基于FDEM的大型海上风机嵌岩单桩基础水平承载特性研究

Research on the lateral capacity characteristics of rock-socketed single-pile foundation for large offshore wind turbines based on FDEM

目前对于海上风机大直径嵌岩单桩基础水平受荷性状的研究尚少,且传统数值计算难以考虑岩基海床破碎对基础承载性能的影响,因此其破坏机制尚不明确。针对海上风机大型嵌岩单桩基础水平承载特性精确数值模拟和分析中存在的难题,首先根据海上风场地质勘测数据,采用有限-离散元耦合程序(FDEM)研究岩基海床中风化花岗岩力学特性;然后通过改进FDEM程序中网格重划分与接触检测部分算法,实现桩-岩界面黏聚力单元控制嵌入的功能,基于自主开发的FDEM前处理程序GiD-Y2D,建立大型单桩-岩基海床相互作用的FDEM平面应变模型;最后对桩-岩接触界面破坏模式与嵌岩桩基水平承载力特性进行分析。研究结果表明:岩基海床破坏模式分为受拉破坏阶段与受压破坏阶段,受拉区破坏时单桩水平位移约为1.37×10^(-4)倍的桩径,局部失效后单位桩长土抗力下降约30%,承载力刚度下降为原来的2/5;受压区破坏时单桩水平位移约为2.17×10^(-3)倍的桩径,失效后基础达到极限承载力,桩周岩体脆性破坏,单位桩长土抗力迅速下降约62.7%。

At present,there are few studies on the horizontal load behavior of large-diameter rock-socketed single pile foundations for offshore wind turbines,and it is difficult to consider the impact of rock foundation breakage on the bearing performance of foundations in traditional numerical simulations,so the failure mechanism is still unclear.In order to solve the difficulties in accurate numerical simulation and analysis of horizontal bearing characteristics of large rock-socketed monopile foundations for offshore wind turbines.Firstly,according to the geological survey data of the offshore wind field,the finite-discrete element method(FDEM)was used to study the mechanical properties of the weathered granite in the rock seabed.Then we improved the algorithm of mesh remeshing and contact detection in the FDEM program,and realized the embedding of cohesion elements in the pile-rock interface.Based on the self-developed FDEM preprocessing program GiD-Y2D,we established the FDEM plane strain model of the pile-rock interaction of offshore wind turbines.Finally,we analyzed the failure mode of the pile-rock contact interface of the offshore wind turbine and the horizontal bearing characteristics of the rock-socketed pile foundation.The results show that the failure modes of rock seabed can be divided into tension failure stage and compression failure stage.When the tension zone is damaged,the horizontal displacement of the single pile is about 1.37×10^(-4)times the diameter of the pile.After local failure,the lateral capacity per unit length decreases by about 30%,and the lateral capacity stiffness decreases to 2/5 of the original.When the compression zone is damaged,the horizontal displacement of a single pile is about 2.17×10^(-3)times the diameter of the pile.After the failure,the foundation reaches the ultimate lateral capacity.Due to the brittle failure of the rock mass around the pile,the lateral capacity per unit length of the pile decreases rapidly by about 62.7%.