双圈管黏土冻结壁形成过程冻胀力模型试验研究

基于相似理论,开展了双圈管同步冻结条件下黏土冻结壁形成过程冻胀力模型试验研究．在试验条件下黏土冻结壁交圈顺序为外圈管、内圈管,两圈管之间,冻结310d后冻结壁发展到井帮位置．随时间发展,外圈管内侧温度分布逐渐均匀,而外圈管外侧仍存在较大温度梯度．结果表明：冻胀力的发展变化与冻结温度场密切相关,且表现出显著的时空不均匀性...     

2013年1月大气环流和天气分析

2013年1月大气环流特征为:北半球极涡呈偶极型,极涡范围及强度较常年偏弱,中高纬环流呈三波型,欧亚大陆槽位于西西伯利亚,位置偏北,引导多股冷空气影响我国北方,月内中高纬环流形势调整较大,上旬以经向型环流为主,中下旬则转为纬向型环流;西太平洋副热带高压接近常年同期,东亚大槽位于西北太平洋西岸,较常年偏强,南支槽位于90°E附近,较常年略偏弱.2013年1月,全国平均气温为-5.2℃,略低于常年同期(-5.0℃).月内气温阶段性调整明显,上旬,较同期偏低3℃,下旬,较同期偏高1.7℃.全国平均降水量为6.5 mm,较常年同期(13.2 mm)偏少50.8％.月内出现一次强冷空气过程,雾霾天气频繁,共出现3次较大范围雾霾过程.南方部分地区遭受低温雨雪冰冻灾害,北方局地遭受雪灾,云南大部、贵州西部及四川南部等地气象干旱持续.     

A simplified analysis method for piled raft foundations in non‐homogeneous soils

A simplified method of numerical analysis based on elasticity theory has been developed for the analysis of axially and laterally loaded piled raft foundations embedded in non‐homogeneous soils and incorporated into a computer program “PRAB”. In this method, a hybrid model is employed in which the flexible raft is modelled as thin plates and the piles as elastic beams and the soil is treated as springs. The interactions between structural members, pile–soil–pile, pile–soil–raft and raft–soil–raft interactions, are approximated based on Mindlin's solutions for both vertical and lateral forces with consideration of non‐homogeneous soils. The validity of the proposed method is verified through comparisons with some published solutions for single piles, pile groups and capped pile groups in non‐homogeneous soils. Thereafter, the solutions from this approach for the analysis of axially and laterally loaded 4‐pile pile groups and 4‐pile piled rafts embedded in finite homogeneous and non‐homogeneous soil layers are compared with those from three‐dimensional finite element analysis. Good agreement between the present approach and the more rigorous finite element approach is demonstrated. Copyright © 2002 John Wiley & Sons, Ltd.     

人工冻结梁构件中不同加筋作用的对比试验研究

考虑土层冻结构件中冻结管的加筋作用,对于增加冻结构件强度,减小变形量,提高人工冻结支护工程经济效益有重要作用。为研究冻结管对人工冻结构件的加筋作用,通过淤泥质粘土人工冻结梁构件三点弯试验,获得了各级载荷下构件的位移值。根据对冻土梁加筋与否,构件特定力学响应的比较,完成了冻结管加筋作用的量化分析。     

青藏公路沿线多年冻土区活动层起始冻融时间的时空变化特征和影响因素

多年冻土区活动层冻融格局对气候系统、能量平衡、水文过程和生态系统有重要的影响,地表冻融时间是反映冻融格局时空变化的重要指标。为了探明多年冻土区活动层起始冻融时间的影响因素和机制,通过对青藏公路沿线8个典型活动层观测场地表起始融化时间（OOT）和起始冻结时间（OOF）进行研究,分析了不同观测场起始冻融时间的时空差异及其影响因素。结果表明：（1）青藏高原多年冻土区活动层起始融化主要发生在4月中下旬,起始冻结主要发生在10月中下旬。OOT的年际变化幅度远大于OOF,每年起始冻结的发生较起始融化更为准时。（2）起始融化发生时的气温普遍比起始冻结发生时高1~4℃。气温对OOT的影响要比对OOF大,其中OOT的变化主要与春季气温有关,冬季气温对其影响不大。（3）植被和土壤水分对OOT和OOF有重要调节作用,土壤含水率越高,植被状况越好,起始融化和冻结的发生时间往往越迟。（4）在起始融化和冻结阶段,厚度较大和持续时间较长的积雪对地温变化有明显的抑制作用,对OOT和OOF有延迟作用。     

Reducing landscape heterogeneity for improved land use and land cover (LULC) classification across the large and complex Ethiopian highlands

This paper presents a land use and land cover (LULC) classification approach that accounts landscape heterogeneity. We addressed this challenge by subdividing the study area into more homogeneous segments using several biophysical and socio-economic factors as well as spectral information. This was followed by unsupervised clustering within each homogeneous segment and supervised class assignment. Two classification schemes differing in their level of detail were successfully applied to four landscape types of distinct LULC composition. The resulting LULC map fulfills two major requirements: (1) differentiation and identification of several LULC classes that are of interest at the local, regional, and national scales, and (2) high accuracy of classification. The approach overcomes commonly encountered difficulties of classifying second-level classes in large and heterogeneous landscapes. The output of the study responds to the need for comprehensive LULC data to support ecosystem assessment, policy formulation, and decision-making towards sustainable land resources management.     

张家湾水库大坝的渗流和稳定分析

以张家湾水库大坝为例,运用有限单元法对除险加固后均质土坝的渗流进行分析计算,同时运用瑞典圆弧滑动法和简化Bishop法对均质土坝的坝体稳定进行分析计算,在此基础上对水库大坝进行了渗流安全评价和稳定安全评价.     

Simulation of frozen ground distribution in northeast China based on a surface frost number model

Journal of Geographical Sciences - Against the background of global warming, environmental and ecological problems caused by frozen ground degradation have become a focus of attention for the...     

A QUANTITATIVE STUDY FOR ABNORMAL FREEZING RAINS AND SNOWSTORMS IN SOUTHERN CHINA IN EARLY 2008

A quantitative diagnosis is carried out for the upward branch of a local meridional circulation over southern China(SC) during the abnormal snowstorms with severe freezing rain from 10 January to 3 February 2008.The diagnostic study shows that the upward branch is mainly associated with the zonal advection of westerly momentum and meridional temperature advection instead of the latent heating(which is commonly the dominant factor in many other storm cases).The corresponding weather analyses indicate that(1) the zonal advection of westerly momentum represents the effect of the upper-level divergence on the anticyclone-shear side in the entrance of a 200 hPa westerly jet with a westward deviation from its climatological location over southwestern Japan;(2) the meridional temperature advection represents the interaction between the mid-lower layer(850 to 400 hPa) warm advection over SC(ahead of temperature and pressure troughs with the latter trough deeper than the former in the Bay of Bengal) and cold advection over north China(steered by an underlying flow at 500 hPa);(3) the relatively weak vapor transport(compared to that of spring,summer and autumn) from the Bay of Bengal and the South China Sea to SC and the existence of a temperature inversion layer in the lower troposphere over SC diminish the effect of latent heating.With the significant increase of vapor transport after 24 January,the role of latent heating is upgraded to become the third positive contributor to the upward branch over SC.     

冻融循环作用下节理岩体锚固性能退化机理和模式

岩土锚固的长期性能和耐久性是当前岩土工程界普遍关注的热点问题,也是影响锚固工程长期安全性的关键问题之一。节理岩体存在不同尺度、程度的损伤和缺陷,为地下水的存储和运移提供场所和通道。当达到孔隙水和裂隙水的冻结温度时,岩体中产生冻胀,并伴随着水分迁移,影响锚固系统的锚固性能,在冻融循环作用下,引起锚固系统长期性能和耐久性的退化。依据孔隙介质的冻结理论,建立了砂浆、岩石、砂浆-钢筋和砂浆岩石接触面静水压力学模型,分析其冻结机理。在总结岩石冻融损伤劣化研究成果基础上,深入系统地分析了节理岩体锚固系统的冻融损伤劣化机理及其影响因素,并建立冻融循环作用下节理岩体锚固性能退化的6种模式及其数学模型。