Estimation of Seismic Compression in Dry Soils Using the CPT

A popular method to evaluate earthquake induced settlements in dry sands is the approach proposed by Pradel (1998) which was based on standard penetration test (SPT) results and is only applicable to clean sands. A simple modification of the Pradel (1998) method is proposed based on cone penetration test (CPT) results and is extended to cover a wide range of unsaturated soils. A key parameter in the method by Pradel (1998) is the small strain shear modulus, Go, which can be estimated from the CPT or measured using the seismic CPT. The CPT can provide a continuous evaluation of seismic compression that allows the expeditious analysis of complicated soil profiles and a framework for sensitivity analyses. Soil parameters, such as soil type, fines content, and equivalent SPT blow count interpolated from CPTs, were compared with adjacent borings and related laboratory test results from a ground improvement site. Both vibro-stone columns and compaction grouting were adopted to mitigate the site seismic settlement. The proposed simple modification of the Pradel method provided a valuable tool to evaluate the effectiveness of ground improvement work.