Effect of Slot on Stability of Riprap around Bridge Piers

An accepted engineering method to deal with local scouring at bridge piers is to place riprap material around the pier foundation. Field experience has shown that riprap stones often disappear with time, with most severe failure occurring during floods; and refilling is frequently needed to replenish the lost stones. Therefore, notice to riprap stability is necessary and has been the aim of this paper. In this research, four sizes of riprap located above, the same level and below the surface of the streambed and two slot sizes continued to the streambed were used. Effect of presence and size of slot on riprap stability and minimum necessary dimensions for finished riprap covering have been studied. The results obtained in the experiments range; show that riprap is more stable when using slot and this stability is more evident with bigger slot. The performance of the two slot sizes decreases when using the bigger stones. Decrease in performance of the big slot using the bigger stones is more than that of the small slot. Furthermore, results show that the slot decreases the finished riprap covering and consequently the riprap volume will decrease effectively. It has been found that the riprap placed above and below the streambed have the most and the lowest stability, respectively.