贵州喀斯特山区的土壤侵蚀性退化及其防治   总被引：36，自引：6，他引：30  

苏维词 《中国岩溶》2001,20(3):217-223

论述了贵州喀斯特山区土壤侵蚀性退化的三种类型(石漠化、土壤贫瘠化、土壤结构性恶化)及特征,从岩性、地貌、人类活动等方面详细剖析了土壤侵蚀性退化的成因机理,指出土壤生态系统的脆弱性是喀斯特山区土壤侵蚀性退化的内因,而不合理的人类活动则是该地区土壤侵蚀性退化的诱因和外动力。在此基础上,根据各喀斯特地域的具体情况,结合实施西部大开发战略中有关生态建设的要求,提出了保护抢救喀斯特山区土壤资源、防治土壤退化的对策措施。   相似文献   

寒区路面   总被引：1，自引：0，他引：1  

GuyDore 《冰川冻土》2002,24(5):593-600

The article mainly discusses several essential problems of cold region pavement, including thermal cracking of asphalt concrete, cracking deterioration and heaving, frost heave, seasonal and long term roughness induced by different frost heave, frost heave cracking, bearing capacity loss during spring thaw. The reason for these problems is that cold region pavements are subjected to intense solicitation by climatic and environmental factors. The author offers several models corresponding to the solicitation. Furthermore in conclusion of the article the author indicates future research for cold region.  相似文献   

Progressive collapse analysis through strength degradation and fracture in the Mixed Lagrangian Formulation     

O. Lavan  M. V. Sivaselvan  A. M. Reinhorn  G. F. Dargush 《地震工程与结构动力学》2009,38(13):1483-1504

The dynamic analysis of progressive collapse faces a great number of obstacles that often lead to the collapse of the analysis prior to the actual analysis of collapse. Hence, the Mixed Lagrangian Formulation that has been shown to be very robust was adopted as a framework to accommodate such analysis. By modifying the loading function and the numerical scheme, the capabilities of this framework were extended to account for strength degradation and fracture, while some insight to its behavior is introduced as well. The examples presented show a very robust and stable behavior of the numerical scheme in terms of the time step size required, even in cases where a sudden fracture takes place. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

A damage model for structures with degrading response          下载免费PDF全文

Thanh. N. Do  Filip. C. Filippou 《地震工程与结构动力学》2018,47(2):311-332

The paper presents a hysteretic damage model for the response simulation of structural components with strength and stiffness deterioration under cyclic loading. The model is based on 1D continuum damage mechanics and relates any 2 work‐conjugate response variables such as force‐displacement, moment‐rotation, or stress‐strain. The strength and stiffness deterioration is described by a continuous damage variable. The formulation uses a criterion based on the hysteretic energy and the maximum or minimum deformation for damage initiation with a cumulative probability distribution function for the damage evolution. A series of structural component response simulations showcase the ability of the model to describe different types of hysteretic behavior. The relation of the model's damage variable to the Park‐Ang damage index is also discussed. Because of its consistent and numerically robust formulation, the model is suitable for the large‐scale seismic response simulation of structural systems with strength and stiffness deterioration.  相似文献   

Influence of deterioration modelling on the seismic response of steel moment frames designed to Eurocode 8          下载免费PDF全文

Antonios Tsitos  Miguel A. Bravo‐Haro  Ahmed Y. Elghazouli 《地震工程与结构动力学》2018,47(2):356-376

This paper assesses the influence of cyclic and in‐cycle degradation on seismic drift demands in moment‐resisting steel frames (MRF) designed to Eurocode 8. The structural characteristics, ground motion frequency content, and level of inelasticity are the primary parameters considered. A set of single‐degree‐of‐freedom (SDOF) systems, subjected to varying levels of inelastic demands, is initially investigated followed by an extensive study on multi‐storey frames. The latter comprises a large number of incremental dynamic analyses (IDA) on 12 frames modelled with or without consideration of degradation effects. A suite of 56 far‐field ground motion records, appropriately scaled to simulate 4 levels of inelastic demand, is employed for the IDA. Characteristic results from a detailed parametric investigation show that maximum response in terms of global and inter‐storey drifts is notably affected by degradation phenomena, in addition to the earthquake frequency content and the scaled inelastic demands. Consistently, both SDOF and frame systems with fundamental periods shorter than the mean period of ground motion can experience higher lateral strength demands and seismic drifts than those of non‐degrading counterparts in the same period range. Also, degrading multi‐storey frames can exhibit distinctly different plastic mechanisms with concentration of drifts at lower levels. Importantly, degrading systems might reach a “near‐collapse” limit state at ductility demand levels comparable to or lower than the assumed design behaviour factor, a result with direct consequences on optimised design situations where over‐strength would be minimal. Finally, the implications of the findings with respect to design‐level limit states are discussed.  相似文献   

生态环境损失价值计算初步研究——以张掖地区为例   总被引：33，自引：2，他引：31  

徐中民  程国栋  王根绪 《地球科学进展》1999,14(5):498-504

生态环境损失价值计算是绿色国民生产总值计算的重要部分,是可持续发展国民生产总值核算的基础工作。黑河流域各种生态环境问题十分突出又各有特点。这些生态环境问题均因水资源的不合理开发利用引起。采用环境经济学的研究方法,从可持续发展的角度对生态环境损失的价值估算进行了初步尝试,并以张掖地区为例进行了实证分析,得到1995年张掖地区与水有关的生态环境损失价值约占当年国民生产总值的3%。  相似文献   

草地退化系统预测与畜种结构调整分析：以西藏聂荣县为例   总被引：3，自引：2，他引：1  

方一平  刘淑珍 《山地学报》1999,17(4):375-379

利用灰色关联方法对聂荣县草地发展的相关因子进行了系统关联分析,得出由牧业人口和载畜量为主的人为因素是影响该县草地退化,沙化的最强因子,利用灰色系统预测方法对草爱化与强关联因素进行１０年的中期预报,并对牧业人口与牲畜结构进行了方案优化与比较。  相似文献   

基于蒙特卡罗方法的广州港航行风险评估     

张静  张志坚  周芯玉 《气象与环境学报》2021,37(3):132-138

为了解不同等级能见度下的广州港航行风险特征,将不同能见度下定性的广州港航行风险定量化,以期增强广州港航行事故风险控制能力,提高广州港资源利用率。通过分析不同能见度下广州港船舶出现事故的频率以及造成后果的严重性,对二者进行概率统计后,分别对3种等级能见度下的事故数据进行蒙特卡罗仿真,有效增加了广州港航行事故的数据样本,得出3种等级能见度下的仿真结果,进而得到能见度在0—12 km内的风险分布特征。结果表明：采用基于蒙特卡罗仿真方法的概率分布模型能有效地解决航行风险小样本问题,风险结果可靠。风险在能见度不良(Vis≤5 km)时最低,良好(Vis≥10 km)时次之;受限(5 km <Vis < 10 km)时最高,近似为另外两种情况的1.7—2.4倍左右。可见该方法可以很好地评估能见度在0—12 km内的广州港航行风险,为划定风险等级标准提供参考。  相似文献   

Assessment of tafoni distribution and environmental factors on a sandstone djinn block above Petra,Jordan     

《Applied geography (Sevenoaks, England)》2013

Through the measurement of tafoni dimensions on an isolated, and unrecorded ‘djinn block’ in Petra's Ordovician Disi Sandstone, minimum surface recession were prevalent on eastern and western faces ranging from 10 to 127 mm/millennia. Moderate tafoni development was identified on northern aspects ranging from 105 to 110 mm/millennia. While on southern vertical faces, the greatest development ranged from 120 to 220 mm/millennia. Solar flux was correlated to the measured tafoni cell dimensions and revealed a minimal recession rate (and depth) of approximately 10–45 mm/millennia above which northern influences increased deterioration ‘moderately’ up to 110 mm/millennia, and southern influences had the greatest exacerbating effect with a maximum recessional rate of 220 mm/millennia – producing the greatest recession of nearly one inch (22 mm) each century. It is speculated that weathering accelerated on shaded (northern) faces through more frequent and longer spans of wetting and drying cycles, in addition to the effects of lichen and cyanobacteria overgrowth. While on regularly sunlit surfaces (southern), increased solar flux (up to ∼3000 MJ/m²/year) accelerated deterioration though more rapid, and extreme heating and cooling cycles. As rarely documented, tafoni on eastern faces were the smallest, and they were only slightly larger on western faces. Slightly increased heating from afternoon temperatures, in tandem with the incidence of frontal precipitation is attributed to the only slightly larger tafoni found on western faces (than on eastern aspects).  相似文献   

2007—2015年北京地区能见度时空变化特征     

姜江  郭文利  王春玲 《气象与环境学报》2019,(1):45-52

利用2007—2015年北京市大兴观象台、28个道面自动气象站、部分区域自动气象站等多种台站观测资料分析了2007—2015年北京地区能见度的时空变化特征。结果表明:2007—2015年北京地区春季平均能见度最高、夏季平均能见度最低,夏季及年平均能见度呈显著增加的趋势,春季和秋季能见度均呈波动增加,冬季颗粒物浓度的显著增加致使北京地区冬季能见度下降的时段集中在2011—2014年;空间上,北京西北地区能见度明显高于中心城区和东南大部地区。秋季和冬季能见度的空间分布特征与年平均能见度的分布特征较一致,表现为能见度自西北向东南方向逐渐递减;与能见度相关性最高的为相对湿度、颗粒物浓度、风向及风速,但不同要素在月、季和年尺度上的相关性差别较大;根据天气现象统计表明,近10 a来北京地区雾、霾、沙尘日均呈增加的趋势,但是山区与城区气象站点低能见度事件的发生频次存在较大的差异。整体来看,小于10 km能见度事件的发生频次在全区以增加为主,而小于1 km能见度事件的发生频次在全区以减少为主。此外,近10 a来北京地区干霾的发生频率为44. 29%,湿霾的发生频率为7. 13%,低能见度事件多由干霾造成,但湿霾发生时,能见度恶化的更明显。  相似文献