Relaxation of piles driven to rock

This paper examines relaxation of end-bearing pile groups driven to bedrock. Several cases of relaxation are reviewed where relaxation was observed in the form of either a decrease in pile load capacity, or a reduction in penetration resistance upon redriving. The affected geologic formations included shale, mudstone, limestone and mica schist which were generally weathered and fractured. It is concluded that the usual mechanism for pile group relaxation is mechanical fracturing of the rock and disturbance of subsequently driven piles. The authors recommend practical guidelines for the prediction, detection, and remediation of relaxation of pile groups drive to rock. A current research effort into the problem using laboratory model simulation is described. Preliminary test results are presented and future research directions are discussed.