lnt curve is drawn according to the temperature data, and then the thermal conductivity calculation formula is used Calculate and output the thermal conductivity of the soil at different depths; the calculated average thermal conductivity of the soil is 2.2455 (W/m ⁇ K);
  • Step S4 Draw a graph of thermal conductivity and soil depth, as shown by the solid line in FIG. 6. The thermal conductivity of different depths is different, corresponding to the difference of the soil within the depth of 95m.
  • Step S5 Stop the heating control module, the optical signal processing control module collects the cooling temperature of the soil to be tested during the cooling process, the cooling collection time t2 is 30 minutes, and the standard deviation ⁇ of the cooling temperature is judged,
  • the thermal conductivity-depth curve obtained in step S4 two depths of 54.1m and 77.1m are selected for further explanation, and the corresponding formation lithologies are silty clay and fine sand respectively.
  • the T-lnt scatter plot was drawn based on the measured temperature-time data at the depths of 54.1m and 77.1m, and the thermal conductivity and formula were obtained according to the invented method at the depths of 54.1m and 77.1m. Plot the T-lnt curve.
  • the scatter diagram and the curve diagram are highly consistent, indicating that the thermal conductivity calculated by the inventive method is highly reliable and has consistent performance in different lithologies.
  • the distance between the optical cables is 3-5cm.
  • the heating power per unit length q is twice the heating power per unit length of a single composite optical cable.
  • the inner diameter of the transducer tube is 30mm, and the outer diameter is 32mm. It is arranged in the center of the drill hole in a double U shape.
  • the transducer tube material is PE100, and the transducer tube is filled with water.
  • Example 2 In the test drilling in Example 2, half a year after the end of the test in Example 2, a DTRT experiment was performed based on the double U-shaped transducer tube 5 to eliminate the influence of the process in Example 2 on the results of the comparative example.
  • the experiment was carried out according to the TRT method in the current shallow geothermal energy exploration and evaluation specification (DZ/T 0225-2009), in which the heating power was 74W/m and the heating time was 48h.
  • the interval between the on-site implementation of the DTRT experiment and the method of the present invention is greater than 6 months, and there is no mutual influence between the two tests.
  • the comparison of the results of DTRT and the test method of the present invention is shown in Fig.
  • the solid line is the result of the inventive method
  • the dashed line is the DTRT result.
  • the average thermal conductivity of the soil obtained by the DTRT test is 2.2464 (W/m ⁇ K).
  • This result and the average thermal conductivity of the soil calculated by the test method of the present invention are 2.2455 ( The difference of W/m ⁇ K) is less than 1%.
  • the result of the test method of the present invention has a larger variation in depth, and can accurately distinguish the difference in thermal conductivity of soils at different depths.
  • the comprehensive energy consumption of DTRT and the test method of the present invention are respectively about 340kW ⁇ h and 3kW ⁇ h, and the test device and test method of the present invention save energy by more than 90%.
  • the heating time of the method of the present invention is 1.6h, and the heating time of DTRT is 48h, which shortens the heating time by more than 95%.
  • test system and test method of the present invention have the advantages of low cost, simple device, simple test steps, short test time, and high test accuracy, and can be real-time , Quickly and efficiently obtain the thermal conductivity of the in-situ soil.

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Abstract

一种分布式土体导热系数测试方法及其测试系统，测试方法包括以下步骤：将复合光缆（1）埋设于待测土体（6）中，复合光缆（1）包括光纤及包覆光纤的热电阻材料层；利用加热控制模块（3）通过热电阻材料层对待测土体（6）加热，利用光信号处理控制模块（2）持续采集地层的加热温度数据；利用光信号处理控制模块（2）对加热温度数据进行处理，根据导热系数计算公式计算并输出待测土体（6）的不同深度的导热系数，并绘制导热系数与深度的曲线图；测试系统体积小巧、便于携带，测试距离长，监测更深范围内岩土体的温度变化，测试效率高，测试结果误差小，在较短的测试时间内获得精细化的地层导热系数。

Description

一种分布式土体导热系数测试方法及其测试系统 技术领域
本发明涉及地质检测技术领域，尤其涉及一种分布式土体导热系数测试方法及其测试系统。
背景技术
岩土体的导热系数是反映岩土体导热性能的关键参数。获取导热系数一方面可以服务于浅层地温能评价、地下工程、冷冻施工或冻融区地基设计等，另一方面还可以通过导热系数间接计算土体含水率和干密度等参数及评价地下水渗流和污染物转移。
获取导热系数的方法包括室内试验和现场测试。室内试验包括平板法和热线法，现场测试为瞬态热线法。对于瞬态热线法，是在测试时将一根金属丝(热线)插入岩土体中，以恒定功率对热线通电加热，热线温度升高，向周围的岩土体中传递热量。热线温度升高速度的快慢与周围岩土体的导热能力有关，通过测量热线温升与时间的对应关系，即可得到岩土体的导热系数。
对于热线法以及相关衍生方法，其测试手段均是热响应测试，即通过热线的温度变化来计算周围岩土体的导热系数。根据热线法计算导热系数的计算公式可知，其需要满足以下两个假设条件：线热源的半径足够小；测试获得的温度为线热源的温度。因此，线热源和温度传感器的性能对岩土体导热系数的计算十分重要。
在地温能的研究领域中，最成熟的热响应测试方法是现场热响应测试(Thermal Response Test，TRT)，其原理是通过水作为传热介质在换能管中循环，在一定的放热量或取热量下，连续记录换能管进出口的水温度，并根据温度随时间变化的规律推知岩土体导热系数。然而，TRT只能得到钻孔处地层的平均热物性参数，无法获得多个地层独立的导热系数。因此，TRT无法确定每一土层的导热系数，进而无法分析各土层在含水率、渗流、温度场等因素不断变化条件下的换热能力，无法定量分析不同因素对土体换热能力的影响。此外，TRT 存在测试设备体积较大不便携带、测试要求高、步骤繁琐、耗时长等问题。
为了解决上述问题，在TRT方法的基础上，一些测试方法将温度传感器(如传统温度计或测温光缆)附着于换能管之上，进而获得不同深度地层的热物性参数。其中，将分布式光纤测温与TRT结合的方法称为分布式热响应测试(Distributed Thermal Response Test，DTRT)。DTRT在现有的换能管的不同深度上布置温度传感器(如点式传感器或者分布式传感器)，从而获得不同深度的温度变化数据，进而可以计算得到不同深度岩土体的导热系数。该方法虽然克服了TRT仅能反映整个钻孔的导热性质的平均水平的主要缺点，但是其测试原理和测试设备没有改变，仍然存在测试设备体积较大不便携带、测试要求高、步骤繁琐、耗时长等问题。此外，TRT和DTRT的热源均是以水为载体，其比热容大且循环的模式会造成整个换能管加热功率不均匀，不利于导热系数的计算。
随着技术的发展，出现了一些非水热源的测试方法，如将一根电缆单独作为热源和测温光缆进行组合，如电缆和测温光缆分别放在换能管中、电缆和测温光缆简单组合后绑在换能管上、钻头牵引直接埋在地层中等。但是仍然没有一个统一且有效的获取导热系数的方法。
此外，出现了一种基于内加热光缆的热响应测试方法，一些学者称为主动加热光纤方法(Actively Heated Fiber Optic method，AHFO)，其主要应用于水分场测试、地下水渗流测试以及管道渗漏检测领域。水分场的测试的目的在于获取非饱和土体的含水率，应用的场景通常为浅地表(一般小于10m)。地下水渗流测试的目的在于获取一定深度范围内的地下水渗流速度，通过对流弥散方程建立温升数据和渗流速度的关系。管道的渗漏监测一般通过温升数据的异常段判断渗漏段。虽然该方法已经得到了一些应用，但是在获取分布式的导热系数方面还没有被提出。明显的是应用于获取其它参数的热响应测试方法，很难满足热线法的假设条件，因此很难满足导热系数的计算要求。因此，亟需一种解决上述问题的导热系数测试方法，其能够短时间获取深层地层的精细化的导热系数，并且体积小巧、便于携带。
发明内容
本发明的目的是针对现有技术中的不足，提供一种改进的分布式土体导热 系数测试系统及其测试方法。
本发明的第一个目的，提供一种改进的分布式土体导热系数测试方法，包括以下步骤：
步骤S1、将复合光缆埋设于待测土体中，所述复合光缆包括光纤及热电阻材料层，用于对所述待测土体加热的所述热电阻材料层包覆所述光纤，所述光纤用于测试所述待测土体的温度；
步骤S2、利用加热控制模块通过所述热电阻材料层对所述待测土体加热，所述热电阻材料层的单位长度加热功率为q，加热时间为t；
利用光信号处理控制模块采集所述待测土体位于深度h的所述待测土体的温度T；
步骤S3、所述光信号处理控制模块根据公式
Figure PCTCN2021100524-appb-000001
计算获得所述深度h的所述待测土体的导热系数λ：
所述待测土体的深度包括多个深度，所述光信号处理控制模块同时获得所述待测土体的所述多个深度的对应位置的所述待测土体的所述导热系数；
步骤S4、绘制所述导热系数与所述深度的曲线图。
一些实施例中，复合光缆为内加热光缆。
本方法可以应用于多种需要测土体导热系数的应用场景，特别适用于以垂直方式埋设于待测土体中的测试。
一些实施例中，在所述步骤S2中，包括：
步骤S21、利用所述加热控制模块以预设功率P0通过所述热电阻材料层对所述待测土体加热，所述热电阻材料层的电阻为R，实时记录电压值V；
步骤S22、根据所述电压值V及所述电阻R计算实时功率P，并对比所述实时功率P与所述预设功率P 0的关系，如果P＞(1±0.05)P 0，结束；如果P≤(1±0.05)P 0，执行步骤S23；
步骤S23、记录所述待测土体的实时温度T i，计算所述待测土体不同监控深度 所述加热时间t的k值，其中，
Figure PCTCN2021100524-appb-000002
对所述k值与所述加热时间t进行线性回归，计算R 2，其中
Figure PCTCN2021100524-appb-000003
如果R 2≥0.95，开始存储所述实时温度Ti为所述待测土体的所述温度T，重复步骤S23，并执行所述步骤S3；
如果R 2＜0.95，停止存储所述温度T，重复步骤S23。
一些实施例中，所述步骤S21之前，还包括：
步骤S20、利用所述光信号处理控制模块采集所述待测土体的初始温度，采集间隔为0.5min时为佳，采集时间t 1≥30min；判断所述初始温度的标准差σ，如果标准差σ≤0.5℃，存储所述初始温度，执行步骤S21；
如果标准差σ＞0.5℃，重复所述步骤S20。
一些实施例中，在步骤S4之后，还包括：
步骤S5、停止所述加热控制模块，所述光信号处理控制模块采集冷却过程中的所述待测土体的冷却温度，冷却采集时间t2为30min，判断所述冷却温度的标准差σ，
如果标准差σ＞0.5℃，重复所述步骤S5；如果标准差σ≤0.5℃，结束。可选地，如果标准差σ＞0.3℃，重复所述步骤S5；如果标准差σ≤0.3℃，结束。
一些实施例中，所述多个深度的间隔为0.4m时为佳；所述步骤S23中，所述不同监控深度的间隔为4-6m。
一些实施例中，所述复合光缆垂直埋设于所述待测土体中，所述复合光缆呈U型布置，其包括下沉段及与所述下沉段相对布置的折返段。
本发明的第二个目的，在于提供一种改进的分布式土体导热系数测试系统，用于测试待测土体的导热系数，所述分布式土体导热系数测试系统包括：
复合光缆，所述复合光缆为内加热光缆，所述复合光缆包括光纤、热电阻材料层和光缆保护层，所述热电阻材料层和所述光缆保护层同心设置，所述光纤位 于所述复合光缆的中心，所述热电阻材料层位于所述光纤和所述光缆保护层之间；
加热控制模块，所述加热控制模块与所述热电阻材料层电连接形成加热电路，其用于通过加热所述热电阻材料层加热所述待测土体；
光信号处理控制模块，其与所述光纤连接形成一光路，光信号处理控制模块用于通过所述光纤采集所述待测土体的温度及计算所述待测土体的导热系数。
在一些实施例中，所述热电阻材料层的材料为铜、不锈钢或碳纤维。
在一些实施例中，所述加热控制模块包括控制单元、电源单元、变压单元及稳压单元，所述控制单元用于控制所述加热电路的连通、断开及电压。
在一些实施例中，所述光信号处理控制模块包括存储模块、温度采集模块、信号处理模块及显示模块，所述温度采集模块用于通过所述光纤采集所述待测土体的温度，所述信号处理模块用于计算所述待测土体的导热系数、所述存储模块用于存储数据、所述显示模块用于向用户显示结果。
本公开中，术语“土体”包括岩体、碎石土、砂土和粉土等。
本公开中，术语“复合光缆”包括但不限于内加热光缆。
由于上述技术方案的运用，本发明与现有技术相比具有下列优点：
(1)该测试系统无需以水循环为基础的换能设备，体积小巧、便于携带；
(2)该测试系统的复合光缆的直径较小，所需的钻孔直径小，使得复合光缆与土体接触关系良好，被热电阻材料层包覆的光纤作为测温传感器测试得到的温度与热电阻材料层的温度可以保持高度一致，因此，复合光缆相比于TRT和DTRT中采用的换能管更满足热线法的假设，在理论上可以提高测试效率；
(3)该系统的测试距离长，能够监测更深范围内岩土体的温度变化，满足浅层地温能的调查评价；
(4)该测试系统的测试效率高，测试结果误差小，能够在较短的测试时间内高效获得精细化的土体导热系数；
(5)功能多样化，既可以进行现场热响应测试，又可以进行长期地温监测；
(6)本测试系统具有较强的鲁棒性，在不同的单位长度加热功率q的测试中均可得到一致的导热系数结果。
附图说明
为了更清楚地说明本发明的技术方案，下面将对实施例描述中所需要使用的附图作简单的介绍，显而易见地，下面描述中的附图仅仅是本发明的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据这些附图获得其他的附图。
附图1为本发明的分布式土体导热系数测试系统在垂向测试中的示意图；
附图2为利用有限元软件进行等比建模的模型示意图；
附图3为附图2中0.75m高度处的T-t曲线图；
附图4为附图2中0.75m高度处的T-lnt曲线图以及拟合曲线图；
附图5为实施例及对比例的测试装置的示意图；
附图6为实施例测试结果数据图；
附图7为实施例与对比例测试结果对比数据图。其中：1、复合光缆；2、光信号处理控制模块；3、加热控制模块；301、控制单元；302、电源单元；303、变压单元；304、稳压单元；4、钻孔；5、换能管；6、待测土体。
具体实施方式
下面结合附图对本发明的较佳实施例进行详细阐述，以使本发明的优点和特征能更易于被本领域的技术人员理解。
下面结合附图和具体实施例来对本发明的技术方案作进一步的阐述。
如图1所示，一种分布式土体导热系数测试系统，包括复合光缆1、光信号控制处理模块2和加热控制模块3，复合光缆1为内加热光缆，所述复合光缆包括光纤、热电阻材料层和光缆保护层，所述热电阻材料层和所述光缆保护层同心设置，所述光纤位于所述复合光缆的中心，所述热电阻材料层位于所述光纤和所述光缆保护层之间。符合光缆1中还可以设有金属铠管作为金属保护层，热电阻材料层的材料可以为铜、不锈钢或碳纤维，光缆保护层为光缆护套。其 中，复合光缆1将同轴设置的线热源和测温传感器集成于一体，热电阻材料层为热源，被热电阻材料层包覆的光纤为测温传感器，该复合光缆1的整体尺寸与普通光缆一致。
用于通过所述光纤采集所述待测土体的温度及计算所述待测土体的导热系数的光信号控制模块2与复合光缆1连接形成一光路。所述光信号处理控制模块包括存储模块、温度采集模块、信号处理模块及显示模块，所述温度采集模块用于通过所述光纤采集所述待测土体6的温度，所述信号处理模块用于计算所述待测土体6的导热系数、所述存储模块用于存储数据、所述显示模块用于向用户显示结果。进一步地，光信号控制处理模块2为光信号解调设备及预处理程序模块，是以分布式光纤监测系统为基础进行开发的。
加热控制模块3所述加热控制模块与所述热电阻材料层电连接形成加热电路，其用于通过加热所述热电阻材料层加热所述待测土体。加热控制模块3包括控制单元301、电源单元302、变压单元303和稳压单元304，控制单元用于控制所述加热电路的连通、断开及电压。电源单元302可以是交流电电源，也可以是直流电电源。变压单元303为便携式变压器，稳压单元304为稳压器。
如图1所示，本发明还提供一种分布式土体导热系数测试方法，包括以下步骤：
步骤S1、将复合光缆埋设于待测土体6中，所述复合光缆1包括光纤及热电阻材料层，用于对所述待测土体6加热的所述热电阻材料层包覆所述光纤，待测土体6可以为多层不同组分构成的复杂土体，所述光纤用于测试所述待测土体的温度；复合光缆1埋设的方法包括但不限于钻孔，埋设方式不限于垂向埋设，可以根据特定需要埋设；
步骤S2、利用加热控制模块3通过所述热电阻材料层对所述待测土体6加热，所述热电阻材料层的单位长度加热功率为q，加热时间为t；
利用光信号处理控制模块采集所述待测土体位于深度h的所述待测土体的温度T；进一步地，在步骤S2中，光信号处理控制模块2采集温度数据的最小采集间隔为5s；
步骤S3、所述光信号处理控制模块根据公式
Figure PCTCN2021100524-appb-000004
计算获得所述深度h的所述待测土体的导热系数λ：
所述待测土体的深度包括多个深度，所述光信号处理控制模块同时获得所述待测土体的所述多个深度的对应位置的所述待测土体的所述导热系数；进一步地，相邻的所述多个深度的间隔为0.4m；
步骤S4、绘制所述导热系数与所述深度的曲线图。
进一步地，在所述步骤S2中，包括：
步骤S21、利用所述加热控制模块以预设功率P0通过所述热电阻材料层对所述待测土体加热，所述热电阻材料层的电阻为R，实时记录电压值V；
步骤S22、根据所述电压值V及所述电阻R计算实时功率P，并对比所述实时功率P与所述预设功率P 0的关系，如果P＞(1±0.05)P 0，结束；如果P≤(1±0.05)P 0，执行步骤S23；
步骤S23、记录所述待测土体的实时温度Ti，计算所述待测土体不同监控深度所述加热时间t的k值，其中，
Figure PCTCN2021100524-appb-000005
对所述k值与所述加热时间t进行线性回归，计算R 2，其中，
Figure PCTCN2021100524-appb-000006
如果R 2≥0.95，开始存储所述实时温度Ti为所述待测土体的所述温度T，重复步骤S23，并执行所述步骤S3；
如果R 2＜0.95，停止存储所述温度T，重复步骤S23。
进一步地，所述步骤S21之前，还包括：
步骤S20、利用所述光信号处理控制模块定时采集所述待测土体的初始温度，定时采集的间隔为0.5min，采集时间t 1≥30min；判断所述初始温度的标准差σ，如果标准差σ≤0.5℃，存储所述初始温度，执行步骤S21；
如果标准差σ＞0.5℃，重复所述步骤S20。
进一步地，在步骤S4之后，还包括：
步骤S5、停止所述加热控制模块，所述光信号处理控制模块采集冷却过程中的所述待测土体的冷却温度，冷却采集时间t2为30min，判断所述冷却温度的标准差σ，
如果标准差σ＞0.5℃，重复所述步骤S5；如果标准差σ≤0.5℃，结束。
在步骤S23a中，土体的不同深度的间隔为4～6m。具体地，光信号处理控制模块3采集复合光缆1的多个位置的温度数据，每个位置对应土体的不同深度，相邻两个位置之间的间隔为4～6m。以间隔为4m为例说明，光信号处理控制模块3采集4m、8m、12m、……、4n m处的复合光缆1的不同时间的温度数据。
实施例1
下面以一具体实施例为例，说明本发明的具体实施过程及测试效果，测试系统的安装参照图1。
步骤S1、将复合光缆1埋设于待测土体6中；
将复合光缆1分别与光信号处理控制模块2和加热控制模块3进行连接以形成光路和加热电路，并分别测试光路和加热电路的连通性。
步骤S20、利用所述光信号处理控制模块定时采集所述待测土体的初始温度，优选地，采集间隔为0.5min，采集时间t1≥30min；
判断所述初始温度的标准差σ，如果标准差σ＞0.5℃，重复所述步骤S20；如果标准差σ≤0.5℃，存储所述初始温度，执行步骤S21。
步骤S21、利用所述加热控制模块以预设功率P0＝26W/m通过所述热电阻材料层对所述待测土体加热，具体地，启动加热控制模块3的变压单元303和稳压单元304，自动选择对应的电压连通电路，对复合光缆1进行加热，所述热电阻材料层的电阻为R，实时记录电压值V；
步骤S22、根据所述电压值V及所述电阻R计算实时功率P，并对比所述实时功率P与所述预设功率P0的关系，如果P＞(1±0.05)P0，结束；如果P≤ (1±0.05)P0，执行步骤S23；
步骤S23、每隔0.4m测试并记录所述待测土体的实时温度Ti，并每隔5m计算所述待测土体的所述加热时间t的k i值，其中，
Figure PCTCN2021100524-appb-000007
对所述k i值与所述加热时间t进行线性回归，计算R 2，其中，如果R 2≥0.95，开始并持续存储所述实时温度Ti为所述待测土体的所述温度T，重复步骤S23，并执行所述步骤S3；
如果R 2＜0.95，停止存储所述温度T，重复步骤S23。
步骤S3、所述光信号处理控制模块根据公式
Figure PCTCN2021100524-appb-000008
计算获得每个所述深度h的所述待测土体的导热系数λ：具体地，相邻的多个深度间隔0.4m，根据温度数据绘制ΔT-lnt曲线，然后根据导热系数计算公式
Figure PCTCN2021100524-appb-000009
计算并输出土体的不同深度的导热系数；
步骤S4、绘制导热系数与土体深度的曲线图。
步骤S5、停止所述加热控制模块，所述光信号处理控制模块采集冷却过程中的所述待测土体的冷却温度，冷却采集时间t2为30min，判断所述冷却温度的标准差σ，
如果标准差σ＞0.5℃，重复所述步骤S5；如果标准差σ≤0.5℃，结束。
具体地，在步骤S1中，利用有限元COMSOL Multiphysics建立了高度为1.5m的圆柱体模型，其中复合光缆1位于圆柱体模型的中央，其余部分为假设的土体，其如图2所示；
以0.75m处高度为例进行说明，其T-t曲线如图3所示，其T-lnt曲线为图4的散点；
根据公式
Figure PCTCN2021100524-appb-000010
绘制ΔT-lnt理论曲线，其为图4的直线；
将图4的散点和图4的直线进行比较，可以看出理论曲线与温度数据高度一致，且在加热时间60min后，理论曲线与温度数据基本重合，即满足S23步骤要求，说明60min的加热时间进行S3步骤，计算导热系数；
然后将拟合曲线的斜率带入导热系数计算公式
Figure PCTCN2021100524-appb-000011
即可获得该位置处的土体的导热系数；
以此类推，即可获得不同深度的土体的导热系数，然后绘制导热系数与土体深度的曲线图。
实施例2
如图5-6所示，以一具体钻孔中垂直测试实施例为例，说明本发明的具体实施过程及测试效果，钻探成孔的深度95m，钻孔的半径153mm，钻孔采用细砂回填，耦合时间大于6个月。
步骤S1、将复合光缆1通过钻探的方法埋设于待测土体6中，复合光缆1呈U型布置在换能管5管壁，其包括下沉段及与所述下沉段相对布置的折返段，下沉段及折返段的间隔为3-5cm，单位长度加热功率q为单根复合光缆单位长度加热功率的两倍。换能管内径30mm,外径32mm,以双U型布设于钻孔中心，换能管材料为PE100。下沉段的上部及折返段的上部分别与光信号处理控制模块2和加热控制模块3进行连接以形成光路和电路，并分别测试光路和电路的连通性。
步骤S20、利用光信号处理控制模块2采集土体的初始温度数据，并且采集时间t1≥30min，并判断30min内的标准差σ≤0.5℃，如果标准差σ＞0.5℃，重复步骤S20；
如果标准差σ≤0.5℃，存储30min的初始温度数据并执行步骤S21。
步骤S21、根据加热功率P0＝26W/m，启动加热控制模块3的变压单元303和稳压单元304，自动选择对应的电压连通电路，对复合光缆1进行加热，并记录实时电压值V和实时温度值T，然后分别执行步骤S23a和步骤S23b。
步骤S21、利用所述加热控制模块以预设功率P0＝26W/m通过所述热电阻材 料层对所述待测土体加热，具体地，启动加热控制模块3的变压单元303和稳压单元304，自动选择对应的电压连通电路，对复合光缆1进行加热，所述热电阻材料层的电阻为R，实时记录电压值V；
步骤S22、根据所述电压值V及所述电阻R计算实时功率P，并对比所述实时功率P与所述预设功率P0的关系，如果P＞(1±0.05)P0，结束；如果P≤(1±0.05)P0，执行步骤S23；
步骤S23、每隔0.4m测试并记录所述待测土体的实时温度Ti，并每隔5m计算所述待测土体的所述加热时间t的k i值，其中，
Figure PCTCN2021100524-appb-000012
对所述k i值与所述加热时间t进行线性回归，计算R 2，其中，如果R 2≥0.95，开始并持续存储所述实时温度Ti为所述待测土体的所述温度T，重复步骤S23，并执行所述步骤S3；本实施例中，满足要求的k i值对应的加热时间为1.6h。
如果R 2＜0.95，停止存储所述温度T，重复步骤S23。步骤S3、所述光信号处理控制模块根据公式
Figure PCTCN2021100524-appb-000013
计算获得每个所述深度h的所述待测土体的导热系数λ：具体地，相邻的多个深度间隔0.4m，根据温度数据绘制ΔT-lnt曲线，然后根据导热系数计算公式
Figure PCTCN2021100524-appb-000014
计算并输出土体的不同深度的导热系数；计算得到的土体平均导热系数为2.2455(W/m·K)；
步骤S4、绘制导热系数与土体深度的曲线图，如图6中实线所示。不同的深度导热系数不同，对应于95m深度范围内土体的差异。
步骤S5、停止所述加热控制模块，所述光信号处理控制模块采集冷却过程中的所述待测土体的冷却温度，冷却采集时间t2为30min，判断所述冷却温度的标准差σ，
如果标准差σ＞0.5℃，重复所述步骤S5；如果标准差σ≤0.5℃，结束。
其中，在步骤S4得到的导热系数-深度曲线中，选取54.1m和77.1m两个深度进一步说明，对应的地层岩性分别是粉质黏土和细砂。根据54.1m和77.1m 两个深度处实测的温度-时间数据绘制了T-lnt散点图，根据54.1m和77.1m两个深度处发明方法得到导热系数和公式
Figure PCTCN2021100524-appb-000015
绘制T-lnt曲线图。散点图和曲线图高度一致，说明发明方法计算得到导热系数可靠性高，且在不同的岩性中有一致的表现。
光缆的间距为3-5cm。单位长度加热功率q为单根复合光缆单位长度加热功率的两倍。换能管内径30mm,外径32mm,以双U型布设于钻孔中心，换能管材料为PE100，换能管中充满水。
对比例
为了说明本发明的测试方法的测试结果的精确性，发明人进行了相关对比实验。
在实施例2中的测试钻孔中，在实施例2测试结束半年后，基于双U型的换能管5进行了一次DTRT实验，以消除实施例2的过程对对比例的结果产生影响。实验根据现行浅层地热能勘查评价规范(DZ/T 0225－2009)中TRT的方法进行，其中加热功率为74W/m，加热时间为48h。DTRT实验与本发明方法的现场实施间隔时间大于6个月，两个测试之间不存在相互影响。DTRT和本发明的测试方法的结果对比如图7所示，实线为发明方法的结果，虚线为DTRT结果。在土体深度为30-95m的范围内，DTRT测试得到的土体平均导热系数为2.2464(W/m·K)，该结果与本发明的测试方法计算得到的土体平均导热系数为2.2455(W/m·K)的差异小于1％。相比于DTRT测试得到的分布式导热系数曲线，本发明的测试方法结果在深度上的变化幅度更大，可以准确的区分不同深度土体的导热系数差异。DTRT与本发明的测试方法在综合能耗方面分别为340kW·h和3kW·h左右，本发明的测试装置及测试方法节约能源90％以上。在热响应测试中本发明方法的加热时间为1.6h，DTRT的加热时间为48h，缩短加热时间95％以上。
从实施例和对比例中可以看出，与现有技术相比，本发明的测试系统和测试方法，具有成本低廉、装置简单、测试步骤简单、测试时间短、测试精度高的优点，能够实时、快速、高效地获取原位土体的导热系数。
上述实施例只为说明本发明的技术构思及特点，是优选的实施方式，其目的在于熟悉此项技术的人士能够了解本发明的内容并据以实施，并不能以此限定本发明的保护范围。

Claims (9)

  1. 一种分布式土体导热系数测试方法，其特征在于，包括以下步骤：
    步骤S1、将复合光缆埋设于待测土体中，所述复合光缆包括光纤及热电阻材料层，用于对所述待测土体加热的所述热电阻材料层包覆所述光纤，所述光纤用于测试所述待测土体的温度；
    步骤S2、利用加热控制模块通过所述热电阻材料层对所述待测土体加热，所述热电阻材料层的单位长度加热功率为q，加热时间为t；
    利用光信号处理控制模块采集所述待测土体位于深度h的所述待测土体的温度T；
    步骤S3、所述光信号处理控制模块根据公式
    Figure PCTCN2021100524-appb-100001
    计算获得所述深度h的所述待测土体的导热系数λ：
    所述待测土体的深度包括多个深度，所述光信号处理控制模块同时获得所述待测土体的所述多个深度的对应位置的所述待测土体的所述导热系数；
    步骤S4、绘制所述导热系数与所述深度的曲线图；
    在所述步骤S2中，包括：
    步骤S21、利用所述加热控制模块以预设功率P 0通过所述热电阻材料层对所述待测土体加热，所述热电阻材料层的电阻为R，实时记录电压值V；
    步骤S22、根据所述电压值V及所述电阻R计算实时功率P，并对比所述实时功率P与所述预设功率P 0的关系，如果P＞(1±0.05)P 0，结束；如果P≤(1±0.05)P 0，执行步骤S23；
    步骤S23、记录所述待测土体的实时温度T i，计算所述待测土体不同监控深度所述加热时间t的k值，其中，
    Figure PCTCN2021100524-appb-100002
    对所述k值与所述加热时间t进行线性回归，计算R 2，其中，
    Figure PCTCN2021100524-appb-100003
    如果R 2≥0.95，开始存储所述实时温度Ti为所述待测土体的所述温度T，重复步骤S23，并执行所述步骤S3；
    如果R 2＜0.95，停止存储所述温度T，重复步骤S23。
  2. 根据权利要求1所述的分布式土体导热系数测试方法，其特征在于，所述步骤S21之前，还包括：
    步骤S20、利用所述光信号处理控制模块定时采集所述待测土体的初始温度，优选地，所述 定时采集间隔为0.5min，采集时间t 1≥30min；
    判断所述初始温度的标准差σ，如果标准差σ≤0.5℃，存储所述初始温度，执行步骤S21；如果标准差σ＞0.5℃，重复所述步骤S20。
  3. 根据权利要求1-2任一权利要求所述的分布式土体导热系数测试方法，其特征在于，在步骤S4之后，还包括：
    步骤S5、停止所述加热控制模块，所述光信号处理控制模块采集冷却过程中的所述待测土体的冷却温度，冷却采集时间t2为30min，判断所述冷却温度的标准差σ，
    如果标准差σ＞0.5℃，重复所述步骤S5；如果标准差σ≤0.5℃，结束。
  4. 根据权利要求1所述的分布式土体导热系数测试方法，其特征在于，所述多个深度的间隔为0.4m；所述步骤S23中，所述不同监控深度的间隔为4-6m。
  5. 根据权利要求1所述的分布式土体导热系数测试方法，其特征在于，所述复合光缆垂直埋设于所述待测土体中，所述复合光缆呈U型布置，其包括下沉段及与所述下沉段相对布置的折返段。
  6. 一种分布式土体导热系数测试系统，用于利用如权利要求1所述的分布式土体导热系数测试方法测试待测土体的导热系数，其特征在于，所述分布式土体导热系数测试系统包括：
    复合光缆，所述复合光缆为内加热光缆，所述复合光缆包括光纤、热电阻材料层和光缆保护层，所述热电阻材料层和所述光缆保护层同心设置，所述光纤位于所述复合光缆的中心，所述热电阻材料层位于所述光纤和所述光缆保护层之间；
    加热控制模块，所述加热控制模块与所述热电阻材料层电连接形成加热电路，其用于通过加热所述热电阻材料层加热所述待测土体；
    光信号处理控制模块，其与所述光纤连接形成一光路，光信号处理控制模块用于通过所述光纤采集所述待测土体的温度及计算所述待测土体的导热系数。
  7. 根据权利要求6所述的分布式土体导热系数测试系统，其特征在于，所述热电阻材料层的材料为铜、不锈钢或碳纤维。
  8. 根据权利要求6所述的分布式土体导热系数测试系统，其特征在于，所述加热控制模块包括控制单元、电源单元、变压单元及稳压单元，所述控制单元用于控制所述加热电路的连通、断开及电压。
  9. 根据权利要求6所述的分布式土体导热系数测试系统，其特征在于，所述光信号处理控制模块包括存储模块、温度采集模块、信号处理模块及显示模块，所述温度采集模块用于通过所述光纤采集所述待测土体的温度，所述信号处理模块用于计算所述待测土体的导热系数、所述存储模块用于存储数据、所述显示模块用于向用户显示结果。
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CN117786282A (zh) * 2024-02-23 2024-03-29 中交第一公路勘察设计研究院有限公司 一种热管地基及其导冷增强系数计算方法、导冷增强方法
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