高速列车振动荷载下水泥改良黄土动力学试验

结合大同-西安高速铁路建设,选取该线路数个不同地貌单元的典型黄土路段采集试验样品,在GDS高级动态三轴测试系统上进行了水泥改良黄土的动力特性室内试验研究.采用正交试验法以优化试验方案.动荷载按照不同黄土层的埋深深度以火车振动衰减规律求取,土样按照不同水泥掺量经击实获得,经过长时间、多振次的动力学试验后获得水泥改良黄土的动弹模、动阻尼以及振陷量;进而探讨土层埋深、水泥掺和比、压实系数、浸水条件和振动次数对土样动力特性参数影响的主次顺序及显著性程度,找出工程最优化方案.结果表明:影响水泥改良黄土振陷量的各因素的主次顺序为:水泥比＞浸水条件＞振动次数＞深度＞压实系数,水泥比和浸水条件影响显著,其它因素无显著影响;动弹性模量影响因素主次顺序;深度＞浸水条件＞水泥比＞振动次数＞压实系数,深度和浸水条件影响高度显著;阻尼比影响因素主次顺序:浸水条件＞水泥比＞振动次数＞压实系数＞深度,水泥比和浸水条件影响高度显著.随着水泥比的增加水泥改良黄土动力特性越好,不存在最优水泥配合比.     

京沪高速铁路的重要土建施工工艺探讨

多年来中国铁路学习借鉴发达国家高速铁路建设技术和成功经验,大力推进技术创新,在京沪高速铁路桥梁设计、施工、科研以及建设管理等方面实现重大跨越,使我国能够站在世界高速铁路技术的制高点上。     

Luminosity characteristics of leaders in natural cloud-to-ground lightning flashes

Using high-speed cameras, we have recorded the leaders contained in four natural negative cloud-to-ground (CG) lightning flashes in the summers of 2006 and 2007 at Conghua, Guangdong, China. It was found that the downward negative leaders preceding the first return stroke could propagate at quite different speeds. In one flash, the average speed of the downward negative stepped leader with no branches is about 2.2 × 10⁶ m s^− 1, while that of the other 3 flashes are all of the order of 10⁵ m s^− 1 with multilevel branches. The luminosity of the leaders shows an increasing tendency in propagating downward to the ground. For the leaders preceding the subsequent strokes, although all of them exhibit high speeds as reported previously. One subsequent leader exhibits an increasing speed from 5.2 × 10⁵ m s^− 1 to 1.7 × 10⁶ m s^− 1 during its propagation from about 1.26 to 0.36 km above the ground, and its luminosity also increased. The speed and luminosity of a leader between subsequent strokes of a natural lightning appear to decrease as it developed downward. Its speed ranges from 1.1 × 10⁶ to 1.1 × 10⁵ m s^− 1, with a height between 1.15 and 0.81 km above the ground.     

Continuing current in multiple channel cloud-to-ground lightning

In this study we analyze the effects of continuing current initiated by strokes following a new channel to ground in multiple stroke flashes using high-speed video records, electric field measurements from a fast antenna and lightning detection network data. We observed that the long continuing current initiated by a stroke that follows a new channel also obeys the pattern in the initiation of long continuing current suggested by Rakov and Uman [Rakov, V.A., Uman, M.A., 2003. Lightning: Physics and Effects, 687pp., Cambridge Univ. Press, New York.]. We also verify that the statement of Rakov and Uman [Rakov, V.A. and Uman, M.A., 1990. Some properties of negative cloud-to-ground lightning flashes versus stroke order, Journal of Geophysical Research. 95, 5447–5453.] reporting that: “...strokes initiating long continuing currents tend to have lower initial electric field peak than regular strokes” is valid for strokes that create a new channel to ground and are followed by long continuing current (CC). Apparently the reduction of peak current value (I_p) when the stroke is followed by a long CC is stronger than the I_p increase that is commonly observed when strokes follow a new channel. We also find that the “exclusion zone” proposed by Saba et al. [Saba, M.M.F., Pinto, O. Jr., Ballarotti, M.G., 2006a. Relation between lightning return stroke peak current and following continuing current, Geophysical Research Letters 33, L23807, doi:10.1029/2006GL027455.] is valid for new channels initiating CC, and finally we verify that a number of strokes in the same channel larger than four or the existence of a long CC current do not always consolidate the channel in a multiple stroke flash.     

高架轨道交通对城市景观的影响及应对措施初探

论文分析了高架轨道交通对城市景观的双重影响:高架桥作为一种新的城市构筑物,为人们提供了欣赏城市的新的观赏点和观赏方式;但处理不当的高架构筑物具有破坏自然景观、影响人们的视觉、造成尺度失调、影响城市色彩和谐、破坏城市原有肌理等负面影响。进而论文提出了高架轨道交通的设计原则及改善轨道交通城市形象的应对措施:第一,巧妙选线,充分利用轨道交通沿线风景资源,形成轨道交通视觉廊道;第二,提升高架桥的空间景观形象:桥下空间综合利用,完善城市功能;桥侧空间精心设计,增强桥体人性化因素;重视高架桥体及附属物的形象设计,达到技术与艺术的完美统一;第三,建设具有地域风格的换乘站。     

蒙阴县京沪高速公路沿线破损山体治理方法探讨

蒙阴县以科学发展观为指导,结合当地实际,积极探索破损山体治理模式,对京沪高速公路沿线破损山体进行了综合治理,取得了较好的治理效果。该文详细介绍了植生穴绿化技术、植生盆绿化技术和雕刻美化治理技术在蒙阴县京沪高速公路沿线破损山体治理中的应用,以及生态修复技术在日后养护中的注意事项,并探讨了治理工程产生的环境效益和社会效益。     

RELATION BETWEEN THE MRT BUILDING AND UNDERGROUND SPACE EXPLOITATION ——A Case in Guangzhou City

On the basis of analyzing the history and characteristics of the underground space exploitation and theurban space development in Guangzhou, and making a thorough study on the underground space exploitation based on the subway building, this paper points out some main problems in the exploitation of underground space in Guangzhou, and emphasizes that Guangzhou must develop the underground space on a large scale with the aid of the subway building, and puts forward a proposal on the urban space coordinate development between on-ground and underground in Guangzhou City.     

Review on the Impacts of Public Rail Transport on Urban Land Use Change:A Citespace-based Quantitative Analysis*

The public rail transport system in cities can promote physical urban transition, resulting in land use and land cover change, changing the public daily behaviors and consequently bringing huge economic benefits to its imminent areas. In this study, based on statistical analysis and visualization tools, by using Citespace and Google Earth, we explored approximately 455 papers from Web of Science and 321 papers from CNKI to obtain current research trends in the assessment of the impacts of public rail transport on land use change. The literature classification, organization and comments on such current studies and hot research topics are valuable for future research. Three conclusions were then drawn: First of all, similar topics have been done by both domestic and oversea scholars, but from slightly different perspective and at different scales. Secondly, public rail transport often causes the increase of housing price for both residential and commercial blocks; the influence on population density is more significant in the outskirts than that in downtown areas, but the influence often emerges with an unfixed time lag. Thirdly, RS, GIS and GPS (3S) technologies are promising tools for the research of the impacts of public rail transport on land use change in the era of "big data". Based on the conclusions, four suggestions were proposed: Firstly, future research in this field will be more comprehensive and humanistic studies. Secondly, overseas development models could not be fully applied in China, and thus corresponding improvement with China's situation are required. Thirdly, theoretically speaking, bicycle sharing can expand the service range of public rail transport. Fourthly, reasonable allocation of buffers is important for obtaining fine statistical area of land change affected by public rail transport.     

区域旅游流空间结构的高铁效应及机理——以中国京沪高铁为例

交通是影响旅游流空间结构最主要因素之一。以京沪高铁线为例,探讨了区域旅游流空间结构的高铁效应及特征,在此基础上,分析区域交通可达性变化,并结合区域旅游资源禀赋、区域旅游接待设施、区域旅游交通网络密度以及区位等影响因素分析区域旅游流空间结构的高铁效应的机理。研究表明:1区域旅游流空间结构的高铁效应表现为马太效应、过滤效应、扩散效应和叠加效应等特征。2区位条件、旅游资源禀赋、旅游接待能力、交通网络密度以及时空压缩程度等影响因素共同作用均非常明显态势下,产生高铁马太效应;旅游资源禀赋、旅游接待能力、交通网络密度均不强,时空压缩程度不显著等旅游节点产生高铁过滤效应;区位条件、旅游资源禀赋、旅游接待能力和交通网络密度均具有很强优势,且时空压缩程度明显等旅游节点可成为扩散源,高铁强化了扩散源旅游流集聚作用,然后向边缘旅游地扩散,呈现为"集聚—扩散"模式;高铁使大尺度空间的不同客源地居民出游空间范围出现叠加现象,但只有区位条件、旅游资源禀赋、旅游接待能力、交通网络密度优势较强且时空压缩程度明显旅游节点产生叠加效应。     

泛亚高铁建设对中国西南边疆地区与中南半岛空间联系的影响

泛亚高铁建设是中国"走出去"战略的重要手段,能够助推中国与中南半岛及东南亚地区的跨境合作。从可达性变化和空间格局演变两方面,探讨了泛亚高铁建设对中国西南(陆域)边疆地区与中南半岛空间联系的影响。结果表明:高铁建设带来可达性在全局和局域层面显著的时空收敛,同时也在一定程度上降低了区域内部的相对差异情况,使各区域享受交通的便捷程度更趋均衡;对区内国土面积、人口与GDP等的服务水平提升并呈现国别分异的层次结构特征;凸显高铁过境市州尤其是昆明的区位优势,以及高铁中线建设对区域一体化的推动作用;强化了中国西南边疆尤其是过境市州与中南半岛的空间联系强度,并形成昆明(曲靖)—曼谷,昆明(曲靖)—河内围合的"^"型主导联系格局。