Numerical analysis of effect of baffle configuration on impact force exerted from rock avalanches

In mountainous areas, channelized rock avalanches swarm downslope leading to large impact forces on building structures in residential areas. Arrays of rock avalanche baffles are usually installed in front of rigid barriers to attenuate the flow energy of rock avalanches. However, previous studies have not sufficiently addressed the mechanisms of interaction between the rock avalanches and baffles. In addition, empirical design approaches such as debris flow (Tang et al., Quat Int 250:63–73, 2012), rockfall (Spang and Rautenstrauch, 1237–1243, 1988), snow avalanches (Favier et al., 14:3–15, 2012), and rock avalanches (Manzella and Labiouse, Landslides 10:23–36, 2013), which are applied in natural geo-disasters mitigation cannot met construction requirements. This study presents details of numerical modeling using the discrete element method (DEM) to investigate the effect of the configuration of baffles (number and spacing of baffle columns and rows) on the impact force that rock avalanches exert on baffles. The numerical modeling is firstly conducted to provide insights into the flow interaction between rock avalanches and an array of baffles. Then, a modeling analysis is made to investigate the change pattern of the impact force with respect to baffle configurations. The results demonstrate that three crucial influencing factors (baffle row numbers, baffle column spacing, and baffle row spacing) have close relationship with energy dissipation of baffles. Interestingly, it is found that capacity of energy dissipation of baffles increases with increasing baffle row numbers and baffle row spacing, while it decreases with increasing baffle column spacing. The results obtained from this study are useful for facilitating design of baffles against rock avalanches.     

A comparative frequency analysis of three standardized drought indices in the Poyang Lake basin,China

Regional drought frequency analysis was carried out in the Poyang Lake basin (PLB) from 1960–2014 based on three standardized drought indices: the standardized precipitation index (SPI), the standardized precipitation evapotranspiration index (SPEI) and the standardized Palmer drought index (SPDI). Drought events and characteristics were extracted. A Gumbel–Hougaard (GH) copula was selected to construct the bivariate probability distribution of drought duration and severity, and the joint return periods (T _a ) were calculated. Results showed that there were 50 (50 and 40) drought events in the past 55 years based on the SPI (SPEI and SPDI), and 9 (8 and 10) of them were severe with T _a more than 10 years, occurred in the 1960s, the 1970s and the 2000s. Overall, the three drought indices could detect the onset of droughts and performed similarly with regard to drought identification. However, for the SPDI, moisture scarcity was less frequent, but it showed more severe droughts with substantially higher severity and longer duration droughts. The conditional return period (Ts|d) was calculated for the spring drought in 2011, and it was 66a and 54a, respectively, based on the SPI and SPDI, which was consistent with the record. Overall, the SPI, only considering the precipitation, can as effectively as the SPEI and SPDI identify the drought process over the PLB under the present changing climate. However, drought is affected by climate and land-cover changes; thus, it is necessary to integrate the results of drought frequency analysis based on different drought indices to improve the drought risk management.     

铀矿勘查中MT数据提取极化信息可行性研究

铀矿勘查中大地电磁测深法(以下简称MT法)的应用十分广泛,而频率域电磁勘探中激电效应切实存在。激电参数作为反映岩、矿石电化学性质的参数,在地质解译过程中常常被认为是金属硫化物的局部富集。为了充分利用铀矿床MT数据辅助地质解译,需要从中提取具有多属性特征的激电参数,能否成功提取该参数一直以来备受关注。文章从激电异常识别和二维反演试算两方面来论述成功提取的可行性。结果表明,仪器能够采集到含矿岩体所产生的激电异常,反演试算结果能够还原理论模型的地下空间展布情况。从而论证了从铀矿床MT数据中提取极化率是可行的。     

基于梯度提升算法的岩性识别方法

传统的岩性识别方法如岩屑录井、钻井取心及测井资料解释等技术,对录井质量的依赖程度较高,识别精度与效率低,泛化能力差。随着计算机技术的迅速发展,将测井资料与计算机技术相结合开展岩性研究已成为岩性识别的有效手段。本文提出了一种基于梯度提升算法XGBoost和LightGBM的岩性识别方法。以苏里格气田苏东41-33区块下碳酸盐岩储层为例进行测试验证,采用该方法结合测井资料中的声波时差、自然伽马、光电吸收截面指数、密度、深侧向电阻率和补偿中子等6种参数进行岩性识别,并与KNN （K近邻分类器）、朴素贝叶斯和支持向量机等传统算法进行对比,结果表明,3种传统算法的岩性识别准确率分别为78.45%、74.43%和78.72%,基于梯度提升算法XGBoost和LightGBM的识别准确率分别达到了98.90%和98.72%,远高于传统算法。     

基于相干特征的岩石薄片序列图像边缘提取及颗粒分割

针对岩石颗粒边缘模糊、结构复杂的特点,为了更有效地识别颗粒边缘,在基于特征值的C3相干算法的基础上,融合多尺度和多角度的特征表达,提出了一种改进的C3相干算法。该算法综合考虑岩石薄片图像角度域光学特征、空间尺度信息和各向异性信息,能更有效地表征颗粒边缘特征,表现出对复杂矿物结构的适应能力。在采集的岩石薄片正交偏光图像上验证提出的算法,实验结果表明,与原生C3相干算法相比,改进后的C3相干算法在全局图像上的方差和灰度差分乘积分别提升了68.41%和22.91%,信息熵下降了21.61%。     

昌宁—孟连结合带北端癞痢头山岩体地球化学特征及其对成岩成矿作用的启示

位于昌宁—孟连结合带北端的癞痢头山岩体,主要由中粗晶花岗闪长岩(MGG)和细晶花岗闪长岩(FG)组成,形成于中三叠世(232 Ma).MGG和FG岩相学特征相似,无明显空间分带关系,呈过渡渐变关系.它们具高硅(w(SiO2) =66.2％～68.2％,平均67.0％),富钾(K2O/Na2O=1.04～2.59,平均1.64),贫碱(w(Na2O+K2O)=5.45％～7.31％,平均5.99％)、低钠(w(Na2O)=1.54％～3.58％,平均2.38％),高镁值(Mg#=47.3～58.7,平均51.5)和过铝质(A/CNK=1.41～2.17,平均1.65)特征,属过铝质高钾钙碱性系列.二者轻、重稀土元素含量比值介于6.91～12.1,表现为轻稀土元素相对富集、重稀土元素相对亏损.岩石富集w(Rb) (54.7～176×10-6),w(U)(1.10～4.77×10-6),w(Th) (9.33～35.30×10-6)等大离子亲石元素,亏损w(Ta) (1.22～1.51×10-6),w(Nb)(14.9～18.5×10-6),w(Zr)(78.4～171.0×10-6)等高场强元素,以及δEu(0.35～0.57)和"TNT"负异常特征,表明初始岩浆以陆壳成分为主并有幔源组分的加入.癞痢头山岩体样品具有较高的A/CNK值(1.41～2.17)和刚玉分子含量(1.87％～8.67％),以及Nb/Ta比值(11.03～13.76)和Zr/Hf比值(23.13～47.85)分别与平均地壳和壳源岩石相应比值一致,显S型花岗岩特征.综合分析,认为癞痢头山岩体属于S型花岗岩,起源于古老地壳物质(贫黏土的古老杂砂岩)部分熔融岩浆和底侵作用带入的幔源岩浆的混合岩浆,是保山—思茅地块陆陆后碰撞阶段力学性质由挤压向伸展转化动力学背景下的产物,具备成矿作用发生的物质基础,有一定的找矿潜力.     

基于连续消光特征分析的岩石薄片分析系统

连续消光是指在正交偏光显微镜下,岩石薄片随载物台旋转而发生消光强弱连续变化的现象。作为人工鉴定岩石薄片的重要依据,提取后的连续消光特征可以用于实现岩石薄片的自动分析。结合数字图像处理技术与聚类划分算法,开发出一套能够分割出孔隙、颗粒轮廓,实现颗粒类别划分,并对结果做定量分析的岩石薄片分析系统。从矿物的消光特征本质出发,连续消光特征提取精确与否是能否有效划分颗粒类别的关键环节。因此,针对系统在连续消光特征提取过程中的消光位对齐与消光基值去除操作分别设置了对照组。以鄂尔多斯盆地某区长6段砂岩薄片在正交偏光镜下的角度域序列图像进行实验,结果表明,所开发的基于岩石薄片分析系统能够提取到更为精确的连续消光特征,且该系统定量分析结果与专业人员鉴定结果基本一致。     

基于主导生态功能的江西省国土空间生态修复分区研究

以地域分异特征、主导生态功能、典型生态问题为基础依据,探讨江西省国土空间生态修复分区,为江西省编制和实施生态修复规划、实现国土空间管控提供科技支撑。在研究方法上,以“生命共同体理论”“三生协调理论”“适宜性管理”等理论为指导,基于主体功能区划和生态功能区划,综合“三生”空间实际生态问题及综合整治需求,采用多因素综合空间分析法,“自上而下”和“自下而上”相结合,实现国土空间生态修复三级分区。研究结果表明,可将江西省国土空间生态修复区域划为赣北平原湖泊生态修复区、赣中丘陵盆地生态修复区、赣西山地丘陵生态修复区、赣南山地丘陵生态修复区、赣东丘陵山地生态修复区5个大区及24个亚区和42个修复小区。通过江西省国土空间生态修复三级分区,摸清国土空间地域特征,明确生态主导功能,确定生态修复重点区域,承上启下,为实施生态修复工程和国土空间管治提供决策依据,为实现国土空间整体保护、系统修复、综合治理提供科技途径。     

利用分布式光纤声传感设备开展青藏高原易贡湖浅层结构探测

地震数据是利用地震学方法探测地下结构的基础条件,然而传统地震仪器难以获得极端环境地区(水下、高原等)的长时间、高密度连续数据。较之国际仪器厂商,国内的DAS研制相对较晚。自2016年起,国产DAS逐步应用于石油测井和城市区域地下结构探测,而运用在极端环境下的探测工作尚未见报道。中国科学院半导体研究所与青藏高原研究所经过多年合作研究,于2021年4月将自主研发的DAS系统首次应用于青藏高原的野外数据采集。本次试验同时记录了地面和水下的连续背景噪声和重锤数据。该研究利用背景噪声成像技术,获得了西藏易贡湖地区地表70 m以内的横波速度结构。本次研究为极端环境下的低成本、高密度数据采集和地下结构探测提供了理论和试验依据。