Study On The Inner Frictional Resistance Of Large Diameter Steel Pipe Piles In Sand

Single pile foundation is the most widely used form of offshore wind turbine foundation.With the continuous increase of the installed capacity of offshore wind turbines,the single pile foundation has shown a large-scale development trend,and the soil plug effect of the large-diameter steel pipe piles is greatly weakened.At present,there is no good method for calculating the inner frictional resistance of steel pipe piles under the condition without plugging.In this paper,the inner frictional resistance of large-diameter and super-large-diameter steel pipe piles in sand is studied.The smallscale model test,geotechnical centrifuge model test and finite element simulation are used to reveal the law of inner frictional resistance inside the steel pipe pile and factors that affect the extent of the inner frictional resistance:(1)The vertical bearing capacity test of steel pipe piles with different diameter-tolength ratio in sand is carried out.The load-displacement curves of partial plugging steel pipe piles are obtained.The law of inner frictional resistance inside the pile was obtained by using the double-wall model pile structure.(2)Through the centrifuge model test of the vertical bearing of the steel pipe pile in the sand,the load-displacement curve and the curve of the inner and outer frictional resistance along the pile body of super-large diameter steel pipe pile without plugging are obtained The laws of the inner and outer frictional resistance of super-large diameter steel pipe piles under different load levels are revealed.(3)The finite element method is used to systematically study the factors and laws of the inner frictional resistance of steel pipe piles.On the basis of verifying the correctness of the finite element calculation method,the vertical ultimate bearing capacity and the inner frictional resistance of the steel pipe piles with diameters greater than 4 m are calculated.The calculation results are compared with the API specification calculation results,and the applicability of the API specification for the calculation of the bearing capacity of large-diameter steel pipe piles is discussed.(4)The concept of introducing the aspect of diameter-to-length ratio in the API specification method is proposed to calculate the inner frictional resistance of steel pipe piles with a diameter larger than 4m in sand.The centrifuge model test verifies the reliability of the proposed method.