Thermal Conductivity Evolution of Saturated Clay under Consolidation Process H. M. Abuel-Naga 1 ; D. T. Bergado 2 ; and A. Bouazza 3 Abstract: This paper presents the results of a study on the thermal conductivity of a soft saturated clay Bangkok clay carried out in relation to an investigation into thermal ground improvement using prefabricated vertical drains. The thermal conductivity of clay specimens was measured, at different porosities and temperature levels, using a simple nondestructive steady-state test method. In addition, a theoretical mixture model to simulate the evolution of thermal conductivity of saturated fine-grained soils has been introduced. It is formulated in terms of thermal conductivity and volume fraction of each soil phase solid and water, and a morphological parameter controlled by the soil fabric condition. The proposed model has been validated against thermal conductivity results reported in the literature and results obtained from the present investigation. Reasonable agreement has been obtained between the predicted and measured thermal conductivity values. DOI: 10.1061/ASCE1532-364120088:2114 CE Database subject headings: Thermal resistance; Thermal properties; Heat flow; Clays; Temperature; Soft soils; Soil consolidation; Soil porosity. Introduction A clear understanding of heat transfer through geomaterials is of great interest in many geoengineering projects involving thermal effects, such as oil and gas pipelines Slegel and Davis 1977, buried high voltage electrical cables Abdel-Hadi and Mitchell 1981, ground heat energy storage Moritz 1995, heat exchanger piles Laloui et al. 2003, and clay barriers for nuclear waste repositories Gera et al. 1996. The validity and efficiency of an innovative thermal technique capable of enhancing the perfor- mance of prefabricated vertical drains in soft Bangkok clay has been investigated recently Abuel-Naga et al. 2006. For this pur- pose, a clear understanding of the factors affecting the thermal conductivity of saturated clay and its evolution under the consoli- dation process is required. Field or laboratory tests can be used to measure the thermal conductivity of soils Valente et al. 2006; Côté and Konrad, 2005b; Roth et al. 2004; Newson and Brunning 2004; Naidu and Singh 2004; Abu-Hamdeh et al. 2001; Morin and Silva 1984. However, field tests are expensive, time consuming, and have no freedom to control the boundary conditions. On the other hand, laboratory tests are relatively inexpensive and simple to conduct. However, great care should be given to soil disturbance and the fitting of the governing equation to the boundary conditions of the test apparatus. Several researchers Usowicz et al. 2006; Côté and Konrad 2005b; Ochsner et al. 2001; Abu-Hamdeh and Reeder 2000; Brandon and Mitchell 1989; Morin and Silva 1984; Farouki 1981; Sepaskhah and Boersma 1979 have shown that thermal conduc- tivity is related to soil properties such as mineralogical composi- tion, dry density porosity, pore fluid, degree of saturation, water content, and temperature. The effect of the geometrical arrange- ment of the soil particles on the thermal conductivity value of the saturated clays has also been discussed by Penner 1963, Mitch- ell 1993, and MidttØmme et al. 1998. Numerous theoretical and empirical approaches have been de- veloped to model the evolution of the thermal conductivity of two-phase composite material as a function of the thermal con- ductivity and the volumetric proportions of the different phases as well as their texture fabric within the medium. These ap- proaches can also be used to model the evolution of the thermal conductivity of saturated soils. The use of theoretical based mod- els is recommended as the validity of empirical equations is al- ways limited to specific conditions. Appendixes I and II include some of the theoretical mixture models that have been developed to simulate the thermal conductivity of the two-phase system. The models listed in Appendix I were derived without taking into consideration the fabric configuration effects on the thermal con- ductivity. Fig. 1 shows the feature of these models in the thermal conductivity-porosity  T - n plane. The parallel and series heat flow modes can be considered as the upper and lower bound of the theoretical models as shown in Fig. 1. On the other hand, the models listed in Appendix II are flex- ible in terms of considering different fabric conditions since they include fabric parameters. However, they also have some limita- tions. According to Johansen 1975, the values of the shape fac- tors used by De Vries 1963 were empirical since they can hardly 1 Senior Lecturer, Dept. of Civil and Environmental Engineering, Faculty of Engineering, The Univ. of Auckland, Private Bag 92019, Auckland Mail Centre, Auckland 1142, New Zealand corresponding author. Email: hossam.abuelnaga@gmail.com 2 Professor, School of Engineering and Technology, Asian Institute of Technology, P.O. Box 4, Khlong Luang, Pathumthani 12120, Thailand. E-mail: bergado@ait.ac.th 3 Associate Professor, Dept. of Civil Engineering, Building 60, Monash Univ., Melbourne, Vic. 3800, Australia. E-mail: malek. bouazza@eng.monash.edu.au Note. Discussion open until September 1, 2008. Separate discussions must be submitted for individual papers. To extend the closing date by one month, a written request must be filed with the ASCE Managing Editor. The manuscript for this paper was submitted for review and pos- sible publication on June 5, 2006; approved on August 7, 2007. This paper is part of the International Journal of Geomechanics, Vol. 8, No. 2, April 1, 2008. ©ASCE, ISSN 1532-3641/2008/2-114–122/$25.00. 114 / INTERNATIONAL JOURNAL OF GEOMECHANICS © ASCE / MARCH/APRIL 2008 Int. J. Geomech. 2008.8:114-122. Downloaded from ascelibrary.org by Yonsei University Library on 08/06/13. Copyright ASCE. For personal use only; all rights reserved.