Pile Installation Assessment of Offshore Wind Jacket Foundation in Completely Weathered Rock: A Case Study of the South China Sea

Abstract

The assessment of pile drivability is the premise of successful pile installation, and completely weathered (CW) rock may bring the risk of pile refusal. This paper presents a case of pile driving refusal that occurred in a CW gneiss layer. The physical and mechanical properties of the CW gneiss are analyzed based on the results of a laboratory test, a cone penetration test (CPT), and a standard penetration test (SPT). By comparing the properties of CW gneiss with those from intact gneiss, the CW gneiss layer in this study was found to be soil-like. Additionally, it is a sand-like layer according to CPT-based soil classification systems. The soil resistance to driving (SRD) in pile driving was calculated with different methods for sand and compared with the SRD inferred from the pile-driving records. The results show that the modified Fugro’s method assuming a fully plugged condition may provide good pile drivability assessment in this study. It was found that it is necessary to determine the properties of the CW rock layer reasonably before conducting pile driving analysis, and a framework is proposed for analyzing the pile drivability in a CW rock layer based on this case study.