Fracture Analysis of Crystalline Rocks: Field Measurements and Field Geomechanical Techniques

摘要

The natural fractures occurring in crystalline rocks are described in terms of their occurrence in granite masses and in metamorphic rocks. Their orientations are shown to be related to the paleo or present stresses which acted or act on the rocks, to the tectonic setting of the rock mass, and in some cases to any igneous banding that might exist. The analysis of fractures in surface outcrops and in boreholes is discussed in detail, and it is shown how estimates of fracture length, fracture area and fracture interconnectivity can be made from relatively simple measurements. The biases inevitably incurred during sampling are discussed in terms of their influence on the analyzed data, and methods for compensating for their effects are also included. The influence of the fracture surfaces on the mechanical properties of rock masses is described, and methods for measuring the shear strengths of fracture surfaces is discussed. The importance of the shear strength of rocks is analyzed in terms of their effects on determining the development of the fracture system. Finally the use of fracture orientations to determine the geotectonic stress field is discussed with examples from different tectonic environments.