Transient water transport in expansive soils under coupled hydraulic, mechanical and thermal boundary conditions: Experimental and numerical study

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Coupled thermal and moisture flows and their consequences on soil behavior are involved in a variety of geotechnical problems such as buried high voltage power cable technology, geothermal energy production from shallow or deep boreholes or oil and gas production. Moreover, thermal and hydraulic aspects are of great importance in the conceptual design of repositories for spent nuclear fuel and medium level nuclear waste. On the other hand, as a consequence of climate change, thermal desiccation of natural soils is expected worldwide and even in areas of central and northern Europe. The typical soils involved in the above mentioned situations often are of expansive nature. However, the experimental study of the coupled thermo-hydro-mechanical (THM) behavior of expansive materials possesses serious difficulties, and it is not a habitual practice in geotechnical laboratories. For this reason, there is a lack of conventional laboratory techniques for THM characterization of expansive soil behavior, and if any experimental procedures are available they usually address soil investigation only under saturated conditions. Experimental data regarding unsaturated THM-material characterization are limited, especially in case of expansive clays. Hence the major aim of the proposed here investigation is to contribute in filling the gap by means of designing an experimental procedure to generate temperature, suction and water content profiles within the expansive soil under thermal and hydraulic gradients. Although experimental work plays an important role in studying the THM processes in soils it may not be self-sufficient because the laboratory tests especially for expansive materials are usually highly time consuming and costly. Therefore, in this project we propose to develop and implement theoretical and numerical modeling concepts for prediction of soil behavior during a particular THM-experiment as well as continuously in a period significantly extending the laboratory test duration. In order to make this study complete the further objectives addressed here are the calibration of the numerical model and the employed material laws via back analysis and the validation of the results by means of model sensitivity analysis.