Browsing by Author "Sujeevan, V"

Now showing 1 - 3 of 3

item: Conference-Abstract
Effects of rainfall on stability of cut slopes in residual soils
Kulathilaka, SAS; Sujeevan, V
Rain induced slope failures are a common geotechnical problem in tropics where residual soils are abundant. Residual soils are characterized by significant differences in the levels of weathering within short distances. Two typical cut slopes from the Southern Transport Development Project were used in theanalysis. The complex geological situation in an unsaturated cut slope is idealized by two cases; a uniform soil and a soil overlying moderately weathered rock. The changes to the pore pressure regime with the progression of the rainfall and consequent reduction of the safety margin of the slope was modeled with SEEP/W and SLOPE/W software. Both the deterministic approach and the probabilistic approach were used in the evaluation of stability. With the continued rainfall, matric suctions depleted, perched water table developed and the safety margins reduced. The presence of a moderately weathered rock layer at a shallow depth was found to be more critical.
item: Article-Abstract
Rain triggered slope failures in unsaturated residual soils
Kulathilaka, SAS; Sujeevan, V
This paper is a continuation ofthe research paper titled "Rainfall Infiltration Analysis in Unsaturated Residual Soil slopes", which discussed the changes in the pore pressure regime ofa slope made of unsaturated residual soils, due to prolonged rainfall. This paper discusses the consequent changes in the safetymargins of the slope. Residual soils, which remain at the location of the parent rock after weathering are characterizcd by different degrees of weathering. difference in the weathered product based on the mineralogical composition of the parent rock and significant variations within a short distance due to above reasons. Zones of different levels of weathering will have significantly different hydraulic and shear strength properties. Rain induced slope failures are a common geotechnical problem in the tropics. In this study the complex geological situations in a residual soil slope is idealized by two states; a uniform soil slope and a slope of weathered rock underlying the soil. Two typical cut slopes from the Southern Transport Development Project were used in the analysis. The variation in the safety margins of the slope with the progression of the rainfall was analyzed by the Bishop's simplified method and the Spencer's method. The analysis was done with the SLOPEW computer software and the data on the changes of the pore pressure regime computed with SEEPW analysis were incorporated. Initially, the safety margins were assessed through the computation of factor of safety and subsequently a probabilistic analysis was done accounting for the uncertainties in the properties of soil such as, friction angle. cohesion. and pore water pressure. Monte-Carlo approach was used in the probabilistic analysis.
item: Article-Abstract
Rainfall infiltration analysis in unsaturated residual soil slopes
Sujeevan, V; Kulathilaka, SAS
Rainfall-induced slope failure is a common geotechnical problem in the tropics where residual soils are abundant. Residual soils are formed due to the weathering of rocks and lie at the location of the parent rock. They are characterized by the significant variations in the level of weathering and the composition of the weathered product over short distances, Quite often, the ground water table is low during the dry season and these soils are in an unsaturated state. The shear strength of the unsaturated soils is enhanced due to presence ofmatric suction. With the infiltration of rainwater, the matric suction will be depleted for some depth, As the rain progresses the depth of depletion increases. This aspect was studied in this research with an infiltration model. The model was applied initially to a slope formed of homogeneous soil and later to a slope where two layers of significantly different levels of weathering exist. In this study, simulated rainfalls of different intensities and durations representative of tropical climatic conditions were applied to the two different cut slope of southern highway in Sri Lanka. Each Cut slope was analyzed by having different types of weathering profiles. A finite element computer package SEEPIW2007 was used to simulate the infiltration through unsaturated soil.