ABSTRACT

Thermal stresses play an important part in the failure of rock when it is subjected to significant low or high temperatures. Thermal stresses can be induced in two kinds of situation, i.e. thermal mismatch and thermal gradient. In thermal mismatch, when uniform temperature changes occur and due to differences in the coefficients of thermal expansion in different parts of the rock, non-uniform thermal dilatation or contraction occurs. In the thermal gradient case, there are differences in temperature at various locations caused by the gradient. For example, solar radiation causes the temperature of an exposed rock surface to rise but, because rock is a poor heat conductor, a thermal gradient occurs. The most severe condition occurs when a sunny, windless day follows a few days of cold weather (Figure 13.1). A similar case arises if there are underground heat sources from geological causes or engineered sources, (Figure 13.2). Both the thermal mismatch and the non-uniform temperature distribution can occur together.