Investigation On Lateral Bearing Capacity Of Offshore Wind Turbine Pile Foundation Under Cyclic Loading

As a new type of clean energy, offshore wind power gets more and more people’sfavour in the21st century.Yellow River delta, as China’s second largest oil base, alsohas rich offshore wind resources, so the stability of pile foundation in silty soil inYellow River delta region gets more and more attention.Because of the complexity of load on pile foundation, simulated with organicglass tube, single pile model tests under lateral static and unidirectional cyclic loads insaturated silty soil foundation were conducted, pile’s strain and displacements undertwo kinds of pile designs and loads were also measured through strain logger anddisplacement meter. In addition, bending moment of pile, pile position shift of pileand soil and soil resistance, etc. under two kinds of loads were measured throughmathematical calculation. By analyzing the following results were obtained:(1)Under lateral static load, for two different ways of pile design, deformation ofsoil around the pile and pile bending moment increased with the increase of load. Dueto pile soil’s pastic yield, lateral constraining force on pile decreased, position of themaximum bending moment moved down, keeping in the range of three to six timesthe pile diameter, from mud surface.However, driving pile’s maximum bendingmoment value is larger than embedded pile.(2)Under lateral static load, influences taken by ways of pile design on soilresistance were mainly to change original soil’s stress state and lower soil resistancezero position. This effect decreased with increasing depth, and therefore the correctionvalue for the Y50tended to increase with increasing depth.(3)Through two kinds of piles’s p-y curves in static load, it was found thatfor soil-pile composite stiffness near soil surface, driving pile was smaller thanembedded pile. Besides this phenomenon was weakened with increasing depth.(4)Due to its conservative calculation of limit soil resistance, API p-y model ofthe soft clay did not apply to silt, so the text Y50was relatively larger to the value from reference.(5)Under unidirectional cyclic load, for two ways of pile design, a linear growthrelationship between load amplitude and peak load maximum pile bending momentwas found. And the slope was associated with cycle value. Therefore, maximum pilebending moment under peak load was the amplitude and cycle-related function. Thelocation of pile maximum bending moment moved down with increasing amplitude,keeping4to5times the pile diameter away from soil surface. Cycle load amplitudewas positively correlated with maximum soil resistance near pile and measuring pointdisplacement. With increasing amplitude, top soil deformation increased, loadtransferred to deeper soil. Thus the soil resistance zero position also moved down.(6)Under unidirectional cyclic load, for two ways of pile, cycle value’s impact onmaximum bending moment, maximum soil resistance and measuring pointdisplacement was complex and changeable.(7)For two ways of pile design, cycle number was positively correlated withmaximum bending moment and soil displacement. And by fitting parameter values inthe function were recommended.Secondly, due to cyclic weakening effect, cycle number showed a negativecorrelation with maximum soil resistance. And through fitting relevant parametervalues were recommended.(8)Dynamic p-y curves’s peak trends showed that relationship beweenmaximum soil resistance and cycles depended on a critical depth. Above critical depthmaximum soil resistance was negatively correlated with cycles, and on the contraryunder critical depth.