S. Sasitharan et al., STATE-BOUNDARY SURFACE FOR VERY LOOSE SAND AND ITS PRACTICAL IMPLICATIONS, Canadian geotechnical journal, 31(3), 1994, pp. 321-334
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.