A soil-water characteristic defines the relationship between soil suction and either water content or degree of saturation, Physically, this soil-water characteristic is a measure of the water storage capacity of the soil under a given soil suction. It is an essential hydraulic parameter for computing transient seepage in unsaturated soils. For better and safer assessment of slope stability, the soil-water characteristic curve (SWCC) of soils is necessary to be fully understood. In this thesis, a new stress controllable one-dimensional volumetric pressure plate apparatus has been developed for investigating the influence of stress state on the soil-water characteristics of a completely decomposed volcanic (CDV). Moreover, the influences of initial void ratio, initial water content, wett...[ Read more ]

A soil-water characteristic defines the relationship between soil suction and either water content or degree of saturation, Physically, this soil-water characteristic is a measure of the water storage capacity of the soil under a given soil suction. It is an essential hydraulic parameter for computing transient seepage in unsaturated soils. For better and safer assessment of slope stability, the soil-water characteristic curve (SWCC) of soils is necessary to be fully understood. In this thesis, a new stress controllable one-dimensional volumetric pressure plate apparatus has been developed for investigating the influence of stress state on the soil-water characteristics of a completely decomposed volcanic (CDV). Moreover, the influences of initial void ratio, initial water content, wetting and drying history, and soil structure have been investigated. The soil-water characteristic is found to be stress dependent, in which the soil specimen subjected to higher stress exhibits lower initial water content, larger air-entry value, and lower rate of desaturation. In addition, the experimental results indicate that initial void ratio, initial water content, wetting and drying history, and soil structure affect the soil-water characteristic in terms of its air-entry value, rate of desaturation, and size of hysteresis loop.

Some of the experimental results are then used as input parameters for simulating transient seepage analysis. Moreover, the influences of surface cover and rainfall pattern on pore water pressure distributions and hence on factor of safety are calculated using the limit equilibrium method. The results of the numerical simulations show that analysis using a stress-dependent soil-water characteristic curve (SDSWCC) predicts an adverse groundwater condition and a lower factor of safety than those obtaining from a conventional SWCC. On the other hand, analysis using 2nd wetting curve predicts a higher factor of safety than those calculated by using drying curve. Moreover, it is found that surface cover can reduce the change in suction and hence improve the stability of the slope during rainfall. Rainfall pattern appears to have no significant influence on the pore water pressure distributions under the low initial suction condition, but have relatively significant effects under high initial suction conditions during a prolonged rainfall. A conventional approach using rainfall with uniform intensity is the most critical case.