Explaining thermal failure in saturated clays

Abstract

Failure conditions in soils at elevated temperatures appear to be strongly dependent on the history of the application of stress and temperature. Four cases of such history leading to various modes of failure are identified and interpreted in terms of thermal Cam-clay models. Particular attention is given to the influence of thermal variability on the coefficient of the critical state, M, or the angle of internal friction. A detailed analysis of the material history offers an explanation of an apparent confusion about whether the soil strength is decreased or increased by temperature. In a companion paper, numerical analysis of the development of axisymmetric thermal and stress fields around a cylindrical heat source suggests that thermal failure may arise in conditions that are far from any mechanically critical situation.

Characterisation of Ground Thermal and Thermo-Mechanical Behaviour for Shallow Geothermal Energy Applications

“…The tendency and magnitude of the shear strength change for different temperatures reportedly depends on a variety of factors, such as soil type, mineralogy, OCR, drainage conditions, and thermal rate. Reference [215] emphasised the importance of previous mechanical and thermal loading. In fact, in drained conditions, in some cases heating causes strengthening in clays (thermal hardening) and a stiffer behaviour can observed during subsequent shearing.…”

“…However, this soil property is less well established, as somewhat contradictory results emerge from the literature. For example, while Reference [229] proposed that the Critical State parameter M may exhibit a linear decreasing relationship with increasing temperature, other studies (e.g., [212,215]) suggested that M tends to increase or remain constant with increasing temperature. Hence, at least for basic thermo-mechanical analyses, it is suggested not to consider M to vary with temperature.…”

Multi-physical processes in geomechanics An introduction to constitutive modelling and coupling aspects

“…Some recent contributions (Cekerevac and Laloui, 2004;Laloui and François, 2009;Hueckel et al, 2009) clarified the friction angle dependency on temperature and the various thermal effects on the failure limit.…”

Editorial: Thermal Behaviour of the Ground

“…These two papers are results of studies into the behaviour of compacted clay used in storage of high-level nuclear waste, a topic covered in the next issue. Hueckel et al (2009) have studied the impact of stress and temperature on failure. They interpreted four case studies to reach a conclusion that thermal failure may occur even if mechanical failure is not imminent.…”