A Simplified Method for Bearing-Capacity Analysis of Energy Piles Integrating Temperature-Dependent Model of Soil–Water Characteristic Curve

Abstract

32 The bearing resistance of energy piles in the presence of temperature effect has not been thoroughly 33 investigated, preventing the perfecting of energy pile design methods. Quantifying the relationship between soil 34 suction and the temperature of unsaturated soils therefore becomes an important step in predicting the bearing 35 resistance of energy piles. A new constitutive model based on interfacial energy and thermodynamic theories is 36 therefore presented to predict the effect of temperature on soil suction as well as the soil-water characteristic 37 curve (SWCC) in this paper. The analytical model for the nonisothermal matric suction was developed by 38 combining five different temperature-dependent functions for the surface tension, air-water contact angle, void 39 ratio, and thermal expansion of solid and water density, thereby providing a more complete approach than the 40 one that considers surface tension only. The proposed formulation is expressed under a simplified form which is 41 believed as a useful and convenient tool to apply to a range of possible field situations. The temperature-42 dependent relationship of soil suction is then used to extend existing isothermal SWCCs to nonisothermal 43 conditions that allow obtaining the SWCC at any temperature. The validity of the proposed model is verified by 44 comparison to several test data sets for five different soils: swelling clay, hard clay, clayey-silty soil, ceramic 45 material, and sand. The satisfactory agreement between predicted and measured curves proved that the proposed 46 model has a good performance in predicting the effect of temperature on the SWCCs of unsaturated soils. The 47 nonisothermal SWCC model was then coupled with the bearing resistance theory to produce a simplified method 48 for analysis of energy piles. The results show that the proposed method successfully predicted pile resistance at 49 various temperatures when compared to experimental data. The pile resistance reduces as the temperature rises 50 for a specific degree of saturation or if the soil is in an undrained condition. However, water evaporation may 51 cause a decrease in water content and an increase in matric suction as the temperature increases. Therefore, as 52 soils dry out, pile resistance may increase with increasing temperature.