The project comprised the demolition of a series of buildings down to basement level, the retention of one listed building on the site, and the construction of a new two level deep basement within a secant wall and underpinning, partially under the retained building.
This was a very tight city centre project with out of balance earth pressure loads. During secant wall installation unforeseen and highly variable ground conditions were encountered necessitating changes of plant and methods.
Wentworth House Partnership designed both the permanent and temporary works retaining walls to the site perimeter for excavation to formation level. This included secant pile, contiguous pile, sheet pile and underpins. The underpins were up to 6m deep and required significant temporary works in their own right.
An innovative propping solution was developed to minimise temporary works zone whilst maintaining the stability of the surrounding structures and highways.
The underpinning and needling scheme to allow two levels of excavation below the existing listed building on site was designed and coordinated with the remaining works.