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461.
动载荷作用下岩石破坏过程的数值试验研究 总被引:3,自引:0,他引:3
采用基于细观损伤力学基础上开发的动态版RFPA2D数值模拟软件,对动载荷作用下应力波延续时间、应力波峰值和围压对岩石试样破坏的影响进行了数值研究,结果表明,应力波延续时间较短,则尾随应力波波前的高应力区范围较窄,应力波衰减较快;相反,应力波延续时间较长,则紧跟应力波波前的高应力区范围较大,岩石处于破坏状态的时间延长,岩石的破碎程度加大。此外,存在一个合适的应力波延续时间,过分地加大应力波延续时间,反而不利于岩石裂隙的发育。动载荷的峰值越大,试样的破坏程度越大,当峰值达到一定值时,试样顶部呈现粉碎状,试样从上到下破坏程度逐渐减弱。在冲击载荷作用下的岩石随着围压的增加更难破碎,但当围压增大到一定程度时,岩石会突然失稳破坏。 相似文献
462.
463.
自然营造力作用下岩体混凝土水力劈裂分析与探讨 总被引:4,自引:2,他引:2
水利水电、矿业等工程在自然营造力作用下的水力劈裂边界条件与人工致裂不完全相同,有其自身的特点。在总结自然营造力作用下水力劈裂特点的基础上,根据研究的尺度不同,将水力劈裂研究分为岩体宏观的、综合的、统计意义上的水力劈裂和单裂纹的水力劈裂研究两种。分析了单裂纹内水流特性,将单裂纹内的水力劈裂分为两个阶段(或两种情况)分别进行研究,并将此问题得以简化,同时还提出了不同阶段裂纹内水流运动分析的模型。 相似文献
464.
465.
由于切割式横缝的联接作用,切割式横缝碾压混凝土重力坝近似为一个整体结构。当遭遇强震作用时,随着切割式横缝的开裂程度不同,碾压混凝土重力坝的抗震安全性也就有所不同。针对切割式横缝的结构特点,在有限元法动力分析中,利用“生死”单元来模拟切割式横缝的联接单元和切割单元,且以整个横缝联接单元弹性模量的不同折减来模拟切割式横缝的不同开裂程度,并应用到金安桥水电站左岸坡坝段群的抗震安全性分析中。分析结果表明:金安桥水电站左岸坡坝段群在设防烈度为IX度的地震作用下,切割式横缝的开裂对左岸坡单个坝段和坝段群的抗震安全性影响不大,且大坝是安全的。这说明了金安桥水电站碾压混凝土重力坝结构设计合理,能够抵御设防地震。 相似文献
466.
467.
阳江抽水蓄能电站岩体水压致裂综合测试与应用研究 总被引:2,自引:0,他引:2
阳江抽水蓄能电站的输水隧洞围岩承受最大静内水压力高达7.83MPa, 因此原地应力状态、围岩自身承载能力及高压透水性状等对工程的科学设计不可或缺。测量结果表明, 工程区现今地壳应力场的总体特征为:水平主应力为最大主应力, 最大水平主应力的优势方向为NW-NWW向; 厂房和高压岔管区围岩的最大主应力值一般为14.5±0.5MPa, 最小主应力值一般为9±0.5MPa; 围岩自身的抗载强度一般为10~14MPa; 在8~10MPa高压力作用下围岩基本不透水。洞室围岩物理力学参数的这些测试成果, 为工程的科学设计提供了可靠依据。 相似文献
468.
Brenda Moraska Lafrancois Suzanne Magdalene D. Kent Johnson 《Journal of Paleolimnology》2009,41(4):603-622
Long-term water quality monitoring data from two riverine lakes in the Upper Mississippi River basin, Lakes St. Croix and
Pepin, were analyzed to compare the long-term average water quality conditions and land use distributions, water quality trends
and loads at lake inlets and outlets, trends from long-term versus short-term monitoring records, and the ability of paleolimnological
cores to accurately infer lake water quality conditions. During the 1976–2004 period, the long-term average concentrations
of nutrients, suspended solids, and chlorophyll-a were consistently lower at the Lake St. Croix inlet versus the Lake Pepin inlet, which drains a greater proportion of urban
and agricultural runoff. Despite these differences, nutrient trends were similar at the inlets to both lakes; reductions in
total phosphorus and ammonium concentrations were attributed to improvements in point source technologies, whereas increasing
nitrate concentrations were attributed to both point source changes and nonpoint source increases. Despite improvements in
several water quality variables, nitrate concentrations are increasing in both lakes, sediment trends indicate persistent
nonpoint source inputs to Lake Pepin, and current total phosphorus concentrations remain well above pre-1950s levels in both
lakes. Since urban development and agriculture are increasing in the Lake St. Croix and Lake Pepin Watersheds, continued point
source regulation and additional nonpoint source control efforts will be needed to further improve water quality in these
lakes. The 1976–2004 trends for most water quality variables were similar at inlet versus outlet sites on Lake St. Croix.
Trends at Lake Pepin inlet versus outlet sites were less similar, but data availability limited the comparison to the 1993–2003
period. While the truncated data record highlighted short-term trends in both lakes, the full data record was most useful
for exploring general patterns in water quality. Length of monitoring record affected our ability to detect trends at the
inlets to both lakes, and altered the magnitude of detected trends. During the two decades of the 1980s and 1990s, paleolimnological
estimates of retained phosphorus loads were similar to those estimated from recent water quality monitoring. These similarities
support the use of paleolimnological approaches to infer past water quality conditions in Lakes St. Croix and Pepin.
This is one of eight papers dedicated to the “Recent Environmental History of the Upper Mississippi River” published in this
special issue of the Journal of Paleolimnology. D. R. Engstrom served as guest editor of the special issue. 相似文献
469.
Heterogeneous characteristics of streambed saturated hydraulic conductivity of the Touchet River,south eastern Washington,USA 总被引:1,自引:0,他引:1
Randal Leek Joan Q. Wu Li Wang Timothy P. Hanrahan Michael E. Barber Hanxue Qiu 《水文研究》2009,23(8):1236-1246
Traditionally a streambed is treated as a layer of uniform thickness and low saturated hydraulic conductivity (K) in surface‐ and ground‐water studies. Recent findings have shown a high level of spatial heterogeneity within a streambed and such heterogeneity directly affects surface‐ and ground‐water exchange and can have ecological implications for biogeochemical transformations, nutrient cycling, organic matter decomposition, and reproduction of gravel spawning fish. In this study a detailed field investigation of K was conducted in two selected sites in Touchet River, a typical salmon spawning stream in arid south eastern Washington, USA. In‐stream slug tests were conducted to determine K following the Bouwer and Rice method. For the upper and lower sites, each 50 m long and 9 m wide and roughly 20 m apart, a sampling grid of 5 m longitudinally and 3 m transversely was used. The slug tests were performed for each horizontal coordinate at 0·3–0·45, 0·6–0·75, 0·9–1·05 and 1·2–1·35 m depth intervals unless a shallower impenetrable obstruction was encountered. Additionally, water levels were measured to obtain vertical hydraulic gradient (VHG) between each two adjacent depth intervals. Results indicated that K ranged over three orders of magnitude at both the upper and lower sites and differed between the two sites. At the upper site, K did not differ significantly among different depth intervals based on nonparametric statistical tests for mean, median, and empirical cumulative distribution, but the spatial pattern of K varied among different depth intervals. At the lower site, K for the 0·3–0·45 m depth interval differed statistically from those at other depth intervals, and no similar spatial pattern was found among different depth intervals. Zones of upward and downward water flow based on VHG also varied among different depth intervals, reflecting the complexities of the water flow regime. Detailed characterization of the streambed as attempted in this study should be helpful in providing information on spatial variations of streambed hydraulic properties as well as surface‐ and ground‐water interaction. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
470.
This paper presents a semi-analytical solution for one dimensional consolidation problem of inelastic clays under cyclic loading considering the effect of the change of the consolidation coefficient of the soil layer. Due to change of the consolidation coefficient, and time-dependant loading, Terzaghi's theory would not be applicable in cyclic conditions. In this research, a method based on the time variable exchange along with the superimposing rule is employed to overcome these shortcomings. Changes in the consolidation coefficient are applied in the solution by modifying the loading and unloading durations introducing a Virtual Time. Based on the superimposing rule a set of continuous static loads in specified times are used instead of the cyclic load in the transformed time space. Each full cycle of loading is replaced by a pair of static loads with different signs. Based on the Terzaghi's theory the pore-water pressure distribution and the degree of consolidation are calculated for each static load and the results are superimposed. A set of laboratory consolidation tests under cyclic load and numerical analysis are performed in order to verify the presented method. The numerical solution and laboratory tests results showed the accuracy of the presented method. 相似文献