Blast Induced Liquefaction Potential and Transient Porewater Pressure Response of Saturated Sands

摘要

An experimental apparatus was developed to investigate transient and long-term porewater pressure responses of saturated soils. The facility is capable of generating compressive shock loadings on the order of 35000 KPa with millisecond rise times to peak stress. This investigation represents an effort to examine and establish an understanding of compressionally-induced liquefaction. Samples of water saturated Monterey No. 0/30 sand were examined at various relative densities and effective stresses. Boundary conditions used for the experiments were one-dimensional, confined, compressive loadings without drainage. Results indicate that it is possible to liquefy MOnterey No. 0/30 sand under these conditions. Significant porewater pressure increases were possible even at high densities and high effective stresses. Liquefaction was generally observed at compressive strains greater than about 0.1%. Threshold strain values, below which substantial porewater pressures increases generally did not occur, were about 0.01% 1x10-2 percent. Data analysis has provided several empirical models that can be used to estimate liquefaction potential as a function of density, effective stress and applied compressive strain. One model uses an empirical scaling law for explosive loadings to predict the extent of porewater pressure increases in the field from buried, contained charges in saturated soils. A finite difference analysis that considers the saturated soil as a two-phase medium has been performed. The analysis accounts for the nonlinear, inelastic behavior of the soil skeleton and has shown that liquefaction is dependent upon the unloading constrained modulus of the soil.