Investigation of effectiveness of preloading method for existing foundation underpinning by centrifuge tests

Abstract

A conceptual preloading method was proposed for reducing loads carried by exiting piles by means of transferring partial loads on existing piles to underpinning piles. For investigation of the effectiveness of preloading method, a model preloading apparatus used for centrifuge tests was developed and a series of tests was performed on an underpinned foundation. In the centrifuge test, a pre-load was firstly applied to the underpinning pile to verify the load transfer effect of the preloading apparatus. Then additional loads were applied to the foundation to evaluate the load sharing behaviour of existing and underpinning piles. The feasibility of the preloading apparatus based on the preloading concept was verified through the experimental results. Moreover, under additional loading, the preloading value affected the load sharing capacity of existing and underpinning piles. Therefore, in the design of underpinning considering preloading, a proper pre-load range which is less than both linear pull-out behaviours of existing foundations and linear compressive behaviour of underpinning piles was suggested.