Bonnet Bay retaining wall collapse

This is one of our most unusual and challenging projects in the 30+ years we have been in business.

This property was set up high from the roadway, and had a history of changing hands every few years. The original Owner built a low sandstone retaining wall of about one metre high.

Subsequent Owners raised the wall higher and higher, without any Structural Engineering advice, until the wall reached approximately 4.0m high – a disaster waiting to happen – and it did.

Severe storm activity releasing abnormally high rainfall resulted in a catastrophic collapse of the entire wall facing and the fill material behind.
The sewer and stormwater pipes were torn from the house rendering it uninhabitable, and for a time the insurer was not accepting liability for the reinstatement.

SGB won the tender to rebuild to the complex Engineering design incorporating 5 separate retaining walls, however, before the construction could commence, the spoil required removal whilst the house stayed in position.

This was enable by the installation of sheet piling and rock anchor installation, in staged levels to enable excavation of the spoil from top to bottom.
McDonald Engineering were our groundworks people, and L J Williams undertook the excavation and waste disposal contracts and worked magnificently with us. The retaining wall blocks are a reconstituted crushed sandstone composite formed into the shapes with different face textures to imitate solid sandstone.

Each block had to be lifted and put in place using a small tractor, so patience and attention to detail were required.
The retaining walls have a system of pipes behind them which are accessible for hose-cleaning out so there will never be the hydraulic pressure build-up again to challenge the wall integrity.

I believe these walls will last over 100 years.