Loose cohesionless materials can collapse during either static or dyna
mic loading, resulting in a rapid buildup of pore pressure and associa
ted reduction in shear resistance. As the cohesionless material collap
ses, it rapidly looses resistance until the acting shear stress decrea
ses to the available residual or steady-state strength. Specially desi
gned stress-path testing has been performed on sand to investigate thi
s collapse process. Results from this test program and previously publ
ished data show that a state boundary can be defined when a cohesionle
ss material moves from peak to steady state along a constant void rati
o stress path regardless of whether it is loaded drained or undrained.
Further. it is demonstrated that the state boundary represents a surf
ace in the effective mean normal stress-deviator stress-void ratio spa
ce. Hence, flow slides and liquefaction can be initiated when the stre
ss path followed during either drained or undrained loading attempts t
o cross this state boundary surface.