Local scour at bridge abutments in cohesive soil

Abstract

The results of a laboratory investigation on local scour at bridge abutments in cohesive soils are presented. Kaolin clay was used as a bed material and vertical wall abutments with three different sizes. Forty experiments were conducted under clear-water conditions in cohesive soil with a clay content ranging from 2 to 20%, compaction ranges from 57 to 88%, liquidity index ranges from 0.03 to 0.99 and the approach flow Froude numbers from 0.3 to 0.55. Equations were developed to predict the equilibrium scour pattern around the vertical bridge abutment, including the maximum scour depth, scour volume, scour width, lateral side slope, and longitudinal slopes of the scour hole, in terms of the dominating factors controlling the scour process, namely the Froude number, clay content, compaction, water content, liquid limit, plastic limit, and vertical-wall abutments dimensions. Also, an equation was developed to predict the development of scour depth with time. Comparisons with previous results are also discussed.

Keywords:

• Bridge abutment
• cohesive soil
• experimentation
• open channel flow
• scour