近海风机超大直径嵌岩单桩全寿命周期动刚度演化规律及机制研究

The geological conditions in Fujian, Guangdong and other provinces with rich wind resources are more complicated than those in Jiangsu, and piles for wind turbines are mostly rock-socketed. However, the large diameter and thin-walled steel rock-socketed piles are very scarce at present, and both the construction and design are very difficult. For the design, the static bearing capacity is easy to satisfy, and the dynamic safety during the whole lifetime of the wind turbine is more difficult to guarantee. Dynamic safety of a turbine is mostly controlled by the dynamic stiffness of the pile, which faces mainly two problems: 1. How to choose the parameters for the rock-socketed pile so that the wind turbines will neither be resonant nor too conservative; 2. Whether the dynamic stiffness change or not under the action of several million times of alternating loads, and what effect will be caused to the dynamic safety of the turbines. Based on an analytical method, the accurate distribution of 3D dynamic stress distribution of the rock-socketed pile and the initial dynamic stiffness are obtained firstly; then combined with elements cyclic loading tests for soil, rock and the grouted material, two kinds of model test with several million times of alternating loads, and the field test for analyzing the redistribution of dynamic stresses and dynamic stiffness evolution. Finally a convenient theoretical model with clear physic foundations will be given to provide a scientific basis for the safe and economic development of wind power in batholithic sea areas.

我国近海风资源极为丰富的福建、广东等省海域，地质条件较江苏海域更为复杂，风机桩基多须嵌岩，而目前对超大直径薄壁钢管嵌岩单桩的研究极为匮乏，施工及设计难度都极大。设计理论方面，嵌岩单桩静力承载力一般较容易满足，但风机整体全寿命周期动力安全问题较难保障。整体动力安全受嵌岩桩动刚度控制，主要面临两方面的问题：1.如何设计嵌岩单桩，才能使其初始动刚度在风机安全性和经济性之间达到平衡？2.嵌岩单桩在全寿命周期上千万次交变荷载作用下是否会发生动刚度弱化，从而影响风机动力安全？本项目拟立足于动力接触解析理论得出嵌岩单桩初始动刚度、桩周精确三维初始动应力分布，再结合土体、岩体、灌浆材料等单元体循环加载试验，两类不同比尺的室内1g模型试验及现场原型实测数据分析桩周动应力重分布规律、单桩动刚度演化规律及机制，最终归纳出物理概念清晰、计算方便的理论模型，为保障岩基海域风电安全、经济地开发提供科学依据。

我国近海风资源极为丰富的福建、广东等省部分海域，地质条件较江苏海域更为复杂，风机桩基多须嵌岩，而目前对超大直径薄壁钢管嵌岩单桩的研究极为匮乏，施工及设计难度都极大，且福建、广东等海域面临较高的地震风险。嵌岩单桩静力承载力一般较容易满足，但风机整体全寿命周期动力安全问题较难保障，主要面临3方面的问题：1.嵌岩单桩动刚度的关键控制参数及机理？2.嵌岩单桩在长期循环荷载作用下是否会发生动刚度弱化，从而影响风机动力安全？3.嵌岩单桩在地震作用下的动力安全特性及影响因素？本项目立足于动力接触解析理论得出单桩初始动刚度、桩周精确三维初始动应力分布，再结合数值分析、单元体试验、室内1g静力及动力循环加载模型试验分析单桩动刚度演化规律及机制，得到了不同嵌岩情况下的嵌岩单桩p-y曲线，且拟合了相关实用公式。研究发现：1.控制单桩动刚度的关键参数包括单桩长径比、单桩厚径比、桩-土-岩相对刚度比、嵌岩深度、岩石风化程度、动荷载幅值、动荷载频率、荷载循环次数等。2.土-岩界面处存在明显的应力集中现象，传统p-y曲线不能准确描述土-岩界面附近的桩身分布土/岩抗力，需要对土层及岩层采用分段p-y曲线模型进行模拟。3.在正常服役期长期循环动力荷载作用下，嵌岩单桩自振频率的变化较小，与风机自振频率监测结果相符；嵌岩单桩桩身累积位移、最大弯矩以及桩基刚度近似与动力荷载作用次数呈对数相关；最终提出了循环应力比相关的p-y曲线循环弱化因子，以及考虑循环次数的桩顶累积位移和桩身内力变化分析方法。4.研究发现在较高烈度地震荷载作用下，嵌岩桩底部附近存在显著的岩体损伤现象，会明显降低单桩动刚度，桩周上部土体发挥的动阻尼也随之减小，且震后桩顶存在较大残余位移及转角，会影响风机继续安全服役，在地震高烈度区进行嵌岩单桩设计时需予以考虑。项目研究成果可为保障岩基海域风电安全、经济地开发提供科学依据。