![]() ![]() ![]() In this case a remote tensile stress, σ n, is applied, allowing microcracks to open slightly throughout the tensile region. Rocks contain many pre-existing cracks where development of tensile fracture, or Mode I fracture, may be examined. C) Brazilian disc test: applied compressive loads parallel to the crack cause the sides of the disk to bulge out and tension to occur on the crack faces. B) Hydraulic fracturing: tension or compression is applied far away from the crack and fluid pressure increases, causing tension on the face of the cracks. A) Axial stretching: tension is applied far from the crack. Most often, fracture profiles will look like either a blade, ellipsoid, or circle.Ĭartoon examples of common tensile fracture mechanisms in laboratory rock samples. Shear fractures are the first initial breaks resulting from shear forces exceeding the cohesive strength in that plane.Īfter those two initial deformations, several other types of secondary brittle deformation can be observed, such as frictional sliding or cataclastic flow on reactivated joints or faults. There are two types of primary brittle deformation processes. Highly fractured rocks can make good aquifers or hydrocarbon reservoirs, since they may possess both significant permeability and fracture porosity.įractures are forms of brittle deformation. Fractures can provide permeability for fluid movement, such as water or hydrocarbons. Fractures are commonly caused by stress exceeding the rock strength, causing the rock to lose cohesion along its weakest plane. A fracture will sometimes form a deep fissure or crevice in the rock. Cracks in rock are a mechanism of brittle deformation in response to stressĪ fracture is any separation in a geologic formation, such as a joint or a fault that divides the rock into two or more pieces. ![]()
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