Bridges

The Sydney Gateway Project comprised numerous bridge structures and various other civil assets including retaining walls, drainage, and major signage structures. The Project alignment traversed various exposure environments, each having unique durability issues. The primary exposure environments which were considered from a durability perspective were Tempe Tip where contaminated lands were identified, Alexandra Canal, a saline waterbody and acid sulphate soils which were identified along Qantas drive. Contaminated lands posed a significant durability risk on the Project as elevated levels of ammonia, magnesium, sulphates, and acidic conditions were identified at pile locations. Bridge structures adjacent to Alexandra Canal were exposed to chloride contents equivalent to seawater with chloride ingress identified as the primary form of deterioration for these in-ground elements. While acid sulphate soils were also encountered along the Project which posed significant durability issues to the buried concrete elements. Each exposure environment encountered across the Project posed its own unique durability issues. This paper discusses the various aggressive ground conditions which the bridge structures encountered along the Project alignment and what durability design solutions and protective treatments were implemented to ensure that the design lives are achieved. Suggestions as to how specifications might be improved on such projects going forward are proposed.