Castle Residences is a 37-storey development is located at 116 Bathurst Street in Sydney’s central business district and is adjacent to the heritage building, Porter House, which was originally built in 1876. The mixed-use development features elegant residences, a hotel and an eight-storey basement. The hotel occupies levels one-to-10 and the rest of tower is primarily used for residential apartments.

BG&E provided structural engineering services for the slender tower, which included:

• a 10-metre cantilever over existing heritage building on level 11;
• major structural steelwork (three four-storey trusses and two one-storey trusses);
• foundation system over the Cross City Tunnel (CCT);
• 25-metre deep excavation; and
• composite structure.

A soldier pile retention wall was utilised along the full perimeter with strict design considerations due to the adjacent heritage and Roads and Maritime Services (RMS) interface.

The CCT runs approximately 20 metres directly below the bulk excavation level of the site, east-to-west. During excavation of the Castle Residences site, a new Sydney Metro tunnel was excavated parallel, underneath Castlereagh Street, which is around five metres from the sites eastern cut rock face. The site is surrounded by RMS’ infrastructure and was designed in accordance with RMS’ Technical Direction for Deep Excavation GTD2012/001.