Mass concrete underpinning system to support a retaining wall adjacent to the construction of a new road and footpath.

We were asked to design a traditional mass concrete underpinning scheme to provide support to a highly sensitive stone retaining wall which was going to be undermined during construction of a new road and footpath.

Larsen carried out crack repairs to the wall and the wall was strapped at the corners and along its face prior to underpinning works commencing.

The maximum excavation depth below the wall was 650mm and we designed a “Hit & Miss” underpinning system consisting of 26No 750mm wide by 800mm deep concrete bays.

We worked on a hit, miss, miss ,hit basis so that no newly poured concrete was supporting the wall until 24 hours after pouring.  We placed starter bars into each underpinning bay to tie the concrete bays together.

The wall was monitored regularly to show any signs of movement during the contract and we completed the underpinning works in 6 working days.

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