Solid foundation complete for new Bay Bridge

Menard Oceania, the company awarded the contract for the treatment of soft soils around the 3500 square-metre project site, said their Controlled Modulus Columns (CMCs) method was used to create a solid foundation for the bridge.

When the company started work in September, Civil Engineer and Menard's Project Leader Kevin Doyle said the first step of a ground improvement project was undertaking soil testing.

The next step was navigating the design process to integrate the solution with the proposed structure.

"Once the design was completed, we started construction of the CMCs," Mr Doyle said.

"We were on site for over two months, which sounds a lot for one bridge approach, however the biggest challenge on this project was the depth requirement combined with the complex interbedded alluvial soil deposits.

"Since inventing this technique some 20 years ago, Menard initially installed CMCs to depths in the order of more than 20 metres. Recently, Menard has achieved depths internationally of over 50 metres. For this project however we went to over 30 metres to get to good soil."

Mr Doyle says the project was in an environmentally-sensitive marine park, with internationally-listed wetlands with mangroves only metres from the project site.

"We needed to make sure no effluent from our works went into the river and carefully managed our materials on site so there were no spills," Mr Doyle said.

"Detailed environmental considerations went into our foundation work due to the unique ecology of the area which also includes substantial natural oyster beds. There were no environmental issues as a result."

"A CMC is essentially a small diameter displacement auger which is pushed into the soil matrix by a modified piling rig, in this case, a Casagrande B250," a Menard Oceania spokesperson said.

"Once the tool has completely penetrated through the compressible soils, the auger is extracted, and concrete or mortar is pumped under pressure through the hollow stem to fill the anulus left by the operation.

"The CMC is then replicated on a grid pattern.

"The matrix of columns ultimately controls the stiffness or modulus (an elastic soil parameter and a measure of soil stiffness) of the soil, hence the name 'Controlled Modulus Column'."

Menard Oceania said CMCs would support transport for NSW's new southern approach to the Batemans Bay Bridge replacement as it continues to be built, eventually replacing an old vertical steel lift truss structure built in 1956 which rises twice daily to let vessels pass under it.

"CMCs will ensure a smooth transition from the uncontrolled embankments into the rigid bridge abutments founded on piles," the spokesperson said.