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

Abstract

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