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Pure and Applied Geophysics

Study on the Thermophysical Properties of Clay Under Repeated Freezing and Thawing HAIQIANG JIANG,1,2 FUJUN NIU,1,2 ENLIANG WANG,3 QINGUO MA,1,2 and LI CHENG1,2 Abstract—The thermophysical properties of soil are crucial factors for understanding the heat distribution in soil layers, especially in cold regions. Therefore, to analyze the effect of freezing and thawing action on soil thermophysical properties, here, samples with varying water content were subjected to different numbers of freezing and thawing cycles from 0 to 11 in a laboratory setting, and the thermal conductivity, thermal diffusion coefficient and volume heat capacity were measured and analyzed. Five previously proposed thermal conductivity models were evaluated, and a novel thermal conductivity model was developed based on the concept of the tortuosity and parallel model. The results showed that the thermal conductivity and volume heat capacity vary in direct proportion with the number of freezing and thawing cycles up to seven cycles. Beyond seven cycles, with repeated freezing and thawing action, samples with varying water content reach a residual porosity ratio of 0.5142–0.5345. Both the water content and freezing and thawing action influence the soil thermophysical properties, with water content playing a more important role than freeze–thaw cycles. Among these five models, the Kersten model was found to be the best, followed by the Johansen model, Lu et al. model, parallel model, and serial model. respectively. The Cote and Konrad model demonstrated the poorest performance. In addition, the tortuosity–parallel model was able to efficiently calculate the thermal conductivity of clay under freezing and thawing action. Keywords: Freezing and thawing, clay, thermophysical properties, tortuosity–parallel model.

1. Introduction Seasonally frozen soil is defined as soil that freezes in the cold season and thaws in the warm

1

South China Institution of Geotechnical Engineering, School of Civil Engineering and Transportation, South China University of Technology, Guangzhou 510640, China. E-mail: [email protected] 2 State Key Laboratory of Subtropical Building Science, South China University of Technology, Guangzhou 510640, China. 3 School of Water Conservancy and Civil Engineering, Northeast Agricultural University, Harbin 150030, China.

season. It accounts for 25% of the world’s total land area. There are many crucial factors that can impact on the formation process of frozen soil, such as temperature, water content and soil texture (Xu et al. 2010). In addition, the intrinsic thermophysical properties of soil are vital factors: thermal conductivity and volume heat capacity determine the level and velocity of frozen depth, further leading to active layer periodic freezing and thawing (Zhang et al. 2018; Tao and Zhang 1983). Generally, freeze–thaw action is recognized as a strong weathering force, which significantly alters the size, shape and distribution of soil grains. Moreover, as many as 100 freeze–thaw cycles can