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851.
考虑拱效应的高面板堆石坝流变收敛机制研究 总被引:1,自引:0,他引:1
采用一种能模拟高围压条件的堆石料幂函数流变本构模型,探讨狭窄河谷条件下堆石体流变变形的发展规律及相应的控制流变变形的工程措施。数值仿真结果表明,在狭窄河谷中的堆石体存在着拱效应。由于拱效应的影响,如果不考虑堆石体流变导致拱效应减弱而增加的附加变形,数值仿真计算得到的大坝变形将小于其真实的变形。受拱效应影响,堆石体初期变形的速率受到抑制,但随着坝体的升高、蓄水后水压力的加大以及堆石体随时间发展等流变变形因素的影响,堆石体中的拱效应逐渐减弱。要减小面板浇筑后由于其下卧的堆石体流变产生的附加变形,可以尽量利用面板过水及堆石体挡水,以加快堆石体流变变形的完成。采取措施,避免大的陡坡突变以及面板浇筑时间滞后其下卧堆石体断面几个月。 相似文献
852.
长江口拦门沙河段潮滩表层沉积物分布特征(英文) 总被引:2,自引:0,他引:2
Sediment samples with high spatial resolution (432 samples in total) and flow data were collected on the tidal flats in the mouth-bar region of the Yangtze Estuary. The data was collected in July 2005, July 2006 and May 2007. The samples were analyzed with a particle sizer, resulting in the sediment distribution. The grain sizes and related parameters were analyzed. The results were presented in a ternary diagram. The sediment mainly consisted of sand, silty sand, sandy silt, sand-silt-clay, silt and clayey silt. And sand skeletons and clay matrices were found. At Nanhui Shoal, silt skeletons could be identified as well. Furthermore, the results were discussed per shoal. Although some depth dependencies were found per shoal, no general relation was found. The results are as follows: sediment located at these tidal flats of the Yangtze Estuary was mainly composed of sand, silty sand and silt. The median grain size in sediment was relatively complex with a range from 2.5 φ to 8 φ. The distributions of sorting coefficients ranging from 1 to 2 were in agreement with median sizes. It was suggested that sediment of the tidal flats was coarser and better sorted or finer and worse sorted. The skewness in sediment distribution varied from 0.1 to 0.8. In addition, the distributions of sorting coefficient and skewness in sediment at Chongming Eastern Shoal, Hengsha Eastern Shoal and Jiuduan Shoal were of similar characteristics because there were closely positive correlated relationships among these parameters. However, due to the location difference between Nanhui Southern Shoal and Eastern Shoal, the values of sorting coefficient and skewness had relatively large distinctions. The tracks of sediment transport could be described based on the distributions of sediment, which might reveal sediment transport controlled by two dominant hydrodynamic factors of current and wave. It was appreciable that coarser sediment with lower sorted coefficient was affected by dominant ebb current action and intense wave action resulted from rapidly dissipated wave energy. Moreover, due to the effects of obstructed branches, guided current and broken wave actions of the Deep Water Channel Project, grain-size in sediment located at two sides of the groyne was of uneven distribution characteristics. 相似文献
853.
854.
Ground temperatures from four of the seven extensively studied highway cross-sections near Gulkana/Glennallen,Alaska during 1954~1962,were chosen to better understand the impacts of highway construction on warm permafrost.Both the thawing of permafrost and seasonal frost action impacted on road surface stability for about 6 years until the maximum summer thaw reached about 3 m in depth.Seasonal frost action caused most of the ensuing stability problems.Unusually warm summers and the lengths of time required to re-freeze the active layer were far more important than the average annual air temperatures in determining the temperatures of the underlying shallow permafrost,or the development of taliks.The hypothesized climate warming would slightly and gradually deepen the active layer and the developed under-lying talik,but its effect would be obscured by unusually warm summers,by warmer than usual winters,and by the vari-able lengths of time of the zero curtains.At least one period of climate mini-cooling in the deeper permafrost during the early 20th century was noted. 相似文献
855.
利用NCEP 1°×1°再分析资料、多普勒天气雷达及5 min地面自动站加密观测资料,对2018年6月8日夜间昆明主城区突发的局地短时强降水天气过程,从环流背景、地形作用、中尺度特征等方面进行分析,结果表明:孟加拉湾低压、切变线与地面冷锋是此次过程的天气尺度影响系统;充沛的水汽条件、对流不稳定条件是强降水天气形成的有利条件;主城特殊的地形及南侧滇池水体对降水有增幅作用。多普勒雷达特征显示",列车效应"明显,强回波集中在中低层,具有明显的辐合;6 min的雷达组合反射率CR和雨强分布RZ与5 min的雨量变化有较好的对应关系。 相似文献
856.