循环荷载作用下海积软土动力特性及细观结构试验研究
发布时间：2018-12-11 21:27
【摘要】：通过吹沙填海方式形成的场地,往往下伏着厚层海相淤泥质软土,加之沿海地区是地震频发的地带,软土的不良工程特性对地震作用有很大的影响。因此本文从工程防震减灾的角度,通过动三轴试验研究北海海积软土在三种不同因素影响下的动力特性,并对循环荷载作用前后的土样进行压汞试验和扫描电镜试验,定性、定量研究土体微细观结构的变化规律及三种要素对细观结构的影响,建立细观结构特征参数与宏观性质参数之间的联系,从细观角度解释土体位移、变形的力学行为。本文的主要研究成果如下:(1)北海海积软土为含砂粒的黏性土,主要矿物成分为石英和高岭土。人工制备样在上覆荷载的作用下,竖向沉降变形量最大达44%,沉降变形速率随着荷载等级的增加而逐渐放缓,最终趋于稳定。制备土样具有孔隙比大,饱和度高的特点。(2)动三轴试验中,随着动荷载幅值的增大,北海海积软土的动变形从弹性稳定状态到塑性扩张状态演化,且不同要素对土体动力特性有不同程度的影响。固结比的增大会降低海积软土的强度和刚度,固结比对土样变形的影响相对较小。固结围压的增大能明显提高土体的抗变形能力,会减小能量在土体中的传递消耗。振动频率为0.05Hz～1Hz时,土样变形曲线呈双曲线稳定型;当频率为2Hz时,变形曲线则呈硬化型;振动频率越低越有利于动变形的开展,频率的降低会减弱土体的强度和刚度。(3)压汞试验中根据海积软土的孔隙特征,将孔径划分为4个等级,原状样孔径呈单峰分布,中孔隙占有绝对优势。对比发现,循环荷载作用后土样总孔隙体积有所增加,但仍以中孔隙含量为主,各组孔径间的分布均有调整,中、小孔隙含量减小,大孔隙含量有所增加。固结比越大,大孔隙含量越小,总孔隙体积越小;固结围压的增加能减少土体孔隙体积;在各因素耦合作用下,振动频率对孔隙分布的影响较复杂。(4)对SEM图像进行定性分析发现,北海海积软土是面-面接触为主、少量面-边接触的黏胶基质片架-镶嵌结构,基本单元体主要是由扁平颗粒片片相叠而成的“黏土畴”叠聚体,叠聚体在空间上犬牙交错,形成架空-镶嵌式孔隙,孔隙发育明显,多呈条带状裂隙,形状极不规则且连通性差。在较大上覆荷载的作用下,土体结构单元呈现出一定的定向排列。(5)利用IPP软件从SEM二值化图像提取各单元体细观结构参数,分析了三种要素影响下的细观结构变化规律。结合北海海积软土动力特性,研究循环荷载作用前后土体细观结构演化规律,总结出细观结构演变的过程:结构微调-结构应力集中-结构整体失稳,对应着宏观变形的三个阶段:弹性变形-应力屈服-塑性变形。建立了孔隙结构特征参数与宏观特性参数之间的联系,从细观角度分析各因素对土体动力特性的影响机理。
[Abstract]:The site formed by sand blowing and reclamation is usually covered with thick layer of marine silt soft soil, and the coastal area is an area where earthquakes occur frequently. The poor engineering characteristics of soft soil have a great influence on earthquake action. Therefore, from the point of view of engineering earthquake prevention and disaster reduction, the dynamic characteristics of Beihai marine soft soil under the influence of three different factors are studied by dynamic triaxial test, and the mercury injection test and scanning electron microscope test are carried out on the soil samples before and after cyclic loading. The variation law of soil micro-structure and the influence of three elements on the micro-structure are studied quantitatively. The relationship between the characteristic parameters of meso-structure and the macro-property parameters is established, and the mechanical behavior of soil displacement and deformation is explained from the point of view of meso. The main results of this paper are as follows: (1) Beihai marine soft soil is sandy clay, and the main mineral components are quartz and kaolin. Under the action of overburden load, the maximum vertical settlement deformation is 44%, and the settlement deformation rate slows down gradually with the increase of load grade, and finally tends to be stable. The prepared soil samples have the characteristics of high porosity and high saturation. (2) in dynamic triaxial tests, with the increase of dynamic load amplitude, the dynamic deformation of Beihai marine soft soil evolves from elastic stable state to plastic expansion state. And different factors have different influence on soil dynamic characteristics. The strength and stiffness of marine soft soil will be decreased with the increase of consolidation ratio, and the effect of consolidation ratio on soil deformation is relatively small. The increase of consolidation confining pressure can obviously improve the deformation resistance of soil and reduce the energy transfer consumption in soil. When the vibration frequency is 0.05Hz~1Hz, the deformation curve of soil sample is hyperbolic and stable, and when the frequency is 2Hz, the deformation curve is hardening. The lower the vibration frequency is, the more favorable the dynamic deformation is, and the decrease of frequency will weaken the strength and stiffness of soil. (3) according to the pore characteristics of marine soft soil, the pore size is divided into four grades, and the pore size of the undisturbed sample is distributed as a single peak. The mesopore has the absolute advantage. It is found that the total pore volume of soil samples increases after cyclic loading, but the main pore content is medium pore content, the distribution of pore size in each group is adjusted, the small pore content decreases and the macropore content increases. The larger the consolidation ratio is, the smaller the macroporous content is, the smaller the total pore volume is, and the higher the consolidation confining pressure is, the less the pore volume of soil is. The effect of vibration frequency on pore distribution is complex under the coupling of various factors. (4) qualitative analysis of SEM images shows that the soft clay in Beihai Sea is a scaffold mosaic structure with surface to surface contact and a small amount of surface to edge contact. The basic unit is mainly composed of "clay domain" stacked by flat granular fragments, which interlaced in space to form aerial and inlaid pores, with obvious pore development, and most of them show banded fractures. Extremely irregular shape and poor connectivity. Under the action of large overburden load, the soil structure element presents a certain directional arrangement. (5) the meso-structure parameters of each unit are extracted from the SEM binary image by using IPP software, and the variation law of the meso-structure under the influence of three elements is analyzed. Combined with the dynamic characteristics of Beihai marine soft soil, the evolution law of soil meso-structure before and after cyclic loading is studied, and the evolution process of meso-structure is summarized: structure fine-tuning, structural stress concentration and overall structural instability. It corresponds to three stages of macroscopic deformation: elastic deformation, stress yield and plastic deformation. The relationship between pore structure characteristic parameter and macroscopic characteristic parameter is established, and the influence mechanism of each factor on soil dynamic characteristic is analyzed from the viewpoint of meso.
【学位授予单位】：广西大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU447
本文编号：2373249
[Abstract]:The site formed by sand blowing and reclamation is usually covered with thick layer of marine silt soft soil, and the coastal area is an area where earthquakes occur frequently. The poor engineering characteristics of soft soil have a great influence on earthquake action. Therefore, from the point of view of engineering earthquake prevention and disaster reduction, the dynamic characteristics of Beihai marine soft soil under the influence of three different factors are studied by dynamic triaxial test, and the mercury injection test and scanning electron microscope test are carried out on the soil samples before and after cyclic loading. The variation law of soil micro-structure and the influence of three elements on the micro-structure are studied quantitatively. The relationship between the characteristic parameters of meso-structure and the macro-property parameters is established, and the mechanical behavior of soil displacement and deformation is explained from the point of view of meso. The main results of this paper are as follows: (1) Beihai marine soft soil is sandy clay, and the main mineral components are quartz and kaolin. Under the action of overburden load, the maximum vertical settlement deformation is 44%, and the settlement deformation rate slows down gradually with the increase of load grade, and finally tends to be stable. The prepared soil samples have the characteristics of high porosity and high saturation. (2) in dynamic triaxial tests, with the increase of dynamic load amplitude, the dynamic deformation of Beihai marine soft soil evolves from elastic stable state to plastic expansion state. And different factors have different influence on soil dynamic characteristics. The strength and stiffness of marine soft soil will be decreased with the increase of consolidation ratio, and the effect of consolidation ratio on soil deformation is relatively small. The increase of consolidation confining pressure can obviously improve the deformation resistance of soil and reduce the energy transfer consumption in soil. When the vibration frequency is 0.05Hz~1Hz, the deformation curve of soil sample is hyperbolic and stable, and when the frequency is 2Hz, the deformation curve is hardening. The lower the vibration frequency is, the more favorable the dynamic deformation is, and the decrease of frequency will weaken the strength and stiffness of soil. (3) according to the pore characteristics of marine soft soil, the pore size is divided into four grades, and the pore size of the undisturbed sample is distributed as a single peak. The mesopore has the absolute advantage. It is found that the total pore volume of soil samples increases after cyclic loading, but the main pore content is medium pore content, the distribution of pore size in each group is adjusted, the small pore content decreases and the macropore content increases. The larger the consolidation ratio is, the smaller the macroporous content is, the smaller the total pore volume is, and the higher the consolidation confining pressure is, the less the pore volume of soil is. The effect of vibration frequency on pore distribution is complex under the coupling of various factors. (4) qualitative analysis of SEM images shows that the soft clay in Beihai Sea is a scaffold mosaic structure with surface to surface contact and a small amount of surface to edge contact. The basic unit is mainly composed of "clay domain" stacked by flat granular fragments, which interlaced in space to form aerial and inlaid pores, with obvious pore development, and most of them show banded fractures. Extremely irregular shape and poor connectivity. Under the action of large overburden load, the soil structure element presents a certain directional arrangement. (5) the meso-structure parameters of each unit are extracted from the SEM binary image by using IPP software, and the variation law of the meso-structure under the influence of three elements is analyzed. Combined with the dynamic characteristics of Beihai marine soft soil, the evolution law of soil meso-structure before and after cyclic loading is studied, and the evolution process of meso-structure is summarized: structure fine-tuning, structural stress concentration and overall structural instability. It corresponds to three stages of macroscopic deformation: elastic deformation, stress yield and plastic deformation. The relationship between pore structure characteristic parameter and macroscopic characteristic parameter is established, and the influence mechanism of each factor on soil dynamic characteristic is analyzed from the viewpoint of meso.
【学位授予单位】：广西大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU447
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