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81.
Exposed roots were used to estimate soil and bedrock erosion on the cut slopes of a 45-year-old road constructed in granitic soils of the Idaho Batholith. The original roadcut surface was defined by projecting a straight line from the toe of the cut past the end of the exposed root to the intersection of a straight line projected along the surface of the hillslope. A cross-sectioning technique was then used to determine erosion to the present roadcut surface. A total of 41 exposed root sites were used to estimate erosion on a 1350 m-long section of road. Average erosion was 1·0 and 1·1 cm/year for soil and bedrock respectively. Buttressing by tree roots caused lower erosion rates for soil as compared to bedrock. Both soil and bedrock erosion rates showed statistically significant correlations with the gradients of the original cut slope. The bedrock erosion data provide a reasonable estimate of the disintegration rate of exposed granitic bedrock exhibiting the weathering and fracturing properties common to this area. The road is located in a study watershed where long-term sediment yield data are available. Sediment data from adjacent study watersheds with no roads were compared to sediment data from the roaded watershed to estimate the long-term increase in sediment yield caused by the road. The increase amounts to about 2·4 m3/year. This figure, compared to the average annual on-site road erosion, provides an erosion to sediment delivery ratio of less than 10 per cent. Based on study results, road construction and maintenance practices are suggested for helping reduce roadcut erosion. 相似文献
82.
Digital Image Based Approach for Three-Dimensional Mechanical Analysis of Heterogeneous Rocks 总被引:2,自引:0,他引:2
Summary This paper presents a digital image based approach for three-dimensional (3-D) numerical simulation and failure analysis of
rocks by taking into account the actual 3-D heterogeneity. Digital image techniques are adopted to extract two-dimensional
(2-D) material heterogeneity from material surface images. The 2-D image mesostructures are further extrapolated to 3-D cuboid
mesostructures by assuming the material surface as a representation of the inner material heterogeneity within a very small
depth. The iterative milling and scanning system is set up to generate the 3-D rock mesostructures. A Hong Kong granite specimen
is used as an example to demonstrate the procedure of 3-D mesostructure establishment. The mechanical responses and failure
process under the conventional Brazilian tensile test condition are examined through numerical analyses. The stress distribution,
crack propagation process and failure model of heterogeneous material cases are simulated with a finite difference software.
The numerical results indicate that material heterogeneity plays an important role in determining the failure behavior of
rocks under external loading. 相似文献
83.
84.
Florence Lansana Margai 《The Professional geographer》2001,53(3):422-434
This study examines the spatial distribution and impact of nonroutine accidental releases of hazardous materials relative to the demographic composition of residents in nearby communities. First, atmospheric dispersion modeling methods are used to delineate the impact zones of worst‐case accidents in two New York counties over the last ten years. Next, using accidental reports for 1997, GIS and statistical operations are used at the census tract level of the two counties to determine whether these incidents disproportionately affected disadvantaged neighborhoods. The results suggest that the areas of high‐impact from accidental releases of hazardous materials are best characterized by a large proportion of families below the poverty line, Hispanics, and other minorities. 相似文献
85.
86.
铜山铜矿床矿化类型可划分为层状含铜黄铁矿型,含铜角砾岩型,含铜夕卡岩型和含铜班岩型,控矿因素为地层,岩浆岩及构造,其中层间断裂与接触带构造是主要的容矿构造,铅,硫,氢,氧同位素特征及成矿温度研究表明矿物质和热液主要来源于铜山岩体,矿床成因为层控夕卡岩型铜矿床。 相似文献
87.
88.
Quantification of salt weathering in porous stones using an experimental continuous partial immersion method 总被引:1,自引:0,他引:1
In this study, an experimental salt weathering simulation and porous stone durability classification are proposed. There are many laboratory tests that quantify durability against salt crystallisation weathering action. These are usually based on the total immersion of samples into a saline solution, which is not representative of the salt weathering mechanism. An experimental test based on partial immersion is suggested. This is a comparable study of weight loss and degradation of visual appearance due to salt crystallisation using, on the one hand, a standard durability test (UNE), and, on the other, the proposed durability test. The weight loss and visual appearance in our test is comparable to the degradation of building stone. The differences between weight loss data in both tests depend on the petrophysical properties: porous media and degree of coherence.
From this testing, a new durability classification as a function of dry weight loss in the partial immersion test is proposed. Four divisions of different types of materials can be made in this classification, which quantifies salt weathering action mainly in environments and mild climatic conditions. 相似文献
89.
对胎体材料中添加稀土元素问题进行了试验研究。对添加稀土和未加稀土的胎体性能进行测试,结果表明,添加稀土比未加稀土的胎体材料的抗弯强度、硬度和冲击韧性均有所提高,其中抗弯强度提高了10%-62%,冲击韧性提高了5%。胎体中添加稀土对提高胎体和金刚石碎岩工具的技术经济指标具有重要作用,并且为在胎体材料中实现以Fe代Co创造了有利条件。 相似文献
90.
内蒙红花沟金矿床同位素地质特征及矿床成因探讨 总被引:4,自引:0,他引:4
通过对红花沟金矿床主要岩类及金矿石的氧、氢、铅、钾-氩和铷锶同位素的测定,研究了该矿的同位素地球化学特征,探讨了成矿物质来源、成矿时代、成矿温度等矿床成因问题。认为成矿物质来自建平群变质岩,元古宙钾长花岗岩的成岩作用使金活化迁出而成矿。成矿热液以岩浆水为主,并有部分大气降水混入,成矿温度为250~350℃。 相似文献