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Rottnest Sea Wall Investigation

Completion year 2018

Disciplines
Structural


Markets
Sports, Culture & the Arts


Offices
Perth


Key People

Rowan Stokes

Structural Section Manager, Australian Discipline Leader, Principal

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Appointed as Project Superintendent for the stabilisation and masonry conservation of the 150-year-old Rottnest Island Seawall, WGE’s Structural engineers worked closely with the Conservation Architect, Archaeologist and Arboriculturalist to preserve the historically significant structure, partly constructed by Aboriginal convicts. Located on the A-class reserve of Rottnest Island, the wall extends 300m across the Thomson Bay frontage and has been the subject of variously successful conservation attempts in the past. This project aimed to address soil retention pressure and the impact of tree roots whilst conserving areas to the front and rear of the wall.

The original structure is a mass ashlar limestone construction which retains approximately 3.5m. Historic tree roots, a build-up of fill over time and slender geometry combined to make the seawall unstable. Juggling the varying demands of wall stability, public safety, tree preservation, social heritage and archaeological considerations, WGE consulted closely with experts to identify the optimal solution.

Excluding the use of vibration or mass excavation, several hundred cubic metres of grout was pumped to create stabilised mass earth blocks, relieving the lateral force on the wall. Drainage paths were created away from the wall and a 1.5m deep root barrier was introduced to hinder reoccurrence, whilst problematic root zones were removed. A significant contribution to the project was made by the heritage stonemason using 150-year-old specialist techniques, such as hot lime mixing and lime-washing to preserve the wall going forwards.

Animal bones, old clay pipes and mysterious voids and blocked up doorways into the wall were uncovered during the work which made for a fascinating and unique heritage experience. All discoveries were documented and conserved by the project Archaeologist in consultation with the Aboriginal Heritage Liaison Officer.

Awards:

Commendation – Conservation or Adaptive Reuse of a State Registered Heritage Place – 2019 Western Australian Heritage Awards