Assessment of Soil Setup from Pile Installation Monitoring and Restrike Tests of Offshore Wind Turbine Foundation Piles

摘要

According to German recommendations for offshore wind turbine foundations, the bearing capacity of axially loaded piles can be verified by dynamic load testing. However, during the pile-driving process, the soil resistances are reduced, requiring additional setup time to increase again. This setup effect has been discussed in several presentations, e.g., at stress wave conferences. The resistance obtained from signal-matching analysis procedures (e.g., CAPWAP~?) are thus a function of the elapsed setup time. In many cases, the static resistance to driving observed at the end of initial driving does not provide adequate capacity, even at final penetration. Thus, restrike tests after a sufficient waiting time after pile installation are typically required to determine the long-term resistance. Especially under the harsh ambient conditions at offshore sites, the performance of restrike tests is a challenge, and many actions and procedures must be considered to obtain reliable capacity results and setup factors.