黄土及一般含细粒土体液化判别方法研究

发布时间：2018-03-07 17:25

本文选题：固结比　切入点：弯曲元　出处：《国际地震动态》2017年05期 　论文类型：期刊论文

【摘要】：黄土液化的判别是工程界长期存疑的问题,现场黄土含水量较低,剪切波速较高,而实验室对其饱和,饱和过程对其土体结构影响还不确定,又由于固结比对土体刚度的影响仍然没有定论,这就导致室内黄土动三轴液化试验结果与现场力学指标一直无法建立联系。另一方面,黄土从颗粒组成来说,属于细粒土范畴,细粒土液化判别方法应可为黄土液化判别提供参照,但由于实验室配制试样相对密度、土体骨架强度及细颗粒赋存形式很难控制,导致细颗粒对土体液化势影响研究饱含争议与矛盾。本文紧密结合工程和科研工作需求,设计了一系列原状黄土在均等固结与偏压固结下的动三轴弯曲元试验,以及原状黄土在动三轴内饱和过程及饱和后的剪切波速试验,并且对一个饱和黄土场地进行了现场原位测试,回顾了现有标贯液化判别方法,对含细粒土体液化判别指标进行了系统研究,改进了细粒土液化初判准则以及含细粒砂性土液化判别式,最后对CPT液化判别方法的可靠性进行了数据检验。具体工作和成果包括:(1)采用动三轴弯曲元试验系统,对兰州市多个场地原状黄土进行了均等固结与偏压固结下剪切波速测试,证实了相关固结比对土体刚度影响的试验研究结果,进一步对比均等固结与偏压固结下试样轴向变形,分析了固结比对土体刚度影响的机理。(2)采用动三轴弯曲元试验系统,首先对原状黄土饱和过程进行了剪切波速跟踪测试,并进一步对比饱和黄土与原状黄土在同一逐级加压的过程中剪切波速与轴向变形测试值,最后通过与现场饱和黄土场地水位上下黄土层实测标贯击数、剪切波速对比,分析了原状黄土遇水及饱和后的软化特征。(3)通过对比唐山、海城地震两个液化地区粉土与砂土的剪切波速与标贯击数统计关系,发现对于剪切波速相同的饱和粉土和砂土,由于粉土的触变性,粉土标贯击数显著小于砂土。结合NCEER推荐的基于SPT与VS的液化判别方法,建立了3个细粒含量下临界剪切波速与临界标贯击数的相关关系,证实了含细粒土体的触变性。(4)回顾了目前国内外有关含细粒土液化研究现状,结合1975年海城地震,1976年唐山地震,1999年土耳其Kocaeli地震和台湾集集地震液化与非液化土数据分析,详细对比了现有液化判别式和初判条件的优劣,改进了细粒土液化初判准则以及含细粒砂性土标贯液化判别式。(5)回顾了NCEER推荐的Robertson的CPT液化判别方法和Olsen的CPT液化判别方法,通过对1999年台湾集集地震液化与非液化土数据分析,并将判别结果与SPT方法判别结果进行比较,指出了CPT液化判别方法还没有达到SPT方法的准确性,但是CPT的土分类图却是其最大的优势所在。
[Abstract]:The identification of loess liquefaction is a long-term problem in engineering circles. The loess has low water content and high shear wave velocity in the field, but the laboratory saturation and saturation process have uncertain influence on the soil structure. Because the effect of consolidation ratio on soil stiffness is still uncertain, the results of indoor loess dynamic triaxial liquefaction test can not be related to the field mechanical indexes. On the other hand, loess belongs to the category of fine grained soil in terms of particle composition. The method of liquefaction discrimination of fine grained soil should provide a reference for the identification of loess liquefaction. However, it is difficult to control the skeleton strength and the occurrence form of fine particles because of the relative density of samples prepared in laboratory. The research on the effect of fine particles on soil liquefaction potential is controversial and contradictory. In this paper, a series of dynamic triaxial bending element tests of undisturbed loess under the condition of equal consolidation and partial compression consolidation are designed in combination with engineering and scientific research requirements. The saturated process and shear wave velocity of undisturbed loess in dynamic triaxial are tested. In situ tests are carried out on a saturated loess site, and the existing standard liquefaction identification methods are reviewed. The discriminant index of liquefaction of fine-grained soil was studied systematically, and the criterion of liquefaction of fine-grained soil and the discriminant of liquefaction of fine-grained sandy soil were improved. Finally, the reliability of CPT liquefaction identification method is tested by data. The concrete work and results include: 1) using dynamic triaxial bending element test system, the shear wave velocities of undisturbed loess in many sites in Lanzhou City are tested under the condition of equal consolidation and partial compression consolidation. The experimental results of the influence of the relative consolidation ratio on the soil stiffness are confirmed. The axial deformation of the specimen under equalization consolidation and partial compression consolidation is further compared, and the mechanism of the consolidation ratio affecting the soil stiffness is analyzed. The dynamic triaxial bending element test system is used to test the effect of the consolidation ratio on the soil stiffness. At first, the shear wave velocity of the saturated loess is measured, and the shear wave velocity and the axial deformation of the saturated loess are compared with that of the original loess in the same step by step compression process. Finally, by comparing the measured penetration number and shear wave velocity with the measured penetration number and shear wave velocity of the upper and lower loess layers at the site water level, the softening characteristics of the undisturbed loess under water and after saturation are analyzed. The statistical relationship between shear wave velocity and standard penetration number of silt and sand in two liquefaction areas of Haicheng earthquake shows that for saturated silt and sand with the same shear wave velocity, due to the thixotropy of silt, The standard penetration number of silt is significantly lower than that of sandy soil. Based on the liquefaction discrimination method based on SPT and vs recommended by NCEER, the correlation between critical shear wave velocity and critical standard penetration number at three fine grain contents is established. It is confirmed that the thixotropy of fine-grained soil mass. (4) the present research status of liquefaction of fine-grained soil at home and abroad is reviewed. Combined with the Haicheng earthquake on 1975, Tangshan earthquake in 1976, the Kocaeli earthquake in Turkey on 1999 and the Jiji earthquake in Taiwan, the liquefaction and non-liquefaction soil data are analyzed. The advantages and disadvantages of the existing liquefaction discriminant and initial judgment conditions are compared in detail, and the criterion of initial liquefaction of fine-grained soil and the standard standard liquefaction discriminant of fine-grained sandy soil are improved. The CPT liquefaction discriminant of Robertson recommended by NCEER and the CPT liquefaction discriminant of Olsen are reviewed. By analyzing the data of liquefaction and non-liquefaction soil of Jiji earthquake in 1999, and comparing the discriminant result with that of SPT method, it is pointed out that CPT liquefaction discriminant method has not reached the accuracy of SPT method. But CPT's soil classification map is its biggest advantage.
【作者单位】：中国地震局工程力学研究所;
【分类号】：TU444

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