Excess Pore-Water Pressure Generation in Cyclic Undrained Testing

A new strain-based model is presented in this paper for assessing the residual excess pore-water pressure ($u_{\mathrm{e}}$) buildup in fully saturated sands. In this model, the generation of residual $u_{\mathrm{e}}$ is quantified by the volumetric strain changes owing to cyclic shearing. The concept of threshold shear strain is introduced into the model. To characterize the generation of residual $u_{\mathrm{e}}$ in this model, a number of tests, including one resonant column test, a series of undrained and drained multistage, and single-stage strain-controlled cyclic triaxial (CTX) tests, are performed with fully saturated fine sand samples. The cyclic shear-volume coupling equation and the correlation between the progressive increase of residual $u_{\mathrm{e}}$ during undrained CTX test and the accumulated volumetric strain during drained CTX test are established. Furthermore, a simple bulk modulus equation is derived by differential method. Finally, the general applicability of the proposed model is validated by the experimental data for the same sand, and independent confirmations are also demonstrated with the original experimental data for four sands, obtained from the literature. The proposed pore-water pressure model provides new insights into the mechanics of residual excess pore-water pressure buildup under undrained cyclic loading conditions.