In situ pore-pressure generation behavior of liquefiable sand

To overcome current limitations in predicting in situ pore-pressure generation, a new field testing technique is used to measure directly the coupled, local response between the induced shear strains and the generated excess pore pressure. The pore-pressure generation characteristics from two in situ liquefaction tests performed on field reconstituted specimens are presented, including the pore-pressure generation patterns at various strain levels, the observed stages of pore-pressure generation, and pore-pressure generation curves. Comparisons of the in situ pore-pressure generation curves with data in the literature and from laboratory strain-controlled, cyclic direct simple shear tests support the in situ testing results. In addition, the effects of effective confining stress on threshold shear strain and pore-pressure generation curves are discussed. Comparisons of the rate of pore-pressure generation among the in situ tests, laboratory strain-controlled tests, and a model based on stress-controlled tests reveal that in situ pore pressures generated in reconstituted soil specimens during dynamic loading develop more similarly to those from cyclic strain-controlled laboratory testing. This observation implies that the evaluation of induced strains rather than induced shear stresses may be more appropriate for the simulation of pore-pressure generation.