偏压隧道偏压应力比特征分析

偏压隧道是公路和铁路建设中经常遇到的隧道类型,由于其受力的不对称性及设计、施工的特殊性,一直是隧道施工研究的热点。以往针对偏压隧道的研究主要集中在偏压隧道的成因、围岩稳定性、应力应变分布规律及施工影响等方面,但缺少对偏压隧道偏压应力比以及公路、铁路设计规范给出条件的偏压应力比的研究,而且公路和铁路设计规范中给出的偏压隧道对应的坡面倾角和隧道埋置深度缺少相关理论来支撑。本文针对铁路双线隧道设计规范给出的临界坡度和覆盖层厚度条件,采用数值模拟的方法,求出地形偏压隧道对称位置的应力比值,定量分析了规范给定条件下偏压应力比的特征值。结果表明：在保证安全的前提下,当Ⅲ级围岩拱肩应力比大于7.45、Ⅳ（土）级围岩拱肩应力比大于2.23、Ⅳ（石）级围岩拱肩应力比大于3.34、Ⅴ级围岩拱肩处应力比大于1.06时,可将隧道考虑成偏压隧道,从而为定量判别偏压隧道提供理论依据。     

上覆压力和剪胀作用下土钉抗拔的有限元模拟

灌浆土钉在边坡加固工程中有着广泛的应用。土钉在不同条件下的抗拔机制仍是进一步研究的课题。通过建立一个三维有限元模型,研究土钉在不同上覆压力和剪胀作用下的土钉抗拔行为。采用摩尔-库仑模型模拟花岗岩土,土与土钉界面采用“接触对”和库仑摩擦模型描述。模型可以模拟土钉发生较大抗拔位移下发生滑移破坏的过程。模型参数通过三轴试验结果进行校正。通过与大尺寸室内抗拔试验结果相比较,验证了模型的有效性。模型展现了土钉在钻孔后和抗拔过程中土钉周围的土压力的变化。最后通过参数分析,研究了上覆压力和剪胀对土钉抗拔力的影响。结果显示,当上覆压力较小时,剪胀角对抗拔应力的影响较小。随着上覆压力的增加,剪胀角对抗拔应力的影响变得更加明显。     

地下曲流河道单砂体内部薄夹层建筑结构研究方法

单砂体内部薄夹层因规模小、薄、不稳定、参数与分布难于确定等,致使覆盖盆地单砂体内部薄夹层及其建筑结构研究较少且难度很大,为此,本文以曲流河道沉积、建筑结构模式为指导,充分利用岩芯、测井、密井网等油田现有资料,提出了‘一整套地下曲流河道单砂体内部薄夹层建筑结构研究方法’,特别是以‘侧积泥、侧积面、废弃河道的识别、恢复、测算;河道几何学、河流工程参数计算;建筑结构理论模式为基础的‘单一侧积泥岩薄夹层建筑结构参数（倾角、倾向、规模）三类13种提取方法’及薄夹层分布密度与河道侧积轨迹研究技术,为这一难题的解决提供了可行的思路与方法。并以杏南油田PⅠ31b单元为靶区,应用该方法确定了曲流河道单砂体内部薄夹层及其建筑结构理论模式和研究区实际模式。     

厚覆盖层矿山地下开采地表塌陷机制分析

随着矿山开采深度的不断增加,厚覆盖层成为部分深部地下矿山的主要特点。以物探调查、变形监测以及理论分析为手段,对某典型厚覆盖层金属矿山地下开采初期地表塌陷的成因与机制进行了分析。结果表明,厚覆盖层中存在的大面积采空区为地表塌陷变形提供了空间,采空区顶板厚度较小为地面塌陷的发展提供了条件,采空区的存在是地表塌陷的主要原因。地表出现塌陷以后,塌陷范围以塌坑为中心继续向外扩展,受覆盖层内采空区走向,断层和岩层分界面等地质缺陷影响,塌坑向西、向南与向北三个方向上的扩展较向东快得多。降雨会增大塌坑向外扩展的速度,因为地表水的下渗加快了塌坑周围岩土体向塌坑方向的移动和下沉。     

Bed Mobility on the Deschutes River,Oregon: Tracer Gravel Results

Tracers are marked particles introduced into streams to obtain information on the movement of sediment in rivers. On the lower Deschutes River, Oregon, the threshold for bed mobility has been of interest in the relicensing of hydroelectric dams, with cross sections plotted from historical US Geological survey gauging records having shown changes at flows as low as 150 to 200 m³ s-¹ and general mobility at approximately 250 m³ s-¹. To obtain direct, empirical evidence of bed mobility, we deployed exotic gravel tracers (quartz particles) on the reach below the dam over four runoff seasons in which peak flows ranged from 146 to 192 m³ s-¹, close to entrainment threshold indicated by the cross section changes. The observed tracer movements indicated the bed experienced partial mobility (with 0-37 % of particles moving). We found no unique relation between grain diameter and critical flow strength (e.g. specific stream power), suggesting that overall bed texture and structure were more important controls on mobility than individual grain sizes.     

Gravitational Sedimentation Behavior of Sensitive Marine Ariake Clays

It has been well documented that natural marine Ariake clays are sensitive clays. In this study, extensive data of marine Ariake clays are obtained to investigate the gravitational compression behavior for sensitive clays. Analysis results indicate that the compression behavior of remolded Ariake clays is not different from that of other remolded/reconstituted soils. But natural Ariake clays do not follow the gravitational compression pattern reported by Skempton (1970) Skempton, A. W. 1970. “The consolidation of clays by gravitational compaction”. In Q. J. Geol. Soc 373–411.  [Google Scholar] for natural sedimentary soils. At a given value of effective overburden pressure, the void ratios of natural Ariake clays are almost independent of liquid limits. Most natural Ariake clays lie above the sedimentation compression line proposed by Burland (1990) Burland, J. B. 1990. On the compressibility and shear strength of natural clays. Gèotechnique, 40: 329–378. [Crossref], [Web of Science ®] , [Google Scholar]. When the liquid limit is larger than 90% and the ratio of natural water content over liquid limit ranges 0.8–1.1, the natural Ariake clays lie around the sedimentation compression line. In addition, the natural Ariake clay with higher value of the ratio of natural water content over liquid limit lies above the natural Ariake clay with lower value of the ratio of natural water content over liquid limit. Salt removal is the most probable cause for such a phenomenon.     

各向异性上覆层对裂缝储层地震AVAz影响的模拟及分析

为认识和研究上覆层为VTI时,垂直裂缝发育储层的地震反射AVAz响应特性,提出了相适应的正演模拟方法。该方法类比Shoenberg传播矩阵法中水平慢度分量的表达形式,引入了用入射角、方位角和VTI介质中相速度来表达的水平慢度分量作为输入,简化了各向异性反射率法的框架。利用该方法模拟和分析了各向异性层状模型的地震反射响应随方位的变化,讨论了入射角、上覆层各向异性程度对目标层顶底界面反射波AVAz特征的影响。结果表明,采用适当大的观测入射角进行AVAz分析更为合理,上覆层为VTI时会减弱目标层的AVAz特征。测井尺度理论模型的数值模拟说明了该方法的实用性。     

安徽西湾铅锌矿含矿层位顶部原生晕特征

安徽西湾铅锌矿位于庐枞火山岩盆地北缘,该区属于第四系覆盖区,勘查难度大。本文利用钻孔岩心样的分析结果,对西湾铅锌矿的原生晕特征进行研究,发现矿化带及其顶、底板的元素含量及异常特征差异明显:矿化带赋存的角砾状灰岩中Pb、Zn、Ag、As、Sb、Bi、Au、Cu、Mo等含量高,异常强度及规模大,具清晰的浓度和组分分带,异常不仅很好地反映了矿体特征,对矿体呈NE向延伸的趋势指示明显;而矿化带顶板的火山岩中As、Sb、Pb、Zn、Ag等含量较高,有较弱的异常,异常无明显的分带特征,仅对采样点附近矿体有一定的指示;底板的硬石膏上述元素含量低,无明显的异常显示。本区As、Sb、Pb、Zn、Ag、Mo为铅锌矿化的指示元素。采集于不同成矿部位的岩心样的元素含量及其异常特征,可以指导矿区的进一步找矿。     

Experimental study on moisture migration of remodeled clay under different overburden pressure and temperature gradients

Unidirectional freezing experiments under overburden pressure were carried out, in order to study the driving force of mois-ture migration of remodeled clay during freezing, through improving the indoo...     

The spatial heterogeneity of riverbed saturated permeability coefficient in the lower reaches of the Heihe River Basin,Northwest China

In arid region, direct infiltration from rainfall contributes little to groundwater compared with localized recharge from streams. How to quantify riverbed infiltration to groundwater systems is an important area of research in hydrology. In this study, saturated permeability coefficient of a riverbed in an arid inland river basin located in the northwest of China was obtained by Guelph Permeameter and laboratory analysis methods. The characteristics of riverbed infiltration and its spatial patterns were analysed using geostatistical method and kriging method. The results showed that the saturated permeability coefficient varied from 0.089 to 2.802 m/d, indicating moderate degree of variability. The Guelph Permeameter and laboratory test methods provided consistent estimates of saturated permeability coefficient. There was a strong spatial correlation for K_fs of the riverbed in this study area when Range (A) was less than 0.276°, suggesting that the maximum sampling distance for saturated permeability coefficient of the riverbed was 0.276° under isotropic conditions. The K_fs near the centre of the riverbed was higher than the value near riverbank. The K_fs values decreased in the direction of upstream to downstream in the Heihe River Basin. The riverbed mechanical composition, initial soil water content and bulk density have significant influence up on the riverbed infiltration. Besides, the topographical factors including the width, altitude and distance factors of the riverbed together impacted the riverbed infiltration and the slope of the riverbed and also influenced the riverbed infiltration. Copyright © 2015 John Wiley & Sons, Ltd.