E H Steger BSc,FICE, FGS, and P H Derbyshire, BSc, AMICE. This paper was first published in GE’s September 1975 edition.
The foundation of one of four multistorey blocks in the new development at Euston Square posed the problem of how to carry a particularly high intensity of loading. Whilst the other three blocks were carried on large diameter under-reamed piles founded in clay, the fourth — Block B — was designed to be carried on straightshafted piles founded in the Thanet Sand. These piles were constructed under bentonite and tests showed that high end-bearing pressures could be developed in the sand. The Euston Square redevelopment comprises four multi-storey blocks (see Fig. 1.). For architectural reasons, block B was positioned immediately adjacent to the existing underground car park and station concourse, and the upper floors of the building are cantilevered out over these existing structures (Fig. 2.). The outer mullions transfer their loads to a 32m square specially reinforced slab at first floor level and then by means of four columns to the 19m square foundation raft. It is the foundation of this block that is described in this article.
Blocks A, C and D were not so restricted in available foundation area and perimeter column loads are transferred directly to single large diameter under-reamed piles, whilst the central cores are carried on groups of under-reamed piles.