Selection of Standard Penetration Test Number for Geotechnical Investigation of a Vertical Cross-section Considering Spatial Variability and Correlation in Soil Properties

The standard penetration test (SPT) is a widely used in situ test for characterizing variation of subsurface soil properties, and results of site investigation are usually simplified as a two-dimensional (2D) vertical cross section for subsequent geotechnical design and construction. Current geotechnical design codes and guidelines only provide general recommendations for selection of an appropriate number of in situ tests (e.g., SPT) (e.g., the greater variability of subsurface conditions, the larger number of SPTs required to obtain sufficient underground information). No quantitative or rational method is available for selecting the appropriate number of SPTs considering spatial variability and correlation in subsurface conditions. A comprehensive parametric study is carried out in this study to investigate the influence of spatial variability in subsurface conditions on the minimum SPT number needed for satisfying an accuracy requirement of site investigation. Random field is adopted to model spatial variation and correlation in soil properties in typical site conditions, and 2D Bayesian compressive sampling is used to interpolate sparse SPT data. Based on the parametric study results, a statistical chart is developed for geotechnical engineers to conveniently select an appropriate number of SPTs in a vertical cross section. Real SPT data from New Zealand are used to illustrate and validate the proposed method.