【作者】 曹振中；

【导师】 袁晓铭；

【作者基本信息】 中国地震局工程力学研究所 ， 岩土工程， 2010， 博士

【摘要】 地震液化震害调查是获取液化震害经验最直接的手段,是抗震理论和分析方法发展的重要基础,而地震液化场地的现场测试与分析,是建立液化预测方法最可靠的途径。以往国内几次大地震液化现场深入的考察和分析研究,对我国乃至世界工程抗震技术的发展都起到了很大的推动作用。2008年5月12日我国四川汶川县发生的8.0级大地震是新中国成立以来破坏性最强、波及范围最大的一次地震,其强度、烈度都超过了1976年的唐山大地震。关于此次地震液化问题尚少报道,目前占主导的认识是认为此次地震液化现象不多,甚至有观点认为此次地震中没有液化现象。我们的考察结果表明,此次汶川地震的液化范围为建国以来大地震中液化分布范围最广的一次,已经调查到以村为单位的118个液化点(带),涉及长约500公里、宽约200公里的区域,据不完全统计,共有20余个村庄的水井、近千亩农田、120多个村庄(自然村)房屋、8所学校、5个工厂不同程度地受到了液化震害的影响,一些房屋建筑、学校教学楼、厂房和水井等废弃。本文分析结果表明,Ⅵ度区内液化、深层土液化以及砂砾土液化是本次地震液化的三个主要特征,液化加重震害以及液化伴随地裂缝现象也较为普遍。但以往关于这些问题的经验尚少,获取系统知识、掌握规律、解释成因、剖析机理和提炼出反映此次地震液化特点的科学和工程问题,是提高关于汶川地震液化问题认识、开展相关深入研究工作的前提和基础。此次地震砂砾土液化分布范围广,造成的危害突出。我国四川省境内特别是成都平原砂砾层分布十分普遍,由于以往工程建设中直接认定砂砾土为非液化土,而忽视了砂砾土的液化可能性,导致砂砾土液化震害十分明显。而目前国内外砂砾土液化场地资料十分有限,对砂砾土液化的认识也存在误区,积累实测资料对于丰富国际液化数据库以及推动砂砾土液化预测方法发展十分重要。同时,目前工程上能够使用的砂砾土液化判别方法均是由砂土液化判别方法间接转换而来,基于实际资料直接建立的砂砾土液化判别方法尚属空白。应指出的是,我们一直认为,砂砾土与砂土分属不同土类,像判别液化这样的力学性能方面的分析,用砂土的公式来计算砂砾土理论上不成立,实际的结果也证明了这一点。我国部分地区砂砾土分布广泛,土石坝很多采用砾石作为垫层,人工填海、高速公路、铁路等工程建设中人工砂砾料应用日益广泛,砂砾土的液化判别方法问题亟待解决。因此,借助汶川地震出现大量砂砾土液化的契机,获取实测数据,检验现有方法,发展合理可靠、符合国际发展趋势、便于工程应用的砂砾土液化判别方法,是势在必行的工作。本文主要工作和成果包括:1.通过大量现场调查,取得了汶川地震液化问题系统和深入的认识,揭示了液化及其震害分布规律,阐明了此次地震液化的宏观特征和震害特征,并从中提炼出了反映此次地震液化特点的科学和工程问题。2.采用实地考察,资料分析以及现场测试的方法,确认了Ⅵ度区内液化、砂砾土液化、深层土液化是此次地震的三个主要特征,依据实测结果合理解释了此次地震液化区内地裂缝的成因,剖析了液化导致建筑物典型破坏的机理。3.研究了震区地质环境和工程地质条件,揭示了本次地震砂砾土液化分布规律,通过试验及与国内、外砂砾土液化实例的对比分析,掌握了此次地震液化砂砾土的土性特点。4.通过现场勘察获取了几十个砂砾土液化场地超重型动力触探和剪切波速资料,极大丰富了现有液化数据库内容,以此检验和分析了现有液化判别方法对砂砾土的可行性,指出了其不适用的根源。5.建立了基于现场测试指标的砂砾土液化判别方法的基本思路,提出了基本指标的选取原则和模型的构造思想,给出了初判条件,根据地震动参数不同确定了复判模型的基本模式。6.建立了基于烈度和加速度以及超重型动力触探击数和剪切波速为基本指标的四种砂砾土液化判别方法,通过了本次和其他砂砾土液化实例的检验,填补了以往基于实际资料直接建立砂砾土液化判别方法方面的空白,公式表达简单明了,为工程应用及规范修订提供了参考和依据。更多还原

【Abstract】 It is remarkably important for seismic resistant design theories and analytical tools improvement to investigate the liquefaction-induced damage and field test in detail. Many significant lessons have been learned from the post-earthquake damage investigation in the past. Field test conducted in the liquefied site is the reliable way to establish a procedure for liquefaction evaluation.The 2008 Wenchuan Earthquake was the most destructive and widely influencing earthquake occurred in China since the 20th century. The intensity and magnitude was larger than those of the Tangshan Earthquake. However,“there was rare occurrence of soil liquefaction”and“the influence of liquefaction was small”are the main opinions in the academe as lack of detailed report of liquefaction. A specific liquefaction investigation team was organized by Institute of Engineering Mechanics, China Earthquake Administration shortly after the great Wenchuan Earthquake. Through months of wide and detailed field investigation, amount to 118 liquefied sites have been investigated, most of which located in the Chengdu plain and Mianyang district Sand boils and water spouts occurred extensively, involving in thousands of mus of farmland, 120 villages, 8 schools and 5 factories, which caused some rural houses, school buildings, manufactory buildings and wells etc. losing function in service. Three main characterizations of liquefaction in the Wenchuan earthquake were: the gravelly soils liquefaction, the liquefaction occurred in seismic intensityⅥ(PGA≈0.05g), and the liquefaction occurred in deep soil layer. Meanwhile, the ground fissures occurred widely in the liquefied zone. It’s very important to examine these phenomenon and explore the mechanism for further corresponding study.In general, the gravelly soils has been regarded as non-liquefiable soils for its large grain size and well drainage condition. However, the geological conditions and soil profiles show that the gravelly soils layer distributed extensively in the Chengdu plain, almost 75% to 80% of 118 liquefaction investigated cases were gravelly soils liquefafied sites. Comparing to the limited data of global gravelly soils liquefaction, the gravelly soils liquefied cases in the Wenchuan Earthquake will enrich the global database enormously. The empirical SPT- and CPT- based procedures for sand liquefaction evaluation are not reliable for gravelly soils because these two types of test could not be conducted in the gravelly soils site. Meanwhile, the currently empirical liquefaction evaluating methods were established almostly based on the sand liquefaction data, which also are not reliable for gravelly soils liquefaction assessment. A new approach is strongly demand to be proposed for gravelly soils liquefaction evaluation according to the field test index, because the gravelly soils has been used very commonly in engineering.The main objects and fruits of this paper are:1. To understand the distribution and characterization of soil liquefaction and liquefaction-induced damage in the Wenchuan Earthquake by detailed field investigating, and to learn useful lessons for further study.2. To examine the truth of the liquefaction occurred in seismic intensityⅥ, the gravelly soils liquefaction, and the liquefaction occurred in deep layer soil by field investigating, collecting and analyzing the material, and field testing. To explore the mechanisms of liquefaction-induced ground fissures and liquefaction-induced structure damage.3. To explore the geology background and soil conditions, to obtain the distribution and characteristics of gravelly soils liquefaction in the Wenchuan Earthquake, and to compare the gravelly soils liquefied case in the Wenchuan Earthquake with the case histories in other earthquakes.4. To conduct the Dynamic Penetration Test (DPT) and Shear Wave Velocity Test (Vs) in several decades gravelly soils liquefied sites, and to verify the reliability of currently SPT-, CPT- and Vs- based procedures for liquefaction evaluation by using the gravelly soils measured data.5. To propose the fundamental model for gravelly soils liquefaction assessment based on the field test index and different ground motion parameter.6. To propose the DPT- and Vs- based procedures for gravelly soils liquefaction evaluation, to verify these procedures by using the gravelly soils liquefied case histories in other earthquakes, and to propose suggestions for seismic code amendment especially in gravelly soils liquefaction resistance evaluation.更多还原