A New Procedure for Measuring Shear Modulus Reduction in the Intermediate Strain Range

Abstract

The focus on acquiring reliable design-governing geotechnical parameters, like shear modulus reduction with strains, increases as the bounds of the novel design solutions for offshore wind structures continue to develop. While shear modulus reduction curves (G/Gmax) traditionally are pieced together by interpolation of results obtained from different test types, for instance resonant column tests at small strains and cyclic triaxial or direct simple shear tests at larger strains, an acknowledged and reliable industry practice for measurements in the intermediate strain range is not yet available. This paper presents results from a research study on the development of an innovative triaxial testing procedure to measure the shear modulus in the intermediate strain range for a clean dense sand. Results reveal that repeatable and reliable shear modulus reduction curves from small to intermediate strains can be obtained in multistage cyclic triaxial tests using multiple pairs of internal small-range linear variable differential transformer sensors (LVDTs). Furthermore, Gmax values obtained from the LVDT measurements compare consistently to Gmax values from bender element measurements. Comparison with results of parallel static testing reveals a significant difference between static and cyclic shear modulus reduction curves.