SCOUR BELOW PIPELINES AND AROUND VERTICAL PILES DUE TO RANDOM WAVES PLUS CURRENT ON MILD SLOPES

Abstract

This thesis presents a stochastic method for predicting the scour depth around vertical circular slender piles and below marine pipelines due to random waves plus current on mild sloping seabeds. An overview of the scour mechanisms around vertical piles and below marine pipelines is given. The background of the scour around vertical piles and below marine pipelines on flat and sloping seabeds under regular waves and random waves alone, as well as random waves plus current is presented.A point model of the wave height distribution, consisting of two two-parameter Weibulldistribution, is chosen to describe the wave condition on mild sloping seabeds includingbreaking waves. For vertical piles, a truncated wave height distribution is developed because the scour formula is valid above a threshold value. Four slopes are considered for waves alone case for the vertical piles and the pipelines. The effect of combined waves plus current on scour is studied. For waves plus current, the relationship between scour depth and the current velocity is presented. A comparison between a stochastic method and an approximate method is made.