The site has a number of different constraints:
• HS1 tunnels;
• Central line tunnels;
• Railway Line tracks and gantries with Overhead Line Equipment (OLE) running directly to the south of the site.
• Utilities around the site (i.e. Thames Water assets).
• Existing buildings surrounding the site to the east and to the north.
• Highways retaining wall (masonry and concrete).
B1 and GF pile cap spans over those assets and take support off secant and bearing piles away from the exclusion zone of those assets.
The building is 14 storeys in the tower block and 3 up to 5 storeys in the other block.
Floors are PT slabs and lateral stability is provided by core walls.
Vibration bearings are required (generally underside of L1 apart from GF bedrooms where a floating slab is provided) to avoid transferring vibrations.
RBG Value Add
RBG were originally engaged to provide stage 2 in support of planning and the building was originally meant to be a modular construction. RBG were then engaged to re-design stage for a concrete option and stage 3-4.
RBG also provided:
- Flood Risk Assessment;
- Asset protection;
- GMA and monitoring.
RBG had early consideration and engagement with NR for the OLE running directly to the south of the site.
Sustainability
Sustainable practices which have been adopted on this development include:
- Use of PT slabs, reducing overall material brought to site, and hence offers a reduction in trucks to site. This also provides a savings in the foundations from reducing overall self-weight of the structure.
- The proposed piles are to be continuous flight auger (CFA) construction method, which avoids the use of temporary casings and negates the requirement for support fluid. The method is also quicker with low noise and vibration. There is an opportunity in the next phase of the design to optimise pile length and numbers to ensure the pile groups are not over designed. Optimising pile group number and depths will reduce muck away from site compared to having a standard pile depth across the site, directly reducing spoil and concrete truck numbers to/from site.
Future opportunities to be investigated:
- An optimisation of raft foundations can also be done to move towards a pile group support system. Rationalising the depth of excavation and using ground beams to transfer column loads to the local pile groups adjacent to the assets can save unnecessary material, excavation and transportation.