Influence of stress history on thermal conductivity of saturated fine-grained soils

Abstract

This research investigated variations in thermal conductivity <i>k</i> for normally consolidated (NC) and overconsolidated (OC) saturated fine-grained soils at different levels of vertical effective stress. A series of undrained heating tests were performed using a specially designed consolidometer with central radial heating arrangement and temperature measurements within a soil specimen. For different soils investigated in this research, <i>k</i> correlated well with soil consolidation characteristics (compression index <i>λ</i> and swelling index <i>κ</i>) and vertical effective stress <i>σ</i><sub>v</sub>ʹ at both NC and OC states. However, the rates of increment of steady- and transient-state values of <i>k</i> (<i>k</i><sub>st</sub> and <i>k</i><sub>tr</sub>, respectively) with <i>σ</i><sub>v</sub>ʹ differed from one soil to another. For OC clays, both <i>k</i><sub>tr</sub> and <i>k</i><sub>st</sub> increased with preconsolidation stress <i>σ</i><sub>c</sub>ʹ. A set of equations were proposed to estimate both <i>k</i><sub>st</sub> and <i>k</i><sub>tr</sub> for saturated fine-grained soils as functions of <i>σ</i><sub>v</sub>ʹ, <i>λ</i>, <i>κ</i>, and stress history. At a particular value of <i>σ</i><sub>v</sub>ʹ, the dependence of <i>k</i> on overconsolidation ratio (OCR) and <i>σ</i><sub>c</sub>ʹ marked the importance of considering stress history in the determination of <i>k</i>. The influence of soil mineral composition on <i>k</i> was also explored. Quantification of soil mineralogical composition and available data on mineral thermal conductivity enabled prediction of <i>k</i><sub>tr</sub> with reasonable accuracy.