Basement Propping Schemes
CGL provides a single source of geostructural guidance to optimise temporary works solutions for piled walls, basement propping and berm stability. Our engineers can also provide temporary works design of propping frames, capping beams, thrust blocks and corbels using software including CADS A3D, Steel Work Member Design (SWMD) and AdSec to develop designs.
Key to ground modelling and the sensitivity of numerical analysis is an understanding of what is an optimum construction sequence. We are experienced in providing economic and sustainable construction sequencing solutions that blend well with complex ground modelling and realistic soil structure interaction to ensure the model reflects a pragmatic approach.
Analysis and modelling for efficiency
CGL combined geotechnical, structural and construction sequence engineering to deliver a fast track deep London basement at 1-9 Seymour Street, London. The project featured challenging complexity and was delivered safely, sustainably and within programme and budget constraints. Our work was shortlisted by Ground Engineering magazine for a major project award.
The temporary works (TW) design uniquely blended skilful construction sequencing and engineering management with sophisticated geostructural analysis, 2D and 3D modelling whilst combining realistic ground modelling and observational techniques.
The TW techniques used were designed efficiently using Finite Element modelling (FEM), which is more often in the domain of permanent works designers than the temporary works designer’s skill set. Examples include the novel use of PLAXIS 3D for the efficient design of reaction pile caps to limit movement of party walls and two tower crane base foundations. These maximised the benefits of sophisticated soil structure interaction so often ignored in conventional temporary works design.
Alternatives to conventional propping
CGL has used buttress piling as an alternative to conventional steel propping and thrust blocks on basement excavations up to 10m deep. The buttress pile approach enabled an accelerated construction programme versus conventional propping systems by eliminating restricted working space within the excavation.
These buttress piles use the same piling system, and indeed largely the same piles as the main wall set either just in front or just behind the line of the retaining wall. The buttress piles are connected to the permanent piled wall by a capping beam to become a single continuum, which increases the overall flexural stiffness of the system and lowers the potential displacement characteristics.
Buttress piles for a basement can either be included in the permanent construction or demolished once the internal floors within the basement can provide the effective propping. Where onsite space restrictions allow, the buttress piles can be installed on the active side of the wall and remain in place post construction.
Our pragmatic approach to basement propping was used in these recent projects:
- 79 Fitzjohns Avenue, Hampstead
- South West Lands, Wembley
- 27 Commercial Road, Aldgate
- Wardian London, Docklands
- Subsea 7 Headquarters, Sutton
- 1- 9 Seymour Street, London
- Kensington Row, London
- Pont Street, London
- 62-63 Pall Mall, London
- 55 St James’s Street, London
- Wandsworth Riverside Quarter
- Camden Lock