An enhanced constitutive model for crushable granular materials

Studies in the past have tried to reproduce the mechanical behaviour of granular materials by proposing constitutive relations based on a common assumption that model parameters and parameters describing the properties, including gradation of individual grains are inevitably linked. However successful these models have proved to be, they cannot account for the changes in granular assembly behaviour if the grains start to break during mechanical loading. This paper proposes to analyse the relation between grading change and the mechanical behaviour of granular assembly. A way to model the influence of grain breakage is to use a critical state‐based model. The influence of the amount of grain breakage during loading, depending on the individual grain strength and size distribution, can be introduced into constitutive relations by means of a new parameter that controls the evolution of critical state with changes in grain size distribution. Experimental data from a calcareous sand, a quartz sand, and a rockfill material were compared with numerical results and good‐quality simulations were obtained. The main consequences of grain breakage are increased compressibility and a gradual dilatancy disappearance in the granular material. The critical state concept is also enriched by considering its overall relation to the evolution of the granular material. Copyright © 2009 John Wiley & Sons, Ltd.     

土压力滑楔理论的统一解

基于滑楔理论计算土压力的基本原理,运用考虑中间主应力效应的统一强度理论,对传统的土压力公式不能反映土体材料强度的中间主应力效应的公式进行了改进,推导了基于滑楔理论的土压力统一解公式,Coulomb和Rankine土压力公式为其特例.通过变换统一强度参数,可获得一系列的解.在工程运用中可根据土质和工程的实际情况,适当选择统一强度参数和应力状态来确定土压力的大小.     

绿地信息提取研究

城市绿地作为城市结构中的主要元素,在城市中起着一个重要的作用。本文基于TM遥感影像,对大连市城市绿地专题信息进行提取,并对绿地格局进行研究和探讨。通过计算各组成分分量和归一化植被指数ND-VI之间的相关系数来进行波段组合,提高了遥感影像的分类精度。结果显示该方法可以准确地得到绿地信息。     

常州市地下水化学特征与成因分析

常州市是长江三角洲地区典型的工业化城市,多年来的快速发展对地下水环境产生了系列影响,地下水化学组分受到天然条件和人为活动的双重因素控制,现状地下水化学成因和影响因素亟需深入研究。本文在地下水赋存条件分析的基础上,综合采用统计分析、离子比值、主成分分析法对常州各层地下水化学特征和成因开展分析。结果表明,区域潜水水化学类型以HCO₃^-—Ca²⁺·Mg²⁺、HCO₃^-—Ca²⁺和HCO₃^-·Cl^-—Na⁺·Ca²⁺型为主,第Ⅰ承压水以HCO₃^-—Na⁺·Ca²⁺和HCO₃^-—Ca²⁺型为主、第Ⅱ承压水以HCO₃^-—Na⁺     

南京河西地区地面沉降成因分析

为了查明南京河西地区地面沉降的成因,笔者等在系统研究水文地质与工程地质条件的基础上,研究了地面沉降的分布特征和发展规律,以及地面沉降与地下水位、软土分布及建筑荷载之间的关系,进而揭示了南京河西地区地面沉降的成因。研究结果表明：南京河西地区不开采地下水,地面沉降与软土层厚度和建筑荷载分布关系密切,地面沉降主要受建筑工程影响,即建筑荷载和深基坑降水的作用。     

资源三号影像中城市高大地物阴影检测方法

针对遥感影像处理中阴影检测和信息补偿不准确的问题,该文在研究已有阴影检测算法的基础上,结合资源三号(ZY-3)影像数据的特性,构建了阴影检测方法:首先对原始图像分别做差值运算和主成分变换,并利用多峰阈值自动提取算法检测出阴影区域;其次将差值运算提取的粗阴影区域与主成分变换提取的阴影区域做并运算生成一个新的阴影区域;然后判断影像中是否含有水体,如果含有水体则利用多峰阈值自动提取算法检测出水体并与新合并的阴影区域影像做布尔运算得到完整的阴影区域,反之则新合并的区域即为完整的阴影区域。实验结果表明该方法针对ZY-3具有较好的普适性、较高的提取精度和提取效率。     

基于主成分分析的植被指数与叶面积指数相关性研究

综合分析了玉米叶面积指数与几种常见光谱植被指数相关性,确定主成分分析方法在反演叶面积指数中的作用。首先,借助MATLAB编程软件,以植被指数与玉米叶面积指数相关性最高为原则,选出遥感影像上各种植被指数,其波段组合为NDVI(752.4/701.5),RVI(752.4/701.5),MSR(752.4/701.5),SAVI(823.7/701.5),MSAVI(823.7/701.5),然后,对这5种植被指数进行主成分分析,建立LAI-VI多元逐步回归模型,并对模型精度进行验证,总体估测精度为96.237%。经实验验证,利用主成分分析方法在反演植被叶面积指数时能够起到较好的效果,具有广泛的应用前景。     

西藏冈底斯成矿带矿化蚀变提取与成矿分析——以尼玛县帮勒地区为例

冈底斯成矿带是我国极具找矿潜力的地带,但受自然条件限制,该地带矿产资源开发程度普遍偏低。选取冈底斯成矿带北部尼玛县帮勒地区为研究区,以Landsat-8OLI数据为主要信息源,采用主成分分析法提取研究区铁染和羟基矿化蚀变信息。在GIS平台上,将提取的蚀变信息结合研究区现有地质、化探、矿产等资料进行综合分析,依据成矿理论,圈定2个成矿远景区。经野外验证,文中获取的矿化蚀变信息分布状况与已知矿点和已探明蚀变带的空间一致性高。矿化蚀变带的探明能够为区域矿产资源开发与勘查提供帮助。     

Evaluation of the relative roles of global versus local sedimentary controls on Middle to Late Pleistocene formation of continental margin strata,Canterbury Basin,New Zealand

Determining the relative influence of eustasy versus local sedimentary processes on strata formation is a fundamental challenge in the study of continental margin stratigraphy. In this paper, the relative contribution of these factors on continental margin evolution during the Middle to Late Pleistocene is evaluated using samples from Integrated Ocean Drilling Program Expedition 317. Core‐logging, biostratigraphy and quantitative X‐ray diffraction mineralogy are used to delineate continental shelf sedimentary systems. Major lithological unconformities bound stratigraphic sequences that contain recurring compositional patterns and that resemble other examples of Middle to Upper Pleistocene sequences. However, a preliminary chronology suggests that sequence boundary formation cannot be linked ‘one to one’ with eustatic cycles and therefore these sequences can contain multiple ca 100 ka eustatic cycles. Smaller amplitude, higher frequency transitions in sediment composition are interpreted as stratigraphic sequences driven by more rapid perturbations in the interplay of accommodation and sediment supply; their stratigraphy is variable in time and across the shelf, suggesting a strong influence of local sedimentary forcing in their formation. Changes in sediment composition after the Middle Pleistocene Transition indicate that sediment transfer from onshore sources in the glaciated Southern Alps to the middle‐shelf occurred over a single 100 ka glacio‐eustatic cycle, with an additional 100 ka lag before the mineralogical signal was preserved on the outer‐shelf. This phenomenon is coincident with rapid shelf progradation in this basin, suggesting a causal relation between across‐shelf sediment transport and margin progradation. This is one of very few studies that provide insights at the core scale into the processes driving continental margin evolution during the Middle to Late Pleistocene. This work shows that compositional changes in mud‐dominated successions can lead to a sequence stratigraphic interpretation and the identification of high‐frequency sequences, which may not be possible using a conventional stratigraphic approach.     

基于ETM~+数据和GIS技术的缅甸铜金矿成矿预测

在利用遥感数据和地理信息系统(GIS)技术的矿产资源勘查与评价中,矿化蚀变信息提取和构造信息提取起着至关重要的作用。以缅甸铜金矿为例,利用ETM+遥感图像,采用比值法、阈值分割和主成分分析(PCA)提取羟基蚀变信息;利用数字高程模型和遥感数据提取与铜金矿化有关的线环构造,结合地质资料和上述信息,利用证据权和分形方法进行整合,确定该研究区的成矿远景区。结果发现,已知铜金矿均分布于成矿靶区中,综合信息可为下一步的矿产资源勘探工作提供决策依据。