The concept of settlement reducing piles (SRPs) is relatively novel. Although little used to date, the technique is both powerful and straightforward. It has the potential to reduce costs considerably in certain ground conditions (eg London Clay) by significantly reducing the number of piles required and the raft thickness necessary. The raft and piles work together in an optimised manner because the piles are only used where they are genuinely needed for displacement control. Soil structure interaction effects which occur between piles and ground bearing slabs is classically a difficult area for engineers. This paper describes a relatively simple method whereby settlement reducing piles can be incorporated into a flexible raft analysis confidently. Pile assisted rafts, or yielding piles, are alternative names for this technique. Settlement reducing piles are used at selected positions under a building or a structure in order to limit otherwise excessive local settlements, for example beneath heavily loaded areas. The principal desirable qualities of settlement reducing piles are that firstly, ultimate shaft resistance is fully mobilised in the working condition. Secondly, that there is very little increase in capacity of the pile with continued settlement, which effectively means that the piles do not mobilise any significant end-bearing. If this can be achieved then pile-raft interaction analysis may be greatly simplified, since a constant pile reaction may be applied in the raft analysis at the pile location irrespective of the actual settlement of the raft at that point within certain limits. The paper briefly describes the case history of a residential and retail development in west London built on a raft supported locally by SRPs.
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