Evaluating changes in shear wave velocity due to blast-induced liquefaction

Blast liquefaction tests were performed in Christchurch, New Zealand in an area that experienced extensive liquefaction during the 2010-2011 Canterbury Earthquake Sequence. To evaluate the changes in shear wave velocity (VS) of the soil profile in the vicinity of the blasting, multi-channel analysis of surface waves (MASW) testing was performed before the blast, immediately following the blast (within 0.5 h), 4 h post-blast, and 24 h post-blast. Three different array setups with varying lengths and number of geophones were analyzed to study the effect of array length on the ability of MASW to capture changes in VS within the blast area. Results of the study show that array length can have a significant effect on the measured changes in VS immediately following blasting due to averaging of the properties inside and outside of the area where blasting induced liquefaction developed; however, these changes decrease at 24 h. Full recovery of pre-blast VS was not observed for all layers at 24 h post-blast. This study provides data for measurements of VS rapidly following liquefaction, which are sparse in the literature.