Mechanism and modelling of shallow soil slope stability during high intensity and short duration rainfall

I. Egeli, H. Firat Pulat
2011 Scientia Iranica. International Journal of Science and Technology  
Shallow landslides in nearly saturated uncohesive to slightly cohesive soils are triggered by high intensity, short duration rainfall which infiltrates into soil and changes intergranular friction and effective stresses. For this, the especially developed Soil-Water Interaction Modelling System (SWIMS) was used with CL-ML type soils. For simplicity, rainfall intensity and duration were kept constant. Results showed that (1) All 35°slopes were failed by translational failure. For the other (15°,
more » ... 25°) slopes, no failures were observed; (2) For all slopes, FOS increased with increasing compaction degree and decreased with increasing slope angle; (3) Other parameters, such as soil density, porosity, saturation degree, water contents, and water permeability may also affect shear strength/slope stability, especially for low degrees of saturation (S < 95%), compared to high degrees of saturation (S =, > 95%). (4) A correlation of SWIMS tests observed that average wetting band depths (h obser ), with the calculated wetting band depths from the Lump Equation (h LE ), were poor, as h obser values were much higher than h LE values. Differences increased for very low degrees of saturation (S), compared to S > 95%. This meant that the Lump equation underestimated wetting band depths. Further, if the Lump equation is still considered valid, this would imply either water-permeability increases, porosity decreases or both occur towards full saturation; a process where the last possibility is the most probable occurrence. .tr (I. Egeli). duration) is one of the most important factors in this question. Slope failures triggered by rainfall cause considerable property damage with loss of life, every year throughout the world. A number of laboratory, numerical and field studies have been conducted to understand interrelations between soil stability and rainfall. A number of landslides in unsaturated soils usually occur during the wet season. Brief background information and scope of work Most soils occur in an 'unsaturated state' in nature. Unsaturated soil mechanics is a very wide and complex subject, due to the involvement and interaction of 4 phases (pore-air, pore-water, menisci and soil grains) with each other. Shallow landslides are some kind of slope failure that may be induced by rainfall infiltration, which causes some changes in total suction (a sum of matric and osmotic suctions) and in soil properties, such as soil shear strength and pore fluid (air, water, dissolved air in water and menisci) properties, in a process where the mechanism of change (from unsaturation to saturation and back to unsaturation) is yet to be clearly understood. There have been extensive studies done by numerous researchers over the years, both in the field and in the laboratory [1-66]. For soils on
doi:10.1016/j.scient.2011.09.010 fatcat:it4mho7mujg6bnv5c7stw4mohu