Experimental study on stability of different types of armor units used in shore protection structure

Abstract

Protection of coast and shore against the erosive force of waves, currents and storm surges can be performed in many ways. Protection of coast and hinterland against flooding adds various types to the protective measure. The role of different types of armor unit is very important in the stability of shore protection structures. Stability of armor units depends on the slope of the bank, subsoil, filter and protection of toe. In this study, C.C. blocks, X-blocks and Tetrapods are considered as an armor unit. C.C. blocks are uniformly and staggeredly placed on the revetment in filter condition-1. Tetrapod and X- block were placed on the revetment in filter condition 1 & 2 (filter condition-1: stone chips were used and filter condition-2: stone chips were not used as filter materials). To investigate the performance of various types of armor units, laboratory experimental studies are carried out in a two dimensional wave flume (21.3 m long, 0.76 m wide and 0.74 m deep) in Hydraulics and River Engineering Laboratory at Bangladesh University of Engineering and Technology. A set of experiment is carried out at 50 cm still water depth with fixed 1:4 slope for four different wave periods (1.5 sec, 1.6 sec, 1.8 sec and 2.0 sec) in the wave flume. Run duration was six minutes for each of 24 runs. A total of 24 run was conducted with six different conditions, the water surface elevations at different locations are measured manually. In this study, Armor unit are designed for 15 cm wave height and 1:4 slopes by using Hudson (1961) equation. The Performance of C.C. block was found good when it was uniformly placed on the revetment for wave period of 1.5 sec but for wave period of 1.6, 1.8, and 2.0 sec revetment was unstable. Moreover, the revetment was stable when C.C. block was staggerdly placed on the revetment for wave period of 1.5 and 1.6 sec. but it was unstable for wave period of 1.8 and 2.0 sec. Again, the revetment was stable when tetrapod placed in filter condition-1 on the revetment for wave period of 1.5, 1.6, and 1.8 sec but for wave period of 2.0 sec the revetment was unstable. Finally, tetrapod was placed in filter condition-2 on the revetment and the performance of tetrapod was found well for all the wave periods. Performance of X-block was well when it was placed in filter condition-1 for wave period of 1.5 and 1.6 sec but the revetment was unstable for wave period of 1.8 and 2.0 sec. Again X-block was placed in filter condition-2 on the revetment and the performance of X-block in filter condition-2 was found well for wave period of 1.5, 1.6 and 1.8 sec but the revetment was unstable for wave period of 2.0 sec. So, the performance of tetrapod in filter condition-2 was better than any other types of block.