STATE-BOUNDARY SURFACE FOR VERY LOOSE SAND AND ITS PRACTICAL IMPLICATIONS

A state-boundary surface defines a boundary in stress - void-ratio spa ce above which no stress state can exist. The applicability of the sta te-boundary surface for sand has not gained widespread attention prima rily because sand is not generally considered to be a difficult soil f rom a design point of view apart from liquefaction. Liquefaction is a phenomenon usually encountered in very loose cohesionless materials. A n experimental study relating the drained and undrained behavior of ve ry loose saturated sand is presented. It is shown that the post-peak p ortion of undrained stress paths travels along the state boundary and that the state boundary can be approximated by a straight line. The sl ope of this straight line appears to stay constant for very loose sand . There are potentially an infinite number of these lines, which form a three-dimensional surface in deviator stress - effective mean normal stress - void-ratio space. Previously published results by various re searchers are used to confirm the existence of the state boundary. Thi s surface is mathematically defined in deviator stress - effective mea n normal stress - void-ratio space. Loose saturated sand samples loade d drained from a stress state on or very close to the state boundary s urface essentially travel along the state boundary surface.