A laboratory study of the strength of four stiff clays

The results of oedometer and triaxial tests on high-quality intact samples of four natural stiff clays are presented and compared with the corresponding results for reconstituted clays, By this means it has been possible to identify the influence of the micro-structure on the compressibility and peak strength of the natural clays, All four clays exhibit rapid loss of strength after peak with well-defined post-rupture strength envelopes, At low confining pressures the post-rupture angles of shearing resistance are all close to the corresponding intrinsic critical state values, but for some of the clays there is a small cohesive intercept, At higher confining pressures the post-rupture angles of shearing resistance are less than the corresponding critical state values, It is concluded that the strength reduction that takes place from peak to post-rupture strength is due primarily to breakage of interparticle bonds, but that at higher confining pressures some particle orientation also takes place.