The results of oedometer and triaxial tests on high-quality intact sam
ples of four natural stiff clays are presented and compared with the c
orresponding results for reconstituted clays, By this means it has bee
n possible to identify the influence of the micro-structure on the com
pressibility and peak strength of the natural clays, All four clays ex
hibit rapid loss of strength after peak with well-defined post-rupture
strength envelopes, At low confining pressures the post-rupture angle
s of shearing resistance are all close to the corresponding intrinsic
critical state values, but for some of the clays there is a small cohe
sive 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 f
rom peak to post-rupture strength is due primarily to breakage of inte
rparticle bonds, but that at higher confining pressures some particle
orientation also takes place.