Residual load development in cast in place piles - a review and a new case history

The development of residual (or locked-in)loads in driven pre-formed piles has been investigated extensively over the past 40 years or so. In contrast, cast-in-situ piles are often erroneously assumed to be free of residual loads. This paper aims to review the limited number of published studies into the processes which lead to the development of residual loads in bored, augered and driven cast-in-situ piles during curing. Unlike precast piles, concrete for cast-in-situ piles must be given sufficient time to cure and develop strength in the ground prior to loading. The interaction between the concrete and surrounding soil is complex and there are a number of processes which influence the strains within the pile during this period. By continuously monitoring strain and temperature development between casting and static load testing, these processes can be identified as initial concrete set, hydration curing and soil disturbance and consolidation effects in the vicinity of the pile. A limited database of reported studies which monitor such processes is presented, together with the proposed methods for deducing the level of residual load from strains present at the time of testing. Finally, a new case study with strain and temperature measurements within a driven cast-in-situ pile is presented.