Abstract:
The Mandurah Estuary Bridge Duplication (MEBD) project involved the construction of a new traffic bridge (Bridge 1090) for the Lakelands Lake Clifton Road to the south of the existing crossing of the Mandurah Estuary (Bridge 1085). The main structures that were required within the Estuary for this bridge project comprised 2 abutments and 7 piers to support the incrementally launched bridge deck and a fishing platform.
The ground conditions below both sides of approach embankment comprise loose sand with interbedded layers of variable strength (soft to hard) clay, underlain by very low strength Leederville Formation Mudstone. This paper presents the development of the geotechnical design and discusses the geotechnical risks and opportunities that were identified, how historical embankment and piling construction records were used in the design, impact of temporary works and construction constraints which resulted in a holistic design that is efficient, economic and environmentally sustainable.
This paper discusses the subsurface conditions and the evolution in design approach from reference to detailed design for both ground improvement and piling aspects. The use of historical records was key to allowing design progression, leading to significant cost and sustainability benefits in the construction phase. The final design adopted conventional earthwork preloading (replacing rigid inclusions) which became feasible by utilising monitoring data from historical embankment construction to support the alternative method. Bored piles were specified at the reference design stage, however, historic piling records from the original bridge construction supported use of driven precast concrete piles for onshore piling and closed-ended steel pipe piles with concrete in-fill for river pier piling. This paper also highlights the impacts of temporary works and presents key monitoring results which provides subsequent confirmatory evidence on the feasibility of the proposed foundation design solutions and ground improvement approach used.