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Laboratory determination of low strain shear behavior or shear modulus of soft saturated clays can be complicated if high-frequency dynamic testing methods are utilized. Cyclic loading can promote fast degradation of moduli for these soils. A monotonic torsional shear device, namely, a triaxial vane device, was equipped with a computer aided data acquisition system to detect low strain shear deformations under quasi-static loading conditions. The average range of electronically measured strain was 10-4 to 1%, which was compatible with that of a high-frequency low-strain dynamic testing method, namely, resonant column. Comparison of the dynamic and static moduli reduction curves of artificially prepared soft kaolinite specimens demonstrated the cyclic degradation effects on strain dependent dynamic moduli. For normally consolidated specimens under confining pressure of 100 kPa, the ratio of maximum static shear modulus to maximum dynamic shear modulus was estimated to be around 0.85. This value and the observed trend of dynamic and static moduli reduction curves at low strains are in agreement with the findings of other investigators. The relatively continuous, high-resolution low-strain static data indicated further gain in understanding of low-strain nonlinearity and yielding behavior of soft marine clays.
triaxial vane, static moduli, dynamic moduli, low strain shear, soft clays
Assistant professor, Lehigh University, Bethlehem, PA
Associate professor, Louisiana State University, Baton Rouge, LA