Foundations and retaining walls for a special extension in Potters Bar.
Some people would like nothing more than an indoor pool to make their home complete. Many dream of adding a purpose built gym or sauna. Many more build an extension to give the kids more room to play. A lucky few may even have the chance to build a golf simulator room. The owners of this home on ‘The Ridgeway’ in Potters Bar now have all of the above.
As foundation specialists, projects like this give us a chance to really show what we can do. This build required multiple methods of stabilisation, retention and sub-structure foundation system implementation. The project acts as a showcase for many of the techniques we use on projects around the country, all in one place.
Projects on this scale and of this design generally start with a large hole in the ground. The very first thing we need to do it to make sure that both the existing structure and also neighbouring properties (and their gardens) are completely unaffected by the excavations. We are a traditional underpinning company; we use tried and tested materials and techniques that work, without fail. The existing home was underpinned in a traditional fashion in order for the ground immediately behind it to be excavated to a suitable depth.
It’s also important that the works have no detrimental effect on the neighbours. In this instance a piled contiguous retaining wall was constructed to completely eliminate the risk of any disturbance to a neighbouring property.
Retaining walls were then constructed along the existing building perimeter, on the southern boundary and on the north side of the new structure.
The project had some complex requirements, giving us the opportunity to utilise various other foundation techniques. For part of the build, standard ground bearing concrete slabs were used. For the pool house, a substructure was formed using a ground beam and pile system. These 500mm wide x 300mm deep ground beams support the entire superstructure of the pool house, with an internal piled slab used to support the modular pool frame itself.
The new ceiling of the lower ground floor would also be utilised as an entertainment deck above. This was constructed using a suspended soffit slab.
Some technical specifications.
Piles for the ground beam and also the pool base were 150mm diameter, steel cased, cast in place driven piles. They were driven to refusal to a depth of between 6 and 7 metres. They have a SWL of 80kN.
All pile use was calculated using the Hiley Formula and meets all the criteria of BS8004. All piles were driven to refusal to achieve a suitable end bearing capacity with a factor of safety (FoS) of 3.0 used.
C40 reinforced concrete was used to construct the full concrete box system with the walls and slab base being 300mm thick.