【作者】 王颖轶；

【导师】 黄醒春；

【作者基本信息】 上海交通大学 ， 结构工程， 2011， 博士

【摘要】 全球许多国家处于地震多发区域,其中智利、日本、美国与中国处于地震频发区域。全世界每年约发生地震500万次,其中有感地震约5万次,造成严重破坏的地震近20次。仅就中国而言,1900年以来,死于地震的人数达55万之多,占全球地震死亡人数的53%。震灾涉及中国22个省(自治区、直辖市),地震成灾面积达30多万平方公里,房屋倒塌达700万间。1976年唐山大地震造成24.28万人罹难;2008年5月12日汶川大地震造成8.7万人罹难,直接经济损失8451亿元人民币。长期以来,为了有效地预防和减轻地震灾害,世界各国围绕地震发生机理、建筑结构物的抗震理论与技术、次生灾害预防、地震灾后评估与灾区重建等进行过大量研究,取得了大量有理论意义和使用价值的研究成果。但由于种种主客观原因,研究的焦点主要集中于运营阶段建(构)筑物抗振性及其振损评价,而对施工期基坑地震反应及其支护结构抗震性能而言,迄今还少有系统研究。随着城市地铁交通、大型地下商场、超高层建筑等工程建设的迅速发展,大型深基坑工程日益增多,地震频发区深基坑施工技术、施工期的防灾减灾、临时设施及养护期混凝土震损检测与评估等将不可避免地成为包括中国在内的地震频发区域和国家建设的重大理论和技术问题。基坑施工期内,维护和支撑结构(包括土钉墙、锚喷、地下连续墙、钢支撑、钢筋混凝土结构支撑及其他临时支撑等)、施工设施、工程机械及施工设备等由于其自身的设置及性能特点,其地震反应及抗震性能与运营期结构有本质的区别,现有的研究成果难以直接应用于施工期基坑抗震防灾及结构震损分析。本文针对地震频发区基坑施工的关键技术和理论问题,在充分调研的基础上采用数值模拟、室内试验及理论分析等综合研究方法,系统研究了强地震作用下不同形式深基坑抗震稳定性、基坑支护体系地震位移及灾变的时程和空间分布、施工养护期混凝土受强地震后强度损失及其评价、早龄混凝土受强地震作用后内部损伤及其评价等。取得了相应有创新意义和工程实用价值的研究成果:1.通过文献资料的系统查询及对汶川地震灾区的现场调研,统计分析了全球地震分布的区域特征,基于调研统计数据建立了全球性地震发生数的时间累积关系及以中国为例的局部区域地震发生数的时间分布;根据现场调研获得的汶川地震基坑及边坡破坏案例,通过力学机理分析,提出和完善了施工期基坑地震破坏模式及其力学成因。2.结合成都地区深基坑工程实例,通过三维动力FEM模拟计算,研究了锚喷支护基坑、地下连续墙加钢支撑基坑的地震稳定性,系统分析了两类基坑在不同传播方向地震荷载作用下基坑结构位移、钢支撑灾变演化及其鞭梢效应。3.通过基坑支撑结构灾变倒塌过程的三维FEM数值模拟,系统研究了不同传播方向强地震荷载作用下基坑钢支撑灾变过程及破坏形式。揭示了强地震作用下基坑支撑体系倒塌危险的区域性分布特征、支撑破坏过程的阶段性时程特性。即支撑破坏过程分为往复振动时域、振动位移急剧增加时域、结构失稳破坏时域。结果对地震频发区基坑施工过程风险防范设施设置和防灾减灾具有重要指导意义。4.利用模拟地震振动台进行室内试验,系统研究了基坑施工不同龄期混凝土受强地震作用后的变形特性、压缩扩容性质及其动力学机理。结果表明:养护期混凝土受强地震作用后其体积应变具有显著的扩容(体积增大)特性且扩容程度与混凝土受振龄期密切相关;混凝土结构扩容的主要力学成因是强地震作用导致结构内部形成随机分布的微观及细观裂纹在外荷载作用下产生位错、转动等从而形成宏观状态下的体积增大。5.通过受振混凝土变形特性的试验研究,提出了早龄混凝土在强地震作用下裂纹产生与发育的受振龄期三阶段特性:振动强化阶段(养护龄期1~10h,包括混凝土液态及粘性可流动状态);振损但能自修复阶段(养护龄期10~60h,包括半固化状态及固化且弹性模量增长状态);振损不可逆阶段(养护龄期大于60h,主要是最终固化状态)。6.通过室内模拟地震试验,系统研究了不同养护龄期混凝土受强地震作用后的强度损失。结果表明:受振龄期为3~30h的混凝土,其强度显著降低;受振龄期大于30h的混凝土,其强度未见明显变化。7.通过受震混凝土的强度及超声波试验研究,建立了受振混凝土强度与超声波波速的相关关系、提出了强地震后混凝土结构强度现场超声波检测的建议方案及实施方法。8.将三维层析技术应用于地震作用后混凝土结构内部损伤的检测与评价,开发了基于任意三维正交立体交汇色谱分析法用于定点评价混凝土内部结构损伤并开发了相应三维解析软件,为混凝土结构内部损伤状态的可视化评价提供了有效的手段。综上所述,本研究的内容和成果涉及地震频发区基坑施工可能面临的关键理论和技术问题,一定程度上填补了国内外在该领域研究的不足。部分研究成果为成都及都江堰等地灾后重建所采用,为灾后重建基坑施工过程风险防范设计提供了依据并产生了良好的技术与社会效益。更多还原

【Abstract】 Many countries around the world are areas with frequent earthquakes. Among those, Chile, Japan, United States and China are typical areas. There are about 5 million earthquakes happens every year around the world. Thereinto, there are about 50,000 felt earthquakes, and 20 of those result in severe catastrophe. Take China as an example, since 1900, there are more than 550,000 people die from earthquake, which is about 53% of the total number around the world. There are 22 provinces affected by earthquakes, which cover more than 300,000 square kilometers, and more than 7 million building are destroyed. In 1976, there were about 242,800 people died in the Tang Shan earthquake. In 2008, there were about 87,000 people died in the Wenchuan earthquake, and result in direct economic loss of about 845.1 billion Chinese Yuan.In order the prevent and reduce seismic catastrophe, researchers around the world conducted many studies on earthquake generating mechanism, structure earthquake resistant theory and technology for structures, secondary disaster prevention, evaluation and reconstruction after earthquake. However, most of the researches are focused on the earthquake resistance and damage evaluation of the structure in operation. There are very few studies on foundation pit seismic response and earthquake resistance performance of support structure during construction period. Along with the rapid development of city subway system, large underground supermarkets and super high-rise buildings, the number of deep foundation pit engineering grows very fast day by day. The issues of deep foundation pit construction technology, prevent and reduce disaster during construction period, temporary constructions and seismic damage evaluation for curing concrete in frequent earthquake areas will definitely become important theory and technology for the all the countries with frequent earthquakes. During foundation pit construction period, the support structures (including soil nailing wall, spray anchor, diaphragm wall, steel support, reinforced concrete support and other temporary support), construction equipment and engineering machinery have different seismic responses and earthquake resistance performances comparing with that of structures in operation. The existing research achievements con not directly apply to the foundation pit disaster prevention and structure damage evaluation during construction period.This paper look into the key technologies and theories of foundation pit construction in frequent earthquake areas. The seismic resistance stability of different deep foundation pit types under strong earthquake, seismic displacement and disaster history and distribution of foundation pit support system, strength loss and evaluation of curing concrete after strong earthquake, interior damage and evaluation of early-age concrete after strong earthquake have been studied by numerical simulation, laboratory test and theoretical analysis and some importance and useful research have been achieved as follow.1. By literature study and on site investigation of Wenchuan, the regional distribution characteristics of earthquakes around the world have been statistical analyzed. The global earthquake number accumulation along time has been studied and China is taken as example for local earthquake number distribution along time study based on statistical data. Based on the on site investigation of foundation pit and side slope destructions cases in Wenchuan, the seismic destruction model and mechanism of foundation pit under construction have been advanced and improved.2. With the data of deep foundation pit project in Chengdu area, the seismic stability of spray anchor foundation pit and steel support foundation pit with diaphragm wall has been studied by three-dimension dynamic finite element method (FEM) simulation. The foundation pit structure displacement, steel support disaster evolution and whiplash effect of the two different foundation pits under seismic load along different directions.3. The catastrophe process and failure pattern of steel support foundation pit under strong seismic effect have been studied by three-dimension dynamic finite element method (FEM) simulation of foundation pit support structure destruction. The regional distribution characteristics of foundation pit support system failure risk and support destroy phase history under strong seismic effect have been revealed, which include reciprocating vibration phase, vibration displacement rapid growth phase, structure failure phase. The conclusions have importance significance to risk prevention, disaster prevention and reduction during foundation pit construction process in the frequent earthquake area. 4. The deformation characteristics, the dilatation under compression and its dynamic mechanism of different curing period concretes during foundation pit construction have been studied by laboratory test of seismic vibration simulator. It is concluded that: 1) the volumetric strain of curing concrete after strong seismic effect possess obvious dilatation property (volume increase) and the dilatation has strong relation with concrete curing period; 2) the mechanism of concrete dilatation is mainly due to the dislocation and rotation of random distributed micro cracks generated after strong seismic effect which result in macro volume increase.5. Based on the laboratory study of after-vibration concrete deformation properties, the three stages of vibration period for crack generation and evolution in early-age concrete have been concluded: (1) vibration strengthen stage (curing age 1-10 hours, including concrete liquid status and viscous fluid status); (2) vibration damage and self-repairing stage (curing age 10-60 hours, including semi-solidification status and solidification status with increasing elastic modulus); (3) vibration damage and irreversible stage (curing age more than 60 hours, mainly final solidification status)6. The strength loss of after-vibration concrete with different curing period has been studied by laboratory seismic simulation. It is concluded that for the concrete with 3-30 vibration time, the strength loss is greatly reduced, while for that of vibration time more than 30 hours, the strength does not change much.7. The relation of concrete strength with ultrasonic wave speed has been established by laboratory tests and the scheme for on site ultrasonic wave speed inspection for concrete structure after strong seismic effect has been advanced.8. By applying three-dimension layer-analise technique to the evaluation of concrete interior damage after earthquake, the three-dimension analysis software has been developed which is based on arbitrary three-dimension orthogonal chromatography. This work provides an effective approach for visual evaluation of interior damage for concrete structure.Based on the above stated, this paper is mainly dealing with the key theories and technologies for the foundation pit construction in frequent earthquake areas. Part of the research achievements have been used for some after-earthquake reconstructions in Chengdu and Dujiangyan Dam. It provides important suggestions for risk prevention during foundation pit reconstruction after earthquake and brings useful technique and social benefits.更多还原