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81.
82.
A simplified procedure for evaluating aseismic stability of slope subjected to earthquake shaking, in which the effect of dynamic shear strength and time-history stress on the yielding angular acceleration of sliding block is taken into account, is presented. The fundamental feature of this procedure is the dynamic shear strength. The numerical computations are performed by using the proposed method. It is shown that the computed sliding displacement for a given core dam, with either method of dynamic shear strength properly considered, is more rational compared with the conventional computational results based on static shear strength. 相似文献
83.
On the origin of rock fragment mulches on Vertisols: A case study from the Ethiopian highlands 总被引:1,自引:2,他引:1
Jan Moeyersons Jan Nyssen Jean Poesen Jozef Deckers Mitiku Haile 《Geomorphology》2006,76(3-4):411-429
Many Vertisols in Tigray, Ethiopia, typically carry a discontinuous rock fragment (RF, size 0.5–> 40 · 10− 2 m) cover with 10 to 100 RFs m− 2. Such RF mulches are of agricultural and environmental significance because they influence the water balance in the underlying soils and the crop yield. Natural RF concentrations are mostly considered as eolian or hydraulic lag deposits, or as the result of lateral transport over the soil surface from a rock outcrop, upslope. In cultivated areas RF mulches can develop by tillage.This paper presents the case of a natural RF mulch whose lithology indicates that the RFs are up-squeezed by the local Vertisol. The study site is located in the pass of Enda Maryam, Tigray, Northern Ethiopia (39°8′ E and 13°36′ N). A circular area of 10 m diameter, about 200 m away from the water divide in the valley has been cleared annually between 01/1999 and 05/2003. During this period, 625 RFs, 17 being > 7.5 · 10− 2 m in size, totalling a mass of nearly 62 kg, have been collected. After correction for measurement procedures, the rate of RF up-warping by the Vertisol at Enda Maryam is assessed at 5 RFs m− 2 in 3 years. At this rate of appearance, the formation of current RF concentrations on top of active valley Vertisols is only a matter of 101–2 years, provided the availability of RFs below the soil surface.Although important underground displacements were measured in the Vertisol between 01/1999 and 05/2002, the supposed link between up-squeezing of RFs and plastic deformations of ‘chimney’, ‘diapir’ or ‘intrusion’-like type in the Vertisol could not be evidenced. Instead, RFs are clearly concentrated on the soil surface as well as in depth, along the existing vertical desiccation cracks, often > 1 m deep which display polygonal configurations at the soil surface. Further, bundles of slickensides containing some RFs, have been mapped at the base of the Vertisol. The slickenside configuration suggests that the RF-bearing substrate is being scraped off.While the underground displacement of RFs along active slickensides seems normal, the process of RFs ascending in ‘upright’ position in the edge of desiccation cracks needs explanation. The closure of a desiccation crack is a peristaltic-like movement, following ascent or descent of the capillary fringe. It is hypothesized that this movement gradually pushes the RF to the surface or to another place or level in the soil profile where the crack closes in last instance.The apparent young age of the valley Vertisol mulches in Ethiopia might indicate the very recent formation of yearly recurrent desiccation cracks of Vertisols in the area. Available information confirms that most valleys in the study area used to be perennially marshy. Under these conditions no movements of RFs in the soil profile are expected to occur. Gullying, leading to pronounced seasonal desiccation of the Vertisols, started in several cases not more than 50 years ago. 相似文献
84.
针对关于求解碾磨机上一点运动的速度及加速度的问题展开讨论,从运动的不同角度考虑,给出了n种不同的解法。并将此问题拓展到一般情况下进行讨论,得出正确结论。并就一些相关问题进行了分析和解释。 相似文献
85.
Mihael Brencic 《Environmental Geology》2006,49(6):804-813
During the planning, designing, construction, operation and maintenance of highways, groundwater can be of important environmental
and constructional constraint that can significantly influence the safety operation of traffic and of big influence on the
operational costs of highways. To classify and conceptualize the relation between groundwater and highways, three important
groups of problems can be determined: groundwater protection from highway influences, protection of highway from groundwater
and economic use of groundwater for highway operation. In the present study, groundwater management strategies are represented
during all life cycles of highways. Greater emphasis is given to groundwater protection and field hydrogeological investigations
for proper groundwater management related to the highway. The approach adopted in Slovenia and the role of hydrogeology is
given as an illustration. 相似文献
86.
华北平原东部淡水资源短缺,旱涝碱成灾害限制了农业生产的可持续发展。海河的治理,解决了排洪排涝排咸出路。春季开发利用地下水包括微咸水和半咸水抗旱灌溉。夏季利用伏雨洗盐排咸,增大降雨入渗,减少径流流失,防治渍涝灾害,把降雨转化为地下水资源。秋冬引蓄河水,回灌地下水补源。以土壤与潜水的地层空间作为调节大气降水、土壤水、地下水、地表水的地下水库,以调控地下水埋深在临界动态为指标,最大限度地把时空分布不均的天然降雨转化为可持续利用的水资源。地表水地下水联合运用,促使水资源采补平衡,降雨灌溉淋洗脱盐强于干旱蒸发积盐过程,地下水淡化强于矿化过程。实现旱涝碱咸综合治理,水土资源可持续利用,经济社会可持续发展,生态环境良性循环。 相似文献
87.
本文论述了2002年运城市地下水超采状况及其引起的环境地质等一系列问题.并遵循可持续发展的思想,提出了地下水资源保护的几点意见. 相似文献
88.
89.
本文基于可持续发展的思想,论述了山西省地下水开发利用现状及存在的问题,分析了地下水的开发利用潜力,提出了地下水资源开发、利用应采取的对策. 相似文献
90.