Loose cohesionless saturated materials have proved responsible for a n
umber of serious or catastrophic flow slides. Liquefaction failures wi
th no obvious triggering mechanism have also been recorded. This pheno
menon of sudden liquefaction without a presence of cyclic shear stress
es is often referred to as spontaneous or static liquefaction. Results
from previously published studies suggest that liquefaction is trigge
red not by the undrained loading and generation of pore pressures but
by the collapse of the metastable sand structure, which in turn genera
tes the driving pore pressures in a saturated material. Hence, the col
lapse is a characteristic response of a material to certain stress sta
tes rather than a result of some enforced undrained loading. This theo
ry is evaluated on very loose dry Ottawa sand. It is shown that the ve
ry loose dry sand when subjected to a constant deviatoric stress path
significantly changes its behavior at a certain discreet stress state,
increases compressibility, and becomes increasingly unstable. This re
sults in collapse - vigorous contraction of the specimen. This structu
ral collapse appears to be equivalent to the pore-pressure generation
in collapsing, very loose saturated sand.