循环荷载下海上风电单桩基础水平承载性能退化研究

发布时间：2018-03-03 03:34

本文选题：海上风电单桩　切入点：水平循环荷载　出处：《中国海洋大学》2015年硕士论文　论文类型：学位论文

【摘要】：海上风电潜能巨大,是国家未来能源战略核心。海上风电单桩基础长期承受风力、波浪、潮流等水平荷载,其水平承载力逐渐退化,累计变形增大,影响风机正常工作,使用寿命变短。如何正确的分析长期低频循环荷载下的海上风电单桩基础稳定性成为设计时面临的严峻挑战。所以,研究海上风电单桩基础长期水平循环荷载作用下的承载性能的退化规律尤为重要。本论文针对上述问题,开展了室内模型试验,结合p-y曲线理论分析研究了单桩承载性能退化及变形规律,具体研究工作如下：(1)通过室内水槽模拟黄河三角洲快速沉积环境,并进行黄河三角洲快速沉积粉土层中单桩水平承载特性模型试验,获得桩身弯矩、位移,以此得到快速沉积环境下饱和粉土中的p-y曲线模型,与API法p-y曲线相比发现浅层土极限土抗力要大,深层极限土抗力则介于黏土与砂土之间。讨论了不同成桩方式对p-y曲线的影响,贯入桩p-y曲线与预埋桩p-y曲线相比具有较小的初始刚度以及较大的极限土抗力;同时贯入桩对浅层土极限土抗力的影响更为显著。(2)通过室内模型试验探讨了不同荷载幅值不同荷载频率的水平循环加载下单桩基础的累计位移的变化规律。桩身位移的发展在前期循环加载时发展较快,在后期逐渐趋于稳定。循环幅值越大,桩顶位移越难以达到稳定；频率越低,桩顶位移越大。(3)由循环加载实验结果给出了土抗力随循环次数的半对数退化模型,并给出了退化指数与累计应变的关系曲线;土抗力的退化与累计塑性应变值有关,累计应变大于0.02是才会衰减；小幅值加载条件下初始地基反力模量几乎不衰减,保持稳定,但是随频率的降低,初始地基反力模量也逐渐变小。(4)循环荷载作用下初始地基反力模量及极限土抗力都会发生衰减,循环荷载对极限土抗力的退化的影响不是很大,因为循环荷载作用下桩周扰动区土体弱化但更大范围上土体依然能够提供足够的土抗力,而桩周土体的弱化引起的初始刚度衰减幅度很大,即产生较小的土抗力却发生较大的土体位移,需要引起足够重视。(5)基于本文推导的土抗力退化模型及其他学者的研究成果,将累计塑性应变与土体模量衰减及强度衰减建立联系,分析初始地基反力模量及土体极限土抗力的退化,给出循环p-y曲线,通过与实测结果对比分析,可以为黄河三角洲地区海上风电单桩基础设计提供相应参考。
[Abstract]:Offshore wind power has great potential and is the core of the country's future energy strategy. The horizontal bearing capacity of offshore wind power single pile foundation, which bears wind, wave, tidal current and other horizontal loads for a long time, gradually degenerates and accumulative deformation increases, which affects the normal work of the fan. How to correctly analyze the stability of offshore wind power single pile foundation under long-term low frequency cyclic load becomes a serious challenge in design. It is very important to study the degradation law of bearing capacity of offshore wind power single pile foundation under long-term horizontal cyclic load. In this paper, the indoor model test is carried out to solve the above problems. Combined with the p-y curve theory, the degradation and deformation of single pile bearing capacity are studied. The specific research work is as follows: 1) simulating the rapid deposition environment of the Yellow River Delta through indoor flume. The model tests on the horizontal bearing characteristics of single pile in the rapidly deposited silt layer of the Yellow River Delta are carried out, and the bending moment and displacement of the pile body are obtained, and the p-y curve model in the saturated silt under the rapid deposition environment is obtained. Compared with the p-y curve of API method, it is found that the ultimate soil resistance of shallow soil is greater than that of deep soil, and the resistance of deep soil is between clay and sand. The influence of different piling methods on p-y curve is discussed. Compared with the p-y curve of pre-buried pile, the p-y curve of penetration pile has smaller initial stiffness and larger ultimate soil resistance. At the same time, the influence of penetration pile on the ultimate soil resistance of shallow soil is more significant. (2) through laboratory model tests, the variation law of cumulative displacement of pile foundation under horizontal cyclic loading with different load amplitude and different load frequency is discussed. The development of displacement is rapid during the early cyclic loading. The larger the cyclic amplitude, the more difficult the pile top displacement is to achieve stability, and the lower the frequency, the greater the pile top displacement.) based on the experimental results of cyclic loading, the semi-logarithmic degradation model of soil resistance with cyclic times is given. The relation curve between the degradation index and the cumulative strain is given, the degradation of soil resistance is related to the cumulative plastic strain value, the cumulative strain is larger than 0.02, and the initial foundation reaction modulus almost does not decay and remains stable under the condition of small value loading. However, with the decrease of the frequency, the initial foundation reaction modulus also becomes smaller. 4) under the cyclic load, both the initial foundation reaction modulus and the ultimate soil resistance will decay, and the influence of the cyclic load on the ultimate soil resistance degradation is not very great. Because the soil is weakened in the disturbed area around the pile under cyclic load, but the soil can still provide sufficient soil resistance on a larger scale, and the initial stiffness attenuation caused by the weakening of the soil around the pile is very large. That is to say, smaller soil resistance but larger soil displacement need to be paid enough attention to.) based on the model of soil resistance degradation derived in this paper and the research results of other scholars, it is necessary to pay more attention to it. The cumulative plastic strain is related to the attenuation of soil modulus and strength, and the degradation of initial foundation's reaction modulus and soil ultimate soil resistance is analyzed. The cyclic p-y curve is given, and the results are compared with the measured results. It can provide reference for the design of single pile foundation of offshore wind power in the Yellow River Delta area.
【学位授予单位】：中国海洋大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU473.1

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