10 Douro Place had previously been converted to four apartments, and the latest phase in the buildings’ lifecycle was a project to return the property to a single, substantial family property, including subterranean accommodation. Bachy Soletanche Specialist Geotechnics was appointed by Rackham Construction, to design and install a complex solution for a basement extension to the property, in the prestigious borough of Kensington in London.
PLANNING AND DESIGN
Access to the property was vastly restricted due to the proximity of other buildings, and this, along with the restricted headroom of the existing basement, the planning and design would be essential to the successful delivery of a scheme.
Along with structural retaining strength, one of the key elements in basement design is ensuring water ingress is reduced at the earliest point, in this case, the core basement walls. The project team developed a permeation grouting solution that involved installing a Tube a Manchette (TaM) grout barrier system, providing a low permeability water cut-off. Utilising this technique would enable the excavation and construction of the basement to be completed in dry conditions.
Prior to any work commencing, the team developed a 3D model of the TaM pipe configuration to ensure the ground would be fully grouted before the excavation commenced.
Bachy Soletanche Specialist Geotechnics installed 79 TaM pipes, which were 50mm in diameter with ports at 330mm centres. The 114mm bore holes were constructed up to 10m in depth and had a range of declinations, to deliver over 2600 grout injections the grout in two phases. The first phase saw the injection of 28m3 of a cement:bentonite grout mix to mass treat the target strata. The second phase saw the injection of 59m3 of a microfine grout mix, a far finer grained grout used to better penetrate the target strata thus ensuring complete treatment. During the latter stages of the second phase, grout volumes reduced whilst injection pressures increased, signifying the tightening up of the soil.
Once the grouting operations were completed, the project was handed back to the main contractor who excavated the basement, which was found to be stable and dry.