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991.
众所周知,水库是可能产生灾难性地震灾害的工程之一,广东省现有大中型水库近三百座(图1),其中土坝占93%,这些水库大多已建成数十年;建库当时也未充分考虑地震影响,为了响应“国际减灾十年”的号召,有关部门要求对这些水库的土坝进行震害预测,以便进行科学的工程决策,达到减轻地震灾害的目的。显然,这项任务既重要又繁重。为此,提出两步评估方法:第一步为初评(或称速评),初评认为地震危害性不高的土坝,原则上可不再进行第二步--详评,这样,大大减少了详评的工作量,已完成的初评结果表明,需进行详评的土坝占全部土坝的12%。 相似文献
992.
长江口北支综合治理刍议 总被引:2,自引:0,他引:2
长江口北支治理方案归纳起来有三类:阻隔型,如建坝方案;开敞型,如近年提出的“南隧北桥”中的北桥方案;半开敞型,如坝部结合型方案。本文从盐沙倒灌、水利、交通、围垦、资源保护和生态环境诸方面综合考虑,认为坝闸方案较为合宜。北支有丰富的土地、水产和潮汐能资源,为求得较大的社会、经济、环境效益,对北支应实行综合开发利用的原则。 相似文献
993.
Bedload-to-suspended load ratio and rapid bedrock incision from Himalayan landslide-dam lake record 总被引:3,自引:0,他引:3
Beth Pratt-Sitaula Michelle Garde Douglas W. Burbank Arjun Heimsath 《Quaternary Research》2007,68(1):111-120
About 5400 cal yr BP, a large landslide formed a > 400-m-tall dam in the upper Marsyandi River, central Nepal. The resulting lacustrine and deltaic deposits stretched > 7 km upstream, reaching a thickness of 120 m. 14C dating of 7 wood fragments reveals that the aggradation and subsequent incision occurred remarkably quickly (∼ 500 yr). Reconstructed volumes of lacustrine (∼ 0.16 km3) and deltaic (∼ 0.09 km3) deposits indicate a bedload-to-suspended load ratio of 1:2, considerably higher than the ≤ 1:10 that is commonly assumed. At the downstream end of the landslide dam, the river incised a new channel through ≥ 70 m of Greater Himalayan gneiss, requiring a minimum bedrock incision rate of 13 mm/yr over last 5400 yr. The majority of incision presumably occurred over a fraction of this time, suggesting much higher rates. The high bedload ratio from such an energetic mountain river is a particularly significant addition to our knowledge of sediment flux in orogenic environments. 相似文献
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996.
连拱坝是挡水盖板呈拱形的一种轻型支墩坝。本文根据连拱坝的受力特点,利用了纯拱法和有限单元法(ANSYS)分别对平桥砌石连拱坝进行了应力稳定分析。计算结果表明:该坝的应力已经不能满足设计时的安全要求;在分析比较了几种加固措施后,给出了经济有效的加固方案。 相似文献
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The Kachchh region of Gujarat, India bore the brunt of a disastrous earthquake of magnitude Mw = 7.6 that occurred on January 26, 2001. The major cause of failure of various structures including earthen dams was noted to be the presence of liquefiable alluvium in the foundation soil. Results of back-analysis of failures of Chang, Tappar, Kaswati and Rudramata earth dams using pseudo-static limit equilibrium approach presented in this paper confirm that the presence of liquefiable layer contributed to lesser factors of safety leading to a base type of failure that was also observed in the field. Following the earthquake, earth dams have been rehabilitated by the concerned authority and it is imperative that the reconstructed sections of earth dams be reanalyzed. It is also increasingly realized that risk assessment of dams in view of the large-scale investment made and probabilistic analysis is necessary. In this study, it is demonstrated that the probabilistic approach when used in conjunction with deterministic approach helps in providing a rational solution for quantification of safety of the dam and in the estimation of risk associated with the dam construction. 相似文献
999.
Earthquake induced liquefaction continues to be a major threat to many engineered structures around the world. Analysis of liquefaction becomes particularly difficult for two-dimensional (and 3D) problems such as dam/foundation systems. Predominantly, analyses for such systems are performed utilizing some type of finite element or finite difference procedure. Verification or validation of the analyses relies on very limited field performance data with reduced knowledge of the full scope of system conditions or loading conditions.Research reported in this paper represents a portion of ongoing work to obtain a database of information useful for numerical model calibration and to gain a better understanding of the complex dynamics of liquefying foundations under earth dams. Specifically, a highly instrumented model of an earth dam with clay core founded on a liquefiable foundation subjected to earthquake loading is being studied. Properties of the liquefiable foundation are varied to determine the related effects on the overlying earth dam. In this paper, results from three centrifuge physical models will be presented. The models are identical, with the exception of the location (depth) of a liquefiable layer in the foundation, and are subjected to the same dynamic excitation. Results and discussion related to the significance of the liquefiable layer location within the foundation and damage to the earth dam are presented. 相似文献
1000.