Field tests on vertical bearing characteristics of large-diameter extra-long steel pipe piles in offshore wind power projects

The steel pipe piles are the main foundation type for offshore wind power projects, but there are relatively few researches on the vertical bearing capacity of large-diameter ultra-long steel pipe piles in the sea. The field tests are conducted on the vertical bearing capacity characteristics of the large-diameter ultra-long steel pipe piles based on their application in an offshore wind power project in Shantou City of China. The variation rules of side shaft friction and tip resistance with pile load are analyzed, and the variation characteristics of tip settlement and top settlement of the pipe piles are compared. Additionally, based on the on-site test results, the method for determining the bearing capacity of the large-diameter ultra-long steel pipe piles is explored. The tests results indicate that there is a significant pile deformation. It was easier to control and adjust the on-site loading amount by using the curve of tip settlement versus load, and it is also easier to judge the ultimate state of bearing capacity. The curve of tip resistance versus pile load shows an "S" shape. In the current code, the load corresponding to the point at which the slope of Q/Q_max~s/d curve begins to change to 0.2 is used as the ultimate bearing capacity to overestimate the vertical compressive ultimate bearing capacity of the large-diameter ultra-long steel pipe piles.