高粘粒含量砂性土液化可能性与动强度评价研究

发布时间：2018-03-10 04:10

本文选题：地震液化　切入点：含粘粒砂土　出处：《浙江大学》2017年硕士论文　论文类型：学位论文

【摘要】：地震液化会导致巨大的财产损失和人员伤亡,液化评价的相关研究具有重要的科学意义和工程价值。目前,基于纯净砂和含粉粒砂土的液化相关研究已经比较完善,而针对较高粘粒含量砂土液化行为的研究则比较匮乏,对于其液化规律和内在实质认识不足。人们早期认为仅纯净砂土会发生地震液化,而具有塑性的较高粘粒含量砂土 /粉土则不发生地震液化。近些年全球范围的多场重大地震中,都出现了细粒土的液化实例,这引起了相关学者对高粘粒含量砂性土液化问题的关注。大量的含粉粒土体液化研究和少量的含粘粒土体液化研究表明,含细粒土体的特性随着细粒含量的变化呈现出不同的特点。低细粒含量时土体表现为类似纯净砂土的动力特性;随细粒含量增加,土体逐渐表现出粘性土特性;而在接近“类砂土”到“类粘土”转换临界细粒含量(TFC)时,土体同时具备砂性土和粘性土的土体特性,这一细粒含量区间也被称为“过渡带”。本文主要针对高粘粒含量砂土,开展一系列室内试验并结合课题组已有研究成果分析粘粒对于土体液化特性的影响。希望通过大量的室内动三轴试验和合理的对照分析,深入理解粘粒对土体液化特性的影响规律,揭示含粘粒砂土地震液化机制,通过建立能够适用于不同粘粒含量的含粘粒砂土CRR-Vs1表征模型,为实际工程场地中含粘粒砂土的液化评价提供科学依据。主要的研究内容包括:1.提出利用超固结比OCR控制低塑性砂性土结构性的试验方法:“点对点”的液化判别方法是通过室内试验结果反应原位土体特性的典型方法,合理设计试验的关键在于采用有效的方法使得室内土体试样的结构性恢复至原位水平,并同时保证试样的孔隙比及应力状态与原位土体保持一致。已有研究提出了一种预振的方法仅能够有效地恢复纯净砂土试样的结构性,而本文所提出的超固结方法,则可以有效恢复较高粘粒含量且具备一定塑性土体试样的结构性。基于土体试样的应力路径、Hardin公式和线弹性理论推导,验证超固结方法的合理性并给出设计超固结比的计算方法。2.粘粒含量(CC)对砂性土刚度特征的影响规律:针对高粘粒含量(CC30、CC40)砂土开展测试剪切波速的分级固结试验,分析试验数据得到CC30、CC40含粘粒砂土的Hardin曲线拟合结果,与已有的低粘粒含量砂土(CCO、CC10、CC15、CC20) Hardin曲线整合分析,拟合Hardin公式中参数(A,n)与粘粒含量(CC)之间的关系。发现以CC20为界限,Hardin公式中参数(A,n)在较低和较高两段粘粒含量(CC)范围内差异较大且随CC呈现不同的变化趋势。考虑本文所用含粘粒砂土(萧山粘土福建细砂)的“类粘土”、“类砂土”转换临界粘粒含量(TFC)是20%左右,因而认为类砂和类粘土的刚度特征差异较大且受粘粒含量影响变化规律不同,应分开考虑。试验过程选择同时考虑砂颗粒和粘土颗粒对土骨架贡献的等效骨架孔隙比作为本次试验的对照标准。3.粘粒含量对砂性土动强度的影响规律:针对CC30含粘粒砂土开展系统的动三轴液化试验,补充特定密实度CC10和CC20的动强度试验,并结合已有的低粘粒含量砂土(CCO、CC10、CC20)动三轴液化试验结果,分析特定等效骨架孔隙比(e*)、不同CC含粘粒砂土的动强度曲线,总结粘粒含量对于土体试样动强度曲线的影响规律。发现不同密实状态(e*=1.0105,e*=0.7977,e*=0.6873)含粘粒砂土的动强度随粘粒含量变化规律不同,结合不同密实度砂土受动荷载作用下的体变特性,分三种情况总结粘粒含量对于含粘粒砂土动强度的影响规律。4.建立含粘粒砂土的动强度剪切波速表征模型:基于不同密实度试样动三轴液化试验结果建立CC30含粘粒砂土的CRR-Vs1表征模型。根据前文的分析结果,将CRR-Vs1表征模型中重要参数(kN, emin, n,)以粘粒含量(CC)替代后得到能够适用于不同粘粒含量含粘粒砂土液化评价的CRR-Vs1表征模型。基于这一表征模型和原位土体的相关信息(剪切波速、饱和密度以及粘粒含量)可直接得到原位土体的抗液化强度,用于指导实际工程中的场地液化评价问题。5.细粒土液化判别工程实例:某工程地震灾害评价专题中粘质粉土依据土性指标被判定为“类粘-类砂土”,即土体特性既具有粘土特性,同时也具备砂土的部分特性。已有的规范方法在针对该层土体进行液化判别的过程中得到了偏不安全的判别结果。本文采用三种液化详判的方法对该层粘质粉土进行液化评价:1)通过室内“点对点”液化判别试验确定了该层粘质粉土在实际设防烈度下的液化可能性;2)分别依据室内试验结果和前面提出的含粘粒砂土 CRR-Vs1表征模型建立该层粘质粉土的CRR-Vs1表征模型并对其进行液化分析,得到了与方法1 一致的判别结果;3)基于原位标准贯入试验测试结果对该层粘质粉土进行液化分析确定其在罕遇地震情况的液化可能。对照液化详判结果验证了CRR-Vs1表征模型在细粒土液化分析方面的适用性。
[Abstract]:Seismic liquefaction will lead to great loss of property and casualties, the related research of liquefaction evaluation has important scientific significance and engineering value. At present, the related research of pure sand liquefaction and powder sand has been more perfect based on the behavior of sand liquefaction high clay content is relatively scarce, for its lack of regularity and liquefaction the intrinsic essence understanding. People think that only happens early pure sand seismic liquefaction, and has a high content of clay sand / plastic silt is not the earthquake liquefaction. A number of major earthquakes in recent years in the world, there are examples of fine grained soil liquefaction, which caused the scholars attention to the high clay content of sand soil liquefaction problem. A large amount of silt liquefaction research and a small amount of clay soil liquefaction research shows that the characteristics of soil containing fine change with fine content is Show different characteristics. When the content of soil is low fine dynamic characteristics similar to pure sand; with fine content increased, the soil gradually showed the properties of clay; and when approaching the "sand" to "clay" conversion critical fine content (TFC), and soil soil characteristics of sandy soil and preparation clay, the zone of fine content is also known as the "transition zone". This article mainly aims at the sand high clay content, carry out a series of laboratory tests and based on the existing research results of clay soil liquefaction characteristics for dynamic analysis of three axis control. To test and reasonable through a large number of indoor, deep to understand the effect of clay on liquefaction characteristics of soil containing clay, reveal the sand liquefaction mechanism, the CRR-Vs1 model containing clay sand characterization can be applied to different clay content, for the actual project site To provide a scientific basis for evaluation of liquefaction of sand with clay. The main research contents include: 1. the overconsolidation ratio OCR control test method of low plastic sand soil structural: "liquefaction methods point" is the typical method through the laboratory test results of in situ soil characteristics, using effective methods to make the indoor soil sample structure restored to the in-situ experimental design is the key to a reasonable level, and at the same time to ensure void ratio and stress state of specimen and in situ soil is consistent. The research puts forward a method of pre vibration only can effectively restore the pure sand sample structure, over consolidation method proposed by this paper, you can the effective recovery of high clay content and have a certain plastic soil sample. The structural stress path of soil sample based on Hardin formula and linear elastic theory is verified The consolidation method is reasonable and the calculation method is proposed to design the overconsolidation ratio.2. clay content (CC) influence on sand soil stiffness characteristics for high clay content (CC30, CC40) classification of sand consolidation tests carried out to test the shear wave velocity analysis, the test data of CC30, Hardin curve fitting results of CC40 containing clay sand low clay content of sand, and the (CCO, CC10, CC15, CC20) Hardin curve analysis integration, parameter fitting formula Hardin (A, n) and clay content (CC). The relationship between the CC20 from the limits of parameter Hardin in the formula (A, n) in the low and high two the clay content (CC) in the range of differences and different trends of change with CC. This paper considers the clay containing sand (Xiaoshan Fujian clay fine sand) "clay", "sand" conversion critical clay content (TFC) is about 20%, so that the sand and clay of the first class Characteristics of the differences and changes of different clay content, should be considered separately. The test process selection considering equivalent skeleton pore sand particles and clay particles on the soil skeleton contribution ratio as control standard.3. clay content in the test of dynamic strength of sand soil was investigated. In three triaxial liquefaction test CC30 with the clay sand to carry out the system, the dynamic strength test of certain density CC10 and CC20, and combined with the low content of clay sand existing (CCO, CC10, CC20) three triaxial liquefaction test results, analysis of the specific equivalent skeleton void ratio (e*), different CC containing clay sand dynamic strength curve, summarize the content of clay the influence of soil sample dynamic strength curve. Different density (e*=1.0105, e*=0.7977, e*=0.6873) of the dynamic strength of clay containing sand changes with different clay content, combined with different density sands by The dynamic characteristics of variable loads, three kinds of dynamic strength of shear wave velocity characterization model summary of clay content for.4. effect of clay sand containing dynamic strength is set up with the clay sand samples with different densities: dynamic results of three liquefaction test to establish CRR-Vs1 representation model based on soil CC30 containing clay sand. According to the above analysis results the CRR-Vs1 representation model of important parameters (kN, Emin, n) with clay content (CC) can be obtained after alternative characterization of CRR-Vs1 model in different clay content evaluation of sand liquefaction clay. Information on this characterization model and in situ soil (based on shear wave velocity, saturation density and clay content) can be directly obtained in situ soil liquefaction strength, used to guide the evaluation of site liquefaction in actual engineering project.5. discriminant of fine grained soil liquefaction: a project of earthquake disaster assessment project price s. On the basis of silt soil index was determined as "viscous type sand", which has the characteristic of clay soil properties, but also have some characteristics of sand. The existing methods for the specification in the process of soil liquefaction are unsafe identification results. Liquefaction evaluation of the clay layer silt using three methods of liquefaction judgement mining in this paper: 1) through the indoor "point to point" liquefaction test to determine the liquefaction potential of the clayey silt layer in the fortification intensity; 2) CRR-Vs1 model establishment of the clayey silt clay sand layer containing CRR-Vs1 representation model respectively according to the indoor test results and proposed and liquefaction analysis on it, and got the consistent results of 1 methods; 3) in-situ standard penetration test results based on the layer of clay silt liquefaction analysis to determine the rare earthquake. The liquefaction possibility of the condition. The results of the comparison of the liquefaction test verify the applicability of the CRR-Vs1 characterization model in the analysis of the liquefaction of fine grained soil.

【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU435

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