共查询到19条相似文献，搜索用时 390 毫秒
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《地震工程与工程振动》2016,(5)
对以往曾经发生显著液化的唐山地区和巴楚地区的土动力学性能进行对比研究,包括两个地区砂土相对密度与剪切波速关系、剪切波速与标准贯入击数关系等,以此深入了解两个重要地区土层的动力性能,为研究区域化液化判别方法提供基础。结果表明:现行抗震规范液化判别方法数据来源主要为唐山地区,明显不适用于新疆巴楚地区的液化判别;唐山地区与巴楚地区液化场地砂土取相同相对密度时,两个地区液化场地砂土剪切波速差别很小;但唐山地区与巴楚地区液化层砂土平均标准贯入击数和V_s~N_(63.5)关系曲线差异显著,表明以V_s~N_(63.5)关系区分不同地区砂土抗液化能力是可能的。 相似文献
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《国际地震动态》2017,(5)
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。 相似文献
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1976年唐山大地震引发了范围广、灾害重的液化震害。铁道部科学研究院等单位于1977、1978年对液化场地进行了单桥静力触探测试。但单桥静力触探在数据指标方面存在缺陷,与国际标准不接轨。中国地震局工程力学研究所与东南大学等单位于2007年对上述唐山地区部分测点再次进行了孔压静力触探（CPTU）测试。本文通过对比2次静力触探数据,利用Robertson土质分类图,进行新孔压静力触探数据土类分层检验,将土类检验结果与单桥静力触探测试时钻孔柱状图进行对比,发现大部分测点土层土类均能较好对应,现场测试力学指标沿深度变化趋势较相符,仅剔除了错误点T2、T3。对所有测点选定液化层,分别建立基于单桥静力触探测试比贯入阻力ps和基于孔压静力触探测试锥尖阻力qc的液化数据库。利用基于静力触探测试（CPT）的我国规范液化判别方法检验了2个数据库,发现对单桥静力触探测试的数据库液化判别效果好,而对孔压静力触探测试的数据库液化判别效果较差,说明经过30年的时间,土层液化可能已发生较大改变。因此,基于孔压静力触探测试的液化数据库可靠性较低,基于该数据库对液化判别方法进行改进意义较小。 相似文献
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《国际地震动态》2016,(3)
剪切波速是建筑工程场地上岩土体介质的一个重要参数。由于其数据结果直观、现场实验简单易行,剪切波速在工程中得到了广泛的应用。对任何一个物理量,测试结果均存在着一定程度的偏差。长期以来,无论专家学者还是工程技术人员,对剪切波速测试结果的可靠性均心存疑虑,希望能够早日了解掌握客观情况,以便制订相关标准进而改进技术。由于剪切波速测试不是一个孤立的量,对地震工程而言,现场剪切波速测试误差直接影响了地震动计算结果。这一结果涉及地震小区划和工程场地地震安全性评价工作。目前,还缺乏对剪切波速测试误差的实测结果,相关工作还无法开展。基于以上原因,本文围绕剪切波速测试误差专项实验展开,对现场剪切波速测试误差及其对震动的影响进行了研究,旨在为评价波速测试误差和确定其对地震动的影响提供依据。首先,本文介绍了剪切波速测试误差及其对地震动影响的研究现状,评述了相关工作的研究进展。目前,对剪切波速测试误差的研究还停留在对波速与深度关系进行拟合的层面上,还缺乏专门的波速测试误差专项实验。对于现场剪切波速测试误差对地震动的影响研究则主要集中在假设波速变化的定性分析上。本文的研究内容填补了国内外波速测试误差研究的空白,提出用专项实验结果来研究现场剪切波速测试误差并研究其影响。其次,本文设计了剪切波速测试误差专项实验并通过实验获得了波速测试误差的初步分布。通过对国内8个地区20个专项实验场地的测试,给出了涵盖4类工程场地的剪切波速测试误差测试结果,证明了波速测试误差客观存在。实验结果表明,噪音是影响波速测试误差的首要因素。再次,本文对剪切波速测试误差进行了分布拟合并进行了验证,论证了剪切波速测试误差的分布符合标准正态分布。通过将每一类场地的波速测试误差进行整合,本文将波速值的偏差变成了无量纲的测试误差百分比,这一结果就将具体场地的波速测试误差结果推广到所有一、二、三、四类场地。研究表明:波速测试误差的标准差约为15%,结合标准正态分布的性质,本文认为,约38%的测试结果精度较高,约68%的测试结果较为可靠。然后,本文利用专项实验结果采用一维等效线性化土层反应分析程序,研究了波速测试误差对加速度反应谱的影响。通过2 160组工况的计算结果,本文总结了剪切波速测试误差对反应谱的影响规律。研究表明:剪切波速测试误差对加速度反应谱有影响,影响程度主要由波速测试误差程度、场地类别和输入的地震波决定。剪切波速测试误差引起的加速度反应谱偏差程度与输入的地震动强度基本无关,只与波速测试误差的大小有关。当输入的地震波周期成分与场地卓越周期相近时,场地易发生共振,波速测试误差引起的反应谱变化明显。最后,本文结合波速测试误差的正态分布特性讨论了不同概率水平下,波速测试误差对地震动的影响程度。本文认为,用PGA和SI作为指标讨论影响程度是合理的。PGA值的变化准确描述了场地最大响应的变化,而SI则代表了能量的变化。研究表明:如果以PGA变化20%为标准,那么均值0.5倍波速测试误差范围内的波速测试误差对PGA基本没有影响,结合波速测试误差的分布进行分析,可以认为,38%的波速测试结果对PGA没有影响,其余62%的波速测试结果对PGA是否有影响,需要结合场地条件和地震波进行分析。均值0.5倍波速测试误差范围内的波速测试误差对造成的SI偏差基本都在5%以内。本文的结语部分对工作进行了总结,指出了现有工作的不足之处和未来工作的重点。 相似文献
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《华南地震》2015,(3)
收集了2008年以来北海市城区44个工程场地地震安全性评价中的土层剪切波速测试资料,采用幂函数模型分别对粘土、粗砂、砾砂、其它土类的土层剪切波速与埋深进行加权回归分析,得到不同土类的模型参数及拟合优度指标(判定系数R2和误差标准差σ),并对回归方程和回归系数进行了显著性检验;最后将土层剪切波速预测值与实测值进行对比,验证回归关系式的合理性和适用性。结果表明:北海市城区土层剪切波速与埋深呈现出较好的幂函数关系,拟合优度均在0.81以上;给出的土层剪切波速回归关系式能较好地预测出不同埋深土层剪切波速,特别是在土层中部和底部推测结果准确性更高,其推测结果可供北海市城区缺乏剪切波速测试资料的场地参考使用。 相似文献
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剪切波速是评估无黏性土力学性质的重要参数。为探究现行剪切波速液化判别方法不适用于砾性土场地的原因,利用自主研发的无黏性土剪切波速与相对密度联合测试系统,以汶川地震液化场地实测资料为参考,通过对福建标准砂和花岗岩圆砾按比例混合配制不同含砾量的砾性土试样在控制相对密度下的K0状态剪切波速试验,研究其含砾量对含砾无黏性土的剪切波速影响规律。试验结果表明:相对密度相同的砾性土剪切波速大于砂土,二者剪切波速比值与砾性土的含砾量成指数函数关系,两者比值最大为1.4;对于砾性土试样,在含砾量40%-60%间存在阀值,当含砾量小于该值,剪切波速随含砾量的增加明显增大,当含砾量大于该值,剪切波速的增长趋势放缓。试验研究指出了现行剪切波速判别方法不适用于砾性土场地的原因,揭示了含砾量与砾性土剪切波速的相互关系,提出了相同相对密度砾性土相对砂土的剪切波速修正公式,为建立新的判别方法提供了理论基础,也为岛礁珊瑚吹填土等宽级配无黏性新工程材料的性能研究拓展了技术手段。 相似文献
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采用Shake 2000程序,以Turkey Flat试验场地为模型,通过输入不同类型下多种强度的地震波,计算研究多工况下剪切波速测试标准差对地表加速度反应谱和峰值加速度的影响。结论为:(1)浅硬场地上剪切波速测试标准差对地震动的影响很大,影响程度与输入地震波的强度和频率以及场地剪切波速计算值有关;(2)如果将反应谱残差大于20%或加速度峰值差别大于20%定义为统计意义上的不可忽略,那么剪切波速测试标准差对计算结果的影响在大多数情况下均不可忽略;(3)当输入波的卓越周期与场地特征周期接近时,浅硬场地上剪切波速测试标准差引起的反应谱变化非常显著;(4)只有当输入波的卓越周期与场地特征周期相差较大且输入波强度偏小时,剪切波速测试标准差引起的反应谱变化才可略去;(5)当浅硬场地上剪切波速实测结果低于统计均值时,地震动计算结果的偏差一般明显大于剪切波速实测结果,高于统计均值时引起的偏差,且地震输入越强表现越明显。 相似文献
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Shear wave velocity (Vs) measurements from seismic piezocone penetration (SCPTU) soundings have been increasingly used for site characterization and liquefaction potential assessments. Several sites in Tangshan region, China liquefied during the Tangshan earthquake, Mw=7.8 in 1976 and these sites were characterized recently using the SCPTU device. Other sites in the same region where liquefaction was not observed are also included in the present field investigations. Three liquefaction assessment models-based on measured shear wave velocity, shear modulus and tip resistance parameters of SCPTU are evaluated in this paper for their accurate predictions of liquefaction or non-liquefaction at the test sites. Analyses showed that the shear wave velocity—liquefaction resistance model with normalized overburden vertical stress have yielded a success rate of 78% in predicting liquefied site cases and another similar approach with mean stress based normalization has a success rate of 67%. The correlation of qc/Go-CRR7.5 based on geological age has correctly assessed the liquefaction potential at most sites considered in this research. Overall, all three models based on shear wave velocity, shear modulus and cone tip resistance are proven valuable in the assessments of liquefaction at the present test sites in the Tangshan region. 相似文献
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A series of cone penetration tests (CPTs) were conducted in the vicinity of the New Madrid seismic zone in central USA for quantifying seismic hazards, obtaining geotechnical soil properties, and conducting studies at liquefaction sites related to the 1811–1812 and prehistoric New Madrid earthquakes. The seismic piezocone provides four independent measurements for delineating the stratigraphy, liquefaction potential, and site amplification parameters. At the same location, two independent assessments of soil liquefaction susceptibility can be made using both the normalized tip resistance (qc1N) and shear wave velocity (Vs1). In lieu of traditional deterministic approaches, the CPT data can be processed using probability curves to assess the level and likelihood of future liquefaction occurrence. 相似文献
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目前,主要依靠室内动力试验对黄土液化势进行评价。由于黄土特殊的结构性,室内试验对其饱和的过程较为复杂,且与实际场地饱和黄土差异明显,导致室内黄土液化试验结果并不能代表现场饱和黄土的抗液化强度。本文选取兰州市西固区寺儿沟村某饱和黄土场地进行钻孔测试,现场实施了标准贯入试验、静力触探试验以及剪切波速测试。应用Robertson的土类指数分类图对该场地不同含水率黄土的土类进行了界定,确定了饱和黄土属于类砂土,有液化势。应用NCEER推荐方法,计算了3组原位试验数据的饱和黄土循环抗力比（CRR）,通过与1976年唐山地震和1999年集集地震液化土CRR对比,得出了饱和黄土抗液化强度很低的结论。 相似文献
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Estimation of residual shear strength ratios of liquefied soil deposits from shear wave velocity 总被引：1，自引：1，他引：0
Pelinzener 《地震工程与工程振动(英文版)》2012,11(4):461-484
For sites susceptible to liquefaction induced lateral spreading during a probable earthquake, geotechnical engineers often need to know the undrained residual shear strength of the liquefied soil deposit to estimate lateral spreading displacements, and the forces acting on the piles from the liquefied soils in order to perform post liquefaction stability analyses. The most commonly used methods to estimate the undrained residual shear strength (Sur) of liquefied sand deposits are based on the correlations determined from liquefaction induced flow failures with SPT and CPT data. In this study, 44 lateral spread case histories are analyzed and a new relationship based on only lateral spread case histories is recommended, which estimates the residual shear strength ratio of the liquefiable soil layer from normalized shear wave velocity. The new proposed method is also utilized to estimate the residual lateral displacement of an example bridge problem in an area susceptible to lateral spreading in order to provide insight into how the proposed relationship can be used in geotechnical engineering practice. 相似文献
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Based on the liquefaction performance of sites with seismic activity, the normalized shear wave velocity, Vs1, has been proposed as a field parameter for liquefaction prediction. Because shear wave velocity, Vs, can be measured in the field with less effort and difficulty than other field tests, its use by practitioners is highly attractive. However, considering that its measurement is associated with small strain levels, of the order of 10−4–10−3%, Vs reflects the elastic stiffness of a granular material, hence, it is mainly affected by soil type, confining pressure and soil density, but it is insensitive to factors such as overconsolidation and pre-shaking, which have a strong influence on the liquefaction resistance. Therefore, without taking account of the important factors mentioned above, the correlation between shear wave velocity and liquefaction resistance is weak.In this paper, laboratory test results are presented in order to demonstrate the significant way in which OCR (overconsolidation ratio) affects both shear wave velocity and liquefaction resistance. While Vs is insensitive to OCR, the liquefaction resistance increases significantly with OCR. In addition, the experimental results also confirm that Vs correlates linearly with void ratio, regardless of the maximum and minimum void ratios, which means that Vs is unable to give information about the relative density. Therefore, if shear wave velocity is used to predict liquefaction potential, it is recommended that the limitations presented in this paper be taken into account. 相似文献
16.
《震灾防御技术》2022,17(4):741-750
1976年唐山大地震导致了范围广、灾害严重的液化震害。地震发生后,已有学者对液化场地进行了2次静力触探测试。本文首先给出基于2次测试数据的唐山大地震CPT液化数据库,利用中国规范方法和NCEER推荐方法对数据库进行液化判别,发现针对第1次测试数据的判别成功率较高,而针对第2次测试数据的判别成功率较低。经30年的时间,绝大多数测试点的液化层强度与埋深均发生了较大变化,第2次测试时土层液化可能性已发生了较大变化,其测试数据对液化判别方法的改进意义较小。利用第2次测试的摩阻比Rf将第1次测试数据ps分解为qc和fs,相比第2次测试数据,分解指标具有更高的可靠性。为此基于第1次测试分解数据构建唐山大地震CPT液化数据库,为液化判别方法改进提供数据支持。 相似文献
17.
Paolo Boncio Sara Amoroso Giovanna Vessia Marco Francescone Mauro Nardone Paola Monaco Daniela Famiani Deborah Di Naccio Alessia Mercuri Maria Rosaria Manuel Fabrizio Galadini Giuliano Milana 《Bulletin of Earthquake Engineering》2018,16(1):91-111
In this study, we analyse the susceptibility to liquefaction of the Pozzone site, which is located on the northern side of the Fucino lacustrine basin in central Italy. In 1915, this region was struck by a M 7.0 earthquake, which produced widespread coseismic surface effects that were interpreted to be liquefaction-related. However, the interpretation of these phenomena at the Pozzone site is not straightforward. Furthermore, the site is characterized by an abundance of fine-grained sediments, which are not typically found in liquefiable soils. Therefore, in this study, we perform a number of detailed stratigraphic and geotechnical investigations (including continuous-coring borehole, CPTu, SDMT, SPT, and geotechnical laboratory tests) to better interpret these 1915 phenomena and to evaluate the liquefaction potential of a lacustrine environment dominated by fine-grained sedimentation. The upper 18.5 m of the stratigraphic succession comprises fine-grained sediments, including four strata of coarser sediments formed by interbedded layers of sand, silty sand and sandy silt. These strata, which are interpreted to represent the frontal lobes of an alluvial fan system within a lacustrine succession, are highly susceptible to liquefaction. We also find evidence of paleo-liquefaction, dated between 12.1–10.8 and 9.43–9.13 kyrs ago, occurring at depths of 2.1–2.3 m. These data, along with the aforementioned geotechnical analyses, indicate that this site would indeed be liquefiable in a 1915-like earthquake. Although we found a broad agreement among CPTu, DMT and shear wave velocity “simplified procedures” in detecting the liquefaction potential of the Pozzone soil, our results suggest that the use and comparison of different in situ techniques are highly recommended for reliable estimates of the cyclic liquefaction resistance in lacustrine sites characterized by high content of fine-grained soils. In geologic environments similar to the one analysed in this work, where it is difficult to detect liquefiable layers, one can identify sites that are susceptible to liquefaction only by using detailed stratigraphic reconstructions, in situ characterization, and laboratory analyses. This has implications for basic (Level 1) seismic microzonation mapping, which typically relies on the use of empirical evaluations based on geologic maps and pre-existing sub-surface data (i.e., age and type of deposits, prevailing grain size, with particular attention paid to clean sands, and depth of the water table). 相似文献
18.
The use of the shear wave velocity data as a field index for evaluating the liquefaction potential of sands is receiving increased attention because both shear wave velocity and liquefaction resistance are similarly influenced by many of the same factors such as void ratio, state of stress, stress history and geologic age. In this paper, the potential of support vector machine (SVM) based classification approach has been used to assess the liquefaction potential from actual shear wave velocity data. In this approach, an approximate implementation of a structural risk minimization (SRM) induction principle is done, which aims at minimizing a bound on the generalization error of a model rather than minimizing only the mean square error over the data set. Here SVM has been used as a classification tool to predict liquefaction potential of a soil based on shear wave velocity. The dataset consists the information of soil characteristics such as effective vertical stress (σ′v0), soil type, shear wave velocity (Vs) and earthquake parameters such as peak horizontal acceleration (amax) and earthquake magnitude (M). Out of the available 186 datasets, 130 are considered for training and remaining 56 are used for testing the model. The study indicated that SVM can successfully model the complex relationship between seismic parameters, soil parameters and the liquefaction potential. In the model based on soil characteristics, the input parameters used are σ′v0, soil type, Vs, amax and M. In the other model based on shear wave velocity alone uses Vs, amax and M as input parameters. In this paper, it has been demonstrated that Vs alone can be used to predict the liquefaction potential of a soil using a support vector machine model. 相似文献
19.
Daniel B. Chu Jonathan P. Stewart Shannon Lee J. S. Tsai P. S. Lin B. L. Chu Raymond B. Seed S. C. Hsu M. S. Yu Mark C. H. Wang 《Soil Dynamics and Earthquake Engineering》2004,24(9-10):647
The 1999 Chi–Chi, Taiwan, earthquake provides case histories of ground failure and non-ground failure that are valuable to the ongoing development of liquefaction susceptibility, triggering and surface manifestation models because the data occupy sparsely populated parameter spaces (i.e. high cyclic stress ratio and high fines content with low to moderate soil plasticity). In this paper, we document results from several large site investigation programs conducted in Nantou, Wufeng and Yuanlin, Taiwan. The seismic performance of the investigated sites include non-ground failure building and free-field sites, building sites with partial foundation bearing failures, free-field lateral spread sites, and free-field level ground sites with sediment boils. Field and laboratory investigation protocols for the sites are described, including cone penetration testing (some with pore pressure and shear wave velocity measurements) and rotary wash borings with standard penetration testing (including energy measurements). Implications of the SPT energy measurements with respect to established guidelines for the estimation of SPT energy ratio (including short rod corrections) are presented. Finally, data for three example sites are shown that illustrate potential applications of the data set, and which also demonstrate a condition where existing liquefaction analysis procedures fail to predict the observed field performance. 相似文献