Mechanical Behavior of Some Clays and Shales from 200m to 3800m Depth

摘要

The mechanical behaviors of a deep clay and three shales are compared. Undrained triaxial compression tests were performed on samples from preserved core, using special methods for the shales. Some shales exhibit both overconsolidated and normally-consolidated behavior, as a function of confining stress, similar to clays. Other shales always exhibit overconsolidated behavior due to their compaction and induration. Both ductile and brittle failure behaviors were observed, depending upon the shale burial depth and also the level of confining stress. Undrained Poisson's ratios much less than 0.5 were measured, due to shale compressibility being similar in magnitude to pore fluid compressibility. The friction angles of all four materials are in the range 11°to 16°. Strength anisotropy was observed, with the bedding acting as weak planes that have low cohesion and low friction angle.