探地雷达应用中的几个基本问题

本文讨论了探地雷达(GPR)应用中的四个基本问题:(1)电磁波在地层中传播的波阻抗;(2)电磁波在地层分界面上场强的反射系数与透射系数;(3)电磁波在地层中的传播速度和反射波相位;(4)GPR的探测深度。为GPR的资料解释工作提供一定的理论依据和方法,也会促进资料解释的研究和发展。     

一种用于突发性场地污染模拟的解析模型

为了及时有效地应对各种突发性环境污染事故,有必要开发一种简单实用、适于各类型污染物的场地污染数学模型。通过污染事故发生后污染物在包气带、饱和带迁移转化的概化,建立了污染物运移的自由入渗模型以及降雨入渗模型并给出各自相应的解析解。无降雨时,考虑污染物在重力作用下随包气带向下渗透的作用,建立一维垂直入渗模型。有降雨时,考虑污染场地（包气带）中污染物迁移和转化的对流作用、扩散作用及挥发、生物降解、吸附、根系吸收等作用,建立包气带剖面二维溶质运移模型和饱和带平面二维溶质运移数学模型。建模过程中,假定降雨量的平均分布及土壤质地、水力参数以及有机物成分、种类均相同,同时假定污染物与多孔介质间的作用为线性吸附,植物根系对污染物的吸附遵循一级动力学。基于模型的解析解,实现案例的模拟计算。模拟结果表明：该模型具有适用范围广、模拟高效快捷等优点,能够较准确预测污染发生后污染物在土壤中的动向、到达饱和带的时间以及饱和带中污染物的迁移情况。     

门源M6.9地震诱发地质灾害特征研究

2022年1月8日发生的门源M6.9地震诱发了崩塌、滑坡、砂土液化、地裂缝等多种同震地质灾害。通过对门源M6.9地震地质灾害进行现场调查,得出了地质灾害的分布特征和各类型地质灾害的主要特点,分析了地震地质灾害不发育的原因,并对地震地质灾害的长期效应进行了分析预测。研究结果表明：门源地震诱发地质灾害主要分布在震中附近;崩塌、落石总体规模较小,滑坡多为岩质滑坡,且以冰碛物和表层岩土体的溜滑为主。受表层土体冻结和孔隙水压力消散的影响,饱和砂土液化沿较窄的地裂缝呈串珠状分布,喷出物多为粉细砂。地震形成了4条左旋左阶斜列的地表破裂带,并在极震区内形成了大量的地裂缝。断层破碎带对地震动的阻隔作用、覆盖层薄、地表土冻结可能是造成本次地震地质灾害总体不发育的主要原因;地震产生的大量地裂缝导致斜坡和堆积体的稳定性减弱,在耦合集中降雨、冻融作用等因素后可能诱发滑坡灾害,松散堆积于沟床处的崩滑物作为物源,可能会增加地震影响区泥石流灾害的风险。     

A comparative study between China and U.S. on seismic design philosophy and practice of a long span arch bridge

This paper presents the first of a series of case studies on the seismic design of long span bridges （cable-stayed bridges, suspension bridges and arch bridges） under a cooperative research project on seismic behavior and design of highway bridges between the State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University and the Multidisciplinary Center for Earthquake Engineering Research, University at Buffalo. The objective of this series of case studies is to examine the differences and similarities on the seismic design practice of long span bridges in China and the U.S., to identify research needs and to develop design guidelines beneficial to bridge engineers in both countries. Unlike short to medium span bridges, long span bridges are not included in most seismic design specifications, mainly because they are location dependent and structurally unique. In this paper, an available model of a steel tied half through arch bridge with a main span of 550m in China is discussed. Analysis is focused on comparisons of the seismic responses due to different ground motions. Seismic design criteria and seismic performance requirements for long span bridges in both countries were first introduced and compared, and then three near field earthquake records with large vertical components were selected as the excitations to examine the seismic behavior and seismic vulnerability of the bridge. Results show that （1） the selected near field ground motions cause larger responses to key components （critical sections） of the bridge （such as arch rib ends） with a maximum increase of more than twice those caused by the site specific ground motions; （2） piers, longitudinal girders and arch crowns are more vulnerable to vertical motions, especially their axial forces; and （3） large vertical components of near field ground motions may not significantly affect the bridge＇s internal forces provided that their peak acceleration spectra ordinates only appear at periods of less than 0.2s. However, they may have more influence on the longitudinal displacements of sliding bearings due to their large displacement spectra ordinates at the fundamental period of the bridge.     

Modified fish-bone model: A simplified MDOF model for simulation of seismic responses of moment resisting frames

This paper presents a simplified Multi-Degree-Of-Freedom (MDOF) model through modification of fish-bone model (or generic frame). Modified Fish-Bone (MFB) model is developed through three enhancements: (i) the moment of inertia for half-beams is reduced slightly to modify the assumption of equal rotation at each story joints, (ii) a number of truss elements are inserted to the fish-bone model to simulate flexural deformation of moment frames due to axial elongation and contraction of columns, and (iii) moment–rotation relationship of representative rotational springs is supposed to be bilinear instead of trilinear in order to consider simultaneous yielding at both ends of the beam in moment frames. The proposed model is evaluated with respect to nonlinear dynamic analysis results of three classic moment resisting frames subjected to 94 records of FEMA-440 ground motion data set. Moreover, the adequacy of this model is compared with the fish-bone model and two predictors of nonlinear seismic demand. The statistical study of predicted interstory drift demonstrates the superiority of the proposed model over the fish-bone model and both seismic demand predictors.     

长周期地震动研究综述

本文对长周期地震动研究的主要方法,即经验统计方法和震源模型方法进行了总结,分析了它们的适用范围和存在的问题。对长周期地震动的研究趋势进行了分析。     

高速铁路建设对我国省际可达性空间格局的影响

以省会城市为网络中的节点,采用加权平均旅行时间指标对我国"四纵四横"高速铁路网及长三角、珠三角和环渤海地区城际客运系统建成前后省际可达性及演变态势进行分析。研究表明,高速铁路建设使东中西地带内、地带间及省区的总体可达性均获得了大幅度提升,可达性中心区的范围沿骨干客运专线向华南、西南和西北地区拓展,圈层状空间格局依然很突出,两极分化趋势在加剧,高速铁路网建设对各地区的空间经济效应还存在很大差异。经过对高速铁路建成前后各省区的地带内、地带间及总体可达性空间格局的对比分析,从客观上论证了高速铁路建设的必要性及加强省际经济联系的重要性。     

煤矿开采对毕节地区地下水环境的影响研究

在对毕节地区煤矿开采现状调查的基础上,探讨煤炭开采对地下水环境的影响,分别从水资源量减少、水质污染、含水层水位变化三个方面进行论述,并指出由此引发的相关的问题,最后提出了煤矿开采区保护水环境、防止水环境恶化的建议。     

人工影响天气后下游地面湿度响应分析探讨

2008年8月8日下午到夜间,针对北京地区西北部、西部和西南部强对流天气进行了人工影响天气作业。为了解大规模进行人工影响天气作业后下游地区地面湿度的变化情况,文章结合空中天气形势,利用北京城区和郊区215个自动站及非自动站资料进行降水分布研究,重点利用其有湿度记录的108个站资料,对大规模人工影响后的地面湿度变化结合同期降水资料进行分析,以期为今后大规模的人工影响天气提供实验依据。结果表明,2008年8月8日夜间北京地区引导气流为西南东北向,天气系统基本沿西南—东北向移动,18：00—00：00的6小时累计降水量,呈东北西南向带状分布,北京城区处在降水量比较少的＂豁口＂处,＂鸟巢＂无降水。人工影响天气部门在北京地区西南部进行大规人工模影响强对流天气作业。作业后,在大规模人工影响作业区下风方带状范围内,地面水汽压随时间具有明显的突变（地面水汽压突然减小,持续时间大致在25分钟左右）,且这种突变从由西南向东北减弱,突变开始的时间逐渐推后。在带状中心轴线附近这种突变比较明显,远离中心轴线这种突变减弱,开始突变的时间也推后;而在带状范围外,则没有这种现象。究其原因,主要由于大规模发射火箭弹进行作业,一是火箭弹尾喷的播撒作用,二是尾喷激起的强大扰动作用,有利于大的雨滴降落,或迅速长大后降落,形成下沉气流,下沉气流将高层的干冷空气带到低层引起地面水汽压减小;此下沉气流沿着引导气流向下游传播,在传播过程中逐渐衰减。进一步分析2008年8月8日20时500 hPa风,根据此高度风速大小估算大规模作业区距离分析地面水汽压发生较大变化测站的时间,发现测站地面水汽压的发生较大变化时间与由上游空气柱移来的时间比较一致。     

HGP桩在地基处理中的应用

通过工程实例,介绍HGP桩复合地基的设计计算及施工工艺,根据现场检测结果,说明采用HGP桩能有效提高地基强度、控制地基变形,而且HGP桩具有施工机具简单、可操作性强、造价低、不受场地条件限制等优点。HGP桩在地基处理中具有很好的推广应用价值。