Rock mechanics

(geophysics) Application of the principles of mechanics and geology to quantify the response of rock when it is acted upon by environmental forces, particularly when human-induced factors alter the original ambient forces.

Application of the principles of mechanics and geology to quantify the response of rock when it is acted upon by environmental forces, particularly when human-induced factors alter the original ambient conditions. Rock mechanics is an interdisciplinary engineering science that requires interaction between physics, mathematics, and geology, and civil, petroleum, and mining engineering. The present state of knowledge permits only limited correlations between theoretical predictions and empirical results. Therefore, the most useful principles are based upon data obtained from laboratory and in-place measurements and from prototype behavior (behavior of the completed engineering works). Increasing emphasis is upon in-place measurements because rock properties are regarded as site-specific; that is, the properties of the rock system at one site probably will be significantly different from those at another site, even if geologic environments are similar. See also Engineering geology.

Because of the interdisciplinary aspects, there is no standardization of rock mechanics terminology. However, the following terms and definitions are useful.

Environmental factors are the natural factors and human influences that require consideration in engineering problems in rock mechanics. The major natural factors are geology, ambient stresses, and hydrology. The human influences derive from the application of chemical, electrical, mechanical, or thermal energy during construction (or destruction) processes.

The ambient stress field is the distribution and numerical value of the stresses in the environment prior to its disturbance by humans.

The term rock system includes the complete environment that can influence the behavior of that portion of the Earth's crust that will become part of an engineering structure. Generally, all natural environmental factors are included.

A rock element is the coherent, intact piece of rock that is the basic constituent of the rock system and which has physical, mechanical, and petrographic properties that can be described or measured by laboratory tests on each such element. The concepts of rock system and rock element enable the concomitant engineering design to be optimized according to the principles of system engineering. See also Systems engineering.

“Rock failure” occurs when a rock system or element no longer can perform its intended engineering function. Failure may be evidenced by fractures, distortion of shape, or reduction in strength. “Failure mechanism” includes the causes for the manner of rock failure. See also Rock burst; Soil mechanics; Tunnel; Underground mining.

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