Abstract: A new model characterized as describing increase in pore-water pressure in fully saturated fine sand specimens, through experimental studies include a resonant column test, a series of drained/undrained multistage strain-controlled cyclic triaxial (MSCCTX) tests and drained/undrained single-stage strain-controlled cyclic triaxial (SSCCTX) tests on a schistous fine sand named “Nanjing sand”, is development in this paper. It follows the theoretical framework of Martin’s semi-theoretical model presented by Martin and Byrne. The increase in pore pressure is caused by the change in volumetric strain under cyclic shear load. Thus, this proposed model is controlled by strain. Based on the drained SSCCTX tests, by introducing the concept of volumetric threshold shear strain (??tv) and a representative volumetric strain in 15 cycles, volumetric strains can be normalized by cyclic shear strains, and then a three-parameter incremental shear-volume strain coupling equation is proposed. Combining experimental results of drained and undrained SSCCTX tests, the relationship between volumetric strain and pore pressure ratio is established. Thus, a new pore water pressure increment model coupling new shear strain-volumetric strain is also established considering volumetric strain increment and elastic rebound modulus. Finally, this new pore pressure model is validated, and the predicted pore pressure ratios in the model match well with those obtained from tests including an undrained SSCCTX test and a stress-controlled cyclic test.

Key words: cyclic triaxial tests, strain-controlled, incremental volumetric strain model, incremental model of pore pressure, dynamic Poisson's ratio, volumetric threshold of shear strain