GFWAust carried out permeation grouting with microfine cement to provide underpining to adjacent properties to limit settlement during sheet pile installation, and to provide sand stabilisation for sewer excavation

ADCO Construction were responsible for the construction of the new multilevel Woolworths at Umina Beach. The building was founded on sand and included one level of basement. McDonalds Sheetpiling were appointed to install sheetpiles to provide a retaining wall for the basement excavation. The site included prefabricated housing along one boundary and a low level brick building founded on shallow footings in the south east corner as part of the public library complex.
During the installation of sheetpiles adjacent to the library complex, settlement occurred creating cracks in the brick walls. GFWAust were instructed to carry out permeation grouting along the interface between the sheetpiles and the brick walls to provide underpinning to the shallow foundations. Microfine cement was injected through small diameter grout spears to create columns of cemented sand. When the sheetpiling was completed the settlement was not only reduced but the cracks created earlier were seen to close up.
A sewer manhole construction in the south west corner required permeation grouting to stabilize the sand to enable excavation. Microfine cements were again used to create a retained section of sand to enable excavation to proceed unhindered.
The work was carried out quickly with rapid mobilization to limit impacts on the program