Estimation of unsaturated small-strain shear modulus in a laboratory test box and field site from a soil-water characteristic curve

The small-strain shear modulus plays a significant role in analyzing soil-structure interactions and the stiffness properties of earth materials under static and dynamic loading conditions. Traditionally, this parameter is determined through seismic wave measurements in the laboratory and in the field. Alternatively, it can be determined in the field by performing dynamic cone penetrometer tests and subsequently converting to California Bearing Ratio (CBR) values using empirical equations, and finally to modulus using another empirical equation. However, this multistep process is both labor-intensive and prone to compounded errors stemming from the use of numerous empirical relationships. In this study, an approach was introduced for estimating the small-strain shear modulus for preliminary analysis based on the soil–water characteristic curve (SWCC) and a saturated small-strain shear modulus. The proposed model, developed using laboratory small-strain shear modulus data, was tested on soils compacted within a laboratory test box. In addition, a correlation was derived from the test box to modify the proposed model to make it applicable to field soils. The modified model was applied to a field site to predict measured small-strain shear modulus, which was determined from shear wave velocity and SWCC fitting parameters derived from textural characteristics and electrical resistivity. The predicted data showed satisfactory agreement with the measured data at the field site. Overall, the study demonstrates the effectiveness of the proposed model in predicting small-strain shear modulus for both small laboratory specimens and field data.