Assessment of 80 years of ancient‐badlands restoration in Saldaña,Spain          下载免费PDF全文

Joaquín Navarro Hevia  José Carlos de Araújo  Jorge Mongil Manso 《地球表面变化过程与地形》2014,39(12):1563-1575

This paper presents the history of badland generated in the Saldaña region, Spain; as well as the main responses eight decades after the start of restoration – in terms of vegetation, soil and erosive processes. The restoration consisted of intense reforestation and construction of more than 100 check dams and numerous wattle fences. Presently, the dense vegetation (87% cover) contrasts markedly with the degraded landscape from the early 20th century (5% cover). The thickness of litter and the natural presence of some species (Quercus pyrenaica, Paeonia broteroi and Lactarius deliciosus) clearly indicate the recovery of the site. The development of the forest cover shows that the intervention has the potential to recover almost 90% of the area. There is also evidence of soil regeneration, although some properties (erodibility, resistance to penetration and shear‐strength resistance) are not that different between the forested and degraded areas. In the restored zones, runoff is negligible, since a thick layer of moss covers the spillways of all the check dams. Erosion has almost been stopped by the effects of vegetation cover, litter and higher infiltration rates (infiltration rate in forested slopes is 43.4 times greater than in bare slopes). Sediment detachment, such as landslides, mudflows and piping, still occur, but are restricted to the degraded zones. Furthermore, even when sediments are mobilized from the upper degraded hillslopes during the larger storms events (2000–2010), check dams and the lower elevation restored forest‐buffers effectively work to reduce the sediment yield into the Carrión River by almost three orders of magnitude (<10² mg L^‐1), compared with data from the 1930s and 1940s (>10⁵ mg L^‐1). Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Seismic stability of earth-rock dams using finite element limit analysis     

《Soil Dynamics and Earthquake Engineering》2014

In this study, a finite element limit analysis method is developed to assess the seismic stability of earth-rock dams. A pseudo-static approach is employed within the limit analysis framework to determine the lower and upper bounds on the critical seismic coefficients of dams. The interlocking force in the soil is considered, and the rockfill material is assumed to follow the Mohr–Coulomb failure criterion and an associated flow rule. Based on the native form of the failure criterion, the lower and upper bound theorems are formulated as second-order cone programming problems. The nonlinear shear strength properties of rockfill materials are also considered. The developed finite element limit analysis is applied to two different types of earth-rock dams. The results indicate that the rigorous lower and upper bounds are very close even for rockfill materials with large internal friction angles. The failure surfaces are easily predicted using the contour of the yield function and the displacement field obtained by the limit analysis method. In addition, the pore water pressures are modelled as external forces in the limit analysis to assess the seismic stability of earth-rock dams in the reservoir filling stage.  相似文献   

陕北黄河中游淤地坝拦沙功能失效的判断标准   总被引：7，自引：0，他引：7  

高云飞  郭玉涛  刘晓燕  何兴照 《地理学报》2014,69(1):73-79

利用2011 年第一次全国水利普查中4157 座骨干坝数据、1989 年陕北淤地坝调查中1640座中小坝数据,分别计算了1950-2011 年期间骨干坝、1956-1989 年期间中小坝的逐年平均淤积比例,得到截至2011 年,1980 年前修建骨干坝的平均淤积比例基本稳定,平均值为0.77,1980 年后开始逐渐下降;截至1989 年,1980 年前修建中小坝的平均淤积比例基本稳定,平均值为0.88,1980 年后开始逐渐下降的变化趋势,确定平均淤积比例0.77、0.88 分别为骨干坝、中小坝拦沙能力失效的判断标准。利用陕北淤地坝调查数据计算得到的骨干坝拦沙功能失效判断一致;在无定河、延河流域,水文站输沙数据的变化趋势与淤地坝是否拦沙显著相关。最后从淤地坝工程结构的角度,剖析了排水排沙位置的改变是判断标准形成的原因。  相似文献   

泥石流拦砂坝底扬压力分布及影响因素试验     

陈兴长  陈慧  游勇  柳金峰 《岩土力学》2018,39(9):3229-3236

泥石流拦砂坝底的扬压力会抵消坝体的部分有效荷重,影响其抗倾覆稳定性。为了研究拦砂坝底扬压力的分布规律及其影响因素,设计制作了拦砂坝模型和扬压力采集系统,开展了不同沟床坡度和不同坝前堆积条件下的扬压力模拟试验。试验结果表明,扬压力自坝踵至坝趾不断减小,且与渗流距离呈线性关系,当坝前有堆积物时相关系数绝对值达到0.98以上;沟床坡度明显影响坝底扬压力的分布。随着沟床坡度的增加,扬压力不断减小,且对坝踵处扬压力的影响较坝趾处更大;坝底和坝前堆积物的渗透性对扬压力的影响也很显著,它们的渗透性越差,扬压力就越小;坝前堆积物的渗透性还显著影响扬压力的分布规律,渗透性越差,其分布规律性就越强。研究成果为深入研究泥石流拦砂坝底扬压力的作用过程和作用机制奠定了基础。  相似文献   

双场点地震危险性分析方法及其应用   总被引：1，自引：1，他引：0       下载免费PDF全文

雷建成  高孟潭  吴健  亢川川 《地震学报》2010,32(3):310-319

提出了双场点地震危险性分析方法,用以计算在相同地震构造环境中,相同地震作用下的相邻两个工程场点同时超越其给定地震动参数的概率.该方法是确定系统的危险段落、场点遭受的附加地震危险的有效工具.基于汶川MS8.0地震后大渡河干流及邻近地区的地震环境,以大渡河干流梯级水电站系统为例,确定了大渡河干流梯级水电站各个河段的地震危险性.其中危险性最高的3个河段是:龚嘴—铜街子河段、沙坪—龚嘴河段和大岗山—龙头石河段.  相似文献   

Effect of ground-motion asynchronism on the equivalent acceleration of earth dams     

Emilio Bilotta  Luca PaganoStefania Sica 《Soil Dynamics and Earthquake Engineering》2010

Under seismic loads the deformability of an earth dam may induce several effects, including ground-motion amplification and asynchronism between different points of the dam embankment. The paper analyses the asynchronous effects occurring in two existing earth dams, representing well-documented case histories: the El Infiernillo Dam (Mexico) and the Camastra Dam (Italy). Asynchronous effects are analysed by theoretical predictions of the dam seismic response by adopting an advanced dynamic approach, which takes into account the main features that dam soils exhibit under cyclic loading conditions. For different potentially unstable masses within the dam embankment, equivalent accelerations were computed as the ratio between the resultant of the inertial forces and the weight of the volume V associated to the unstable mass. With the exception of very cortical sliding surfaces – not significant for dam stability – in most of the analysed cases the equivalent seismic coefficients do not exceed the peak acceleration at the dam base.  相似文献   

Seismic performance sensitivity and uncertainty analysis of gravity dams          下载免费PDF全文

M. Alembagheri  M. Seyedkazemi 《地震工程与结构动力学》2015,44(1):41-58

Uncertainties in structural engineering are often arising from the modeling assumptions and errors, or from variability in input loadings. A practical approach for dealing with them is to perform sensitivity and uncertainty analysis in the framework of stochastic and probabilistic methods. These analyses can be statically and dynamically performed through nonlinear static pushover and IDA techniques, respectively. Of the existing structures, concrete gravity dams are infrastructures which may encounter many uncertainties. In this research, probabilistic analysis of the seismic performance of gravity dams is presented. The main characteristics of the nonlinear tensile behavior of mass concrete, along with the intensity of earthquake excitations are considered as random variables in the probabilistic analysis. Using the tallest non‐overflow monolith of the Pine Flat gravity dam as a case study, its response under static and dynamic situations is reliably examined utilizing different combinations of parameters in the material and the seismic loading. The sensitivity analysis reveals the relative importance of each parameter independently. It will be shown that the undamaged modulus of elasticity and tensile strength of mass concrete have more significant roles on the seismic resistance of the dam than the ultimate inelastic tensile strain. In order to propagate the parametric uncertainty to the actual seismic performance of the dam, probabilistic simulation methods such as Monte Carlo simulation with Latin hypercube sampling, and approximate moment estimation techniques will be used. The final results illustrate the possibility of using a mean‐parameter dam model to estimate the mean seismic performance of the dam. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

基于多目标遗传算法的巨型水库群发电优化调度   总被引：2，自引：0，他引：2  

魏加华  张远东 《地学前缘》2010,17(6):255-262

低碳时代,水电作为清洁可再生能源,节能发电调度为梯级水电联合调度运行带来了难得的历史机遇,如何有效地开展梯级水库群优化调度,充分合理利用水能资源,是流域梯级电站管理迫切需要解决的问题。文章在对清江梯级与三峡梯级径流特征分析的基础上,建立了以水库群整体发电量最大和弃能最小为目标的梯级调度模型。根据电力系统对三峡、葛洲坝、水布垭、隔河岩、高坝洲水电站的要求,用1951—2002年的月径流资料和典型年的日径流资料进行长期和短期优化调度,采用多目标遗传算法得到清江3个电站、三峡-葛洲坝2电站单独运行和联合优化调度发电指标,5库联合优化调度系统多年平均发电量增加约21亿kW.h;短期(日)优化调度较长期(月时间尺度)优化调度发电效益有进一步提升,增发电量约9.68亿kW.h。研究表明,充分利用清江和三峡梯级实际运行位置相近、水力联系紧密、互补性强的特点,统一安排电站机组运行模式,合理分配机组出力,可在来水量相同的条件下获得更大的效益。  相似文献   

南京江宁区某退役小型硫铁矿尾矿库的治理方法     

邢姝  陈征宙  邹春江  韩非  缪世贤 《地质灾害与环境保护》2009,20(4):62-66

针对江宁区某退役小型硫铁矿出现的不良地质现象,对该尾矿坝进行了抗滑以及抗渗稳定性计算和分析,指出坝体处于不稳定状态,并提出具体治理方法。治理的方案包括降低坝体高度减载,在坡脚处反压坝体增加坝体稳定性,设置排渗设施降低浸润线高度,修筑排水沟阻止地表水停留在库区表面。最后需验证治理后尾矿坝在地震作用下的稳定性,运用时程分析法对设计后的坝体进行了动力有限元的分析,结果表明坝体内部和整体处于较稳定的状态。  相似文献   

Dynamic properties and liquefaction resistance of two soil materials in an earthfill dam—Laboratory test results     

V.C. Xenaki  G.A. Athanasopoulos 《Soil Dynamics and Earthquake Engineering》2008,28(8):605-620

Results are presented of laboratory resonant column and cyclic triaxial tests on specimens of two compacted soils (a sandy–silty clay and a sand–gravel mixture), planned to be used in the core and the shells, respectively, of a proposed earthfill dam. The values of low-amplitude shear modulus of the clayey material were found to increase with increasing confining pressure and decreasing water content, with deviations of ±20% from the predictions of the “Hardin equation”. On the other hand, the low-amplitude damping ratio was found to be at least four times higher than the values corresponding to natural undisturbed cohesive soils. The proposed G/G₀−γ_c curve for the compacted cohesive soil was found to be independent of confining pressure and small variations of the water content on either side of the optimum value and showed a remarkable agreement with recently published similar curves for natural cohesive soils. For the case of the sand–gravel mixture, normalized G/G₀–γ_c and D–γ_c curves are proposed, based on recently published results for gravelly soils and the limited data of the present study. The liquefaction resistance of the saturated sand–gravel mixture was found to be strongly dependent on its relative density, especially for high values of cyclic stress ratio. A relative density of at least 55% was found to be necessary to assure safety against earthquake-induced liquefaction of the material. The results presented herein may be used (directly or as guide) in the seismic analysis of (new or existing) earth dams constructed from similar soil materials and in addition they provide insight into the dynamic behavior of compacted soils.  相似文献