强震作用下松散海床地基的动力响应

海上和沿海区域砂性土地基在强震作用下需同时考虑液化、震陷以及流滑效应。选用杨朝晖叠套屈服面模型,提出了获取计算参数的简化方法,用OpenSees验证了该模型模拟液化的能力;开发了OpenSees与ANSYS的接口,对处于强震地区、地基土为松散砂性土的印尼某进水明渠堤坝进行了非线性有限元动力计算,判断了场地的液化情况,预测了堤坝及地基的震陷量和侧向流滑,计算结果对该类地基的加固处理具有一定的指导意义     

爆炸液化场地中浅埋钢筋混凝土结构动力响应的现场试验研究

饱和砂土地基在爆炸荷载作用下会发生液化,地基上的结构物将受到爆炸荷载及地基液化的双重作用,从而产生不均匀沉降和破坏性变形。基于大型现场爆炸液化试验,对场地上钢筋混凝土(RC)结构的动力响应和地基液化后RC结构的变形进行了分析研究。结果表明:液化场地中浅埋RC结构产生了明显的不均匀沉降,且最大沉降量达到结构高度的10%,结构差异沉降达到最大沉降量的1/5,结构沉降变形在液化后15 h时基本稳定;RC结构表面未产生明显的裂缝,动态拉、压应变均在400??以内,不会对结构造成显著破坏;结构动力响应表现为柱侧加速度峰值明显大于梁侧,但柱侧动力稳定所需时间较梁侧短,即柱承受了更大的瞬时冲击力且其抵抗瞬时冲击力的能力更强。研究结果可以为在可液化地基中的浅埋RC结构稳定设计等工程情况提供参考。     

石佛寺水库主坝坝基液化分析与防治

运用标贯法和seed简化方法对坝基的抗震液化进行了分析判别,发现坝基中粉砂和细砂层存在严重液化问题,中砂层局部存在液化问题,液化深度一般为7～9m,最大液化深度可达13.2m。依据坝坡稳定分析结果,确定上、下游坝脚内15m,坝脚外5m为坝基液化处理范围,粉砂、细砂层为主要处理地层。在实际防治工作中,采用振冲碎（砂）石桩或振动沉管砂石桩,结合水平排水对坝基的地震液化进行处理。处理后对各区砂土层的密实度及饱和砂土的地震液化进行检验,结果表明处理厚的坝基基本上达到了基础处理的目的。     

自由场典型液化特征数值模拟试验

应用FLAOD实现自由场液化数值模拟试验.试验结果验证了砂土液化典型特征:超静孔隙水压升高,有效应力降低,体积压缩积累增大.证实了液化的隔振作用:砂土在液化状态变为流体,不能传递剪力,液化时砂土位移、速度、加速度振幅显著降低,剪应力降低,动水向上渗流,土体向下沉降,水平残留不可恢复位移.球压应力、有效压应力、动水压力满...     

可液化土层隧道围岩的动力响应及液化区发展分析

隧道可液化土层围岩对地震动作用非常敏感,可液化土层动孔压的产生和发展使得地下结构受到上浮作用,从而影响地下结构的稳定性.通过对可液化土层中隧道动力响应计算,研究了不同静应力场隧道围岩动孔压场分布、围岩液化区域分布以及衬砌结构仰拱底与拱顶的动孔压差变化.研究结果表明,不同静应力场对围岩可液化土的动孔压分布、液化区域分布及...     

A fundamental procedure and calculation formula for evaluating gravel liquefaction

Field investigations following the 2008 Ms8.0 Wenchuan earthquake identified 118 liquefaction sites, most of which are underlain by gravelly sediment in the Chengdu Plain and adjacent Mianyang area, in the Sichuan Province. Gravel sediment in the Sichuan province is widely distributed; hence it is necessary to develop a method for prediction and evaluation of gravel liquefaction behavior. Based on liquefaction investigation data and in-situ testing, and with reference to existing procedures for sandy soil liquefaction evaluation, a fundamental procedure for gravel liquefaction evaluation using dynamic penetration tests (DPT) is proposed along with a corresponding model and calculation formula. The procedure contains two stages, i.e., pre-determination and re-determination. Pre-determination excludes impossible liquefiable or non-liquefiable soils, and re-determination explores a DPT-based critical N120 blows calculation model. Pre-determination includes three criteria, i.e., geological age, gravel contents, gravel sediment depths and water tables. The re-determination model consists of five parameters, i.e., DPT reference values, gravel contents, gravel sediment depths, water tables and seismic intensities. A normalization method is used for DPT reference values and an optimization method is used for the gravel sediment depth coefficient and water table coefficient. The gravel liquefaction evaluation method proposed herein is simple and takes most influencing factors on gravel sediment liquefaction into account.     

FOSM在水平场地液化概率评价中的应用

为了更好地进行场地液化评价,将可靠度理论引入水平场地液化概率评价中。以标准贯入试验(SPT)实测数据的统计分析结果为基础,用一次二阶矩法(FOSM)建立水平场地液化概率评价模型,分析了测试数据变异系数对抗液化安全系数与液化概率的影响,并建议了水平场地液化概率评价标准。实例分析表明,新建水平场地液化概率评价模型各参数的物理意义与统计指标明确,相比传统的确定性分析方法,不仅能判定液化的发生与否,还能给出液化发生的概率,这为进行基于风险分析的抗震设计提供了可能。     

浙江宁波穿山水道的海底稳定性评价

在测深、钻探、室内测试、水文泥沙测验等勘测资料基础上,详细分析宁波穿山水道海域水文气象、工程地质、地震活动性、浅层气、滑坡、沙土液化、岸坡和冲刷槽冲淤动态等因素,这些分析结果表明穿山水道海底稳定,海岸和海洋工程环境适宜.     

New insights into the size and timing of the Lawn Hill impact structure: relationship to the Century Zn – Pb deposit

The Lawn Hill circular structure in northwest Queensland contains unambiguous evidence of an extraterrestrial impact, including planar deformation features in quartz, impact diamonds, widespread shatter cone formation and impact melt breccia in the Mesoproterozoic basement. The question of its relevance to ore genesis is investigated because the world-class Century Zn – Pb deposit is situated at the conjunction of the 100+ km Termite Range Fault and the previously defined margin of the impact structure. The impact structure is considered to be a 19.5 km wide feature, this constrained in part by the outer margin of an annulus of brecciated and highly contorted limestone. New evidence is presented indicating impact into this Cambrian limestone, including: (i) ‘dykes’ of brecciated Cambrian limestone extending hundreds of metres into the Mesoproterozoic basement; (ii) highly contorted bedding in the limestone annulus compared with essentially undeformed limestone away from the impact site; as well as (iii) a 1 Mt megaclast of Mesoproterozoic Century-like ore suspended in the limestone. Through aerial photograph analysis, large-scale convoluted flow structures within the limestone are identified, and these are interpreted to indicate that parts of the Cambrian sequence may have been soft or only semi-consolidated at the time of impact. This highly contorted limestone bedding is suggested to represent slump-filling of an annular trough in response to impact-induced partial liquefaction of a sediment veneer. The age of impact is therefore considered to be concurrent with limestone formation during the Ordian to early Templetonian, at 520 – 510 Ma. Formation of the Century deposit is found to be unrelated to impact-generated hydrothermal activity, although some minor hydrothermal remobilisation of metals occurred. However, there was macro-scale remobilisation of gigantic ore fragments driven by impact-induced lateral and vertical injection of limestone into the Proterozoic sediments. The limestone-filled annular trough surrounds a 7.8 km diameter central uplift, consistent with formation of a complex crater morphology.