Liquefaction and residual strength of sands from drained triaxial tests

The state of knowledge with regard to static and cyclic liquefaction has progressed tremendously since the mid-1960s. In fact, it is generally accepted, based on the steady-state concepts of Casagrande, Castro, and Poulos that the end or steady-state condition of a liquefied loose sand is the same whether due to monotonic, cyclic, or dynamic undrained loading. Even so, a straightforward and fundamental explanation of the initiation and end-state liquefaction behavior is still needed. Toward that end, an effective stress approach that allows the assessment of the whole undrained stress-strain curve (including the peak and residual strength values) and the undrained effective stress path of a monotonic test from drained triaxial tests is presented. Results from three series of tests are shown to demonstrate the validity of the method. This method makes it possible for a geotechnical firm with the capability of performing the traditional drained test with volume change measurements to participate in static liquefaction and residual strength assessment. More importantly, it provides the conditions and logic for the development of complete versus limited liquefaction (and even dilative) response.