Axisymmetric Strain Path Tests on Nellis Baseline Sand

Abstract

Abstract : This report documents results of laboratory tests in which the responses of cylindrical specimens of Nellis baseline (NBH) sand were measured under imposed axisymmetric stain path loadings. Two strain path shapes (designates as shapes 2 and 3) were investigated, each having three levels of strain magnitude for a total of six strain paths. It was found that a unique stress path was produced by following a given strain path. This was true for all six strain paths investigated. All strain path tests which followed shape 3 reached a point of continuing strain with little change in the applied stresses. These specimens appeared to be yielding or flowing as the stress path moved along a failure envelope. Reverse strain path tests (test which followed a stress path generated by a previous strain path test) proved that a unique strain path was not necessarily produced by following a given stress path. When stress paths developed by strain path shape 3 were followed, several different strain paths were produced. Resulting strain magnitudes were directly dependent upon the length of time the stress path spent moving along the failure envelope. Results of a series of strain-rate tests indicated that the NB sand exhibited an 18% increase in peak stress difference when loading times were decreased from 133 to 4 minutes.