on packed stone foundations whilst creating a 3-storey parking basement below it .
Temporary Bracing The main façade on Bree Street was stabilised by utilising the inherent buttressing effect of the walls framing the entrance foyer and the return wall down Mechau Street . A horizontal box-girder was installed to brace the top end of the Bree Street façade back to the return walls and stiffeners spanning between the girder and ground level were provided to brace the façade vertically .
New Support System The vertical load of the façade and entrance foyer was transferred onto ‘ needles ’ ( corbels ) projecting into the walls from the new ground floor RC structure which was subsequently undermined to create space for the parking basement below . The load of the façade and the edge of ground floor structure is carried on mini-piles placed just inside the façade , in positions chosen to suit the parking bays below . Holes were left in the slab for the main internal structural columns which are not connected to the structure at this point .
In places , RC lintols had been provided over wide door openings formed during a previous renovation . Permanent steel columns were placed on either side of these openings , on top of the new slab , to support the RC lintol and brickwork above .
Somewhat fortuitously , there was a shallow basement below the entrance foyer . Support for the existing basement foundations was temporarily maintained by encasing an ‘ island ’ of sub-soil material below them on three sides ( with temporary gunite cladding and anchors ) as the surrounding parking garage basement was excavated . New foundations and columns were cast on either side of the ‘ island ’ to support an RC beam and slab grillage which was constructed in the existing shallow basement space under the entrance foyer . The entrance foyer walls are supported on yoke beam elements of the grillage structure .
The ‘ island ’ of material under the entrance foyer was subsequently excavated away and the load transferred onto the new structure .
The challenge was to maintain the heritage façade and foyer and to create space for the parking bays required for the development , at feasible cost . It is testament to the boldness of the client , innovative engineering and cooperation between designers and constructors that this goal was achieved at minimal cost .
Touchstone House 395