STRAIN AND STRENGTH OF ROCKS IN PERMAFROST ZONES ON HUMAN IMPACT: EARTHQUAKE HAZARD ASSESSMENT

Abstract

Strain properties of rocks were classified as a function of lithology, origin, porosity, water content, and permafrost in the Baikal region. Velocities of elastic waves were found to overlap for rocks of different origins and lithologies, the rocks close to monolithic as to the degree of preservation. Relations were derived between velocities in rocks treated as two-and three-component media with a fixed porosity as they pass from a frozen to a thawed (water-saturated) state. Poisson's ratio was found to increase with the increasing porosity. A quantitative relation was derived between this ratio and velocities of elastic waves. Experiments on the strength of the rocks revealed that, according to the bilinear strain theory, failure in rocks took place under shearing forces in clusters of rock skeleton particles in the range of particle velocities 0.8-3.2 m/s, the lower limit corresponding to elastic shear waves, the upper, to elastic-plastic waves. Quantitative strength limits were determined for porous rocks in relation to Poisson's ratio. The strength limit as a function of the ratio of compressional to shear wave velocity was determined for soft water-saturated soils. Recommendations were given as to how the strength of rocks is to be incorporated when specifying seismic excitation.