THE QUANTITATIVE EFFECT OF HYDROSTATIC CONFINING PRESSURE ON THE COMPRESSIVE STRENGTH OF CRYSTALLINE ROCKS

Abstract

The effect of hydrostatic confining pressure on compressive strength of crystalline rocks is investigated in some detail on the basis of the available published experimental data.It is found that the pressure dependence of the compressive strength of rocks is same, in spite of different origins, for the same rock type and that there is no appreciable difference in the effect of confining pressure on compressive strength among diorite, diabase and peridotite, and among carbonate rocks. The quantitative relation of these facts to the bulk hardness of rock are discussed. A strong positive correlation was observed between the effect of pressure on compressive strength and the bulk hardness for silicate crystalline rocks.If the relation between compressive strength C and confining pressure p is expressed with the empirical formula; C/C0=1+K(p/C0)n, where C0 is the uniaxial compressive strength, then both K and n are found to be constants according to rock type. Then, a practical estimation of the compressive strength of a rock at any confining pressure can be made if only the uniaxial compressive strength of the rock is known, once the values of K and n for elach rock type are determined.