Stability Analysis of an Unsaturated Silty Slope under Nonisothermal Conditions

2020

E3S Web Conf.

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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.

Section: Temperature Dependent Ultimate Pile Bearing Capacity In Unsamentioning

confidence: 99%

Section: Temperature Dependent Ultimate Pile Bearing Capacity In Unsamentioning

confidence: 99%

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A model for ultimate bearing capacity of piles in unsaturated soils under elevated temperatures

2020

E3S Web Conf.

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“…The matric suction depth profile generally varies depending on the soil type, effective degree of saturation, and the depth of the water table. Using Darcy's law, one can express the matric suction in terms of depth and hydraulic parameters [19]. A one-dimensional matric suction profile under hydrostatic conditions as a temperature-dependent quantity is expressed as [12][13][14][15]:…”

Section: Temperature-dependent Suction Stress Profile Versus Depth Unmentioning

confidence: 99%

Effect of Elevated Temperatures on Lateral Earth Pressures in Unsaturated Soils

2020

E3S Web Conf.

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Near-surface unsaturated soils can be exposed to elevated temperatures due to soil-atmospheric interactions under drought events, wildfires, heatwaves, and warm spells, or the heat induced by emerging geotechnical and geo-environmental technologies such as geothermal boreholes and thermally active earthen systems. Elevated temperatures can affect the hydro-mechanical characteristics of unsaturated soils, which in turn can alter lateral earth pressures developed in the backfill soil. The main objective of this study is to quantify the effect of elevated temperatures on active and passive earth pressures of unsaturated soils. For this purpose, the paper presents the derivation of an analytical framework to extend Rankine’s earth pressure theory to account for the effect of temperature under hydrostatic conditions. The equations are derived by incorporating the effect of temperature into the soil water retention curve and a suction stress-based effective stress representation. The proposed effective stress equation considers the temperature-induced changes in the contact angle, surface tension, and enthalpy of immersion. To investigate the impact of temperature on active and passive earth pressures, the proposed method is then used in a set of parametric studies to determine active and passive earth pressure profiles for three hypothetical soils of clay, silt, and sand at different temperatures. Results suggest that elevated temperatures can cause variation in active and passive earth pressures for all the soils considered. The findings of this study can contribute toward analyzing earth retaining structures subjected to elevated temperatures.

“…In many of the geotechnical and geoenvironmental applications mentioned above, changes in temperature may occur, which have an additional effect on the elastic moduli of unsaturated soils. Further, other geotechnical applications involving elevated temperatures include earthen structure-atmospheric interaction under a changing climate, storage of nuclear waste, energy piles, soil-borehole thermal energy storage systems, buried high voltage cables, and thermally active earthen structures (e.g., Gens and Olivella, 2001;Laloui and Di Donna, 2013;Robinson and Vahedifard, 2016;Vahedifard et al, 2015Vahedifard et al, , 20162017;2018a;McCartney et al, 2016;Başer et al, 2018;Thota et al, 2019;Shahrokhabadi et al, 2020). Several experimental studies have illustrated the effects of temperature on the shear strength, volume change and stiffness of saturated and unsaturated soils (e.g., Cekerevac and Laloui, 2004;Uchaipichat and Khalili 2009;Coccia et al, 2013;Alsherif and McCartney, 2015;Zhou and Ng, 2016;Ng et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

Temperature-Dependent Model for Small-Strain Shear Modulus of Unsaturated Soils

J. Geotech. Geoenviron. Eng.

Cao

et al. 2020

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Near-surface soils in geotechnical and geoenvironmental applications are often unsaturated, and natural or imposed changes in temperature may lead to a softening effect at constant suction that causes a change in stiffness. To capture thermal effects on the stiffness of unsaturated soils, this paper presents an effective stress-based, temperature-dependent model for the small-strain shear modulus of unsaturated soils, with an emphasis on silts. Temperature dependency of the model is accounted for by employing temperature-dependent functions for matric suction and effective saturation characterized using the soil-water retention curve. To validate the proposed model, laboratory tests using a modified triaxial apparatus with bender elements are carried out on Bonny silt to measure the small-strain shear modulus at 23 and 43°C for varying matric suctions of 0 to 110 kPa. The results from the proposed model are in a reasonable agreement with the experimentally measured values, and demonstrate the importance of considering temperature effects on the shear modulus of unsaturated soils. The accuracy of the model is further validated by comparing the predicted values with laboratory test results on silts reported by two independent studies reported in the literature.