Stress Wave Monitoring for a Friction Pile During Driving: A New Analysis Procedure

Abstract

A pile-driving analysis procedure coupled with stress-wave monitoring, is developed for friction piles in clay or argillaceous rock. Emphasis of the analysis procedure is placed on treating an elastic-perfectly plastic constitutive law of the shaft interface, within the framework of one-dimensional wave propagation along with the method of characteristics. The analysis procedure thus developed is applicable to two types of pile-driving analysis: one is the inverse analysis for identifying the constitutive parameters of the shaft interface from a recorded stress waveform; and the other is the drivability analysis, in terms of the already identified material parameters, for predicting the displacements or stresses in the pile caused by any single hammer blow. Both aspects of the proposed analysis procedure are examined against laboratory pile-driving tests on a “perfect” friction pile with no point resistance. In those tests, a steel pipe pile of 2. 5 cm in outer diameter is quasi-statically jacked into a remarkably homogeneous mudstone, along a slightly undersized guide-hole, and then subjected to striking by a free-falling steel bar. It is then confirmed that there is good agreement between the calculated and measured pile-driving performances.