Simplified Method for Design of Underpinning Piles

Abstract

Existing buildings sometimes experience excessive settlement under their design load or face the prospect of excessive settlement in the future if a change of building use is required and increased foundation loadings will occur. Several methods of foundation enhancement are available to arrest settlements or improve the future performance of existing foundations. The method of underpinning by piles is widely used, but despite the long-standing use of this method, approaches to the design of piles for underpinning are not well developed. For practical purposes, a simple method is required for designing underpinning piles. In this paper, a design method based on the concepts of pile-raft interaction is developed. The general concept of the simplified design method is described, and then the method is formulated and explained in detail. The application of the simplified method to a series of problems analyzed by finite element methods is then described. Finally, comparisons are made between the results of the simplified analysis and data from model footing tests.