Liquefaction of crushable soils

Crushable soils when sheared in a dense state have stress paths which are similar to those for loose, hard-grained sands; however, because of their angular nature they do not liquefy as easily under cyclic loading. In the Hyogo-ken Nambu, 1995, earthquake, there was widespread liquefaction of land areas reclaimed from the sea using a crushable, highly angular, decomposed granite soil, Masado, which was previously regarded as a high-quality fill material with little risk of liquefaction in earthquakes. Results are presented from monotonic and cyclic triaxial tests on three types of crushable soil, namely Masado, Shirasu volcanic sand and Dogs Bay carbonate sand, together with standard silica Toyoura sand, to establish liquefaction criteria which can be applied not only to hard-grained silica sands but also to more angular crushable sands. In monotonic triaxial testing the stress paths passed through a point of phase transformation, with each material exhibiting large strains after this point. Normalization of the stress—strain curves and stress paths with respect to the effective consolidation stress brought the phase transformation points closer together. For loose soil, liquefaction failure occurred, while for dense sand cyclic mobility was evident, where the stress path cycled through or close to zero-p' conditions while the cyclic axial strain increased at a steady rate to large values. The liquefaction strength was defined in terms of the number of cycles to cause a double-amplitude strain of 5%, for both types of failure. A relationship was established between the normalized deviator stress required to cause liquefaction failure after 20 cycles and the normalized phase transformation strength obtained from monotonic tests. This relationship was independent of relative density and type of material. Les sols concassables, quand Us sont cisaillés à ľétat dense, ont des parcours de contrainte qui sont similaires à ceux des sables boulants à grains durs mais en raison de leur nature angulaire, Us ne se liquéfient pas aussi facilement souscharge cyclique. Lors du tremblement de terre de Hyogoken Nambu en 1995, it šest produit une liquéfaction très étendue des zones de terre regagnées sur la mer en ut lisant un sol de granite décomposé trèos angulaire et concassable, le Masado, qui était auparavant considéré comme un matériau de remplissage de haute qualité présentant pen de risque de liquéfaction lors ďun séisme. Nous présentons ici les résultats ďessais tr