Optimal Octagonal Hooked Collar Countermeasure to Reduce Scour Around a Single Bridge Pier

Abstract

Pier modification countermeasures are essential as they play a vital role in protecting pier against local scour action. Current study investigates experimentally the scour around vertical pier of octagonal cross section with pier modification such as newly proposed octagonal hooked collar is explored, in steady uniform state, under clear water condition. The results of pier scour without any modification were used as a reference to compute the efficiency of hooked collar provision around octagonal pier. The results show that by increasing the hooked collar width up to 2.5 Wp reduced maximum scour depth significantly. However, the experimental investigation revealed that the best combination to be with a hooked collar width of 2.5 Wp, having sidewall height 0.45 Wp. The best combination minimized around 73.3 % of scour hole depth, compared to octagonal pier without any modification. Using experimental results, a new equation is proposed to predict the scour depth around a bridge pier fitted with hooked collar. Moreover, a relation was developed for maximum scour depth and scour hole volume. Results indicate that the scour hole volume around a bridge pier increases quadratically with maximum scour depth.

Performance Evaluation of Scour Protection around a Bridge Pier through Experimental Approach

“…Hence, a range of combinations with four different widths (H w = 1.5W p , 2W p , 2.5W p , 3W p cm) and three sidewall heights (H wh = 0.15W p , 0.3W p , 0.45W p cm) is examined. The hooked collar thickness is adjusted as 5 mm [28]. Whilst the ratio of flume breadth 'B' to width of pier, B/W p is 20, at the contracted cross section no bed degradation is noticed; this agrees well with [37] that reported that contraction scouring effect becomes minimum when B/W p > 10.…”

“…4. The scouring hole depth gradually progresses for the pier without any protection and approaches to a maximal depth and then asymptotically reaches a normal state as reported by [28]. Thus, it may also be mentioned that the rise in the depth of scour decreases temporally.…”

“…They reported that pier with octagonal cross section was observed to be more effective in minimizing local scouring compared to other pier shapes. Recently, Farooq et al [28] performed experiments to optimize the octagonal hooked collar and assess its efficiency on octagonal cross-sectional pier. A collar with hook provision having width and side wall height of 2.5W p and 0.45W p , respectively, was the best in reducing scour depth for octagonal pier shape, where W p is the pier width.…”

“…Various researchers have recently examined a new form of collar having provision of hook around circular and octagonal pier shapes [26,28]. They concluded that the performance of pier protected with hooked collar is satisfactorily improved in comparison to pier protected with simple collar.…”

“…They concluded that the performance of pier protected with hooked collar is satisfactorily improved in comparison to pier protected with simple collar. Therefore, it is of utmost importance to optimize the dimensions of hooked collar around rectangular cross-sectional piers, based on the optimization procedure recommended by Farooq et al [28].…”