Kinematic Stability Evaluation of the Cut Slopes Along Islamabad–Muzaffarabad Dual Carriageway (IMDC), Pakistan

This research kinematically evaluates selective rock cut slopes, comprised of alternate beds of sandstone, mudstone, siltstone, claystone, and shale, along the Islamabad–Muzaffarabad Dual Carriageway (IMDC), Pakistan. Thirteen instability-prone sites were selected, and discontinuity-orientation data were collected using the window mapping method. The representative geological cross sections for all slopes were prepared, and pronounced failure modes were recorded. Fresh rock samples were collected to evaluate the potential for the disintegration of the various rock units by determining the slake durability index. In interlayered rock units, the higher weathering rate of lower incompetent units removes the support and triggers the gravitational falling of the competent rock blocks. Despite dipping into the slope—a most favorable condition—due to differential weathering, one of three prominent joints dips toward the slope resulting in plane or wedge failures that ultimately fall as rock blocks. In the present study, a kinematic criterion is proposed for predicting undercutting-induced instabilities that are not identified by conventional kinematic analyses. The results showed that the undercutting is more pronounced along gentler bedding joints either into or out of the slope; on the other hand, it has less effect on the slope where the strike is across the slope, dipping on either side at steep to very steep angles.