An integrated geotechnical-geophysical procedure for the prediction of liquefaction in uncemented sands
This project represents an in depth study into the inter-relationships between the seismic shear wave velocity of uncemented sands and their liquefaction potential. This was achieved by combining the concepts of steady / critical state soil mechanics with the measurement of shear wave velocity. In the laboratory this was facilitated with the use of a modified triwdal cell, allowing both the shear wave velocity behaviour and liquefaction susceptibility of a particular sand to be quantified. Use of this equipment illustrated that for a specific sand, acritical shear wave velocity Iine'may be defined, dividing sand states of potentially contractive or dilative behaviour. Further, these studies also show that a shear wave velocity derived state inde)ý V, may be statistically correlated with other more conventional indices of sand consolidation state. The results of the laboratory study are then applied to a real field situation, the Fraser River Delta, located in earthquake prone south-westem British Columbia. Currently, many of the sub-aerial sediments have been identified as being potentially liquefiable. Offshore, the difficulties associated Wth sampling seabed sediments in-situ have limited past attempts to quantify liquefaction potential. Laboratory shear wave data, based upon laboratory analysis of sediment samples from the Fraser Delta and in-situ shear wave velocity field data, have been used in an attempt to quantify the risk of liquefaction for part of the offshore delta, namely Roberts Bank. The data presented in this study, based upon both conventional and proposed shear wave methods of analysis, suggest that there is a significant risk of liquefaction on the offshore Fraser Delta, particularly around Roberts Bank.