Estimating Shear Strength Properties of Soils Using SPT Blow Counts: An Energy Balance Approach

Abstract

The subsurface exploration of a site is often the aspect of a project that gets overlooked during the design process. Many clients will get standard soil borings, but do not want to pay for a full laboratory analysis. Lack of data forces the designer to estimate important engineering properties of the soil. Very often the Standard Penetration Test (SPT) blow counts are used to estimate the shear strength properties of soil in foundation designs. Few correlations are widely used. However, no clear explanation is found to justify the selection most of these mathematical equations. This manuscript describes a new approach to estimate the shear strength parameters based on the SPT blow counts. In this method, the standard penetration test is treated analogous to driving a miniature pipe pile. The energy input to the soil is used to correlate the SPT blow count to the shear strength parameters of the soil at the depth of testing. Soil boring records from few different sites were analyzed and a statistical analysis revealed that the proposed method can provide a better estimation than the widely used existing correlations.