Abstract: Based on literatures on the titled subject, factors affecting the generation of pore water pressure were discussed herein. Conventional consolidated-undrained tri-axial tests were conducted on three undisturbed normally-consolidated clays, and nonlinear equations of pore water pressure, critical pore water pressure and unique effective stress path were proposed for various total stress paths, respectively. Comparison of some in-situ measurements and theoretical calculations showed that the agreement was good.