Abstract
Geo-energy applications such as energy piles can expose unsaturated, deep foundation soils to elevated temperatures. This paper presents a closed-form equation for the ultimate bearing capacity of piles in unsaturated soils subject to elevated temperatures under drained conditions. For this purpose, a temperature-dependent effective stress model was incorporated into calculations of skin resistance and end bearing resistance of piles. The proposed temperature-dependent model is an extension of the modified β method for determining the ultimate pile bearing capacity of unsaturated soils under drained conditions. Employing the proposed model, a parametric study was carried out to evaluate the ultimate pile bearing capacity for hypothetical clay and silt soils at temperatures ranging from 25 °C to 55 °C. For both clay and silt, the results indicated that the ultimate pile bearing capacity varies with an increase in temperature. Different trends with temperature were observed for clay and silt. A monotonic increase in pile resistance was observed in clays. For silt, the pile resistance increased at relatively low matric suction whereas it decreased at higher matric suctions.
Highlights
Introduction and BackgroundPiles improve the mechanical behavior of in situ soils by invoking load transfer to deeper depths, resisting horizontal and uplift movements, and resisting excessive settlement
Uchaipichat [2] performed a parametric study by using a semi-empirical formulation by varying pile capacities installed in unsaturated clay soils in which undrained shear strength controlling pile capacity at various matric suctions were back calculated via laboratory tests
The ultimate pile bearing capacity for drained unsaturated soils was extended in the paper to account for the effect of temperature
Summary
Piles improve the mechanical behavior of in situ soils by invoking load transfer to deeper depths, resisting horizontal and uplift movements, and resisting excessive settlement. Previous studies have conducted experimental and theoretical evaluations to better understand the ultimate pile bearing capacity of unsaturated soils under ambient temperature conditions. Uchaipichat [12] presented an expression to determine the ultimate pile bearing capacity of unsaturated soils for undrained heating Most studies in this area are limited to dry or saturated conditions and are not applicable to unsaturated conditions. This study presents an analytical model for the ultimate bearing capacity of piles in unsaturated soils subject to elevated temperatures under drained conditions. The model was developed by incorporating the temperature dependent effective stress concept into formulations of skin and end bearing resistance of piles for unsaturated soils. A modified β method for the ultimate pile bearing capacity of unsaturated soils [1] was utilized and extended to temperature-dependent conditions in this study. The first term of Eq 2 represents the contribution from the shaft/skin segment of the pile and the second term represents the contribution from the tip/base segment of the pile
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