Abstract: One-dimensional compression and swelling tests are carried out to investigate the responses of pore water pressure under unloading. Effects of various magnitudes and rates of unloading on changes of pore water pressure are analyzed. Based on Terzaghi’s one-dimensional consolidation theory, a calculation method is proposed for predicting the pore water pressure responses under linearly loading and unloading conditions. Coefficients of consolidation under compression and swelling are measured by consolidation and permeability combined testing. The applicability of the proposed calculation method to the pore water pressure responses under unloading conditions is evaluated. The results show that negative excess pore water pressure increases with the increases of magnitude and rate of unloading. At the beginning of unloading, excess pore water pressure reduces at a relatively high rate. This is followed by a reduction of excess pore water pressure at an approximately constant rate. However, this type of pore water pressure response behavior cannot be satisfactorily modelled by the calculation method established based on Terzaghi’s one-dimensional consolidation theory.

Key words: one-dimensional consolidation, swelling, magnitude of unloading, unloading rate, negative excess pore water pressure