| Geotechnical engineers are particularly concerned about the stability of slopes.Traditional slope stability analysis approaches have omitted the impacts of surface cracks and depths present on the slope’s surface due to alternate wetting and drying cycles,earthquakes,freezig and thawing phenomena.Moreover,matric suction or unsaturated behaviour have also been ignored.The soil above the phreatic line possesses negative pore-water pressure owing to the capillary action of the soil.In most of the cases,rainfall is the core concern regarding the stability of the slope.It results in loss of matric suction due to the penetration of water into the soil and increases the positive pore-water pressure inside the slope body.In case of cracked slopes,more water seeps into the soil.The infiltration of rainfall is influenced by a number of factors like soil material,rainfall length and intensity,slope height,slope angle and hydraulic conductivity of the soils.The selected slope for the current study is situated in Pakistan and of heterogeneous nature,comprised of fill and bed material soils.Floods in several regions of Pakistan during the rainy season are the most recent severe climatic occurrences to affect Pakistan.So,in order to protect the public and structures from flooding,a flood protection embankment(slope)has been constructed by the Water and Power Development Authority(WAPDA)of Pakistan which is situated near the confluence of five rivers of Pakistan.The flood protection embankment was analyzed using two rainfall conditions with intensities of 1 × 10-7(m/sec)and 1 × 10-5(m/sec),considering steady-state and transient flow.Boundary conditions were applied on the upstream and downstream of slope to simulate ground water level.This study assumes the five different time steps(0,6,12,18 and 24 hours).The presence of cracks on the slope surface is common,which can impair the stability of the slopes.Seep-W software analyses soil’s saturated and unsaturated behaviour by defining soil water characteristics curve(SWCC)and hydraulic conductivity function.The results of initial pore-water pressure have been studied while the flow is in a steady-state.Pore-water pressure for transient flow was also computed for both the rainfall intensities and all of the slopes.After calculating the pore-water pressure,the same results have been imported to SlopeW to calculate the safety factors for each time step and for all cracked and uncracked slopes considering the Morgenstern-Price method.The effect of crack depth and location has been investigated considering a shallow crack of 3m depth and a deeper crack of 5m depth present on the slope’s crest and middle of slope.This study reveals that less rainfall intensity only changes the pore-water pressure only in the upper part of cracked and uncracked slopes.As the rainfall intensity increases beyond the saturated hydraulic conductivity,ponding occurs and drastically increases the positive porewater pressure.Moreover,the impact of a shallower crack is less than a deeper crack because,in the case of a deeper crack,water penetrates into the soil up to a greater extent.The effect of the crack present on the slope’s crest is more significant than that on the middle of the slope.A crack on the slope crest will intersect the slip surface and change pore-water pressure in the upper part of the slope.While crack present in the middle of the slope does not intersect the slip surface just changes pore-water pressure in deeper layers of soil. |
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