High rock stresses as a consequence of glaciation

Abstract

Knowledge of the stress field in the Earth's crust is crucial for the understanding of processes such as faulting and fracturing. It is also of fundamental importance for the design and construction of underground structures. The two most common methods used for in situ stress determinations for engineering geology purposes are (1) the stress relief method, in which the differences in strain resulting from induced stress relaxation are studied, and (2) the hydraulic fracturing method, in which one of the presumed principal stresses is replaced by a hydraulic pressure. Of these, the stress relief method is more applicable to design and construction problems as it enables the three-dimensional stress tensor to be measured. The in situ rock stress measurements reported here were carried out in a 500-m deep borehole in Precambrian bedrocks in Sweden and show high stress levels throughout the rock mass. A comparison between the actual recorded stresses and the theoretical stress field from a 2,000 m-thick land ice may provide a possible explanation for the measured stress situation.