吹沙型填海场地动力响应演化特征的模拟研究

发布时间：2018-05-19 00:16

本文选题：吹填砂 + 海积软土　；参考：《广西大学》2015年硕士论文

【摘要】：吹沙填海场地与自然沉积地块具有截然不同的成因属性及工程属性。原深厚的海积软土变成新陆域大面积的软弱下卧层；各土层欠固结且持续受外界因素扰动,“边成型、边固结、边承载”；海积软土直接覆盖在海底基岩之上,由基岩导入的地震波可直接进入,加之这类地块处于地震频发地区,是远场强震产生长周期震害的“高风险区”。故研究其动力特性对吹填地块陆后工程防震减灾具有指示防范作用。本文以北部湾吹填场地软土层的固结度和吹填砂层的密实度为切入点,以广西防城港企沙填海区的吹填砂及海积软土为研究对象。采用实验室模拟技术制备不同密实程度下的土样,并通过固结等常规力学实验获取吹填场地各土层的基本性能指标。利用ANSYS有限元软件,分析不同密实程度下,吹沙填海场地卓越周期的演化特征及对基底垂直入射水平剪切波的动力响应。并在给定吹填各土层密实程度的介质框架内,研究各土层厚度对其动力特性及动力响应的影响机理,为陆后工程建设提供依据。本文主要研究内容及成果如下：1、通过对不同密实程度下的吹填场地进行模态分析可知：吹填场地各阶固有频率是呈线性增长的,且增长曲率与密实程度呈指数正相关关系；高阶振型对场地动力作用影响剧烈,然其振型参与系数较小。且随着场地土层密实程度的增大其水平振动所占的比例逐渐增大,竖向振动则反之,当密实程度达到一定值,扭转振动所占的比例剧增且分值较大。2、施加水平地震加速度反应谱,经谱分析可知：随着场地土层刚度的增加,节点位移越来越显著尤其表现在中间软土层区域,并逐渐往基岩方向发展,而吹填砂层振动位移表现出逐步缓慢稳定的趋势；场地卓越频率逐渐往高频率成分方向发展,且随着土层密度的增大呈指数增长趋势。3、基底垂直入射水平剪切波,经地震时程分析可知：吹填场地对水平地震作用的放大效应随土层深度的变化十分显著,并在吹填砂层表面达到最大值,但并不是与土层深度呈正相关关系。对竖向地震动中的长周期成分具有明显的过滤作用,且随着密实程度的增大,过滤作用越显著,而对V/H谱比的影响反之。故对高层建筑进行抗震设计,应充分考虑土层密实程度对其竖向地震动的影响。4、对不同海积软土层厚度场地进行时程分析可知：地表峰值加速度放大效应与土层厚度呈线性负相关关系,这是由于较厚的海积软土层具有更大的隔振、滤波功能所致。反应谱曲线存在两个马鞍形的双峰,且随着土层厚度的增加主导频率由单峰逐渐向多峰演变,卓越周期成分的地震能量逐渐减小,场地卓越周期逐渐增大,对地震波的高频部分减震作用增强,竖向地震放大效应逐渐减小。5、对不同吹填砂层厚度场地进行时程分析可知：地震放大效应随着吹填砂层厚度的增加而减小,场地卓越周期逐渐往短周期方向发展；当吹砂层厚度增大到某一值后,再继续增加吹砂层厚度,地震响应放大倍数反而会增加,此时场地会出现多个卓越周期,不利于工程抗震设防。
[Abstract]:The sand blowing site and the natural sedimentary block have distinct genetic attributes and engineering properties. The original deep sea soft soil is transformed into a weak subsurface layer with large area of the new land area; the soil layers are under consolidation and are constantly disturbed by external factors, "edge forming, side consolidation, side bearing", and the soft soil is covered by the base rock on the bottom of the bottom of the sea floor. The seismic waves introduced are directly entered, and this kind of block is in the area of frequent earthquake occurrence, which is a "high risk zone" for the earthquake damage of the long field strong earthquake production. Therefore, the study of its dynamic characteristics has a directive and preventive effect on the earthquake prevention and disaster reduction of the land after land engineering of the dredger fill massif. As the breakthrough point, taking the dredger sand and the soft soil in the Fangchenggang reclamation area of Guangxi as the research object, the soil samples with different compaction degree are prepared by the laboratory simulation technology, and the basic performance indexes of each soil layer in the filling site are obtained by the consolidation and other conventional mechanics experiments. The ANSYS finite element software is used to analyze the different compaction degree. The evolution characteristics of the excellent period of sand reclamation and the dynamic response to the horizontal shear wave of the vertical incident on the base, and the mechanism of the influence of the thickness of the soil layer on the dynamic characteristics and dynamic response of each soil layer in the medium frame of the density of the soil layers of the given fill, are provided for the construction of the post land engineering. The main contents and results of this paper are as follows 1, through the modal analysis of the filling site under different compaction degrees, it is found that the natural frequencies of each order of the filling site are linearly increasing, and the growth curvature and the degree of compactness are exponentially positively correlated; the high order modes have a strong influence on the dynamic action of the site, but the coefficient of the vibration mode is smaller. The proportion of the horizontal vibration increases gradually, and the vertical vibration is the opposite. When the density reaches a certain value, the proportion of the torsional vibration increases sharply and the value is larger.2. The horizontal seismic acceleration response spectrum is applied. The spectrum analysis shows that with the increase of the soil layer stiffness, the node displacement is becoming more and more obvious in the middle soft soil. The layer area is progressively developing in the direction of the bedrock, and the vibration displacement of the fill sand layer shows a gradual and steady trend; the site excellent frequency gradually develops to the high frequency component, and increases exponentially with the increase of the soil density. The vertical incident shear wave in the basement can be seen by the seismic time history analysis. The amplification effect of the horizontal earthquake is very significant with the depth of the soil layer, and the maximum value is reached on the surface of the sand layer, but it is not positively correlated with the depth of the soil layer. It has obvious filtration effect on the long period components in the vertical ground motion, and the effect of filtration is more significant with the increase of the density, and the effect on the V/H spectrum ratio On the contrary, the seismic design of high rise buildings should take full account of the influence of the degree of soil compaction on its vertical ground motion,.4. The time history analysis of different sea floor thickness sites shows that the amplification effect of the surface peak acceleration and the thickness of the soil layer has a linear negative correlation, which is due to the thicker soft soil layer. There are two saddle shaped Shuangfeng in the response spectrum curve. With the increase of the thickness of the soil, the dominant frequency gradually evolves from single peak to multi peak. The earthquake energy of the excellent periodic component gradually decreases, the site excellent period gradually increases, the high frequency part of the seismic wave is enhanced and the vertical seismic amplification effect is gradually increased. With the reduction of.5, the time history analysis of the thickness of different sand bed thickness shows that the seismic amplification effect decreases with the increase of the thickness of the dredger fill sand layer, and the excellent period of the site gradually develops to the short period. There will be many remarkable periods in the site, which will be unfavorable for earthquake protection.
【学位授予单位】：广西大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU435

【参考文献】