【作者】 陈晖；

【导师】 曹立华；

【作者基本信息】 中国海洋大学 ， 海洋地质， 2003， 硕士

【摘要】 为了得到埕岛海域浅水区构筑物地基及周边底床稳定性，本文通过高分辨率的回声测深、旁侧声纳及浅地层剖面等声学仪器勘查，并结合钻孔、现场和室内的实验分析，采用新的计算方法，对埕岛海域浅水区人工构筑物地基及周边底床稳定性进行了计算、分析和评价。得到了对构筑物安全稳定性有着直接影响的要素值，包括构筑物及周边冲刷量、构筑物地基沉降量及液化深度，并且讨论了在不同海洋环境参数下的底床响应。本文还着重考虑了构筑物对周边底床演化的影响和水下底坡上发育的不稳定灾害现象与构筑物的互动耦合关系。 分析认为，浪流的冲刷作用是研究区水深地形演化的主要动力，构筑物的存在，使埕岛海域浅水区人工构筑物周边水域实测年水深增加幅度约0.3m／a，地基附近水深增加速率0.25m／a，边坡坡度平均每年以5‰减缓，而计算得出的海洋水动力冲蚀速率在水下底坡为0.2m／a，在构筑物地基冲蚀速率达0.35m／a。这种差异除水动力冲蚀外，另一个重要的原因是浅地层土体块体运动使局部浅水区表层沉积物向深水洼地填充，减缓了深水洼地加深速率。这种不稳定块体运动由波浪循环荷载诱发，其结果使底床整体坡度减缓，水深加大，而且不稳定的块体运动具有小区域、多发性和溯源侵蚀的特点，将继续影响着海域以后的水深地形的发展演化，并不断改变着该区的流场与底床地层条件，对构筑物地基土的稳定性产生着动态的影响。 通过对底床在波浪下的响应分析，对于研究区底床上层较硬而第二层较软的情况，超静孔隙水压力幅值在层间交界处迅速衰减，在临近硬、软地层交界处前，水平有效应力增至最大，剪切应力在底床厚度大约2.7米左右达到峰值，然后减小，到硬、软层土交界位置，达到最小，因此这个界面就是最容易发生破坏的工程软弱面，现场勘查证明，即使在正常海况下，构筑物也会沿坡以此交界面为滑动面，缓慢向“盆”底滑动。在强暴风浪下，底床表层1.75米以上均有可能产生液化现象，而在构筑物前形成的完全驻波，甚至能够造成6.16米的液化深度，构筑物地基部分失去支持力，将直接导致构筑物的滑动，也就是说，在地基部分液化、软弱层的存在以及构筑物沿坡重力分力的共同影响下，构筑物将向“盆”底方向发生更大的滑动，甚至可能发生倒塌。造成灾难性后果。 通过对构筑物及周边不稳定因素的计算，本文给出了相应的措施建议。这篇论文揭示了构筑物地基土的工程稳定性及与周边海域互动祸合关系，研究了浅水区构筑物底床在波浪等水动力作用下的动力响应，丰富了构筑物周边水下底坡稳定性研究的内容，为海上工程设施的地基设计提供了良好的理论指导性建议，对保障海上安全生产、保证海洋设施的完整及使国家财产免受损失也有重要的现实意义。更多还原

【Abstract】 To get the stability of shallow structure foundation and adjacent seabed in Cheng Dao shallow sea area, we have made an investigation on high resolution echo depth side sonar and shallow strata section etc. and made use of experiment Analysis of core , in situ , indoor to compute , analyze and assess the stability on new computing method. We have got factor values which influence directly safety and stability, including structure and around wash load structure foundation sink value and liquefaction depth, and we discuss underlying bed response in different marine environment parameters. The paper do also consider the influence of structure to around underlying bed evolvement and couple relation of instability damage phenomenon on bottom and structure.Through analysis, we conclude that washing action of wave and flow is main power of evolvement of region of interest landform, structure lead to the fact that water area around shallow structure in Cheng Dao sea field has an increase about 0.3m/a through actual measurement, water depth increase rate around foundation is 0.25m/a, slope gradient of side slope averagely has a decrease of 5%o a year, however marine hydropower wash rate through compute is 0.2m/a on underwater bottom, the wash rate on structure foundation is 0.35m/a. Except hydropower wash, another important cause of the difference is that shallow stratum soil mass bulk movement make local shallow surface sediment fill deep water bottomland, so slow up the deep rate of deep water bottomland. This kind of instability bulk movement is induced by wave cyclic loading, as a result the slope of bottom bed decrease, water depth increase, and instability bulk movement has the character of subregion, regularity and head erosion, thus it will influence evolvement of region of interest landform, and change flow field and bottom stratum condition continually, so will lead to dynamic influence on structure foundation soil.Through analyzing bed’s response to wave, in the condition that super-stratum ismore hard and second-stratum is more soft in region of interest, super static interstitial hydraulic pressure amplitude die away rapidly between stratums, before in sight of boundary between hard and soft stratum, plane effective pressure increase to max. Shear stress reach peak value when bed thickness is approximately 2.7 meters, then it will decrease to the minimum on the place where the flexible soil has a common boundary with the rigidity, so the boundary is the most destroy plane on engineering. On the basis of reconnaissance in situ, In normal situation of sea, the structure slides to the basin along the boundary. In the storm, the part on surface layer of the underlying bed will produce the liquefaction, the absolute standing wave that form the front of the structure may bring 6.16 meter depth of the liquefaction, so the foundation of structure will lose part of the supporting force ,the structure will slide in this situation. That is to say, because of the foundation partly liquefaction, the exist of soft layer and the component force of gravity, the structure slide further to the basin and collapse, which leads to disastrous consequence.By calculating instability factor in research area, this paper gives some corresponding suggestion. This paper shows engineering instability around instrument foundation and coupling relation to the circumjacent seabed, and research the dynamic response between wave and seabed, and enriches the research content of instability of seabed around instrument foundation and give some appropriate suggestion to foundation planning of ocean engineering, also it prevents instrument , facility and property of state from losing and risking.更多还原