SEISMIC RESISTANCE OF RETAINING WALL WITH REINFORCED BACKFILL

Abstract

Random Rubble dry boulder retaining wall are most commonly used in Himalayan region which is also a active seismic zone. These are extensively used for low height retaining walls. But its stability under earthquake condition needs evaluations and ways are thought to improve its performance.This can be done either by increasing wall strength or by reducing the earth pressure acting over it. Use of reinforced earth was an attempt in that direction. An experimental study has been conducted to investigate the effect of different quantity of reinforcement provided in the backfill. To obtain this a retaining wall of height 1.0m having 48.0cm base width and 20.Ocm top width with earthface vertical and other face inclined straight was constructed. Its courses were laid inclined towards backfill having slope 3H:1V. In the first test, there was a dry, cohesionless sand as backfill whereas in the second test backfill was reinforced with Nylon niwar strips of 5.2cm width and 60.0cm length. Strips were placed in horizontal planes and perpendicular to the wall face at vertical and horizontal spacing of 20.Ocm each. In the third test length of reinforcement was increased to cover the whole backfill and it was tied properly to the back wall of the tank. These arrangements were done in a 3.Om x 2.Om x 1.2m tilt-table tank. Wall was constructed such that there was a 1.05m space for backfilling. All the three models were tilted slowly till failure. All models failed at the inclination of 12° showing no effect of reinforcement. It was then inferred that no friction mobilisation between sand and reinforcement took place. Analyses of the wall at failure condition indicate that it is the weight of the backfill over the plane of repose whose normal component causes failure of the wall. On the basis of this study, it was concluded that R.R. boulder walls have much less strength under seismic condition as compared to other Gravity retaining walls and reinforcement of the backfill does not improve its performance under dynamic condition.