TIME-DEPENDENT STRAINS AND CREEP IN ROCK AND SOIL STRUCTURES.

Rock and soil masses are composed of a vast variety of minerals and occur in an almost infinite rnage of conditions, from crystalline solids to aggregations of independent particles. The majority of the minerals are based on silicate chemistry but many creep problems occur in the minority groups, the carboniferous deposits, crystalline salt, and limestones due to their mining importance. A vast variety of internal and external stress may exist due not only to crystallization stress and to self weight but due also to tectonic and siesmic forces. The combination of large regional stress fields and the stress concentrations which arise at material or physical discontinuities will often bring the weakest component of the rock system near to its yield threshold. Under such circumstances only a small additional change may initiate a creep condition.