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A discontinuity may exist as a single feature (e.g. fault, isolated joint or fracture) and in some circumstances, a discontinuity is treated as a single discontinuity although it belongs to a discontinuity set, in particular if the spacing is very wide compared to the size of the engineering application or to the size of the geotechnical unit.
Often, the specific origin of the stresses that created certain joints and associated joint sets can be quite ambiguous, unclear, and sometimes controversial. The most prominent joints occur in the most well-consolidated, lithified, and highly competent rocks, such as sandstone, limestone, quartzite, and granite. Joints may be open fractures or ...
Input Chart for determining RMR parameter intact rock strength Input Chart for determining RMR combined parameters RQD and discontinuity spacing. The details for calculating RMR are given by Edumine [4] and provide a series of tables for RMR determination while the latest charts for the same purpose are given in the references and further reading.
A cemented discontinuity or a discontinuity with cemented infill has higher shear strength than a non-cemented discontinuity if the cement or cemented infill is bonded to both discontinuity walls. Note that cement and cement bounds that are stronger than the surrounding intact rock ceases the discontinuity to be a mechanical plane of weakness ...
Laubscher uses a graph for the spacing parameter. The parameter is dependent on a maximum of three discontinuity sets that determine the size and the form of the rock blocks. The condition parameter is determined by the discontinuity set with the most adverse influence on the stability.
Tilt test on a fitting discontinuity. In geomechanics, a tilt test is a simple test to estimate the shear strength parameters of a discontinuity. [1] [2] Two pieces of rock containing a discontinuity are held in hand or mounted in test equipment with the discontinuity horizontal. The sample is slowly tilted until the top block moves.
The concentric circles in this sandstone in Arizona are plumose (plume-like) structures that can form during the formation and propagation of a fracture. Fractures in rocks can be formed either due to compression or tension. Fractures due to compression include thrust faults. Fractures may also be a result from shear or tensile stress.
In folded alternations of sandstone and mudstone the cleavage has a fan-like arrangement, divergent in the mudstone layers and convergent in the sandstones. This is thought to be because the folding is controlled by buckling of the stronger sandstone beds with the weaker mudstones deforming to fill the intervening gaps. [ 3 ]