Change in pile capacity with time: case histories

Abstract

Four case histories where important changes in pile capacity were observed with time are presented. Two show an increase of pile capacity for shaft bearing piles driven into deep sand deposits. The increase occurred over a period longer than needed for pore pressure dissipation. In one case, increases of 33 and 85% in pile capacity were measured 2 and 51 days, respectively, after pile driving. The other two case histories deal with the decrease of pile capacity of close-toe pipe piles driven to shale bedrock. The decrease, determined using dynamic monitoring during initial driving and at restriking a few days later, ranged from 11 to 25%. It is concluded that restriking should be currently practiced on all construction sites to investigate any change in pile capacity after driving. This procedure is particularly recommended for toe bearing piles on shale bedrock. Key words: pile capacity, shaft bearing piles, toe bearing piles, relaxation, soil setup, pile dynamic analysis, shale, time factor, case histories.