Experimental investigation of scour effects on regular and breaking wave loads on a monopile

Abstract

This study conducted a series of model tests to assess the variations of regular and breaking wave loads on monopile foundations during the scouring process. The wave forces acting on the pile were determined by measuring the strain distributions along the pile depth using fiber Bragg grating technology. Under regular wave conditions, the horizontal loads on the pile above the pre-scour (initial) mudline are minimally affected by the local scour, while the lateral shear forces and moments on the pile body within symmetric scour holes are amplified. In asymmetric scour holes, the pile section partially that is partially exposed to water waves experiences both wave-induced shear forces and active/passive soil pressures simultaneously. Based on the Morison equation and appropriate wave theories, a novel approach incorporating the increased exposure area within scour holes is introduced to evaluate the horizontal wave forces on a monopile under scour conditions. In contrast to regular wave loads, breaking wave loads consist of Morison forces and slamming forces. A new method for dividing Morison forces and slamming forces based on the characteristics of wave motion is proposed. A comparative analysis indicates that the slamming coefficient is minimally affected by scour, while the behavior of Morison forces of breaking wave forces resembles that of regular waves.