SDS Design Engineers were civil and structural design engineer for Lidl GB on the brand new eight storey over basement office building in Wimbledon, London. The existing Lidl GB head office was to be demolished on the same site. A new two storey Lidl store would be located on ground and first floor with a warehouse storage area at basement level. To maximise the floor space in the basement, it was proposed to utilise the existing basement walls. This posed many challenges including temporary propping and permanent construction of the new basement floor 1.5 metres below the existing floor level.


In order to maximise the basement floor area a combined permanent works and temporary works solution to basement construction was required. Temporary concrete pads to support temporary works shores need to be co-ordinated with the permanent works foundations. The permanent works foundations were constructed in a granular clay layer over London clay. The foundation layers of the London clay were on the margins. An option to review a non-piled solution was given careful consideration.


The temporary works shores were designed to be installed prior to the demolition of the ground floor. Following the installation of the temporary works shores in the basement, the demolition of the ground floor slab can be carried out. Having the temporary works in place will also enable the excavators to remove the basement slab where required and the breaking out of the existing pile caps. The design required the that the temporary concrete pad support for the temporary shore be coordinated and constructed to fit between the permanent foundation pile caps or pads.



SDS Design Engineers carried out a survey and design assessment of the existing basement wall. It was discovered to be lightly reinforced. Analysis of the wall in the temporary and permanent condition revealed it was possible to construct a new underpin wall section extending the height of the retained wall and maximise the usable space in the basement level. Innovative thinking allowed the lower wall section to be designed as a horizontal beam between pad foundations.