Initial shear modulus of sandy soils and equivalent granular void ratio

The small strain/initial shear modulus, G(O), for clean sands has been extensively studied over the last few decades, and it is generally accepted that G(O) is a function of the effective mean stress, p' and void ratio, e. However, natural sandy soils often contain some fines (particle size <= 75 mu m) and systematic studies on the effect of fines on G(O) are relatively limited. Two different approaches for capturing the effects of fines on G(O) have been reported. However, both approaches assumed that the G(O) values for a range of fines content specific to the sand and fines type are known in advance, and thus they cannot be used as predictive tools. This paper presents an alternative approach for evaluation of G(O) based on the equivalent granular void ratio, e*. Unlike earlier attempts, the proposed method does not rely on back-analysis and e* can be calculated from e and other conventional grading properties of sandy soils. The proposed approach approximately leads to a single relationship between G(O) and (e*, p') irrespective of fines content. Thus, it provides a framework for estimating G(O) at different fines content from data on clean sand.