Abstract:The flexible large-diameter rock-socketed steel pipe piles in a coal wharf is a new form of structure,which consists of 7 large-diameter rock-socketed steel pipe piles. The steel pipe pile is rare in the domestic and international engineering,with its outside diameter of 1 400 mm,thickness of 16 mm,lengths of 30.74~32.24 m,and 4.94~5.63 m socketed into rock. In order to verify the safety of structures and the quality of construction as well as to improve the design methods,a field test on two piles under lateral load is carried out. This full scale test shows that the design and the construction are excellent,and meet the demand of the original design. However,the improvement of design methods for lateral load piles is a complex problem,as it requires the determination of relevant properties of soil and soil-pile. So a new calculation method for lateral loaded pile,named composite stiffness principle with biparameter method,is presented and verified by comparing its results with available field test data. Thus the regulation of the pile-soil interaction and the range of composite stiffness EI and biparameter 1/n with a is obtained. These parameters can be used in the design of other long piles nearby. At the same time,the pile-soil parameters for the large-diameter rock-socketed steel pipe piles are accumulated for development of this new method.