A levee breach induced by internal erosion in Western Australia

Abstract

This case study presents a levee breach induced by piping erosion under cyclonic conditions in 2019. The levee is a 2.5 m-high, 500 m-long, mass earth-fill embankment; with no cutoff trench, core or ancillary structures. Located near Port Hedland on the north coast of Western Australia, its purpose is diversionary: to redirect cyclonic surface water away from the nearby Great Northern Highway. The levee was founded directly on alluvium in 1987; it is formed of locally sourced clayey sandy gravel. In 2003, the levee was partially excavated to enable the placement of a buried pipeline through the levee. Following a cyclonic event in 2019, a 27 m length of the levee breached, resulting in significant scour of the foundation and downstream soil. A site visit and investigation were conducted shortly thereafter, where in situ testing and laboratory soil tests on the levee and foundation materials were conducted. Analysis of the site observations and laboratory testing data led to the probable failure mechanism being theorized as having been initiated within the foundation by piping erosion within sand-rich beds of alluvium. The large quantity of water ponding upstream of the levee then caused a progressive washout and breach of the levee. Thematic collection: This article is part of the Role of water in destabilizing slopes collection available at: https://www.lyellcollection.org/cc/Role-of-water-in-destabilizing-slopes