Unique Relationship Between Small Strain Shear Modulus and Effective Stresses at Failure for Dilative Soils

University Of Rhode Island, Kingston RI

Investigators

Abstract

This grant provides funding to investigate whether a unique relationship exists between small strain shear modulus and effective stresses at failure during triaxial compression for dilatant soils. This hypothesis was developed based on preliminary tests involving isotropically consolidated drained triaxial compression tests on an artificially cemented silty sand with shear wave velocity measurements made throughout shearing. There were two important findings from these tests: 1.) the ratio of small strain shear modulus to principal effective stress at failure was constant for the given soil, independent of the degree of cementation, density, and consolidation stress; and 2.) there was a clear trend of the small strain shear modulus increasing during shear to a maximum value and then decreasing despite continued increases in the deviator stress up to failure. To test this hypothesis, Ko-consolidated drained triaxial compression tests will be performed on three different soils in a dilative state: coarse, angular sand, non-plastic silt, and high plasticity clay. Shear wave velocity measurements will be made throughout the consolidation and shear phases of each test. If these findings are representative of dilatant or structured soils in general, then there are several important implications for engineering practice. A significant application of this concept would be the estimation of effective stress strength parameters directly from in situ shear wave velocity measurements in soils that have been traditionally problematic to sample and test in the laboratory, such as dense sands and silts or sensitive clays. Establishment of the proposed relationship would potentially change how geotechnical site investigations and laboratory testing program are designed. Another application would be that in situ shear wave velocity measurements, for example from cross-hole or seismic cone penetration tests, could be used as an early warning system for the onset of failure in cemented, structured, or sensitive soils during staged construction of embankments and natural slopes which fail progressively.