Introducing ring collars and effective spiral threading elevation for cylindrical pier scour control

Abstract

In this study, laboratory experiments are conducted to assess the effects of a set of novel ring-type collars and prevalent spiral threading around a circular pier on scouring in a clear-water flow regime in non-cohesive bed materials. Also, numerical simulations are conducted to reveal the flow field in the scour hole around a pier with spiral threading. Various angles and spacings of the ring collars are considered to find the best configuration. Moreover, four test scenarios of spiral threading with different elevation levels are considered to investigate the optimum upper bound of spiral threading elevation. Results show that the ring collars (Angle = 45˚, relative spacing = 4/3 of pier diameter) are the best configuration and reduce the scour depth by 29% according to the scour depth around a plain pier. This configuration of ring collars reduces maximum scour depth three times better than the best configuration of single spiral threading (suggested by previous research). Furthermore, the ring collars reduce the scour rate while the spiral threading has no considerable effect on the scour rate. The spiral threading under the initial bed level plays a major role in reducing local scour.