Comparison of site classification using SPT and seismic downhole survey to evaluate liquefaction severity: A Case study in Serang-Panimbang Section III Toll Road Project

Abstract Evaluating liquefaction risk, as an indirect consequence of seismic events, is crucial for mitigating geohazards and achieving sustainable developments in infrastructure projects. The Serang-Panimbang Toll Road, a National Strategic Project in Banten, Indonesia, aims to connect intra-districts, bolster local tourism and establish a new industrial region. In this context, site classification plays a substantial role in determining the impact of earthquakes on soil behavior. This study compared the site classification of two soil investigations, including the Standard Penetration Test (SPT) and the downhole seismic ( V s ) survey at eleven sites along the toll route. A marginal sensitivity was observed in the classification as small variations in field measurements could lead to a shift in site class, resulting in significant changes in the surface-level seismic wave amplification. Notably, the correlation between SPT N-values and V s is often weak. Studies have confirmed the superior reliability of V s for soil profiling, suggesting that its adoption as a mandatory practice should be considered. Analysis of the investigation data classified the sites as belonging to site classes SD, SE, and SF. The Simplified Procedure method was employed to evaluate the liquefaction factor of safety, by considering the Cyclic Stress Ratio (CSR) and the Cyclic Resistance Ratio (CRR). The evaluation utilized parameters derived from the Indonesia Seismic Code, with a 7% likelihood of exceedance in 75 years. The analysis revealed that most areas, predominantly clayey soils, exhibited no liquefaction potential. However, specific sections containing sand lenses displayed a low-level Liquefaction Severity Index (LSI) as identified in three boreholes.