Stability of unsaturated residual soil slopes as affected by rainfall

The objective of this research was to study the effect of rainfall on the stability of unsaturated residual soil slopes. The effect of evaporation and infiltration on the pore-water pressure distribution in a slope was determined. Then the effect that the change in pore-water pressure distribution had on the stability of the slope was assessed.Master of Engineering (CSE

Infiltration effects on stability of a residual soil slope

Many slope stability studies have indicated that the infiltration of rainwater into a slope decreases the stability of the slope. However, the difficulty of quantifying the effect of rainwater infiltration on slope stability still exists. It would be advantageous to know what percentage of rainfall enters a slope as infiltration and how much this infiltration decreases the stability of a slope. Numerical models were used to study how infiltration into a slope varied with respect to rainfall intensity and how this infiltration affected the stability of the slope. A numerical study revealed that the amount of infiltration was highest at the crest of a slope. A case study revealed that it was difficult to quantify the amount of infiltration occurring in a slope with the numerical model. The numerical model was, however, able to illustrate the effect of infiltration on slope stability through the combined use of seepage and slope stability analyses.Accepted versio

Instrumentation of an unsaturated residual soil slope

The stability of slopes has become a major concern in areas that experience frequent periods of heavy rainfall such as the tropical areas of Southeast Asia. Previous research has indicated that rainfall has a detrimental effect on the stability of residual soil slopes. The reason for this is that the additional shear strength that exists in unsaturated soils due to negative pore-water pressures is lost as a result of rainwater infiltration into the soil. To study the infiltration characteristics in slopes, a residual soil slope in Singapore was instrumented. The instruments were used to determine the changes in the pore-water pressure distribution throughout the slope in response to evaporation and infiltration. Tensiometers were used to measure negative pore-water pressures, piezometers were used to measure the groundwater level, and a rain gage was used to measure rainfall intensities on the slope. An automated data acquisition system was used to collect the data from the slope. This paper describes the instrumentation program and the procedures associated with the installation of the instruments into the slope. Typical measurement data collected from the slope are presented, and their interpretations are discussed.Accepted versio

Rainfall-induced slope failures

Two-thirds of Singapore's land area is covered with residual soils from the Sedimentary Jurong Formation and the Bukit Timah Granite Formation. Rainfall-induced slope failures often occur in these residual soils as a result of tropical rainfall events. These slope failures can be dangerous, disruptive to the development of infrastructures and quite costly to repair. Therefore, it is timely and appropriate that a better technology for preventing these failures be developed with special consideration being given to the local climate and geology. This appropriate technology can be developed only if the mechanism of rainfall-induced slope failures is properly understood

Role of topography in the behavior of the matric suction of unsaturated fill slopes

[[abstract]]This paper presents the result of a field study on the influence of topography on the distribution of the matric suction of the soil in unsaturated slopes subjected to rainfall. The matric suction was measured in the lower, middle and upper parts of planar, ridge-like and gullied slopes before and after two significant rainfall events. Jet-filled tensiometers were used for depths of >1.2 m and the filter paper method at depths of <0.9 m. It was found that in the dry season the matric suction of the soil at a shallow depth in the gullied slope is significantly less than that in the planar and ridge-like slopes while following a rainfall event the decrease in the matric suction is smallest in the gullied slope and greatest in the ridge-like slope, irrespective of the amount of the accumulated precipitation