On August 10, 2005 a landslide of approximately 133,000 m3 occurred along the Lahore-Islamabad Motorway (M- 2) near the village of Simbal, in the Salt Range area of Pakistan. A program of research was undertaken to evaluate the likely impacts of percent saturation and bulk density on mobilized shear strength along the basal rupture surface of the Simbal Landslide. A series of direct shear tests [1] were performed on remolded samples at different densities. The percent saturation was then varied on these samples to evaluate its impact on mobilized shear strength. The results of these tests suggest that soil cohesion and friction tended to decrease with increasing percent saturation. The tests also showed that the shear strength parameters tended to increase with increasing dry density; however, all of the samples exhibited a noticeable loss of shear strength with increasing degree of saturation, independent of soil density. Limit equilibrium slope stability analyses were performed along the most probable failure planes, based on shear strength parameters corresponding to degrees of saturation, varying between 20% to 100% over a wide range of in-situ densities. The results of these analyses suggests that the factor of safety drops significantly, (from FS = 1.6 down to 0.41) as the degree of saturation approaches unity.


A significant landslide occurred on 10th August, 2005 near village Simbal along the Lahore-Islamabad Motorway (M-2) in Pakistan’s Salt Range, after a period of intense precipitation. This resulted in a large volume of slide debris (approximately 91,500 m3 of colluvium and 41,000m3 of limestone and shale) moving down the slope, blocking a portion of the motorway. The relationship between the shear strength and degree of saturation for different soils has been studied by various researchers outside of Pakistan [2-6].

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