Institute for Disaster Management and Reconstruction, Sichuan University, Chengdu, Sichuan, China.
State Key Laboratory of Hydraulics and Mountain River Engineering, College of Water Resource and Hydropower, Sichuan University, Chengdu, Sichuan, China.
PLoS One. 2023 Jun 23;18(6):e0286973. doi: 10.1371/journal.pone.0286973. eCollection 2023.
Mountainous areas in southwest China are rainy in summer. The rainfall infiltration process involves complex soil thermal-hydraulic-mechanical (THM) coupling problems. The researches on soil THM coupling are mostly focused on numerical simulations, whereas the corresponding model tests are relatively few, and the existing model test studies often ignore the effect of temperature gradients in the soil. However, temperature gradients in the soil can cause water migration and affect the THM behavior of soil, so it cannot be ignored. This paper describes an experimental device that can test the changes of temperature, moisture and displacement in unsaturated soil columns with temperature gradients under rainfall infiltration conditions. By using the apparatus, the model tests of homogeneous soil column (H), homogeneous soil column with infiltration (HI), and preferential flow soil column with infiltration (P) under different temperature gradients are respectively conducted, and the results of moisture and heat migration and deformation properties in soils under different conditions are presented and discussed. A rainfall of low intensity and long duration is applied in the experiments, and the temperature of infiltration rainwater is consistent with that of the soil upper boundary. The results show that: (1) The infiltration of rainfall will increase the temperature of the soil column. The appearance of preferential flow results in faster heat transfer within the soil column, but causes the steady-state temperature to be lower than that of the homogeneous soil (HI); (2) Under infiltration conditions, the preferential flow soil column has an earlier outflow time but a later time for water field to reach steady state, while its water distribution is different from that of the homogeneous soils, with accumulation occurring near the end of preferential flow channel; (3) Under the action of temperature gradient, water migration occurs in homogeneous soil column (H), accompanied by soil settlement, while the infiltrated columns (HI and P) exhibit an increase in both water content and top displacement. In addition, the larger the temperature gradient, the more obvious the thermally induced hydraulic-mechanical response. The research results in this paper can provide experimental evidence for the theoretical study and numerical simulation of the soil THM coupling problems.
中国西南山区夏季多雨。降雨入渗过程涉及复杂的土壤热-水-力-力学（THM）耦合问题。土壤 THM 耦合的研究大多集中于数值模拟，而相应的模型试验相对较少，并且现有的模型试验研究往往忽略了土壤中温度梯度的影响。然而，土壤中的温度梯度会引起水的迁移，从而影响土壤的 THM 行为，因此不容忽视。本文介绍了一种实验装置，该装置可以在降雨入渗条件下测试具有温度梯度的非饱和土柱中的温度、水分和位移变化。利用该装置，分别进行了均质土柱（H）、有入渗的均质土柱（HI）和有入渗的优势流土柱（P）的模型试验，给出并讨论了不同条件下土壤中水分和热量迁移及变形特性的结果。实验中采用低强度、长时间的降雨，入渗水的温度与土壤上边界的温度一致。结果表明：（1）降雨入渗会增加土柱的温度。优势流的出现会导致土柱内的热量传递更快，但会使稳定状态的温度低于均质土（HI）；（2）在入渗条件下，优势流土柱的流出时间更早，但水场达到稳定状态的时间更晚，而其水分分布与均质土柱不同，在优势流通道末端附近会有积水；（3）在温度梯度的作用下，均质土柱（H）中发生水分迁移，伴随土壤沉降，而入渗土柱（HI 和 P）则表现出含水量和顶部位移的增加。此外，温度梯度越大，热诱导水力学-力学响应越明显。本文的研究结果可为土壤 THM 耦合问题的理论研究和数值模拟提供实验证据。
