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71.
在基坑、隧道开挖等过程中,不同部位的土体会经历不同的应力路径,在不同的应力路径下,土体可能表现出截然不同的静力学特性。同时,在工程实际中,土体的工作应变经常处于小应变范围,而在小应变情况下,土体的静力特性表现出更强的非线性和应力路径依赖性。基于广泛分布于东部地区,并且表现出诸多不良工程特性的软黏土,进行一系列不排水和排水条件下的应力路径静力试验,以研究应力路径对饱和软黏土静力特性,尤其是小应变情况下割线模量的影响。试验结果表明,不管在不排水还是在排水条件下,应力路径都对饱和软黏土的静强度产生巨大的影响,表现为围压增加的加载应力路径增大了静强度,而围压减小的卸载应力路径降低了静强度。同时,应力路径对割线弹性模量产生了更大的影响,围压增加的加载应力路径降低了割线模量,而围压减小的卸载应力路径增大了割线模量。应力路径对割线模量的影响在小应变时表现的更加明显,而这种影响主要原因是应力路径方向改变造成的土体各向异性。 相似文献
72.
73.
Quantifying distributional behavior of extreme events is crucial in hydrologic designs. Intensity Duration Frequency (IDF) relationships are used extensively in engineering especially in urban hydrology, to obtain return level of extreme rainfall event for a specified return period and duration. Major sources of uncertainty in the IDF relationships are due to insufficient quantity and quality of data leading to parameter uncertainty due to the distribution fitted to the data and uncertainty as a result of using multiple GCMs. It is important to study these uncertainties and propagate them to future for accurate assessment of return levels for future. The objective of this study is to quantify the uncertainties arising from parameters of the distribution fitted to data and the multiple GCM models using Bayesian approach. Posterior distribution of parameters is obtained from Bayes rule and the parameters are transformed to obtain return levels for a specified return period. Markov Chain Monte Carlo (MCMC) method using Metropolis Hastings algorithm is used to obtain the posterior distribution of parameters. Twenty six CMIP5 GCMs along with four RCP scenarios are considered for studying the effects of climate change and to obtain projected IDF relationships for the case study of Bangalore city in India. GCM uncertainty due to the use of multiple GCMs is treated using Reliability Ensemble Averaging (REA) technique along with the parameter uncertainty. Scale invariance theory is employed for obtaining short duration return levels from daily data. It is observed that the uncertainty in short duration rainfall return levels is high when compared to the longer durations. Further it is observed that parameter uncertainty is large compared to the model uncertainty. 相似文献
74.
Pawe? Koperski 《Limnologica》2010,40(3):233-240
Reduced biological diversity in freshwater habitats situated in urban areas has been discussed in numerous studies. Certain municipal areas, however, can help save animal diversity of freshwater invertebrates. In the present study animals were collected or observed alive in 13 freshwater environments localized in Warsaw - the second largest city of Central Europe - in a densely populated, urban building complex close to the city, and also in suburban areas. Leech assemblages in all the environments under observation were numerically dominated by a few common species, but on the whole 19 species were collected or observed. The populations of six rare leech species inhabit both flowing and standing waters in Warsaw. Five of these species are on the Polish Red List of Species and one is strictly protected. The shallow Lake Powsinkowskie is the richest freshwater environment in the studied area in terms of species richness and rarity and also one of the richest lakes in Poland. Taxonomic diversity in the environments under study seems not to be directly related to the size of the water body or the level of degradation but rather to the habitat complexity, especially the diversity of the bottom in littoral zone. Certain freshwater habitats located inside this great urban complex still create good conditions for rare, highly specialized species. 相似文献
75.
Aleksey S. Telyakovskiy Gastão A. Braga Satoko Kurita Jeff Mortensen 《Advances in water resources》2010
For certain initial and boundary conditions the Boussinesq equation, a nonlinear partial differential equation describing the flow of water in unconfined aquifers, can be reduced to a boundary value problem for a nonlinear ordinary differential equation. Using Song et al.'s (2007) [7] approach, we show that for zero head initial condition and power-law flux boundary condition at the inlet boundary, the solution in the form of power series can be obtained with Barenblatt's (1990) [2] rescaling procedure applied to the power series solution obtained in Song et al. (2007) [7] for the power-law head boundary condition. Polynomial approximations can then be obtained by taking terms from the power series. Although for a small number of terms the newly obtained approximations may be worse than polynomial approximations obtained by other techniques, any desired accuracy can be achieved by taking more terms from the power series. 相似文献
76.
CHI HO SHAM JOHN W. BRAWLEY MAX A. MORITZ 《International journal of geographical information science》2013,27(4):463-473
Abstract Waquoit Bay, a shallow bay on Cape Cod, Massachusetts, is exhibiting symptoms of eutrophication, largely attributed to septic nitrogen inputs. This study assessed septic nitrogen inputs by linking a three-dimensional ground-water model, a geographic information system (GIS), and a customized spatio-temporal nitrogen loading program. Owing to the slow speed of ground-water movement, the bulk of septic nitrogen entering the bay lags behind development by nearly a decade. Even if residential development is held at 1989 levels, nitrogen input from septic systems wilt increase by 36% over the current levels. At full residential build-out (i.e., development), septic nitrogen loading will eventually increase to more than twice the current levels. 相似文献
77.
ALEX HAGEN-ZANKER BAS STRAATMAN INGE ULJEE 《International journal of geographical information science》2013,27(7):769-785
Fuzzy set map comparison offers a novel approach to map comparison.The approach is specifically aimed at categorical raster maps and applies fuzzy set techniques, accounting for fuzziness of location and fuzziness of category, to create a similarity map as well as an overall similarity statistic: the Fuzzy Kappa. To date, the calculation of the Fuzzy Kappa (or K-fuzzy) has not been formally derived, and the documented procedure was only valid for cases without fuzziness of category. Furthermore, it required an infinitely large, edgeless map. This paper presents the full derivation of the Fuzzy Kappa; the method is now valid for comparisons considering fuzziness of both location and category and does not require further assumptions. This theoretical completion opens opportunities for use of the technique that surpass the original intentions. In particular, the categorical similarity matrix can be applied to highlight or disregard differences pertaining to selected categories or groups of categories and to distinguish between differences due to omission and commission. 相似文献
78.
Abstract The design and construction of a special-purpose laboratory catchment and rainfall simulator is described. The equipment consists of a soil catchment area that can be inclined at various angles. Additional instrumentation then measures the flow of water across the surface of, and through, the soil bed. Precipitation is provided by a unit that simulates rainfall at particular rates with uniform distribution. The equipment was used to examine infiltration, runoff and other hydrological properties of a number of soils under different rainfall intensities and with different catchment slopes. Correlations were obtained for these variables. 相似文献
79.
《International Geology Review》2012,54(7):816-832
The newly discovered Jiyuan Cu–Ag–(Pb–Zn–Au) deposit is located in the southern section of the eastern Tianshan orogenic belt, Xinjiang, northwestern China. It is the first documented deposit in the large Aqikekuduke Ag–Cu–Au belt in the eastern Tianshan orogen. Detailed field observations, parageneses, and fluid inclusion studies suggest an epithermal ore genesis for the main Cu–Ag mineralization, accompanied by a complicated hydrothermal alteration history most likely associated with the multi-stage tectonic evolution of the eastern Tianshan. The Jiyuan Cu–Ag ore bodies are located along the EW-striking, south-dipping Aqikekuduke fault and are hosted by Precambrian marble and intercalated siliceous rocks. Early-stage skarn alteration occurred along the contact zone between the marble layers and Early Carboniferous diorite–granodiorite and monzogranite intrusions; the skarns are characterized by diopside–tremolite–andradite–pyrite–(magnetite) assemblages. Local REE-enriched synchysite–rutile–arsenopyrite–(clinochlorite–microcline–albite) assemblages are related to K–Na alteration associated with the monzogranite intrusions and formed under conditions of high temperature (310°C) and high salinity (19.9 wt.% NaCl). Subsequent hydrothermal alteration produced a series of quartz and calcite veins that precipitated from medium- to low-temperature saline fluids. These include early ‘smoky’ quartz veins (190°C; 3.0 wt.% NaCl) that are commonly barren, coarse-grained Cu–Ag mineralized quartz veins (210°C; 2.4 wt.% NaCl), and late-stage unmineralized calcite veins (140°C; 1.1 wt.% NaCl). Tremolite and Ca-rich scapolite veins formed at an interval between early and mineralized quartz veins, indicating a high-temperature, high-salinity (>500°C; 9.5 wt.% NaCl) Ca alteration stage. Fluid mixing may have played an important role during Cu–Ag mineralization and an external low-temperature Ca-rich fluid is inferred to have evolved in the ore-forming system. The Jiyuan auriferous quartz veins possess fluid characteristics distinct from those of the Cu–Ag mineralized quartz veins. CO2-rich fluid inclusions, fluid boiling, and mixing all demonstrate that these auriferous quartz veins acted as hosts for the orogenic-type gold mineralization, a common feature in the Tianshan orogenic belt. 相似文献
80.
综合优势相似法在短期气候预测中的应用 总被引:1,自引:0,他引:1
综合优势相似法是建立在相似因子群的多项相似与动态相似基础之上的,因此更能反映大气天气过程的实际演变,其预测趋势可最接近天气气候实况。综合优势相似法中相似和不相似这两个预报时段的气象序列的对比分析和严格检验是不可缺少的一部分,只有相似和不相似两者呈显著差别,才能认定相似有效,以相当高的可信度保证了预报的客观性和可靠性。综合优势相似法操作简便,在2002年濮阳和2004年郑州汛期降水趋势预报中效果良好,可作为目前短期气候预测业务中的基本工具。 相似文献