可液化地基中地铁车站周围场地地震反应分析

地基液化是地铁车站结构在地震中发生严重震害的重要威胁之一。基于对砂土液化大变形本构模型的研究,建立了可液化地基–地铁车站结构非线性静动力耦合相互作用分析模型,分析了该相互作用体系的地震反应规律。首先,对地铁车站结构周围地基的动孔隙水压力、位移和加速度的时空分布规律进行了分析,重点分析了可液化地基上车站结构上浮、周围侧向地基地表的地震沉降、车站结构周围地基的液化区分布特性及其位移矢量场特征;其次,对车站结构周围可液化地基的地震反应对地面结构的地基稳定性及其所处地震环境的影响进行了初步研究,研究成果可对控制可液化地基上地铁车站结构地基的震害及其对地面结构造成的震害影响提供科学依据和参考。     

液化危害估计

前言自1964年日本新揭地震、美国阿拉斯加地震和我国1966年邢台地震以来,地基土液化造成的大量地面和结构物严重破坏引起了人们的注意。我国科研和工程技术人员对此进行了广泛深入的室内外研究和观测工作,提出了许多液化判别方法及针对不同液化程度应采取的工程措施,以减轻或消除地基液化所引起的工程震害。     

基于FLAC3D的地基土地震作用下孔压的变化分析

利用FLAC3D有限差分软件对地基土在地震作用下孔隙水压力的变化进行了流固耦合分析,探讨了地基土在地震作用下孔压的变化规律,结果表明地基孔隙水压力的分布与地震激励、场地土的土质、组成和埋藏条件等因素都有密切关系,对进一步加深液化地基震害的理解具有重要的意义。     

液化侧向扩展地基中桩基抗震设计研究

根据有限元计算模型,考虑桩土共同工作的非线性关系,对液化土层地基反力系数进行折减,并对土弹簧单元施加侧向位移模拟液化侧向扩展地基中土体产生的水平位移,借助ANSYS有限元程序分析桩基在地震惯性力及液化侧向扩展产生强迫位移作用下的受力特性,并根据震害和分析结果提出防止桩基破坏的技术措施。     

地下生命线工程防御地震液化产生地面大位移的对策

液化引起的地面水平大位移在我国唐山、海城地震中已有诸多表现，１９９５年日本阪神地震也由此引起一系列震害，因此，日本拟将防液化流动对策列入抗震规范。本文结合地下生命线工程特点，对防御地面大位移震害提出一些基本措施，包括勘察、位移值预估、流动土体对管线等工程结构的作用力及地基加固等。     

台湾美浓6.7级地震框架结构震害调查与分析

2016年2月6日我国台湾高雄市美浓地区发生MS 6.7级强地震及多次余震,对台湾南部地区造成严重影响。为了研究台湾美浓地震中框架结构的震害原因,在对台南地区震害调查的基础上,首先,根据新化、草岭、善化、台南市、七股等五个台站的地震动数据,从地面峰值速度、脉冲属性和频谱特性等方面,分析了地震动的主要特征|然后,从整体结构、梁柱构件、填充墙、非结构构件和地基土液化等方面,阐述了其震害特征|最后,结合震害调查工作,从近断层脉冲型地震、地基土液化防治、抗震概念设计及隔震减震技术应用等方面,对建筑抗震设计提出了建议。     

液化地基上隔震结构群桩与土动力相互作用振动台模型试验研究

开展了液化场地–桩–隔震层–上部结构动力相互作用体系的大型振动台模型试验,再现饱和砂土地基液化诱发的地基震陷震害,详细阐述了隔震结构群桩基础与地基的地震响应特征和饱和土体孔压发展规律。试验结果表明：隔震结构群桩基础的角桩桩身应变幅值明显高于中间桩,中间桩顶部应变幅值又明显高于角桩;隔震结构地基液化后上部结构摇摆和基础转动反应急剧增加,进而导致群桩基础桩顶弯矩急剧增加,使得桩身最大弯矩幅值由地基液化前的桩身中上部转移到地基液化后的桩顶位移,同时隔震结构下部桩顶弯矩幅值比桩身弯矩幅值也要大得多,充分说明在土–桩–隔震层–上部结构的动力相互作用下桩顶更易造成严重的地震破坏。     

汶川8.0级地震液化特征初步研究

 针对目前对汶川8.0级地震液化认识尚少的现状,通过较详尽的现场调查以及相关水文、地质资料分析和现场勘察,讨论本次地震的液化分布及特征问题。研究结果表明,本次地震液化范围广,涉及长约500 km、宽约200 km的区域,但分布很不均匀。液化集中在长约160 km、宽约60 km的长方形区域并呈6个条带分布,在VIII度区内最为集中,与各地区的区域水文地质和工程地质条件呈良好的对应关系。通过调查和分析,发现本次地震液化具有与以往不同的3个突出特征：(1) VI度区内出现显著液化及其震害现象,实地发现10处液化点,分布在5个不同地区,其中有2处液化直接导致了房屋的破坏;(2) 深层土液化,4个不同地区的村庄均出现了液化喷水高度达10 m以上,专门的勘察确认了此次地震20 m处液化的真实性;(3) 砂砾层液化,专门的勘察验证这一现象,并且通过液化喷砂量和喷水时间以及工程地质资料的综合分析,推断此次地震中砂砾层液化应占很大比重。     

液化场地群桩基础地震反应离心机试验及损伤数值模型研究

地基液化导致桩基础破坏是地震中建筑物和公共基础设施震害的主要原因。开展离心机振动台试验探究液化场地中直、斜群桩基础地震反应，并建立动静耦合边界非线性砂土液化大变形桩基塑性损伤有限元数值模型，进行地震作用下群桩基础的塑性反应分析。研究结果表明：地震作用下，地基土液化最先出现在群桩基础周围的地基土表面处，随着地震动峰值加速度的增大，液化范围逐渐向地基深处和桩基础两侧发展；群桩基础的动弯矩在桩底、地基土表面、承台嵌固位置较大；直群桩基础桩身变形较大位置出现在桩底部和地基土表面位置处，斜群桩变形较大位置则出现在桩身中间处；地基土超孔压比在地基浅层最大，并随输入地震动峰值增大而增大；地基土受地震动影响产生液化的同时，会在桩周20倍桩径范围内产生地基隆起，远桩区域产生地基震陷；地震作用下，直、斜群桩受压损伤较小，受拉损伤严重，0.3 g强震工况直、斜群桩桩底受拉破坏。     

液化大变形下的桩基震害防治措施

根据液化大变形下桩基震害调查研究背景,总结液化大变形下桩基破坏模式,分析桩基震害的原因,并从液化地基的处理及桩基震害防治两方面,提出针对性的防治措施,旨在为工程实例提供参考。     

Liquefaction in Tohoku district during the 2011 off the Pacific Coast of Tohoku Earthquake

Information on the liquefaction and the liquefaction-induced damage in the Tohoku district during the 2011 off the Pacific Coast of Tohoku Earthquake has been compiled. The liquefaction in this report was mainly identified by sand boils. It caused damage to earth structures and residential houses, as well as the uplift of manholes. A comparison of geological maps and aerial photos, before and after the earthquake, shows that many of the liquefied sites were old river beds and developed areas. Liquefaction in the tsunami-affected areas was difficult to identify as the evidence of liquefaction had been washed away by the tsunami. However, the liquefaction was identified through interviews with residents and by photos and videos taken before the arrival of the tsunami. Liquefaction was also observed at Sendai Airport, but the runaway was not damaged because it had been remediated against soil liquefaction.     

Damage statistics (Summary of the 2011 off the Pacific Coast of Tohoku Earthquake damage)

The 2011 off the Pacific Coast of Tohoku Earthquake, which occurred on March 11, 2011, caused enormous damage, particularly to the strip of land along the Pacific Ocean from the Tohoku Region to the Kanto Region, due to seismic motion and the tsunami it triggered. This report presents an outline of the earthquake and summarizes the associated seismic damage to social infrastructure facilities.     

胜利—果园村液化带工程地质条件及液化土层特性分析

砂土液化是地震主要次生地质灾害之一,其是否发生及液化程度如何与地层结构、地下水、土层类型及特征等工程地质条件密切相关,通常饱和砂土和饱和粉土容易发生液化。5.12汶川地震中,在以砾石为主要地层的德阳等地发生了严重的砂土液化现象,这在以往地震中少见。胜利—果园村液化带是德阳地区诸多典型液化带之一,通过现场钻探和试验表明:液化带主要土层为砾石和粘土,发生液化的土层为全新统砾石层;液化砾石层结构松散,颗粒大小分布曲线较平缓,平均粒径和不均匀系数较大,曲率系数较小;地面喷出物是粗砂,其颗粒组成与液化砾石层相差很大。     

松原Ms5.7级地震砂土液化场地地脉动特性

基于松原Ms5.7级地震砂土液化场地为研究对象,探究液化场地和非液化场地的地脉动H/V谱的卓越频率和波形的相关特性,为地震应急期间快速判别砂土液化提供基础资料。本文首先介绍此次地震砂土液化震害情况,其次讨论不同水平组合方式、不同窗函数、不同步长对数据处理的结果影响,最后通过对比分析选定合理数据处理参数,并对26个场地地脉动测试数据进行分析。结果表明:发生液化场地的地脉动H/V谱比的卓越频率范围为0.8～1.8 Hz,波形呈现单一或者双个波峰,且波形趋于某一谱比值;而未发生液化场地的地脉动H/V谱比的卓越频率为1.6～1.7 Hz,波形呈现单一波峰或者呈现出无明显波峰,且波形呈现递减趋势。     

从郯庐地震带安丘地区地震成因土层构造认识地震破坏作用

在郯庐地震带的安丘地区,发现始新世朱壁店组厚层冲积层中发育一些同沉积的地震扰动岩土层。通过野外观测和比较地震地质学研究,识别出了振动液化砂脉、液化砂墙、裂隙充填砂质卵石墙、震塌落体、地震层内断裂及地震沉陷构造等地震成因土层构造。它们是5～8.5级强烈地震事件的记录。根据这些强烈地震成因土层构造的动力学特征进行分析,认为强烈地震对地基土的破坏作用有几种方式:液化作用、地震裂隙充填作用、振动塌落作用、断裂破坏作用和震沉陷落作用。     

挤土桩对土层液化影响研究

本文建立了挤土桩作用下厚液化土层在水平振动下的动力应变模型 ,经过分析 ,得到了振动情况下液化发展特性。结果表明 ,桩距为 4～ 6D时可使液化土的物理力学性质得到改善 ,液化危害性降低 ,液化的发展速度变速 ,最大液化深度减小     

地震荷载作用下饱和砂层孔隙水压力的增长与消散

本文用有限元法对地震荷载和不同排水条件下陡河水库土坝砂基中孔隙水压力的增长与扩散过程,以及振动结束后孔隙水压力的重分布与消散过程进行了计算分析。通过动力三轴试验,给出了饱和砂的残余孔隙水压力的全量表达式和不同液化破坏阶段的临界孔隙水压力比的表达式。本文定义了液化势评价准则,并对该坝在1976年唐山大地震时的稳定性进行了分析。得到的结果能较好地说明宏观破坏现象,同时也表明砂砾井和砂砾层有明显的排渗作用。     

Zoning for Liquefaction and Damage to Port and Harbor Facilities and Others During the 2005 Fukuoka-Ken Seiho-Oki Earthquake

On March 20, 2005, an earthquake of magnitude 7.0, which was named as the 2005 Fukuoka-ken Seiho-oki Earthquake, occurred in the northwest part of Fukuoka City. During the earthquake, liquefaction occurred mainly in the reclaimed lands of the Hakata Bay area, resulting in structural damage. In this paper, the distribution of the sites where liquefaction occurred and the characteristics of the gradation of sand boils collected at the sites were clarified. Further, the occurrence of liquefaction in the reclaimed land was discussed with reference to some instances, and structural damages, mainly to port and harbor facilities, and a flow failure of sloping ground due to liquefaction were summarized. Furthermore, liquefaction analysis was performed using a program for one-dimensional seismic response analysis and several soil profiles of the reclaimed land and alluvial ground in order to investigate the relationship between the occurrence of liquefaction and the distribution of acceleration; this was estimated from the analyses and the mechanical and physical properties of the soils.     

Building damage associated with geotechnical problems in the 2011 Tohoku Pacific Earthquake

An overview of the geotechnical aspects of the building damage due to the 2011 Tohoku Pacific Earthquake is presented, based on field reconnaissance made after the earthquake. It is shown that (1) Extensive soil liquefaction occurred along the coast of Tokyo Bay and around the floodplain of the Tonegawa River. Liquefaction was primarily found within the relatively newly reclaimed area, with numerous sand boils and large ground settlements up to 60 cm, accompanied by the settlement/tilting of wooden and reinforced concrete buildings supported by spread foundations. The extent and the distribution of the damage were significantly affected by the local soil conditions, including the thickness and the age of the reclaimed fills, the depth to the bedrock or the natural site period, and whether remedial measures had been taken against soil liquefaction, as well as the effects of structure–soil–structure interaction. (2) Numerous houses in Sendai's hilly residential areas constructed with the cut-and fill method were badly damaged not only by the simple collapse of retaining walls, but also by slope failures in the fills. It was found that most of the slope failures occurred on earth fills. (3) Several pile-supported buildings tilted and settled not only in the Tohoku region, but also on the Kanto plain, implying damage to pile foundations. Ground subsidence with sand boils around those buildings suggests that soil liquefaction might have played a significant role in intensifying the damage. (4) Within Onagawa and Rikuzen-Takata, several steel and reinforced concrete structures were knocked over by tsunami surges, probably after having suffered damage to their pile foundations. Much of the pile damage was concentrated (a) at the joints between pile caps and the piles themselves and (b) near the pile heads. The buildings suffering such damage were old; apparently their pile foundations were not designed to withstand earthquakes.     

Lessons for countermeasures using earth structures against tsunami obtained in the 2011 Off the Pacific Coast of Tohoku Earthquake

Since many infrastructures, such as sea walls, sand beaches, forests, etc., were severely damaged or destroyed by the tsunami that occurred due to the 2011 Off the Pacific Coast of Tohoku Earthquake, it is said that the resistant functions of the above structures against tsunami attacks did not perform well. However, some structures are known to have resisted the tsunami, based on field surveys conducted after the earthquake by the authors and others; and thus, the resistant functions of those infrastructures against tsunami should be estimated more properly. This paper focuses on earth structures, including river levees and road embankments, both damaged and undamaged, at 13 sites in Miyagi Prefecture, Chiba Prefecture, and Ibaraki Prefecture. They have been investigated through field surveys and other related data, such as satellite photographs taken before and/or after the tsunami. Furthermore, 10 dug pools, eroded by the flood stream on the back side of sea walls and banks during the tsunami, are also investigated to clarify their effects against tsunami attacks for use as future hardware countermeasures. Based on the above field investigations, several important lessons on hardware countermeasures against tsunami, using earth structures, are discussed. And, performance-based design concepts for reconstruction after this earthquake and for the reduction of future tsunami damage are discussed and proposed.