Multi-Storey Retention

Temporary supports, reclaimed land and close proximity structures.

TGE was appointed to develop a series of options for temporary support of excavation walls for a multi-storey commercial building with basement carparking in the Wynyard Quarter. The chosen option was then taken through to detailed design by TGE.

The project is situated in an area of reclaimed land comprising variable fill materials over very-soft marine sediments.

The excavation was bordered by new and existing structures and the wall therefore had very tight limits on allowable lateral deflections. The depth of excavation was just beyond the limits for cantilevered sheet piles, so some form of propping was required.

It was not possible to anchor beneath the adjacent building and internal propping was not favoured due to the cost and clashing with work activities within the excavation.

TGE’s solution was a deep soil-mixing operation resulting in a thick slab of cement stabilised soil propping the sheets at the excavation level. The cement ratio above the slab zone was reduced resulting in a stiff dry coil which was easily excavated without swamp mats or groundwater controls.

The excavation progressed without any hitches and wall deflections were well within required limits.