Study of Dynamic and Static Failure Envelopes

Laboratory tests indicate that the maximum drained shear resistance of cohesionless soils is essentially insensitive to test duration whereas purely cohesive and combined soils offer increased shear resistance described solely by a change in the apparent cohesion intercept of the failure envelope at higher strain rates. The consistent failure envelope trends provide a basis for estimating the dynamic shear resistance if the static failure envelope is available. These trends also show general agreement with hypothetical failure envelope presentations by other investigators. An extensive investigation indicates that variations in moisture content, dry density, grain size, soil structure, and pore fluid do not significantly alter the ratio of dynamic to static apparent cohesion intercepts. A specially constructed direct shear device was used to experimentally test and compare the maximum dynamic (impact) and static shear resistances of a wide variety of soils. The practical application of such results to cratering phenomena and dynamic footing response is also indicated.