SHEAR STRESSES AND THE HYDRAULIC FRACTURING OF EARTH DAM SOILS

Abstract

Stiff clays and shales forming part of earth dams contain cracks in their structure. Cracks develop in these materials during and after the construction of the dams. It has been suggested that hydraulic fracturing after the first reservoir filling causes the growth of the cracks that develop into continuous channels through which concentrated water leaks take place. Current methods of analysis of crack propagation in earth dams assume that the cracks grow when water pressures on the walls of the cracks become greater than the dam stresses acting normal to the walls of the cracks. Current methods of analysis do not take into consideration the effect on crack propagation of any shear stresses that could act parallel to the plane of the cracks. In the present study, a theoretical approach for the interpretation of crack growth in earth dams is presented. This is a new approach and it is based on Linear Elastic Fracture Mechanics theory. Using this theory crack propagation and interaction in earth dams are studied considering not only the water pressures and normal stresses acting on the cracks but the effect of any shear stresses as well.