TENSILE AND SHEAR FRACTURING IN PREDOMINANTLY COMPRESSIVE STRESS-FIELDS - A REVIEW

Many rock engineering geologic problems can be better solved if the genesis of rock fractures (rock joints) is understood. This paper concentrates on tensile fractures and shear fractures created in predominately compressive stress fields; such fractures prevail in many areas. Stress-based and fracture-mechanics-based concepts are introduced. They are used to show how tensile fractures are created, how shear fractures can be produced through coalescence of tensile fractures and how shear fractures and tensile fractures can be created simultaneously. Which of these mechanisms acts, depends on the particular combination of stress field and material properties. Laboratory experiments and observations in nature obtained from an extensive literature review strongly support the theoretical predictions. They also show that actual fracture patterns are often produced by a combination of mechanisms acting simultaneously or in sequence. The better understanding of fracture genesis which should result from this paper is not only interesting by itself but is useful when interpreting exploration results. © 1990.