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Basements for dwellings and small buildings have been the subject of great interest in recent years because they represent a big gain in space within the same footprint. There are many other factors in favour of basements including the inherently good energy efficiency and the fact that many sites require fairly deep excavation even if a basement is not included. The demand for authoritative guidance has resulted in the production of an Approved Document1 but because of limitations in the design methods and assessment of loads it was not possible to include plain masonry walls. It is clear that plain masonry walls should be appropriate in many situations but the absence of a sustainable design method is inhibiting their use. An empirical design method for very specific conditions based on German practice is included in Eurocode 62 but this is of limited applicability to UK conditions. The research programme described in this paper has reviewed all the design information available and proposes a design basis for plain masonry basement walls. The investigation has found that by refining the underlying design assumptions which form the basis of EC 6 a 20% improvement in the performance of unreinforced masonry can be achieved. A detailed method of design is presented for typical UK dwelling construction. It is unlikely that any further gain in design economy for plain masonry walls can be achieved by further refinement of the design assumptions for the masonry. There would be significant gains to be made by rationalising the loading assumptions for shallow basement walls but further research is required before this can be justified. Eur ing Prof. J. J. Roberts, Hons DSc, BSc (Eng), PhD, CEng, FIStructE, FICE, FBMS, FRSA, MICT Dean, Faculty of Technology, Kingston University, Kingston upon Thames, Surrey KT1 2EE A. K. Tovey, CEng, FIStructE, MCIArb Tecnicom, Crowthorne, Berks Dr. A. N. Fried, BSc (Civ) Eng, MSc, PhD, FBMS Kingston University
The redevelopment of Knightsbridge Crown Court for Harrods was a highly complex mixed-use project consisting of seven storeys above ground and seven storeys below ground. A 25m deep basement was constructed using 800mm thick diaphragm walls and top-down techniques.The lowest level of the basement is linked to Harrods by a 5m diameter, 75m long tunnel accessed by a set of freight lifts. Top-down methods were also used to construct the lift shafts from an existing narrow lightwell within the main building. Ground movement is inevitable with this type of construction. Conventional methods were used to keep it to a minimum, and a comprehensive monitoring system was installed.Compensation grouting, based on the observations from the monitoring work, was successfully carried out to control settlements resulting from the tunneling (detailed explanation of geotechnical considerations and design is published elsewhere by others1, 2, 3 & 4). The complex transfer structures needed to deal with the different grids required at different levels are described and so are the constraints imposed on the project by the need to retain an existing facade along one of the major elevations. Awards: This project won a Structural Heritage Award 2002 from the IstructE R. E. Slade, BSc, CEng, FIStructE WSP Group A. Darling, BSc, CEng, MICE WSP Group M. Sharratt, MSc WSP Group