波浪作用下黄河三角洲海床失稳机制与评价方法

发布时间：2018-01-07 17:04

本文关键词：波浪作用下黄河三角洲海床失稳机制与评价方法　出处：《中国海洋大学》2015年博士论文　论文类型：学位论文

【摘要】：针对波浪作用下海床失稳这一科学技术问题,以具有风暴潮等特殊海洋动力环境与粉土沉积等特殊工程地质条件的黄河三角洲为背景区域,基于海洋土力学的理论框架和基本方法,根据问题的因果联系,依次对波浪作用下海床孔隙水压力响应、波浪作用下海床失稳方式与地质灾害评价、海床失稳对海上风电桩基设计的影响展开探讨,致力于理清与海床失稳相关的系列问题发生发展的物理力学机制,并构建相应的定量评价方法,服务于黄河三角洲地区的海底地质灾害评价和海上风电开发。主要工作和创新如下：(1)波浪作用下海床孔隙水压力机制与计算。基于水槽试验实测数据,揭示了岩土材料的等压屈服特性、剪胀性和波浪引起的附加应力路径的重要影响。分析指出应力-变形-孔隙水压力是贯穿以Biot理论为基础的弹性、孔隙水压力发展模式和弹塑性三类计算模型的主线,弹性模型只能计算瞬态孔隙水压力,孔隙水压力发展模式只能计算累积孔隙水压力,弹塑性模型可同时计算瞬态和累积孔隙水压力,是由其物理力学实质决定的。瞬态孔隙水压力机制对应于波高较小、周期较长的波浪与颗粒较粗、密度较大的土体组合,累积孔隙水压力机制对应于波高较大、周期较小的波浪与颗粒相对较细、密度相对较小的土体组合。波浪作用下黄河三角洲粉土海床的孔隙水压力响应计算结果显示,瞬态和累积机制同等重要,波浪越极端,海床超孔隙水压力越大,影响深度越深,超孔隙水压力并未达到或超过海床土的有效应力,但超孔隙水压力比在海床表层2m范围内最大,浅层海床发生失稳的可能性最大。(2)波浪作用下海床失稳方式与地质灾害评价。波浪作用下海床失稳有冲刷、液化、渗透失稳和剪切滑动等多种方式,各失稳方式可能单独或耦合发生,超孔隙水压力在海床失稳过程中发挥重要作用。其中,波浪作用下海床冲刷受到渗流力和床面高密度流的显著影响；波浪作用下海床的浅层滑动是一种低应力状态下的渐进破坏,可通过比较波浪引起的剪应力与海床土的临界状态强度进行判别；渗透失稳是波浪作用下粉土海床失稳的一种重要形式；海床液化与渗透失稳的判别式是等价的,二者发生与否取决于土体的级配和外力所引起的渗流压力梯度。波浪作用下海床滑动的渐进破坏特性和临界状态特性,以及计算所得2m的最大滑动深度,很好的解释了黄河三角洲海底滑坡及复活现象。波浪引起的渗流压力梯度在海床表层3m范围内最大,与塌陷凹坑深度相对应,海床渗透失稳及后继的冲刷效应是黄河三角洲塌陷凹坑的可能成因。波浪引起的最大冲刷深度在2-10m之间,波浪冲刷及单向流引起的净输运可导致粉砂流及冲沟地貌,海床浅层滑动及粉砂流均可能产生滑塌、陡坎地貌。海床失稳及再固结可引起海床密化,海床局部渗透失稳可引起海床粗化,海床局部密化粗化可形成扰动地层,大范围密化粗化可形成硬壳层。(3)海床失稳对海上风电桩基变形的影响。单桩基础是适合黄河三角洲海上风电场的桩基形式,风、浪、流等荷载引起的水平变形是海上风电单桩安全稳定的决定性因素。以10m水深处典型5 MW海上风电机尺寸和机构参数为例,黄河三角洲地区的特征荷载组合下,作用于风机叶轮和结构上的风荷载能引起较大的弯矩,作用于水下桩柱的波浪荷载能引起较大的水平力,潮流荷载影响非常小。考虑风、浪、流荷载的非均布效应,应用积分方法求取的作用于桩头之上的水平力和弯矩用于桩基设计更为精确合理。应用粉士p-y曲线法的计算结果显示,黄河三角洲地区饱和粉土海床在50年一遇极端工况下,直径6m的风电桩基插入海床深度不应小于18-20 m；若考虑波浪引起的海床冲刷效应,则应加大桩基插入深度10 m；若考虑波浪引起的超孔隙水压力对土抗力的折减效应,需额外增加3-5 m的插入深度以抵消其影响。
[Abstract]:According to the wave induced instability of the problems of science and technology, with special engineering geological conditions of storm surge and other special marine dynamic environment and silt deposition in the the Yellow River Delta region as the background, theoretical framework of marine soil mechanics and basic methods based on the problems according to the causation, turn on the seabed pore water pressure wave under the action of wave induced response, loss evaluation and geological hazards stability, seabed instability effect on sea wind power pile design is discussed, and is committed to sort out problems related to seabed lost steady development of physical mechanism, and construct the quantitative evaluation method of the evaluation of submarine geological disasters and marine development wind power services in the Yellow River Delta area. The main work and innovation are as follows: (1) wave induced pore water pressure mechanism and calculation. Flume experiments based on measured data, Jie The pressure of rock and soil materials yield characteristics, the additional important influence path of dilatancy and wave induced stress. Analysis shows that the deformation of pore water pressure is through to Biot based on the theory of elasticity, the main pore water pressure development model and elastic-plastic three calculation model, calculation of transient pore water pressure elastic model only, only development model of pore water pressure calculation of accumulative pore water pressure, elastoplastic model can also calculate the transient and accumulative pore water pressure, is determined by the physical and mechanical nature. The transient pore water pressure mechanism corresponding to Yu Bo high waves and particles smaller, longer period of coarse soil larger portfolio the density, pore pressure accumulation mechanism corresponding to Yu Bo high waves and particles larger, smaller cycles are relatively thin, relatively low density of the soil pore water. The combination of the the Yellow River delta silty seabed under waves The calculation results show that the transient pressure response, and accumulation mechanism are equally important, more extreme wave, the excess pore pressure is, the more deep influence depth, effective stress and pore water pressure did not reach or exceed the seabed soil, but the excess pore water pressure ratio on the seabed surface within the range of 2M maximum, the shallow seabed lose stability is possible. (2) under the action of wave seabed loss evaluation and geological hazards stability. Under the action of wave seabed instability has scour, liquefaction, seepage instability and shear slip in a variety of ways, the instability may occur alone or coupled, excess pore water pressure loss play an important role in the process of seabed stability the wave induced scour significantly affected by seepage force and bed surface high density flow; shallow sliding wave induced progressive failure is a low stress condition, can be caused by comparing the shear wave To determine the critical state of stress and strength of seabed soil; seepage instability is an important form of wave induced silty seabed instability; seabed liquefaction and seepage instability criterion are equivalent, the occurrence of the two depends on the soil gradation and the external force caused by the seepage pressure gradient of wave action. The progressive failure characteristics of seabed sliding and critical state characteristics, and calculated the maximum 2m sliding depth, a good explanation of the the Yellow River delta submarine landslide and resurrection phenomenon. The wave induced seepage pressure gradient in the seabed surface within the range of 3M, and the corresponding collapse pit depth, seabed instability and subsequent penetration scouring effects may cause collapse of the Yellow River Delta. The maximum depth of scour induced by wave between 2-10M wave erosion and the net transport one-way flow caused by transport can lead to silt flow and gully landform, shallow seabed Sliding and silt flow may produce collapse scarp topography. Seabed instability and reconsolidation can cause seabed densification, seabed local seepage instability can cause coarsening of seabed, seabed local dense coarsening can form a wide range of disturbance to the ground, dense coarsening can form a crust layer (3). Seabed instability effect on sea wind power. The deformation of pile foundation pile foundation is suitable for the Yellow River delta offshore pile foundation form, wind wind, wave, flow and deformation caused by load level is the decisive factor of offshore wind power. The safety and stability of the single pile parameter in 10m deep water typical 5 MW sea motor size and mechanism for example, the characteristics of load combinations in the Yellow River Delta, the wind load on the fan impeller and the structure can cause large bending moment acting on the wave load, underwater pile can cause large horizontal force, the trend of load effect is very small. Considering wind, wave, flow load Non uniform effect, using integral method to obtain the horizontal force acting on the pile head and bending moment of the pile foundation design for more accurate and reasonable calculation. Application of powder + p-y curve method. The results show that the the Yellow River delta saturated silty seabed in 50 years under extreme conditions, the diameter of 6m wind power pile into the seabed the depth should not be less than 18-20 m; if considering the effect of wave induced seabed erosion, should increase the pile depth of 10 m; if considering the wave induced excess pore water pressure on soil resistance reduction effect, the need for additional depth of insertion of 3-5 m to counteract its influence.

【学位授予单位】：中国海洋大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：P731.2;P75

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