阅读说明：本技术 一种冻土导热系数测试修正方法 (Frozen soil heat conductivity coefficient test correction method ) 是由 叶茂松 黄雄飞 肖建勇 刘博� 陈之祥 潘林 夏锦红 张来栋 于 2021-07-15 设计创作，主要内容包括：本发明提供一种冻土导热系数测试修正方法,通过确定冻土未冻水含量,绘制冻融过程中未冻水含量与温度的关系曲线,进行冻土导热系数热线法测试、判别热线法测试最终温度对应未冻水含量与冻土温度对应的未冻水含量关系,修正冻土导热系数值。本发明的有益效果是：与传统方法对比预测精度提升了24.8％；精度的提高能够最大限度的缩小冻土导热系数测试值与实际值之间的误差,为更科学合理的预测冻结法施工过程中的土体温度场提供科学依据。(The invention provides a frozen soil heat conductivity coefficient test and correction method, which is characterized in that the heat conductivity coefficient of frozen soil is corrected by determining the unfrozen water content of the frozen soil, drawing a relation curve of the unfrozen water content and the temperature in the freezing and thawing process, and carrying out hot-wire method test on the heat conductivity coefficient of the frozen soil, judging the relation between the unfrozen water content corresponding to the final temperature and the unfrozen water content corresponding to the temperature of the frozen soil in the hot-wire method test. The invention has the beneficial effects that: compared with the traditional method, the prediction precision is improved by 24.8%; the improvement of the precision can reduce the error between the test value and the actual value of the heat conductivity coefficient of the frozen soil to the maximum extent, and provide scientific basis for predicting the soil temperature field in the construction process of the freezing method more scientifically and reasonably.)

1. A frozen soil thermal conductivity coefficient test correction method comprises the following steps:

1) respectively measuring the temperature T in the soil body cooling process by adopting a nuclear magnetic resonance method_t(-25℃＜T_tUnfrozen water content W below 0 DEG C_dtAnd temperature T in soil body temperature rising process_t(-25℃＜T_fkUnfrozen water content W below 0 DEG C_rt；

2) Determining the temperature T in the soil body cooling process according to the step 1)_tLower unfrozen water content W_dtDrawing a relation curve of the temperature and the unfrozen water content, and recording as an unfrozen water curve in the freezing process; meanwhile, the temperature T determined in the step 1) in the soil body temperature rising process is adopted_tLower unfrozen water content W_rtDrawing a relation curve of the temperature and the unfrozen water content, and recording as an unfrozen water curve in the melting process;

3) setting the power Q of the heat conductivity coefficient of the frozen soil measured by a hot wire method, and measuring the temperature T of the frozen soil by the hot wire method_m(-25℃＜T_tTemperature T < 0 ℃ to which_nSimultaneously recording the starting time t of measuring the heat conductivity coefficient of the frozen soil by a hot wire method₁And an end time t₂；

4) Inquiring the frozen soil temperature T on the unfrozen water curve in the freezing process determined in the step 2)_mCorresponding unfrozen water content W_dm(ii) a Inquiring the frozen soil temperature T on the unfrozen water curve in the melting process determined in the step 2)_nCorresponding unfrozen water content W_rn；

5) When the unfrozen water content W determined in the step 4) is_rnNot more than the unfrozen water content W_dmIn time, the heat conductivity coefficient lambda of the frozen soil is calculated by adopting a formula (1), wherein the formula (1) is as follows:

in the formula (1), lambda is the coefficient of heat conductivity of frozen soil; q is the power of the heat conductivity coefficient of the frozen soil determined by the hot-line method in the step 3), t₁And t₂Respectively measuring the starting time and the ending time of the heat conductivity coefficient of the frozen soil by a hot line method in the step 3); t is_mIs the frozen soil temperature; t is_nFrozen earth at temperature T at power Q_m(-25℃＜T_tThe temperature to which it is raised at < 0 ℃; pi is the circumference ratio;

6) when the unfrozen water content W determined in the step 4) is_rnGreater than the unfrozen water content W_dmIn time, the heat conductivity coefficient lambda of the frozen soil is calculated by adopting a formula (2), wherein the formula (2) is as follows:

in the formula (2), lambda is the coefficient of heat conductivity of the frozen soil; q is the power for determining the heat conductivity coefficient of the frozen soil by a hot-line method in the step 3); pi is the circumference ratio; t is t₁And t₂Respectively measuring the starting time and the ending time of the heat conductivity coefficient of the frozen soil by a hot line method in the step 3); t is_mIs the frozen soil temperature; t is_nFrozen earth at temperature T at power Q_m(-25℃＜T_tTemperature T < 0 ℃ to which_n；Q_LCalculating the latent heat of phase change caused by the content difference of the unfrozen water according to a formula (3), wherein the formula (3) is as follows:

Q_L＝Lρ_d(W_rn-W_dm) (3)

in the formula (3), Q_LLatent heat of phase change caused by the difference of unfrozen water content; l is the phase transition heat of water, and 333.51kJ/kg is taken; rho_dIs the dry density of the frozen soil; w_dmThe temperature T of the frozen soil on the unfrozen water curve in the freezing process_mThe corresponding unfrozen water content; w_rnThe temperature T of the frozen soil on the unfrozen water curve in the melting process_nCorresponding unfrozen water content.

Technical Field

The invention belongs to the field of frozen soil engineering, and particularly relates to a frozen soil heat conductivity coefficient test correction method which can be used for correcting defects of a hot wire method in the process of determining the frozen soil heat conductivity coefficient.

Background

The thermal conductivity is the amount of heat transferred per unit thickness of a substance through a unit area in 1 second under the action of a unit temperature difference, and is expressed as W/(m.K). Thermal conductivity is the amount of heat transferred by a substance and does not include the amount of heat absorbed by the substance during heat transfer. The frozen soil is a mixture consisting of soil particles, ice bodies, unfrozen water and gas, and in the frozen soil thermal conductivity coefficient test process, the heat applied to the frozen soil cannot be completely transferred out, but a part of the heat is absorbed by the melting of the ice bodies in the frozen soil, and the part of the heat cannot be expressed by the raised temperature of a soil sample. Therefore, the thermal conductivity of frozen earth with phase change determined according to heating-temperature rise includes the influence of latent heat.

Patent No. 201710226098.6 provides an apparatus and a method for measuring the thermal conductivity of frozen earth in each direction, which can only measure the thermal conductivity of frozen earth in different directions, and does not consider the latent heat absorbed by the ice melt during the heating-warming process of frozen earth. Patent No. 201510403799.3 shows a device and method for testing the heat conductivity of frozen earth in a near phase transition region, without considering the phase transition problem in the process of testing the heat conductivity of the frozen earth. Literature [ Xu\25989;, Zhangzu, Wangjiacheng, Zhang Xin. frozen soil physics [ M ]. Beijing: the scientific publishing company 2010:353-354 provides a thermal conductivity test device, which uses frozen soil as a whole material to measure the temperature rise of a soil sample under the condition of a constant-temperature heat source, and does not consider the influence of the latent heat of ice melting absorption in the frozen soil on the test value of the thermal conductivity of the frozen soil. Although patent 201910000654.7 discloses a frozen soil thermal conductivity coefficient test correction method based on hot wire method, because the content of unfrozen water at the same temperature in the soil body cooling process and the soil body melting process is different, the technique only reduces the test error to a certain extent, and even causes the condition of result distortion for clay; meanwhile, the specific heat of the frozen soil is required to be calculated in the formula (3) of the method, and the application difficulty of the method is greatly increased due to the problem that the specific heat changes along with the nonlinearity of the negative temperature.

Related frozen soil heat conductivity coefficient test equipment does not give a frozen soil heat conductivity coefficient calculation formula considering the difference of unfrozen water and the latent heat effect in the freezing and thawing process, and similarly, the influence of ice body melting absorption latent heat on a heat capacity test value also exists in the specific heat mixing calorimetric process of the frozen soil. The predicted value of the temperature field obtained by substituting the heat conductivity value and the specific heat value of the frozen soil affected by latent heat into the temperature field calculation formula has larger error with the actual condition. In order to scientifically and reasonably predict the soil body temperature field in the freezing method construction process, a test method of the heat conductivity coefficient of the frozen soil required by the calculation of the temperature field needs to be corrected.

Disclosure of Invention

The invention aims to provide a frozen soil heat conductivity coefficient test correction method, which is beneficial to the determination of the real heat conductivity coefficient of the frozen soil.

In order to achieve the purpose, the invention provides a frozen soil heat conductivity coefficient test correction method, which comprises the following steps:

1) respectively measuring the temperature T in the soil body cooling process by adopting a nuclear magnetic resonance method_t(-25℃＜T_tUnfrozen water content W below 0 DEG C_dtAnd temperature T in soil body temperature rising process_t(-25℃＜T_fkUnfrozen water content W below 0 DEG C_rt；

2) Determining the temperature T in the soil body cooling process according to the step 1)_tLower unfrozen water content W_dtDrawing a relation curve of the temperature and the unfrozen water content, and recording as an unfrozen water curve in the freezing process; meanwhile, the temperature T determined in the step 1) in the soil body temperature rising process is adopted_tLower unfrozen water content W_rtDrawing a relation curve of the temperature and the unfrozen water content, and recording as an unfrozen water curve in the melting process;

3) setting the power Q of the heat conductivity coefficient of the frozen soil measured by a hot wire method, and measuring the temperature T of the frozen soil by the hot wire method_m(-25℃＜T_t＜0C.) temperature T to which it is raised_nSimultaneously recording the starting time t of measuring the heat conductivity coefficient of the frozen soil by a hot wire method₁And an end time t₂；

4) Inquiring the frozen soil temperature T on the unfrozen water curve in the freezing process determined in the step 2)_mCorresponding unfrozen water content W_dm(ii) a Inquiring the frozen soil temperature T on the unfrozen water curve in the melting process determined in the step 2)_nCorresponding unfrozen water content W_rn；

5) When the unfrozen water content W determined in the step 4) is_rnNot more than the unfrozen water content W_dmIn time, the heat conductivity coefficient lambda of the frozen soil is calculated by adopting a formula (1), wherein the formula (1) is as follows:

in the formula (1), lambda is the coefficient of heat conductivity of frozen soil; q is the power of the heat conductivity coefficient of the frozen soil determined by the hot-line method in the step 3), t₁And t₂Respectively measuring the starting time and the ending time of the heat conductivity coefficient of the frozen soil by a hot line method in the step 3); t is_mIs the frozen soil temperature; t is_nFrozen earth at temperature T at power Q_m(-25℃＜T_tThe temperature to which it is raised at < 0 ℃; pi is the circumference ratio;

6) when the unfrozen water content W determined in the step 4) is_rnGreater than the unfrozen water content W_dmIn time, the heat conductivity coefficient lambda of the frozen soil is calculated by adopting a formula (2), wherein the formula (2) is as follows:

in the formula (2), lambda is the coefficient of heat conductivity of the frozen soil; q is the power for determining the heat conductivity coefficient of the frozen soil by a hot-line method in the step 3); pi is the circumference ratio; t is t₁And t₂Respectively measuring the starting time and the ending time of the heat conductivity coefficient of the frozen soil by a hot line method in the step 3); t is_mIs the frozen soil temperature; t is_nFrozen earth at temperature T at power Q_m(-25℃＜T_tTemperature T < 0 ℃ to which_n；Q_LCalculating the latent heat of phase change caused by the content difference of the unfrozen water according to a formula (3), wherein the formula (3) is as follows:

Q_L＝Lρ_d(W_rn-W_dm) (3)

in the formula (3), Q_LLatent heat of phase change caused by the difference of unfrozen water content; l is the phase transition heat of water, and 333.51kJ/kg is taken; rho_dIs the dry density of the frozen soil; w_dmThe temperature T of the frozen soil on the unfrozen water curve in the freezing process_mThe corresponding unfrozen water content; w_rnThe temperature T of the frozen soil on the unfrozen water curve in the melting process_nCorresponding unfrozen water content.

The invention has the following effects: the method considers the difference between the soil body freezing process and the heat conductivity coefficient test process, corresponds the hot wire method heat conductivity coefficient test process and the melting process, eliminates the influence of phase change latent heat on the frozen soil heat conductivity coefficient test value, and more scientifically expresses the physical process of content change of each phase in the frozen soil in the heating-warming process. Through comparison, the prediction accuracy of the calculation method is improved by 24.8% compared with that of the traditional method. The improvement of the precision can reduce the error between the test value and the actual value of the heat conductivity coefficient of the frozen soil to the maximum extent, and provide scientific basis for predicting the soil temperature field in the construction process of the freezing method more scientifically and reasonably.

Drawings

FIG. 1 is a schematic diagram of a frozen soil thermal conductivity test modification method according to the present invention;

FIG. 2 is a diagram illustrating the effect of the frozen soil thermal conductivity test correction method of the present invention;

fig. 3 is a flowchart of a frozen soil thermal conductivity λ test according to the frozen soil thermal conductivity test correction method of the present invention.

Detailed Description

The method for testing and correcting the heat conductivity coefficient of the frozen soil is described by combining the attached drawings.

The invention discloses a principle of a frozen soil heat conductivity coefficient test correction method, which comprises the following steps: latent heat of phase change is derived from the variable quantity of the unfrozen water content in the frozen soil before and after heating, and the process of testing the heat conductivity coefficient by a hot wire method is the process opposite to the cooling of the soil body, namely the melting process of the frozen soil. The real value of the heat conductivity coefficient of the frozen soil is determined by determining the unfrozen water content of the frozen soil in the freezing and melting processes, and deducting the heat equivalent to the actually increased unfrozen water content from the applied total heat in the heat conductivity coefficient test.

As shown in fig. 1 to 3, the frozen soil thermal conductivity test correction method of the present invention includes the following steps:

1) respectively measuring the temperature T in the soil body cooling process by adopting a nuclear magnetic resonance method_t(-25℃＜T_tUnfrozen water content W below 0 DEG C_dtAnd temperature T in soil body temperature rising process_t(-25℃＜T_fkUnfrozen water content W below 0 DEG C_rt；

2) Determining the temperature T in the soil body cooling process according to the step 1)_tLower unfrozen water content W_dtDrawing a relation curve of the temperature and the unfrozen water content, and recording as an unfrozen water curve in the freezing process; meanwhile, the temperature T determined in the step 1) in the soil body temperature rising process is adopted_tLower unfrozen water content W_rtDrawing a relation curve of the temperature and the unfrozen water content, and recording as an unfrozen water curve in the melting process; as shown in fig. 1;

3) setting the power Q of the heat conductivity coefficient of the frozen soil measured by a hot wire method, and measuring the temperature T of the frozen soil by the hot wire method_m(-25℃＜T_tTemperature T < 0 ℃ to which_nSimultaneously recording the starting time t of measuring the heat conductivity coefficient of the frozen soil by a hot wire method₁And an end time t₂；

4) Inquiring the frozen soil temperature T on the unfrozen water curve in the freezing process determined in the step 2)_mCorresponding unfrozen water content W_dm(ii) a Inquiring the frozen soil temperature T on the unfrozen water curve in the melting process determined in the step 2)_nCorresponding unfrozen water content W_rn；

5) When the unfrozen water content W determined in the step 4) is_rnNot more than the unfrozen water content W_dmIn time, the heat conductivity coefficient lambda of the frozen soil is calculated by adopting a formula (1), wherein the formula (1) is as follows:

in the formula (1), lambda is the coefficient of heat conductivity of frozen soil; q is the power of the heat conductivity coefficient of the frozen soil determined by the hot-line method in the step 3), t₁And t₂Respectively measuring the starting time and the ending time of the heat conductivity coefficient of the frozen soil by a hot line method in the step 3); t is_mIs the frozen soil temperature; t is_nFrozen earth at temperature T at power Q_m(-25℃＜T_tThe temperature to which it is raised at < 0 ℃; pi is the circumference ratio;

6) when the unfrozen water content W determined in the step 4) is_rnGreater than the unfrozen water content W_dmIn time, the heat conductivity coefficient lambda of the frozen soil is calculated by adopting a formula (2), wherein the formula (2) is as follows:

in the formula (2), lambda is the coefficient of heat conductivity of the frozen soil; q is the power for determining the heat conductivity coefficient of the frozen soil by a hot-line method in the step 3); pi is the circumference ratio; t is t₁And t₂Respectively measuring the starting time and the ending time of the heat conductivity coefficient of the frozen soil by a hot line method in the step 3); t is_mIs the frozen soil temperature; t is_nFrozen earth at temperature T at power Q_m(-25℃＜T_tTemperature T < 0 ℃ to which_n；Q_LCalculating the latent heat of phase change caused by the content difference of the unfrozen water according to a formula (3), wherein the formula (3) is as follows:

Q_L＝Lρ_d(W_rn-W_dm) (3)

in the formula (3), Q_LLatent heat of phase change caused by the difference of unfrozen water content; l is the phase transition heat of water, and 333.51kJ/kg is taken; rho_dIs the dry density of the frozen soil; w_dmThe temperature T of the frozen soil on the unfrozen water curve in the freezing process_mThe corresponding unfrozen water content; w_rnThe temperature T of the frozen soil on the unfrozen water curve in the melting process_nCorresponding unfrozen water content.

Example (b): for a dry density of 1.45g/cm³The red clay saturated soil sample is combined with the inventionThe frozen soil thermal conductivity coefficient test correction method corrects the result, and the result is shown in fig. 2. By comparing the values before and after correction with the test values under other powers, the test correction method for the frozen soil heat conductivity coefficient can improve the test precision by 10.9% when the heating power of 0.87W is adopted; when the heating power of 2.19W is adopted, the test and correction method for the frozen soil heat conductivity coefficient can improve the test precision by 24.8%.

The above description is only for the purpose of illustration in conjunction with the present calculation process, and it will be apparent to those skilled in the art that various changes and modifications may be made in the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.