A Physical and Numerical Investigation on the Stability of Shallow Tunnels in Strain Softening Media   总被引：11，自引：0，他引：11  

D. Sterpi  A. Cividini 《Rock Mechanics and Rock Engineering》2004,37(4):277-298

Summary The behaviour up to failure of shallow underground openings is discussed on the basis of some laboratory, small-scale model tests and of finite element simulation. The experimental results are first illustrated. They were obtained from two-dimensional (plane strain) and three-dimensional tunnel models tested under standard gravity conditions. Then, the phenomenon of strain localisation that characterizes the medium surrounding the model tunnels is discussed, recalling two alternative approaches for its numerical interpretation. On this basis, a finite element procedure for strain softening analyses is outlined and applied to the simulation of the tests in both two- and three-dimensional conditions. The comparison between experimental and numerical results leads to some conclusions on the influence of strain localisation on the overall behaviour of shallow tunnels and on the stability of their headings.  相似文献   

Curie Point Depths Beneath Precordillera Cuyana and Sierras Pampeanas Obtained from Spectral Analysis of Magnetic Anomalies   总被引：1，自引：0，他引：1  

Francisco Ruiz  Antonio Introcaso   《Gondwana Research》2004,7(4):1133-1142

A gravity and magnetic survey has been carried out with the purpose of investigating geophysical features of the crusts beneath three geological provinces in western Argentina: Cuyo Precordillera, the Sierras Pampeanas of San Juan and La Rioja, and Famatina System, the results of which are displayed in three maps: Bouguer anomaly, total field magnetic anomaly and total field reduced to the pole.

The top and bottom boundaries of the magnetized crust were calculated from power-density spectra of the total-field anomalies from our terrestrial database in 90 2D windows. The depths obtained for the bottom of magnetized crust are assumed to correspond to Curie point depths. The values thus obtained for the Precordillera range between 29 and 40 km, whereas for the Sierras Pampeanas, in the Sierra de Pie de Palo, and other mountain chains along the Bermejo-Desaguadero lineament or Valle Fértil lineament, such depth ranges between 20 and 35 km. These results are consistent with Curie point depths determined on different continental regions in the world.

A map of regional heat flow has been prepared in the present work based on the depth of the Curie point isotherm, which shows that heat flow patterns in Precordillera are different from those found in Sierras Pampeanas.

A significant heat flow extending in Northeast-Southwest direction seems to be directly related to Juan Fernández Ridge trace.

The results of the present investigations also point out a possible relationship between the base of the magnetized crust and the boundary separating the brittle from the ductile crustal regime.  相似文献   

Exhumation of high-pressure rocks of the Kokchetav massif: facts and models   总被引：1，自引：0，他引：1  

N.L. Dobretsov  V.S. Shatsky 《Lithos》2004,78(3):307-318

The exhumation of ultrahigh-pressure (UHP) metamorphic units from depths more than 100-120 km is one of the most intriguing questions in modern petrology and geodynamics. We use the diamondiferous Kumdy-Kol domain in the Kokchetav Massif to show that exhumation models should take into consideration initially high uplift velocities (from 20 down to 6 cm/year) and the absence of the deformation of UHP assemblages. The high rate of exhumation are indicated by ion microprobe (SHRIMP) dating of zircons from diamondiferous rocks and supported by the low degree of nitrogen aggregation in metamorphic diamonds.Diamondiferous rocks in the Kumdy-Kol domain occur as steeply dipping (60°-80°) thin slices (few hundred metres) within granite-gneiss. Using geological, petrological and isotopic-geochemical data, we show that partial melting of diamondiferous metamorphic rocks occurred; a very important factor which has not been taken into account in previous models.Deformation of diamondiferous rocks at Kumdy-Kol is insignificant; diamond inclusions in garnet are often intergrown with mica crystals carrying no traces of deformation. All these facts could be explained by partial melting of metapelites and granitic rocks in the Kumdy-Kol domain. The presence of melt is responsible for an essential reduction of viscosity and a density difference (Δρ) between crustal rocks and mantle material and reduced friction between the upwelling crustal block, the subducting and overriding plates. Besides Δρ, the exhumation rate seems to depend on internal pressure in the subducting continental crustal block which can be regarded as a viscous layer between subducting continental lithosphere and surrounding mantle.We construct different models for the three stages of exhumation: a model similar to “corner flow” for the first superfast exhumation stage, an intermediate stage of extension (most important from structural point of view) and a very low rate of exhumation in final diapir+erosional uplift.  相似文献   

基于等高线的DEM生成算法研究和实现   总被引：5，自引：0，他引：5  

刘锦中  马辉 《现代测绘》2004,27(3):34-35,48

数字高程模型是近年来发展起来的为地理信息系统提供空间分析和辅助决策的数据基础。随着科学技术特别是计算机技术的迅速发展，DEM在数据获取方法、数据存储和数据处理速度等方面已经取得突破性进展。通过系统介绍生成DTM过程中等高线的离散化方法，DELAUNAY三角网的特性和基于等高线数据的TIN的建立，以及对产生的问题的一些解决方法。  相似文献   

Curie-point depth from spectral analysis of magnetic data in central-southern Europe   总被引：3，自引：0，他引：3  

P. Chiozzi  Y. Okubo  M. Verdoya 《Physics of the Earth and Planetary Interiors》2005,152(4):267-276

The basal depth of the outer layer with internal magnetic sources was calculated from magnetic data available within a roughly 500 km wide and 1200 km long area, running from central Germany to southern Italy. The dataset, deriving from different aeromagnetic surveys, is reduced to the reference altitude of 3000 m a.s.l. and a reference year of 1980.0. The adopted method, which transforms the spatial data into the frequency domain, provides a relationship between the two-dimensional spectrum of the magnetic anomalies and the top and centroid depths of the magnetic sources. The magnetic layer bottom depth (MLBD) thus obtained is 29-33 km deep in the stable areas (central Europe Variscan units, Corsica-Sardinia Variscan block) and corresponds to the Moho, having an average temperature of 560 °C. From the Alps to the Apennines, MLBD ranges between 22 and 28 km and is clearly shallower than the Moho. In these units, the wide variation of MLBD appears to be compatible with the presence of shallow magnetised bodies, consisting of lower crustal rocks (Ivrea-Verbano zone), ophiolitic units (Penninic zone and Voltri Massif) and intrasedimentary basic volcanic bodies (Po Basin). An average value of 25 km can be attributed to MLBD, which corresponds to a temperature of 550 °C. In the peri-Tyrrhenian zone and the Ligurian Sea, MLBD is below the Moho, which ranges from 17 to 20 km depth, and it has a temperature matching approximately to the Curie temperature of magnetite (580 °C).  相似文献   

Model identification for hydrological forecasting under uncertainty   总被引：2，自引：2，他引：2  

Thorsten Wagener  Hoshin V. Gupta 《Stochastic Environmental Research and Risk Assessment (SERRA)》2005,19(6):378-387

Methods for the identification of models for hydrological forecasting have to consider the specific nature of these models and the uncertainties present in the modeling process. Current approaches fail to fully incorporate these two aspects. In this paper we review the nature of hydrological models and the consequences of this nature for the task of model identification. We then continue to discuss the history (“The need for more POWER‘’), the current state (“Learning from other fields”) and the future (“Towards a general framework”) of model identification. The discussion closes with a list of desirable features for an identification framework under uncertainty and open research questions in need of answers before such a framework can be implemented.  相似文献   

FBX三维模型自动转换为OBJ三维模型方法研究     

闻平  王冲  吴小东  桂林 《测绘与空间地理信息》2016,(1):113-115

本文研究实现了一种FBX三维模型自动转换为OBJ三维模型的方法,包括几何信息和材质信息的自动转换,所述方法包括获取数据、几何信息处理、材质信息处理、OBJ格式输出和材质库文件输出等步骤。  相似文献   

四川地形谱特征及中尺度模式水平网格分辨率选取   总被引：1，自引：0，他引：1       下载免费PDF全文

黄永杰  崔晓鹏 《Acta Meteorologica Sinica》2016,74(1):114-126

四川地形复杂多样,暴雨频发,常诱发山洪、泥石流等灾害。在利用中尺度模式对复杂地形区域的暴雨进行研究时,模式水平分辨率的选取缺乏定量依据。为了揭示四川地形的复杂特征和给中尺度模式水平网格分辨率的选取提供定量依据,利用二维离散余弦变换,对四川地形高度场和暴雨分布场进行谱分解,根据暴雨分布特征分区讨论了四川盆地地形特征,同时利用地形谱方差和数值试验定量讨论了数值模式水平分辨率的选取问题,得到主要结论有:(1)二维离散余弦变换能较好地表现出研究区域各向异性的复杂特征;(2)雅安地区和四川盆地西北部的地形谱与降水谱有较好的同相关系,盆地东北部和盆地中部的地形谱与降水谱在波长较大处出现反相关系;(3)针对某个区域的地形特征,可以通过计算模式能分辨的地形方差与总地形方差的比值来确定合适的中尺度模式水平网格分辨率。  相似文献   

辽宁地区不同降水云系雨滴谱参数及其特征量研究   总被引：1，自引：0，他引：1  

房彬  郭学良  肖辉 《大气科学》2016,40(6):1154-1164

利用位于辽宁省沈阳市和辽阳市的Parsivel（Particle Size and Velocity）激光雨滴谱仪观测到的雨滴谱资料按照积雨云降水系统、积层混合云降水系统和层状云降水系统分析雨滴谱特征量和谱参数的平均特征及随时间的演变特征。结果表明:Gamma分布拟合谱参数N₀和λ按照层状云、积层混合云和积雨云的顺序减小,谱参数μ按照层状云、积层混合云和积雨云的顺序增大;直径小于1 mm的降水粒子对数浓度的贡献最大,直径大于1 mm的降水粒子对雷达反射率的贡献最大;M-P分布的谱参数N₀与雨强I具有幂函数关系,并且随着雨强I的增大而增大,谱参数λ与雨强I具有指数函数关系,随着雨强I的增大而减小。  相似文献   

Evaluation of a rule-based compositing technique for Landsat-5 TM and Landsat-7 ETM+ images     

《International Journal of Applied Earth Observation and Geoinformation》2016

Image compositing is a multi-objective optimization process. Its goal is to produce a seamless cloud and artefact-free artificial image. This is achieved by aggregating image observations and by replacing poor and cloudy data with good observations from imagery acquired within the timeframe of interest. This compositing process aims to minimise the visual artefacts which could result from different radiometric properties, caused by atmospheric conditions, phenologic patterns and land cover changes. It has the following requirements: (1) image compositing must be cloud free, which requires the detection of clouds and shadows, and (2) the image composite must be seamless, minimizing artefacts and visible across inter image seams. This study proposes a new rule-based compositing technique (RBC) that combines the strengths of several existing methods. A quantitative and qualitative evaluation is made of the RBC technique by comparing it to the maximum NDVI (MaxNDVI), minimum red (MinRed) and maximum ratio (MaxRatio) compositing techniques. A total of 174 Landsat TM and ETM+ images, covering three study sites and three different timeframes for each site, are used in the evaluation. A new set of quantitative/qualitative evaluation techniques for compositing quality measurement was developed and showed that the RBC technique outperformed all other techniques, with MaxRatio, MaxNDVI, and MinRed techniques in order of performance from best to worst.  相似文献