郯庐断裂带中段安丘-莒县断裂(F_(5))为中国东部重要的地震活动断裂,其最南段展布于淮河—女山湖之间,长约20km,最新活动时代为全新世早期。针对F_(5)断裂淮河—女山湖段的前期工作侧重于在不同地段开挖探槽以揭示断裂的最新活动时代、...郯庐断裂带中段安丘-莒县断裂(F_(5))为中国东部重要的地震活动断裂,其最南段展布于淮河—女山湖之间,长约20km,最新活动时代为全新世早期。针对F_(5)断裂淮河—女山湖段的前期工作侧重于在不同地段开挖探槽以揭示断裂的最新活动时代、结构特征及运动性质,并报道了零星的古地震事件。本次在该段选取关键地段开挖探槽并结合前期探槽资料,开展了古地震事件的综合对比研究;通过测量探槽附近断层陡坎的高度,并结合相关地层测年数据,计算了断裂的垂直滑动速率;基于该段古地震研究成果,结合其他学科资料,分析了苏皖交界地区的地震危险性。研究表明:(1)F_(5)断裂淮河—女山湖段中更新世晚期以来至少发生过5次古地震事件,厘定的最近2次事件的年代为20.36~(18.7±0.3) ka BP和10.92~7.83ka BP;(2)F_(5)断裂淮河—女山湖段紫阳山一带的垂直滑动速率约为0.05mm/a,陡山一带的垂直滑动速率约为0.07mm/a,该段整体属于弱活动断层;(3)F_(5)断裂泗洪—明光段为历史地震地表破裂空段,最近1次古地震的离逝时间较长,现今小地震不活跃,闭锁程度较高,易于应力积累,存在发生7级及以上强震的危险性。展开更多
The effective stress method is developed to predict the axial capacity of piles in clay. The effective stress state changes due to the resulting pore pressure change and therefore, the strength and stiffness of the so...The effective stress method is developed to predict the axial capacity of piles in clay. The effective stress state changes due to the resulting pore pressure change and therefore, the strength and stiffness of the soil will change. In this work, the finite element method is utilized as a tool for the analysis of pile-soil systems in undrained condition. The computer program CRISP was developed to suit the problem requirements. CRISP uses the finite element technique and allows predictions to be made of ground deformation using critical state theories. Eight-node isoparametric element was added to the program in addition to the slip element. A pile loading problem was solved in which the pile-soil system is analyzed in undrained condition. The pile is modelled as elastic-plastic material, while the soil is assumed to follow the modified Cam clay model. During undrained loading condition, the settlement values increase by 22% when slip elements are used. The surface settlement increases by about three times when the load is doubled and the surface settlement at all points increases when using slip elements due to the mode of motion which allows smooth movement of the adjacent soil with respect to the pile. The vertical displacement increases as the distance decreases from the pile and negligible values are obtained beyond 10D (where D is the pile diameter) from the center of the pile and these values are slightly increased when slip elements are used. The vertical effective stress along a section at a distance D from the pile center is approximately the same for all load increments and lower values of effective vertical stress can be obtained when slip elements are used.展开更多
文摘郯庐断裂带中段安丘-莒县断裂(F_(5))为中国东部重要的地震活动断裂,其最南段展布于淮河—女山湖之间,长约20km,最新活动时代为全新世早期。针对F_(5)断裂淮河—女山湖段的前期工作侧重于在不同地段开挖探槽以揭示断裂的最新活动时代、结构特征及运动性质,并报道了零星的古地震事件。本次在该段选取关键地段开挖探槽并结合前期探槽资料,开展了古地震事件的综合对比研究;通过测量探槽附近断层陡坎的高度,并结合相关地层测年数据,计算了断裂的垂直滑动速率;基于该段古地震研究成果,结合其他学科资料,分析了苏皖交界地区的地震危险性。研究表明:(1)F_(5)断裂淮河—女山湖段中更新世晚期以来至少发生过5次古地震事件,厘定的最近2次事件的年代为20.36~(18.7±0.3) ka BP和10.92~7.83ka BP;(2)F_(5)断裂淮河—女山湖段紫阳山一带的垂直滑动速率约为0.05mm/a,陡山一带的垂直滑动速率约为0.07mm/a,该段整体属于弱活动断层;(3)F_(5)断裂泗洪—明光段为历史地震地表破裂空段,最近1次古地震的离逝时间较长,现今小地震不活跃,闭锁程度较高,易于应力积累,存在发生7级及以上强震的危险性。
基金Project(RG086/10AET) supported by the Institute of Research Management and Monitoring (IPPP),University of Malaya (UM) under UMRG grant number,Malaysia
文摘The effective stress method is developed to predict the axial capacity of piles in clay. The effective stress state changes due to the resulting pore pressure change and therefore, the strength and stiffness of the soil will change. In this work, the finite element method is utilized as a tool for the analysis of pile-soil systems in undrained condition. The computer program CRISP was developed to suit the problem requirements. CRISP uses the finite element technique and allows predictions to be made of ground deformation using critical state theories. Eight-node isoparametric element was added to the program in addition to the slip element. A pile loading problem was solved in which the pile-soil system is analyzed in undrained condition. The pile is modelled as elastic-plastic material, while the soil is assumed to follow the modified Cam clay model. During undrained loading condition, the settlement values increase by 22% when slip elements are used. The surface settlement increases by about three times when the load is doubled and the surface settlement at all points increases when using slip elements due to the mode of motion which allows smooth movement of the adjacent soil with respect to the pile. The vertical displacement increases as the distance decreases from the pile and negligible values are obtained beyond 10D (where D is the pile diameter) from the center of the pile and these values are slightly increased when slip elements are used. The vertical effective stress along a section at a distance D from the pile center is approximately the same for all load increments and lower values of effective vertical stress can be obtained when slip elements are used.
