A remote-sensing technique for the identification of aeolian fetch distance     

KEVIN LYNCH  DEREK W. T. JACKSON  J. ANDREW G. COOPER 《Sedimentology》2006,53(6):1381-1390

This paper describes a new method for assessing aeolian fetch distances in beach/dune systems. The remote‐sensing technique has advantages over currently used proxy measures of fetch distance, such as those based on tide gauges and beach profiles. The method uses a digital camera, global positioning system surveying, and a geographical information system software package to produce a rectified image of the beach surface. From this, direct measurements of the wet–dry beach boundary can be combined with wind direction measurements to determine fetch distance. The method offers an improvement on current approaches to sediment transport estimates: a 28‐day study on Magilligan Strand, Northern Ireland, showed that the commonly used high water mark approach overestimated fetch distance by 30% compared with the technique reported here.  相似文献   

基于梯度塑性本构理论的岩样侧向变形分析(II): 尺寸效应及弹性回跳   总被引：8，自引：0，他引：8  

王学滨  刘杰  王雷  潘一山 《岩土力学》2004,25(7):1127-1130

提出了利用不同尺寸试件的轴向应力-应变曲线得到轴向应力-侧向应变曲线的一种方法，并研究了结构尺寸对轴向应力-侧向应变曲线的影响。根据尺寸不同试件的轴向应力-轴向应变曲线的实验结果，并基于梯度塑性理论的解析解，在应变软化阶段，确定出了各种试件的剪切带条数。由此求出了不同宽度试样的轴向应力-侧向应变曲线。剪切带条数与试件宽度之比是决定轴向应力-侧向应变曲线特征的关键指标。若该比率为常量，则上述曲线不具有尺寸效应。当宽试件及窄试件在局部化启动后，在试件内部都出现一条剪切带时，随着试件宽度的增加，该曲线越陡，甚至出现回跳。上述方法也可用于分析轴向应力-环向应变曲线的尺寸效应问题。尺寸效应的原因是局部化，但局部化并非总引起尺寸效应。  相似文献   

沿空留巷上覆岩层关键块稳定性力学分析及巷旁充填体宽度确定     

李迎富  华心祝 《岩土力学》2012,33(4):1134-1140

由于沿空留巷服务时间较长,巷道围岩变形较大,合理地计算巷旁充填体宽度至关重要。根据沿空留巷上覆岩层的活动规律,建立了关键块和直接顶的力学模型,分析了关键块与沿空留巷围岩相互作用机制,推导出巷旁支护阻力的计算公式,并引入了关键块稳定性系数K1、K2及其稳定性影响因素的敏感度。研究结果表明,当K1>1时,关键块发生挤压变形失稳;当K2>1时,关键块发生滑落失稳。以淮南谢一矿512（5）工作面为工程背景,确定了合理的巷旁充填体宽度,计算出关键块稳定性系数,获得了各影响因素对关键块稳定性的敏感度。实例分析表明,采高对关键块的稳定性影响较大,在大采高工作面中进行沿空留巷较为困难。  相似文献   

开挖岩体边坡卸荷带宽度的计算方法   总被引：1，自引：0，他引：1  

陈洪凯  易丽云  唐红梅  何晓英 《地震学刊》2011,(4):358-363

卸荷带的判别与计算,直接关系到岩体边坡的长期稳定性及致灾安全性。针对均质岩体边坡,采用弹性理论楔形体力学模型,提出了开挖岩体边坡力学模型,建立了开挖岩体边坡应力的计算方法;从开挖高度、开挖坡度、台阶宽度、岩体粘聚力、内摩擦角及岩体容重等方面,通过敏感性分析,探讨了开挖岩体边坡卸荷带宽度的变化规律,据此采用量纲分析法,建立了开挖岩体边坡卸荷带宽度的计算公式。  相似文献   

Using air photos to parameterize landscape predictors of channel wetted width          下载免费PDF全文

B. G. Rawlins  L. Clark  D. S. Boyd 《地球表面变化过程与地形》2014,39(5):605-613

We investigated which landscape and climate‐related data (including information on hydrological source of flow) were statistically significant predictors of channel wetted width (WW) across a sizeable (2200 km²) region of the UK. This was conducted specifically when flow was less than mean daily flow (MDF) and where channels are in a near natural state. Orthorectified air photos at 25 cm spatial resolution were used to measure WW, with the magnitude of the errors in these measurements quantified. We used flow information from local gauging stations to ensure that channels were below MDF for the days on which the air photos were captured. The root mean squared difference between the field and air photo measurements of WW (n = 28 sites) was small (0.14 m) in comparison to median WW (3.07 m). We created points along sections of channels visible in air photos and used a terrain model to create drainage catchments for these points and computed their catchment area (CA). We selected a subset of points (n = 472) and measured their WW from air photos, and computed landscape‐related data for each of their catchments (mean slope, mean annual rainfall, land cover type, elevation) and also mean BFIHOST, a quantitative index relating to hydrological source of flow. We used a linear mixed model to predict WW by including the landscape data (including CA ^0.5) as fixed effects, plus a spatial covariance function estimated by residual maximum likelihood to determine unbiased estimates of the predictors. There was no evidence for retaining the spatial covariance function. With the exception of land cover, all the predictors were statistically significant and accounted for 76% of the variance of WW. When CA ^0.5 alone was used as a predictor it captured 54% of the variance. The vast majority of this difference was due to inclusion of an interaction between CA and hydrological source of flow (BFIHOST). As catchment area increases, those channels with larger mean catchment BFIHOST values (greater proportion of baseflow contribution) have narrower WW in comparison with those having smaller mean BFIHOST for the same CA. Improved predictions of channel WW (based on our findings) could be used in channel restoration. © 2013 British Geological Survey. Earth Surface Processes and Landforms © 2013 John Wiley & Sons, Ltd.  相似文献   

中心岛法实用设计计算方法研究     

顾问天  陈敏华 《岩土力学》2013,34(4):996-1000

在城市建设中越来越多的大面积深基坑采用中心岛顺作、周边预留土台逆作的开挖支护方式。该法不仅节约工程造价,而且节省大量工期,但目前仍缺乏简单、合理的设计计算方法。基于Rankine土压力理论,采用图解法得到中心岛被动土压力的分布模式,该土压力分布在单一土质条件下随埋深呈现为3段折线。根据上述土压力分布和基坑工程手册[1]有关悬臂结构的设计思路,提出中心岛法围护结构的设计计算方法,并提供一个算例。经算例验证该法简单实用,便于工程师使用。  相似文献   

碳酸盐岩缝洞体宽度估算方法   总被引：2，自引：0，他引：2       下载免费PDF全文

李凡异  狄帮让  魏建新  杨童 《地球物理学报》2012,55(2):631-636

定量估算缝洞体宽度是碳酸盐岩缝洞型油气藏勘探开发过程中的一个实际问题.在根据空间子波理论推导横向地质体HTA(水平道振幅)函数的基础上,定量分析了偏移成像确定地质体宽度的能力并发展了一种估算碳酸盐岩缝洞体宽度的方法.将此方法应用于物理正演模拟数据,获得了理想的结果.  相似文献   

Alternate bars in a sandy gravel bed river: generation,migration and interactions with superimposed dunes          下载免费PDF全文

Stephane Rodrigues  Erik Mosselman  Nicolas Claude  Coraline L. Wintenberger  Philippe Juge 《地球表面变化过程与地形》2015,40(5):610-628

A field study was carried out to investigate the development of alternate bars in a secondary channel of the Loire River (France) as a function of discharge variations. We combined frequent bathymetric surveys, scour chains and stratigraphical analysis of deposits with measurements and modelling of flow dynamics. The channel exhibited migrating bars, non‐migrating bars and superimposed dunes. Possible mechanisms of bar initiation were found to be chutes associated with changes of bank direction and instability resulting from interactions between existing bars during the fall in water level after floods. We propose that the reworking of bar sediments during low flows (high width‐to‐depth ratio β), reinforced by high values of the Shields mobility parameter, can explain the formation or re‐generation of new alternate migrating bars during a subsequent flood. The migration pattern of the bars was found to be cyclic and to depend mainly on (i) channel layout and (ii) the dynamics of superimposed dunes with heights and lengths depending on location and discharge value. For instance, the hysteresis affecting the steepness of dunes influences the flow resistance of the dunes as well as the celerity of migrating bars during flood events. We compare the findings from the field with results from theoretical studies on alternate bars. This gives insight in the phenomena occurring in the complex setting of real rivers, but it also sheds light on the extent to which bar theories based on idealized cases can predict those phenomena. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

隧道施工诱发地表沉降估算方法及其规律分析     

朱才辉  李宁 《岩土力学》2016,37(Z2):533-542

通过搜集大量文献,系统地总结了地表沉降槽特性参数的取值方法,并以中国20多个城市的地铁工程地表沉降实测资料为背景,基于Peck公式反演分析法,获取了隧道在不同相对埋深 、不同地层条件和不同施工方法下的地表最大沉降量 、沉降槽宽度k、地层损失率 等参数的变化规律。研究结果表明,（1）采用Peck法估算地表沉降需要基于大量实测资料和结合地域特性和具体施工方法才能得到比较合理的预测结果,不同地区地铁隧道的相对埋深 为0.55～4.43,其地表最大沉降量 为 1.5～ 146.0 mm,沉降槽宽度系数 为0.13～1.60,地层损失率 为0.06%～6.90%,其中 和k与 呈反相关, 受施工工艺和地层条件影响较大;（2）砂性土地层中浅埋暗挖法及其辅助工法的灵活性优于盾构法,黏性土及其互层地层中的盾构法施工在控制地层损失上较浅埋暗挖法要好。  相似文献   

基坑的尺寸效应及考虑开挖宽度的抗隆起稳定安全系数计算方法     

王洪新 《岩土力学》2016,37(Z2):433-441

相比于宽基坑,狭窄基坑具有更好的稳定性和更小的变形,表现出明显的尺寸效应,相同挖深时窄基坑围护结构的入土深度可适当减小。目前设计采用的基坑稳定性分析方法基本上都没有考虑开挖宽度对安全系数的影响,导致狭窄基坑设计偏于保守。为保证窄基坑滑裂面也能够形成,通过移动滑动圆弧圆心方法,使滑裂圆弧通过围护墙底和基坑底与对侧围护墙的交点,以该滑裂面计算的抗隆起稳定安全系数 值可以考虑基坑宽度的影响。基于该理念,根据宽窄不同,把基坑分为不同种类,分别对应不同的Ks值计算方法。该方法可以在基坑足够宽时过渡到现有规范方法,保证与既有规范的统一,在狭窄基坑时, 。计算分析表明,在基坑设计时忽视尺寸效应,片面强调插入比是不科学的。由于仍然采用传统的抗隆起稳定安全系数的滑裂面形式,计算方法没有过大变化,适合在基坑设计和施工中推广应用,文中方法为狭窄基坑减小围护插入深度提供了理论依据。  相似文献