ABSTRACT

This paper presents the wedge failure analysis at different pier locations for a railway bridge proposed at about 350 m above the ground level, crossing a river and connecting two huge rock slopes in Himalayas, India. The site is located in a highly active seismic zone. Static and seismic slope stability analysis confirmed the global stability of the slope. However, the rock slopes are highly jointed and the joint spacing and orientation are varying at different locations. Hence it is very likely that there could be wedge failures possible at some of the pier locations. This paper presents the results from kinematics of right abutment slope for the wedge failure analysis based on stereographic projections. Some very important conclusions regarding the local stability of the slope at various pier locations and field observations are presented with appropriate recommendations.

1 INTRODUCTION

Stability of rock slopes mainly depends upon the geologic and geotechnical characteristics of the rocks that compose the slopes. Though the strength of the rock plays an important role in the slope stability, many times, the geological structure of the rock governs the stability of rock slopes. Geologic structure refers to the location, orientation, and spacing of discontinuities within the rock mass. These discontinuities include bedding planes, rock joints, faults, and shears.

Kinematic analysis is generally is used to evaluate the possibility of blocks or masses of rock moving along geologic structures and sliding out of the face of a slope. The first step in the kinematic analysis is the accurate identification of the features of discontinuities. This is normally done by aerial photographs, surface mapping and examination of borehole cores. Once the discontinuities are mapped, kinematic analysis is usually carried out using graphical stereographic projection approach explained by Goodman (2000) and Philips (1971). Application of kinematic analysis for rock slope stability assessment is well documented in literature (e. g. Goodman, 1995; Leung and Kheok, 1987; Yoon et al., 2002; Jeongi-gi Um and Kulatilake, 2001; Haswanto and Abd-Ghani, 2008).

2 DESCRIPTION OF THE ROCK SLOPE

A railway line is being laid in Jammu and Kashmir, India and this line is crossing the river Chenab at a height of about 350 m. A bridge is being constructed with total 18 piers at this place connecting two hillocks. Among these piers, 4 piers (P10, P20, P30 and P40) are resting on left abutment and the other 14 piers (P50-P180) are resting on right abutment. Slope stability analysis of the right abutment is taken up in the present study. The section of the bridge and abutments along with the foundations that could affect the stability of the slope is given in Figure 1. Figure 2 shows the photograph taken at the site of proposed bridge.

The rocks present at the bridge site are heavily jointed. The subsurface at the extent of the bridge site considered for slope stability analysis essentially consists of dolomitic limestone with different degrees of weathering and fracturing.

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