Soil Arching Mechanisms Resulting from Excess Pore Pressure Dissipation Following Blast-Induced Liquefaction

Abstract

This paper evaluates the stress changes and settlements following dissipation of local, 3D excess pore pressure fields induced by controlled blasting. Field data gathered during a blasting experiment in medium dense sand deposits at the Port of Portland, Oregon, were used to validate the numerical simulations. The field measurements included cone penetration tests, excess pore pressure (ue), dissipation, and ground surface and subsurface settlements. The proposed numerical framework consisted of a 2D finite-element approach using a critical state–based hypoplasticity constitutive soil model capable of reproducing changes in void ratio, thus capturing soil densification to study soil arching mechanisms as a result of the dissipation of the local ue field. The soil parameters were calibrated to match laboratory test results performed on reconstituted specimens of medium dense sand and intact specimens of medium stiff silt obtained at the project site. The methodology was validated using the field measurements in terms of changes in tip resistance, shear wave velocities, and distribution of ground surface and subsurface volumetric strains and displacements. The field measurements and numerical results were used to draw conclusions regarding the variability of the postdissipation stress field within the blasted area due to soil arching. The main variables contributing to the development of liquefaction-induced soil arching as a result of controlled blasting were analyzed in a parametric study. The effects of the extent of the blasting zone as a function of the width-to-height ratio (W/H) and blasting intensity quantified with the excess pore pressure ratio (ru) were investigated. Results of the parametric study include the identification of significant reductions in mean effective stresses occurring within the blasting zone for small W/H ratios regardless of the input ru. A discussion regarding blast-induced cone tip resistance (qt) changes with time to explain qt reductions through the lens of case histories and implications for soil arching concludes this study.