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991.
Morched Zeghal 《Geotechnical and Geological Engineering》2009,27(4):549-558
This paper presents the results of a study of grain crushing in road construction and its effect on road behaviour. Sieve
analyses of field samples confirmed that grain crushing occurs during compaction of the base layer despite the good quality
of aggregates used. Laboratory testing indicated that grain crushing reduces the resilient modulus of the aggregate material
by half and increases the permanent deformations by onefold to threefold depending on the state of density and stresses considered.
Road design and analyses undertaken to delineate the effect of grain crushing on performance showed that particle breakage
yields a significant increase in rutting and longitudinal and alligator cracking of roads. 相似文献
992.
More than 200 venusian channels and valleys have been mapped based on analyses of Magellan SAR images. Sinuous rilles are the most abundant channels among six types of venusian channels, and they are widely distributed on Venus. Morphological characteristics of venusian sinuous rilles include sinuous narrowing reaches, source depressions, and length of several 10s to a few 100s of km. This type of channels is known to exist on the Moon and possibly on Mars. Valley networks on Venus often occur in the vicinity of or in connection to sinuous rilles. Cross-sectional morphologies of sinuous rilles and valley networks are of special importance in discussing their formation processes both qualitatively and quantitatively. We reconstructed cross-sectional profiles of 6 sinuous rilles and 2 valley networks using a new radar clinometric method. Reconstructed cross-sections revealed that floors of the channels and valleys are clearly lower than the surrounding plains. This finding implies that the sinuous rilles and the valley networks have erosional origins. Longitudinal depth profiles of the sinuous rilles show distinct decreasing trends toward the termini. Such decreasing trends of depths are qualitatively in agreement with theoretical models and laboratory experiments of thermal erosion. In order to verify this assertion quantitatively, we conduct simple 1-dimensional model calculations under the assumption that both channel-forming lavas and ground substrate are tholeiitic basalt. For initial lava thicknesses in the range 2-6 m, the model calculations yield good matches to the depth profiles. Estimated duration of lava effusion ranges from several months to a few years. These numerical results support thermal erosion of the sinuous rilles but do not necessarily exclude contributions from mechanical erosion processes. Valley networks seem to have formed under a strong structural control in comparison to sinuous rilles. The valleys vary widely in characteristics of the depth profile and flow directions relative to surface slopes. Therefore valley networks appear to have originated from diverse formation mechanisms. 相似文献
993.
994.
Bruno Capaccioni Laura Valentini Marco B. L. Rocchi Giovanni Nappi Damiano Sarocchi 《Bulletin of Volcanology》1997,58(7):501-514
Computer-assisted image analysis can be successfully used to derive quantitative textural data on pyroclastic rock samples.
This method provides a large number of different measurements such as grain size, particle shape and 2D orientation of particle
main axes (directional- or shape-fabric) automatically and in a relatively short time. Orientation data reduction requires
specific statistical tests, mainly devoted to defining the kind of particle distribution pattern, the possible occurrence
of preferred particle orientation, the confidence interval of the mean direction and the degree of randomness with respect
to pre-assigned theoretical frequency distributions. Data obtained from image analysis of seven lithified ignimbrite samples
from the Vulsini Volcanic District (Central Italy) are used to test different statistics and to provide insight about directional
fabrics. First, the possible occurrence of a significant deviation from a theoretical circular uniform distribution was evaluated
by using the Rayleigh and Tukey χ
2 tests. Then, the Kuiper test was performed to evaluate whether or not the observation fits with a unimodal, Von Mises-like
theoretical frequency distribution. Finally, the confidence interval of mean direction was calculated. With the exception
of one sample (FPD10), which showed a well-developed bimodality, all the analysed samples display significant anisotropic
and unimodal distributions. The minimum number of measurements necessary to obtain reasonable variabilities of the calculated
statistics and mean directions was evaluated by repeating random collections of the measured particles at increments of 100
particles for each sample. Although the observed variabilities depend largely on the pattern of distribution and an absolute
minimum number cannot be stated, approximately 1500–2000 measurements are required in order to get meaningful mean directions
for the analysed samples.
Received: 9 April 1996 / Accepted: 26 December 1996 相似文献
995.
996.
中等植被覆盖区金矿蚀变TM及JERS-1OPS遥感信息增强技术 总被引:3,自引:1,他引:3
本文分析了与金矿化相伴的蚀变矿物(铁氧化物、粘土矿物、碳酸盐矿物)的反射光谱吸收特征及金矿区上覆植被反射光谱对金矿化蚀变信息的干扰,同时介绍了利用植被指数法、比值-主成份变换法和植被掩模法对陆地卫星TM、JERS-1OPS等遥感图像进行处理,压抑植被反射光谱干扰信息和增强金矿化蚀变反射光谱信息的方法和效果。 相似文献
997.
The aim of the present study is to prepare a landslide susceptibility map of a region of about 120 km2, between Gökcesu and Pazarköy (around Mengen, NW Turkey) at approximately 10 km north of the North Anatolian Fault Zone, where frequent landslides occur. For this purpose, mechanisms of the landslides were studied by two-dimensional stability analyses together with field observations, and the parameters controlling the development of such slides were identified. Field observations indicated that the failures generally developed within the unconsolidated and/or semiconsolidated soil units in forms of rotational, successive shallow landslides within the weathered zone in Mengen, Cukurca and Sazlar formations. Although consisting of residual soils, Capak and Gökdag formations do not exhibit landslides as the natural slopes formed on these, do not exceed the critical slope angles. Statistical evaluations and distribution of the landslides on the topographical map showed that such parameters as cohesion, angle of internal friction, slope, relative height, orientation of slopes, proximity to drainage pattern, vegetation cover and proximity to major faults were the common features on the landslides. Digital images were obtained to represent all these parameters on gray scale on the SPOT image and on the digital elevation model (DEM) of the area using image processing techniques. Soil mechanics tests were carried out on 36 representative samples collected from different units, and parameters were determined for two-dimensional stability analyses basing on “sensitivity approach” and for the preparation of digital shear strength map. In order to determine the critical slope angle values for the residual soils, a series of sensitivity analyses were realized by using two-dimensional deterministic slope stability analyses techniques for varying values of cohesion, angle of internal friction and slope height along with varying saturation conditions. According to the results of the sensitivity analyses, the Mengen formation was found to be most susceptible unit to landslides, covering about 33.5% of the region studied in terms of surface area. The distribution of the critical slopes were determined by superimposing the critical slope values from sensitivity analyses on slope map of the study area. On the other hand, iso-cohesion and iso-friction maps were produced by locating the values of cohesion and internal friction angles in a geographic coordinate system such that they coincide with sample locations on the DEM and by further interpolation of the values concerned. The pixel values were evaluated in gray scale from 0 to 255, 0 representing the lowest pixel value and 255 representing the highest. Sensitivity analyses on cohesion and angle of internal friction to investigate the effects of these parameters only on stability, revealed that cohesion was effective at a rate of 70% by itself, while angle of internal friction alone controlled the stability by a rate of 30%. The iso-cohesion and iso-friction maps previously obtained were digitally combined in these rates and a “shear strength map” was prepared. The geographic setting of the study area is such that northern slopes usually receive dense precipitation. In relation to this fact, about 42% of the landslides are due north. Thus, a slope orientation map was prepared using the DEM, and slopes facing north were evaluated as being more susceptible to sliding. Proximity to the drainage pattern was another important factor in the evaluation, as streams could adversely affect the stability by either eroding the toe or saturating the slope, or both. When considered together, in conjunction with the field observations, faults and landslides showed a close association. In the area, about 88% of the landslides were detected within an area closer than 250 m to major faults, therefore, a main discontinuity map was produced using the SPOT image of the region, and “proximity to major faults” was evaluated as a parameter as most of the landslides developed in areas where the vegetation was rather sparse. A vegetation cover map was therefore obtained from the SPOT image, and the areas with denser vegetation were considered to be less susceptible to sliding with respect to the areas with less or no vegetation. Having prepared the maps accounting for the distribution of critical slopes, shear strength properties, relative height, slope angle, orientation of the slopes, vegetation cover, proximity to the drainage pattern, geographic corrections were carried on each of these, and a potential failure map was obtained for the residual soils by superimposing all these maps. Next, a classification was performed on the final map and five relative zones of susceptibility were defined. When compared with this map, all of the landslides identified in the field were found to be located in the most susceptible zone. The performance of the method used in processing the images appears to be quite high, the zones determined on the map being the zones of relative susceptibility. 相似文献
998.
本文从分析TM各波段图像信息特征入手,在冰雪和植被等环境因素干扰严重的地区,试验应用了图像掩膜、波段比值、主成分分析等技术,成功地从TM图像中提取了与金成矿有关的蚀变围岩信息。在此基础上,进一步研究了蚀变与断裂构造和围岩类型的关系,确定了金矿找矿远景区。 相似文献
999.
GIS辅助下的基于知识的遥感影像分类方法研究——以土地覆盖/土地利用类型为例 总被引:23,自引:1,他引:23
提高计算机遥感影像的分类精度,是遥感应用中研究的主要问题之一。作者以规则的形式表示遥感影像解译知识,使用TM影像数据和DEM、坡度、土地利用图等地理辅助数据,从遥感影像处理/地理数据/专家知识一体化的角度出发,使用基于知识的方法进行了研究,改善了分类精度。实例研究证明了方法的正确性。 相似文献
1000.
赤潮藻的显微图形测量方法研究 总被引:2,自引:0,他引:2
介绍了一种在实验室环境下通过显微镜及CCD成像的办法观察采集微小藻类图像,并通过计算机软件进行图像识别统计,最终得到所测藻类统计信息的方法。 相似文献