基于高光谱影像数据的戈壁表面砾石粒径定量反演潜力评估

在新疆哈密境内的噶顺戈壁选取样地,采集不同粒径砾石的光谱数据,分析光谱吸收特征,并利用光谱混合分析技术,以地物光谱为端元从EO-1 Hyperion 高光谱影像中提取了不同粒径的丰度图,分析戈壁表面砾石与高光谱影像的相关关系。结果表明:获取的地物光谱特征显示出粒径的差异对光谱具有明显的影响。所有光谱都展现出在2 250 nm处具有Al–OH 的吸收特性,而且粒径d=41 cm的吸收特性比其他粒径都更显著。而与更小粒径相比,粒径d=53 cm和d=83 cm在480 nm和920 nm处具有较弱的Fe³⁺ 吸收特性。粒径d=0.8 cm(R²=0.637)、d=3.4 cm(R²=0.687)、d=16.3 cm(R² =0.644)及d=41 cm(R²=0.622) 与相应的丰度影像具有显著相关性,而粒径d=53 cm(R²=0.181)和d=83 cm(R²=0.167)与相应的丰度影像相关性不显著。EO-1高光谱影像适用于对戈壁区砾石分布特征的确定,在进一步的研究中将高分辨率影像与高光谱影像相结合,可以提高判别精度。     

基于CT扫描的土石混合体三维数值网格的建立

根据CT扫描得到土石混合体切面图像信息,通过二值化和砾石边界识别技术提取砾石表面点云数据,应用逆向工程软件重构砾石的三维模型。编写APDL代码,在ANSYS中快速生成土石混合体的几何模型,借助ANSYS ICEM CFD强大、灵活的网格划分功能,对砾-土界面处网格进行加密,得到土石混合体的三维数值网格,采用接口程序,将数值网格导入FLAC3D中进行模拟计算。通过与无砾石模型计算结果的对比,说明了建立表征土石混合体结构特征的精细三维数值网格可以更加准确地描述土体,特别是砾-土界面的受力情况和变形特征,从而提高土石混合体数值模拟的精确度及可靠度。     

Effect of overconsolidation ratio on dynamic properties of binary mixtures of silica particles

Overconsolidated soils are ubiquitous in nature due to multiple mechanisms; however, the stress-history-based studies of small strain stiffness on binary mixtures, such as silty sand, are limited even though natural sand deposits are commonly mixtures of sand particles with varying amounts of fines. Consequently, this study quantified the stress-history-based dynamic properties of binary mixtures, such as sand-sand mixtures with different size small particles, and silty sand mixtures with small amounts of non-plastic fines, up to the critical fines content. By performing bender element tests on those mixtures according to fines content, size ratio, and overconsolidation ratio, the stress-history-based G_max of binary mixtures was evaluated. For the relevant data analysis, the OCR (overconsolidation ratio) exponent in the G_max formulation was expressed in terms of stress exponents during loading and unloading. It was found that the effect of OCR on the estimation of G_max increased with a decrease in size ratio (or increase in size difference), since the stress exponents during loading increased more significantly with a decrease in size ratio due to the pronounced change in interparticle coordination between large grains. However, the variation of stress exponents during unloading of different mixtures was relatively small due to the prevalent elastic deformation. It was demonstrated that the maximum stress history effect of tested mixed soils was observed at a fines content of approximately 5%, which was smaller than critical fines content of silty sand. This behavior was attributable to the delay in critical fines content observed during unloading, when compared to that observed during loading.     

Non-linear modeling of seismic isolation systems made of recycled tire-rubber

This article considers the effectiveness of a seismic isolation system composed of a shallow layer of soil mixed with sand and rubber from shredded tires. A thorough review of past work is first provided, which is then followed by an evaluation of the constitutive properties of sand-rubber soil mixtures when these undergo large states of deformation and slip. Finally, a comprehensive set of simulations that involve a structure underlain by a strongly non-linear, seismic isolating layer when subjected to a variety of actual earthquakes scaled to various peak accelerations, are considered in detail. It is shown that the concept of using soil-rubber mixtures for the purposes of seismic isolation appears promising. A thickness for the rubber–soil mixture of just 2–3 m is likely to be enough to achieve good levels of reductions in the seismic response of the structure. This suggests the desirability of following these analyses with large-scale experimental verifications, not only to fully validate the concept, but also to quantify and assess the numerical predictions with our simple even if non-linear mechanical models, and verify the large-strain constitutive properties of the soil mixtures inferred from laboratory analyses.     

一种大型循环单剪试验装置研究

循环单剪试验被认为是研究地震场地中土体动力特性最合适的方法。为减小尺寸效应影响及解决工程中广泛存在的加筋土及粗颗粒土动力特性测试问题,研究大尺寸循环单剪试验方法具有重要意义。基于此,介绍了一种大型循环单剪试验装置,采用竖向线性滑动轨道约束上加载板和采用水平滑动轨道约束下加载板,确保前者仅发生竖向平动,后者仅发生水平平动,采用层叠的、带层间橡胶膜、分离式4点支撑的钢筋环构成的柔性剪切箱为试验提供侧向边界约束,确保了对单剪土样加载边界条件的真实模拟。针对土工格室加筋橡胶砂的测试结果表明：大型循环单剪试验装置得到的土动应力-动应变关系较好地反映了土在循环荷载作用下的滞回性、非线性和棘轮特性,大型循环单剪试验装置得到的 - 和 - 曲线变化规律与常规尺寸试验基本一致,证明其具有可行性;大尺寸试验得到的动剪模量特性与常规尺寸试验之间的差异,与单剪试验尺寸效应结论相符;试验中阻尼比特性受尺寸效应影响的规律性不明显。     

土石混合体斜坡地质结构精细探测新途径及其应用

土石混合体滑坡具有分布范围广、发生频率高、规律性差等显著特点,是西部山区及其重大工程建设中最为常见的灾害类型之一,其内部复杂的土-石结构是构成该类滑坡防治困难的关键因素。为了获取土石混合体斜坡接近真实的地质结构,提出通过探窗组合法,即采用高分辨的地球物理勘探方法进行地质结构探测,并借助探坑土石结构的图像处理技术予以补充,以初步实现地质结构的精细探测及宏-细观结构模型的统一。应用该方法,对湖南省南岳区拜殿乡土石混合体斜坡进行地质结构探测,获得了该斜坡接近真实的精细地质模型。该研究方法可为揭示滑坡形成演化的结构控制机制提供基础,使滑坡的预测和防治工作更加科学合理。     

轮胎碎片-砂混合土抗剪性能优化试验研究

废旧轮胎碎片-砂混合土有诸多优点,作为轻质填料目前已有应用。对轮胎碎片-砂混合土进行系列剪切试验,探讨碎片含量和纵横比、密实度等不同因素对混合土抗剪性能的影响规律。研究结果表明,加入轮胎碎片后,混合土摩尔-库仑包线呈非线性,且随碎片含量增加,抗剪强度、内摩擦角相应增加,非线性特征更明显。通过优化轮胎碎片纵横比、增加碎片含量和密实度,混合土内摩擦角可以增加8%～89%。其他条件相同时,单纯改变轮胎碎片宽度对抗剪性能影响不明显,但纵横比影响很大,对于给定宽度的轮胎碎片,仅有惟一的某个长度值使得混合土内摩擦角达到最大,且最大值可达65°。     

膨润土加砂混合物膨胀特征试验研究

运用自行研制的膨胀仪对膨润土加砂混合物进行了一系列膨胀力及膨胀应变等膨胀特性的试验研究,分析了膨胀力随时间的变化规律、两向膨胀力之间的关系和膨胀应变与时间及吸水量之间的关系。试验研究表明,膨润土加砂混合物的最大膨胀力以及最大膨胀应变主要取决于混合物的最初干密度和膨润土含量,并且随着二者的增大而增大;膨润土加砂混合物的水平膨胀力与竖向膨胀力之比随着混合物干密度的增大减小,并且与干密度近似成线性关系;不同膨润土含量的膨润土加砂混合物的膨胀应变与时间成双曲线关系,与吸水量近似呈S型曲线关系,并且其最大膨胀应变与膨润土含量存在指数关系。试验结果对高放废物深处置库中的缓冲回填材料设计具有一定的参考价值。     

武汉市地表亮温与植被覆盖关系定量分析

利用2002年7月9日的ETM影像,提取武汉市的下垫面类型、地表亮温和植被覆盖度,探讨不同下垫面类型对地表亮温的影响;并采用分形维度计算方法, 研究代表样带的地表亮温和植被覆盖的分维值之间的相关性。结果表明:植被覆盖度越高,地表亮温越低。除水域外的下垫面类型中植被覆盖度与地表亮温存在显著的负相关,这种相关性高于地表亮温与NDVI之间的相关关系。对于样带的地表亮温和植被的分维值研究表明,亮温和植被覆盖度的分维值之间的相关系数高于亮温和NDVI的分维值之间的相关系数。