STABILITY OF SLOPESSEEPAGE CONTROL MEASURES AND SLOPE PROTECTION
a finite slope AB, the stability of which is to be analyzed.
The method Consists of assuming a number of trial slip circles, and finding the factor of safety of each.
The circle corresponding to the minimum factor of safely is the critical slip circle.
Let AD be a trial slip circle, with r as the radius and O as the centre of rotation
Let W be the weight of the soil of the wedge ABDA of unit thickness, acting through the centroid G.
The driving moment MD will be equal to W x, where x, is the distance of line of action of W from the vertical line passing through the centre of rotation O.
if cu is the unit cohesion, and l is the length of the slip arc AD, the shear resistance developed along the slip surface will be equal to cu • l, which act at a radial distance r from centre of rotation O.
When slip is imminent in a cohesive soil, a tension crack will always DevelOP by the top surface of the slope along which no shear resistance can develop,
The depth of tension crack is given by
The effect of tension crack is to shorten the arc length along which shear resistance gets mobilised to AB' and to reduce the angle δ to δ'.
The length of the slip arc to be taken in the computation of resisting force is only AB', since tension crack break the continuity at B'.
The weight of the sliding wedge is weight of the area bounded by the ground surface, slip circle arc AB' and the tension crack.