Silk Park

This landmark development in Hendon, being undertaken by St George Plc and Sainsbury’s, will provide 1309 apartments on the existing supermarket site, as well as a larger replacement supermarket.

The development is to be undertaken in two phases, with Phase 1 including 870 apartments, the new 8,998m² Sainsbury’s store, other commercial spaces, and associated parking.  Phase 2 will follow the subsequent decanting and demolition of the existing Sainsbury’s Store.

Gravity have been appointed to undertake the structural and civil engineering detailed design on Phase 1.

The key challenges have been:

• The large column grid required within the Sainsbury’s store, where the required column spacings are 16.1m x 16.1m. 
• The transfer slab over the Sainsbury’s store supporting the apartment blocks over, where we provided an innovative and economic design.
• The client’s requirement to avoid movement joints through the podium slab, which has overall dimensions of 152m x 90m.
• The interface between Phase 1 and the future Phase 2 alongside the existing store, and the incursion of Blocks 6 and 7 into the Phase 2 basement area.

Among the most interesting and challenging parts of the project; for us has been the level 4 transfer slab.  At the time of our appointment there was a previous structural scheme in place including a 1.5m to 2m deep solid insitu concrete transfer slab supporting the buildings over, which we believe would have needed localised increases to 2.5m depth given the exceptionally large spans.  On review we found that this was not the most efficient scheme and therefore provided an opportunity for us to offer an innovative design solution.

We have delivered a comprehensive and detailed pack of structural drawings in line with the client’s design programme, and have achieved a number of efficiencies in the design, including:

• Reduction of the basement dig by approximately 450mm following review of structural zones and levels with the design team.
• Removal of heave mat under the basement by reviewing the magnitude of heave forces and designing the basement slab to resist these forces.
• Undertook a review of the basement extents to allow the basement walls to be pulled back from the highway boundary, reducing materials and dig and avoiding a potentially lengthy highways application.
• Provided an efficient column grid in the superstructures to keep all columns within party walls rather than in apartments, thus keeping the rebar content of the slabs low.
• We have also provided an alternative scheme for Blocks 6 to 8 using off-site precasting and prefabrication in order to accelerate the programme following the occupation of the Sainsbury’s store.
• This approach had the advantages of reducing concrete volumes, reducing the structural weight and therefore achieving savings in the foundations, and a lower risk of thermal and shrinkage cracking compared to a thick insitu concrete slab.