饱和砂土地震液化判别的分形插值模型

借鉴分形基本理论,提出了基于分形插值模型的饱和砂土地震液化判别方法.该方法首先选取影响饱和砂土地震液化判别的7个主要因素,根据分类标准,采用在每级标准中随机内插的方法,得到40个标准样本,用于构建饱和砂土地震液化判别的分形插值模型;其次根据最大似然分类原则确定每个饱和砂土地震液化判别指标的评价分维数;然后利用加权求和法计算样本的综合评价值,并根据样本综合评价值与经验等级之间的关系建立分形插值评价模型;最后,进行了实例分析结果表明:该模型的评价结果合理、客观,计算得到的每个样本具体得分值,即使对属于同一级的样本也可以给出其地震液化程度的顺序,为饱和砂土地震液化评价工作提供了一种新的研究方法与思路.     

复杂场地条件下砂土液化的判别问题

从简单场地条件下砂土液化的判别入手,系统介绍一般场地液化判别的基本步骤,重点分析在复杂工程场地条件下,如何全面考虑各种因素以合理选取地震液化判据。文中结合某大桥地基土液化判别实例,多方位探讨判别特殊重大工程地基土液化的有效方法,讨论了液化深度问题,与此同时,尚考虑到液化和滑塌等地质灾害的相关效应     

基于灰色理论的场地卓越周期的计算

本文以灰色理论为基础，提出了考虑砂土液化影响，对场地类别进行灰色评判的方法，得出了计算场地与标准场地的关联度向量，由此最终导出了卓越周期的计算公式。     

汕尾市区砂土液化分析

采用标准贯人试验法对抽取的汕尾市区34个野外钻孔资料进行液化分析,计算液化指数,判断液化等级,进而划分液化小区。结果表明,汕尾市区滨海堆积平原普遍存在砂土液化地震地质灾害,液化等级轻微、中等至严重均有分布,以中等液化为主。根据建筑物类别和工程建设场地的实际情况提出抗液化措施的建议。     

液化判别的可靠性研究

本文根据收集到的30次地震800余例砂土和粉土液化调查资料,采用优化方法建立和改进了砂土和粉土的液化判别式,其中包括应力比比值法、能量法、规范法和简化应力比比值法的液化判别式。文中首次提出液化判别可信度的概念,指出可信度与回判成功率的区别,说明可信度能更恰当地度量液化判别结果的可靠性。文中应用信息熵理论,提出综合评价液化判别式好坏程度的定量指标。应用上述方法研究优化后的液化判别式可靠性发现,它们对砂土液化判别的适用性是好的,对粉土液化判别的适用性是理想的。但应指出,当以烈度表示地震作用强度时,规范法的适用性是好的,并对10—15m深的砂土或粉土的液化判别也是适用的;当以加速度表示地震作用强度时,用规范法判别液化则遇到了困难。本文引进模糊烈度概念,修改了规范法。修改后的规范法能强好地适用于已知地面加速度情况下的液化判别。 一个场址所受到的地震作用强度可用烈度、地面加速度、震级和震中距等指标表示。本文给出的几种液化判别方法分别适用于上述不同情况。     

某长江大桥深度超过15米的砂土层液化势的综合评价

不同抗震设计规范的砂土液化判别方法或国内外其他有代表性的液化判别方法所采用的地震动参数和土性指标及其埋藏条件是不同的,因而采用这些方法对同一工程场地进行液化势预测时其评价结果通常有一些差异,甚至会得到相反的结论。为了给重大工程建设提供较为合理、可信的地基液化势预测结果,采用多种液化判别方法进行场地液化势的综合评价是比较客观的,也是必要的。本文结合某长江大桥桥基工程,采用建筑抗震设计规范的砂土液化判别方法、国内外有代表性的液化判别方法、有限元数值分析法等多种方法逐一对该工程场地砂性土层进行液化判别,并结合室内动三轴液化试验结果,对主桥墩不考虑冲刷条件和考虑一般冲刷深度5m条件时的砂性土层进行了液化势的综合评价,并将各土层的液化势分为液化、可能液化和不液化3个等级,得到了较为合理可靠的判别结果。     

国家规范中液化判别特征深度的适用性研究

我国抗震规范砂土液化初判条件中,若砂层上覆土层深度超过特征深度即判为不液化或不考虑液化影响,利用近期地震液化调查数据对其适用性进行了检验。采用1995年日本阪神地震和1999年台湾集集地震的液化调查资料,发现我国规范液化判别特征深度取值会产生不可忽视的误判,而造成偏于危险的结果;采用2011年新西兰Ms6.3级地震液化调查资料,初步估计按我国规范液化判别特征深度取值会将65%的液化场地判为非液化场地,严重偏于危险。因此我国规范液化初判条件液化特征深度取值已不适用,需要研究改进。     

河北省地质钻孔资料分析

地质钻孔资料是工程地质、矿产勘察等报告中广泛使用的资料,具有重要的二次开发和使用价值,对于工程项目的启动如:规划、设计、施工等具有重要意义。搜集河北省现有地质钻孔资料,给出该省钻孔分布图、场地类别分布图、各市等厚线图;以钻孔资料中剪切波速作为液化判别指标,判断场地液化情况;以邯郸地区钻孔资料为例,进行三维地层划分,与磁县断裂结合分析,发现断裂在地下的分布状态直观可见,从而为断裂分析提供一种直观手段。     

泉州市规划区场地抗震性能与土地适宜性分区研究

在泉州市土地适宜性分区规划的编制过程中，建立了比较详细的钻孔资料数据库，给出了泉州规划区内不同土类的剪切波速按埋置深度进行修正的经验公式，并用这些经验公式计算了无实测波速资料的钻孔的等效剪切波速。文中按等效剪切波速和覆盖层厚度进行了场地类别的划分；采用震后残余应变和软化模量的思想和分层总和方法，综合考虑了软土厚度、埋深、地下水位对软土震陷量的影响，使软土震陷量计算结果更为合理。在充分考虑规划区内地形地貌、工程地质条件、场地类别、砂土液化、软土震陷、砂层及软弱土层的厚度分布、滑坡崩塌等对场地抗震性能影响的基础上，给出了更适合规划区的场地抗震性能评价标准，绘制了泉州场地抗震性能与土地适宜性分区图。     

液化规范判别与实际震害现象的差异对比——以唐山地震震害为例

砂土液化判别是地震地质灾害判定和预测的一项重要工作,判别方法以规范为主,但在实际工作中发现规范的判别结果与实际情况存在差异。本文在查阅大量唐山地震震害资料的基础上,选择3个典型工程场地,根据实际钻孔现场标贯原位测试数据,采用《建筑抗震设计规范》中的方法进行液化判别,发现规范判别结果与实际震害现象之间存在着一些差异。分析认为,抗震设防烈度与实际地震动不同、地下水位变化、上覆非液化土层的厚度、局部场地效应、地震动持时以及实验造成的人为误差等,均是造成差异的原因。分析结果也表明,规范中的判别方法具有较普遍的适用性和较强的实用性,但由于基础数据的局限性及判别公式本身存在的定性异常,其判别结果的合理性还有待于进一步研究论证,这也是造成判别结果与实际震害现象存在差异的原因之一。本文的研究结果对地震液化的机理认识、判别方法的完善,均具有一定的意义。     

GIS-based soil liquefaction susceptibility map of Mumbai city for earthquake events

The problem of liquefaction of soil during seismic event is one of the important topics in the field of Geotechnical Earthquake Engineering. Liquefaction of soil is generally occurs in loose cohesionless saturated soil when pore water pressure increases suddenly due to induced ground motion and shear strength of soil decreases to zero and leading the structure situated above to undergo a large settlement, or failure. The failures took place due to liquefaction induced soil movement spread over few square km area continuously. Hence this is a problem where spatial variation involves and to represent this spatial variation Geographic Information System (GIS) is very useful in decision making about the area subjected to liquefaction. In this paper, GIS software GRAM++ is used to prepare soil liquefaction susceptibility map for entire Mumbai city in India by marking three zones viz. critically liquefiable soil, moderately liquefiable soil and non liquefiable soil. Extensive field borehole test data for groundwater depth, standard penetration test (SPT) blow counts, dry density, wet density and specific gravity, etc. have been collected from different parts of Mumbai. Simplified procedure of Youd et al. (2001) is used for calculation of factor of safety against soil liquefaction potential. Mumbai city and suburban area are formed by reclaiming lands around seven islands since 1865 till current date and still it is progressing in the area such as Navi Mumbai and beyond Borivali to Mira road suburban area. The factors of safety against soil liquefaction were determined for earthquake moment magnitude ranging from M_w = 5.0 to 7.5. It is found that the areas like Borivali, Malad, Dahisar, Bhandup may prone to liquefaction for earthquake moment magnitude ranging from M_w = 5.0 to 7.5. The liquefaction susceptibility maps were created by using GRAM++ by showing the areas where the factor of safety against the soil liquefaction is less than one. Proposed liquefaction susceptibility map of Mumbai city can be used by researchers for earthquake hazard analysis, for the preventive measures in disaster management, for urban planning and further development of Mumbai city and suburban area.     

基于GIS的2013年吉林前郭M 5.8震群砂土液化灾害的研究

应用GIS技术,以Arcgis为操作平台,对2013年松原市前郭尔罗斯蒙古族自治县发生M5.8震群后砂土液化地震灾害进行综合分析研究,并建立了此次地震事件砂土液化灾害的数据资料库。利用Arcgis中的ArcCatalog对图形信息、数据属性信息等进行综合管理,方便地震行业相关数据的输入、存储、查询、管理和分析。运用Arcgis中的Arcmap对数据资料进行叠加和空间分析,使此次地震事件中的砂土液化灾害以直观的地图形式展示出来,方便进行更深入的地震灾害研究,也便于决策部门更明确此次地震砂土液化灾害发生的地理位置等情况,为今后的地震灾害研究提供数据基础和可参考的空间分析方法。     

利用qc,D50评价砂土地震液化势研究

本文根据国内外地震液化调查资料，建立了利用双桥静力触探锥头阻力ｑｃ和平均粒径Ｄ５０判别地震液化势的半经验性方法。这种方法对评价地震液化势是颇为有效的。     

模糊模式识别在天津滨海区轻亚黏土地震液化预测中的应用

基于模糊数学的基本原理和方法,分析了轻亚黏土地震液化的影响因素,采用较为合理的模糊模式识别的方法对轻亚黏土液化与否及液化的轻重程度进行了预测,并以天津滨海区轻亚黏土为实例得出其模糊模式识别评判图。预测结果表明,用本文建立的方法对轻亚黏土液化进行预测的结果与宏观调查结果基本吻合。     

A new approach to liquefaction hazard zonation: Application to Laoag City,Northern Philippines

To help mitigate liquefaction hazards in the Philippines, an inexpensive yet effective approach to liquefaction hazard zonation was developed in this study. The proposed approach is also useful in other areas especially where funds for more rigorous procedures may not be available. The approach utilizes the geomorphology-based criteria to identify liquefaction-prone deposits based on geology and grain characteristics, and generate a preliminary liquefaction susceptibility map. Then, microtremor recordings, popularly used in site effect estimation, are gathered to derive qualitative information on the density and thickness of these deposits and generate a site classification map. This latter map is also essentially a ground shaking hazard map in that it shows those areas where thick, soft deposits likely to amplify and prolong the duration of ground motion can be found. Therefore, it also identifies areas where seismic demand can be high that the possibility of liquefaction being triggered is likewise high. Combining the two maps, an integrated liquefaction hazard zonation map is produced which provides not only an improved characterization of the soils’ capacity to resist liquefaction but also integrates qualitative information on the seismic demand on these deposits as well. With information about the relative thickness of the deposits, the severity of potential damage can likewise be inferred from the map since thicker deposits relate to more serious damage. The proposed approach was applied to Laoag City, Northern Philippines, where it was shown to reliably identify areas that are vulnerable to the hazard.     

Spatial variability of liquefaction potential in regional mapping using CPT and SPT data

Cone penetration test (CPT) and standard penetration test (SPT) are widely used for the site specific evaluation of liquefaction potential and are getting increased use in the regional mapping of liquefaction hazard. This paper compares CPT and SPT-based liquefaction potential characterizations of regional geologic units using the liquefaction potential index (LPI) across the East Bay of the San Francisco Bay, California, USA and examines the statistical and spatial variability of LPI across and within geologic units. Overall, CPT-based LPI characterizations result in higher hazard than those derived from the SPT. This bias may result from either mis-classifications of soil type in the CPT or a bias in the CPT simplified procedure for liquefaction potential. Regional mapping based on cumulative distribution of LPI values show different results depending on which dataset is used. For both SPT and CPT-based characterizations, the geologic units in the area have broad LPI distributions that overlap between units and are not distinct from the population as a whole. Regional liquefaction classifications should therefore give a distribution, rather than a single hazard rating that does not provide for variability within the area. The CPT-based LPI values have a higher degree of spatial correlation and a lower variance over a greater distance than those estimated from SPTs. As a result, geostatistical interpolation can provide a detailed map of LPI when densely sampled CPT data are available. The statistical distribution of LPI within specific geologic units and interpolated maps of LPI can be used to understand the spatial variability of liquefaction potential.     

Fluid flow and sediment entrainment in the Garonne River bore and tidal bore collision

A detailed field study was carried out on a tidal bore to document the turbulent processes and sediment entrainment which occurred. The measured bore, within the Arcins Channel of the Garonne River (France), was undular in nature and was followed by well‐defined secondary wave motion. Due to the local river geometry a collision between the Arcins channel tidal bore and the bore which formed within the main Garonne River channel was observed about 800 m upstream of the sampling site. This bore collision generated a transient standing wave with a black water mixing zone. Following this collision the bore from the main Garonne River channel propagated ‘backward’ to the downstream end of the Arcins channel. Velocity measurements with a fine temporal resolution were complemented by measurements of the sediment concentration and river level. The instantaneous velocity data indicated large and rapid fluctuations of all velocity components during the tidal bore. Large Reynolds shear stresses were observed during and after the tidal bore passage, including during the 'backward' bore propagation. Large suspended sediment concentration estimates were recorded and the suspended sediment flux data showed some substantial sediment motion, consistent with the murky appearance of the flood tide waters. Copyright © 2015 John Wiley & Sons, Ltd.     

Assessment of liquefaction evaluation procedures and severity index frameworks at Christchurch strong motion stations

The objective of the study presented herein is to assess three commonly used CPT-based liquefaction evaluation procedures and three liquefaction severity index frameworks using data from the 2010–2011 Canterbury earthquake sequence. Specifically, post-event field observations, ground motion recordings, and results from a recently completed extensive geotechnical site investigation programme at selected strong motion stations (SMSs) in the city of Christchurch and surrounding towns are used herein. Unlike similar studies that used data from free-field sites, accelerogram characteristics at the SMS locations can be used to assess the performance of liquefaction evaluation procedures prior to their use in the computation of surficial manifestation severity indices. Results from this study indicate that for cases with evidence of liquefaction triggering in the accelerograms, the majority of liquefaction evaluation procedures yielded correct predictions, regardless of whether surficial manifestation of liquefaction was evident or not. For cases with no evidence of liquefaction in the accelerograms (and no observed surficial evidence of liquefaction triggering), the majority of liquefaction evaluation procedures predicted liquefaction was triggered. When all cases are used to assess the performance of liquefaction severity index frameworks, a poor correlation is shown between the observed severity of liquefaction surface manifestation and the calculated severity indices. However, only using those cases where the liquefaction evaluation procedures yielded correct predictions, there is an improvement in the correlation, with the Liquefaction Severity Number (LSN) being the best performing of the frameworks investigated herein. However scatter in the relationship between the observed and calculated surficial manifestation still remains for all liquefaction severity index frameworks.     

Liquefaction analysis from seismic velocities and determination of lagoon limits Kumluca/Antalya example

This study analyzes liquefaction in the Kumluca/Antalya residential area and surroundings, using seismic velocities of soil deposits and the predominant period of the earthquake wave. The liquefaction analysis calculates shear–stress ratio, shear–resistance ratio and safety factor. Shear wave velocity used in liquefaction analysis was determined through surface waves. Moreover, the dynamic parameters of the ground were calculated through seismic velocities. Distributions of groundwater, shear wave velocity, adjusted shear wave velocity, predominant period of vibration, soil amplification and ground acceleration of the research area were mapped. In addition, the liquefied and non-liquefied areas as a result of liquefaction analysis in Kumluca were determined and presented as maps. Examining these maps, among all these maps, the limits of the lagoon sandbar and the old lake area were determined using only the liquefaction map.