| Offshore wind power is clean energy and it is developing rapidly in recent years around the world.Monopile is widely used in domestic offshore wind power project.The diameter of monopile is generally 4 to 6 meters,even up to 10 meters.It is complex to confirm its bearing characteristics due to large volume of soil plug inside.Soil plug effect affects greatly on the bearing characteristics of steel pipe pile.However,the study of soil plug effect is mostly about small and medium diameter steel pipe pile at present,and little research is done on that of large and super-large diameter steel pipe pile.This article unifies the National Key Basic Research and Development Program(973 Program,project number 2013CB036304)sub-project "Deep foundation bearing behavior under complex environment design evolution and long-term performance" and the SPIC JIANGSU ELECTRIC CO.,LTD project "Study on bearing capacity of large diameter steel pipe pile foundation in Jiangsu offshore wind power project"(project number 2015-065-JSD-KJ-X),using the finite element software ABAQUS to simulate the vertical and horizontal bearing characteristics of different diameter steel pipe piles.The bearing capacity of different diameter steel pipe piles is calculated by using domestic and foreign codes.Finally,according to the numerical simulation and calculation results,the coefficient of base bearing capacity of the pile is corrected considering the pile diameter and the depth of the pile end penetrating the bearing layer.The main research work and achievements are as follows:(1)This paper summarizes current research status of soil plug effect and bearing capacity of steel pipe piles.The numerical simulation of wind farm test pile was carried out by using ABAQUS software.The simulated vertical bearing capacity agrees well with the field test results,indicating that the model parameters of ABAQUS simulation are reasonable.(2)Based on the selected model parameters,the vertical load characteristics of steel pipe piles with the same pile length,different diameters and wall thickness were numerically simulated under the same engineering geological conditions.The Q-S curve of the vertical loading of the steel pipe pile was obtained.The value of outside friction,inner friction and the ring capacity of the pile are calculated and their percentages in total capacity are computed to analyse the influence of pile diameter on bearing capacity of steel pipe pile.The results show that the total bearing capacity of the steel pipe pile is linearly changed with pile diameter,while the percentage of out shaft bearing capacity in the total bearing capacity decreases linearly with the increase of the pile diameter.The proportion of inner shaft bearing capacity keeps at a low level(less than 20%)when the diameter changes,while the annual base resistance increases at a fast rate with the diameter.(3)The soil plug effect of 6m diameter engineering steel pipe pile is carried out by theoretical method.The results show that the soil plug effect of the pile is small.The soil plug effect of the 6 meter engineering pile is calculated.The result shows that the engineering pile is not fully pluged.The vertical bearing capacity of different diameters steel pipe piles are calculated theoretically according to domestic and foreign norms.The results show that the percentage of shaft friction in the total bearing capacity calculated by the Code for Pile Foundation of Harbor Engineering(JTS 167-4-2012)keeps between 76%and 86%,while that calculated by the Technical Code for Building Pile Foundation(JGJ 94-2008)is the same when the pile end penetrates the depth of the holding layer more than 5 times the pile diameter.According to the numerical simulation and the calculation results,the soil plug effect coefficient of the base capacity in the formula in domestic norms is revised considering the pile diameter and the depth of the pile end penetrating the bearing layer.(4)The influence of different height of soil plug,different internal and outside friction coefficient and different pile diameter is analyzed by numerical simulation.The results show that the influence of the height of soil plugs and internal friction coefficient on the horizontal bearing capacity of the steel pipe pile is small,while that of the outer friction coefficient is great.When the aspect ratio is small,the steel pipe pile displays some characteristics of rigid pile.When a pile is subjected to a horizontal force at the top,the deformation of the pile body is very small while the displacement of pile top is increased because the pile rotates around a certain point. |
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