Design of Stable Rock Slopes for the World’s Highest Railway Bridge

Abstract

Stability analysis of the two abutment slopes of a railway bridge proposed at about 359 m above the ground level, crossing a river and connecting two huge hillocks in the Himalayas, India, is presented in this paper. The rock slopes are composed of highly jointed rock mass and the joint spacing and orientation are varying along the elevation of the slopes. Geological mapping was carried out to characterise discontinuities present along different elevations of the slopes. Rock mass present along both the slopes was classified using rock mass rating (RMR) and geological strength index (GSI). Strength and deformation properties of intact rock and rock mass were estimated using different laboratory tests, in-situ tests and empirical relations. Since the slope sections support bridge piers, bearing capacity was estimated with the help of in-situ tests and various empirical and analytical relations. Global stability and stability of individual sections of slopes were checked using different methods i.e. finite element, stereographic projections and wedge failure analysis. It was observed that slopes were globally stable however there was a possibility of wedge failure at some slope sections. Suitable rock anchors were installed at unstable slope sections. In addition to the stability analysis of the slopes, various challenges encountered during excavation and stabilisation of the suggested slope profile such as transportation of rock mass debris without allowing it to fall into the river and slope monitoring is discussed.