Effects of Membrane Compliance on Pore Water Pressure Generation in Gravelly Sands under Cyclic Loading

The paper deals with an experimental study of the undrained cyclic behavior of a natural coarse sand and gravel deposit located in Tehran, a megacity situated on the continental side of the Alborz Mountain in Iran. Membrane compliance that plays a significant role in inhibiting redistribution of pore pressure and liquefaction in undrained cyclic triaxial tests performed on coarse granular soils is studied in this paper. Currently there is no or little satisfactory method for accounting for this phenomenon for gravelly soils, and thus the non-compliant cyclic loading resistance of granular soils and the evaluation of the behavior of such material in natural and in situ state are not easily determined. A procedure has been proposed in this paper for consideration of membrane compliance effects on the pore pressure measurements during cyclic loading. A method is also introduced to verify the proposed procedure by employing lightly cemented specimens. In addition, some new correlations for excess pore water pressure ratio against the number of cycles to failure have been presented for a non-compliant system under various effective confining and deviatoric cyclic stresses applied on reconstituted and isotropically consolidated specimens. Initial liquefaction has been observed during the tests with or without consideration of membrane compliance; however, the number of cycles to initial liquefaction is higher for the compliant case.