A discrete numerical method for brittle rocks using mathematical programming     

J. Meng  J. Huang  C. Yao  D. Sheng 《Acta Geotechnica》2018,13(2):283-302

A computational formulation of discrete simulations of damage and failure in brittle rocks using mathematical programming methods is proposed. The variational formulations are developed in two and three dimensions. These formulations naturally lead to second-order cone programs and can conveniently be solved using off-the-shelf mathematical programming solvers. Pure static formulations are derived so that no artificial damping parameters are required. The rock is represented by rigid blocks, with interfaces between blocks modelled by zero-thickness springs based on the rigid-body–spring network method. A modified Mohr–Coulomb failure criterion is proposed to model the failure of the interfaces. When the interface’ strength limits are reached, a microscopic crack forms and its strength is irreversibly lost. The microscopic elastic properties of the springs are related to the observed elastic behaviour of rocks with the developed empirical equations. The program is first validated with three simple tests. Then, numerical uniaxial and biaxial compression tests and the Brazilian tests are conducted. Furthermore, the proposed approach is employed to study the rock crack propagation and coalescence using cracked Brazilian disc test. The results are in good agreements with reported experimental data, which shows its potential in modelling mechanical behaviour of brittle rocks.  相似文献   

Retreat rates of debris-covered and debris-free glaciers in the Koshi River Basin,central Himalayas,from 1975 to 2010     

Yang Xiang  Tandong Yao  Yang Gao  Guoqing Zhang  Weicai Wang  Lide Tian 《Environmental Earth Sciences》2018,77(7):285

Debris-covered glaciers are common in the Himalayas and play a key role in understanding future regional water availability and management. Previous studies of regional glacial changes have often neglected debris-covered glaciers or have mixed them with debris-free glaciers. In this study, we generated a new glacier data set that includes debris-covered and debris-free glaciers to study the glacial surface area change in the Koshi River Basin in the central Himalayas. Long time-series Landsat data were used to extract the glacier boundaries using automatic and manual classification methods. The glacial area decreased by 10.4% from 1975 to 2010 at a rate of 0.30% a^?1, with accelerated melting since 2000 (0.47% a^?1). Small glaciers melted faster than large glaciers. In terms of distinctive glacier types, debris-free glaciers shrank at a rate of 0.45% a^?1, faster than debris-covered glaciers (0.18% a^?1), while debris-covered glaciers larger than 5.0 km² retreated at a rate faster than debris-free glaciers of the same-sized group. We also studied the potential interactions between 222 supraglacial lakes and debris-covered glaciers. Debris-covered glaciers with glacial lakes melt faster than glaciers without lakes. This study can improve our understanding of the differences in the changes between debris-covered and debris-free glaciers in the central Himalayas and help evaluate water resource changes in the Himalayas.  相似文献   

Pressure transient analysis of multi-fractured horizontal wells in tight oil reservoirs with consideration of stress sensitivity     

Shan Huang  Yuedong Yao  Shuang Zhang  Jinghao Ji  Ruoyu Ma 《Arabian Journal of Geosciences》2018,11(11):285

Multi-fractured horizontal well (MFHW) is an effective technique to develop unconventional reservoirs. Complex fracture network around the well and hydraulic fractures is formed during the fracturing process. Fracture network and hydraulic fractures are the main seepage channel which is sensitivity to the effective stress. However, most of the existing models do not take the effect of stress sensitivity into account. In this study, a new analytical model was established for MFHW in tight oil reservoirs based on the trilinear flow model. Fractal porosity and permeability were employed to describe the heterogeneous distribution of the complex fracture network, and the stress sensitivity of fracture was considered in the model. The Pedrosa substitution and perturbation method were applied to eliminate the nonlinearity of the model. By using the Laplace transformation method, the analytical solutions in Laplace domain were obtained. Then, validations were performed to show that the model is valid. Finally, sensitivity analysis was discussed. The presented model provides a new approach to the estimation of fracturing effect and can be also utilized for recognizing formation properties of tight oil reservoirs.  相似文献   

Investigation of the anisotropy of black shale in dynamic tensile strength     

Xiaoshan Shi  Da’an Liu  Wei Yao  Yirui Shi  Tiewu Tang  Bonan Wang  Weige Han 《Arabian Journal of Geosciences》2018,11(2):42

Shale usually exhibits strong anisotropy due to depositional environment and pre-existed microcracks caused by geological loading for a long time. Characterizing mechanical anisotropy properties of shale, especially the tensile strength anisotropy, plays an important role in the successful exploitation of shale gas. In this work, static and dynamic tests with semi-circular bending (SCB) specimen are conducted using hydraulic servo-control machine and modified split Hopkinson pressure bar (SHPB) system, respectively. To survey the tensile strength anisotropy of shale induced by stratification, samples are cored and cut into half by diametrical cutting along different angles relative to the stratification (0°, 30°, 45°, 60°, 90°, C0°). For dynamic tests, the utilization of pulse shaping technique ensures that the samples obtain dynamic equilibrium. The tensile strength values exhibit clear anisotropy under both static and dynamic loading conditions and show typical loading rate dependence at a given angle. An anisotropic index named α_k is defined to describe the tensile strength anisotropy at a certain loading rate. The outcomes illustrate that the anisotropic index decreases as the loading rate increases. In addition, failure pattern owns different characteristic under different loading angles with respect to the stratification. These phenomena may be explained by the pre-existing microcracks, and cracks interaction during dynamic loading conditions.  相似文献   

Genesis of the Ore-related Granite Porphyry and Molybdenite Re-Os Age of Laomiaogou Porphyry-skarn Mo Deposit,Western Henan Province: Implications for Regional MineralizationEI北大核心CSCD     

Zhou D.  Jin C.  Gao X.  Zhao T.  Bao Z.  Yao J. 《大地构造与成矿学》2018,(3):534-549

The newly discovered Laomiaogou porphyry-skarn Mo deposit is located south of the Machaoying fault in western Henan province. The ore-body is hosted in the contact between the Laomiaogou granite porphyry dyke and the Duguan Formation. LA-ICP-MS U-Pb analyses for zircons from the granite porphyry yield a weighted mean 206Pb/238U age of 152.1±0.6 Ma, and seven molybdenite separates yield a weighted mean age of 151.9±0.9 Ma and isochron age of 151.6±5.1 Ma. Thus, the granite porphyry dyke and Mo mineralization are contemporaneous. The ore-related granite porphyry dyke is a peraluminous I-type granite with high contents of SiO2 and K2O. The rocks are strongly depleted in P, Nb, Ta and Ti, indicative of intensive fractionation of apatite and Fe-Ti oxides, and characterized by low whole-rock εNd(t) (-20.6 to -17.6) and zircon εHf(t) values (-26.9 to -22.6). The old tDM2(Nd) ages (2.37 to 2.61 Ga) and zircon tDM2(Hf) ages (2.62 to 2.88 Ga) suggest that the granite porphyry was likely derived from an ancient crustal source. Considering the tectonic evolution and geochemical characteristics of the granite as well as other Mesozoic granites in the southern margin of the North China Craton, we suggest that the Laomiaogou granite porphyry dyke and Mo were most likely derived from partial melting of the Taihua Group metamorphic rocks under extensional tectonic regime related to the subduction of the paleo-pacific plate. © 2018, Science Press. All right reserved.  相似文献   

Reverse Weathering in River-dominated Marginal Seas   总被引：1，自引：1，他引：0  

Bin Zhao  Peng Yao  Zuosheng Yang  Zhigang Yu 《地球科学进展》2018,33(1):42-51

In estuarine regions and marginal seas, reverse weathering refers to the formation of authigenic aluminosilicate and carbonate minerals promoted by large inputs of terrestrial weathering products and intense remineralization of Sedimentary Organic Carbon (SOC), which is opposite to land weathering process. Compared with the process in open ocean, the formation of authigenic aluminosilicate and carbonate minerals caused by reverse weathering in estuarine regions and marginal seas is rather rapid, playing an important role in the maintenance of ocean acidity and elements cycles. At present, there are two research methods regarding the reverse weathering process, i.e., direct observation and chemical detection. The first method is used to study the structure and chemical composition of authigenic minerals and the second is mainly used to do quantified studies of authigenic minerals. The reverse weathering is very important to the cycles of Si, C, major ions (F^-, Li⁺, Na⁺, K⁺, Ca²⁺ and Mg²⁺), and alkali metal cations (Fe, Mn and Al) in marine environments, which promotes the burial of these elements in marine sediments. Due to large inputs of weathering products rich in Fe, Mn and Al oxides, precipitation of labile OC and biogenic silica, intense remineralization process and suboxic/anoxic conditions, estuarine and marginal seas are suitable sites for reverse weathering studies. The reverse weathering studies in sub-tropical and temperate estuaries should be emphasized in the future.  相似文献   

内蒙古敖仑敖包早白垩世A型花岗岩锆石U-Pb年龄、地球化学特征及其构造意义     

姚百赫  来林  徐文坦 《江苏地质》2018,42(2):264-276

内蒙古苏尼特右旗位于兴蒙造山带中段,其东北部敖仑敖包岩体主要由二长花岗岩组成,LA-ICP-MS锆石U-Pb年龄为(138.5±1.4)Ma,时代为早白垩世,是区域岩浆活动最频繁的燕山期。地球化学分析结果表明,敖仑敖包岩体具高硅(72.03%~76.37%)、高碱(8.06%~8.58%)、低铝(13.04%~13.81%)、富铁、贫钙、贫镁特征,属于高钾钙碱性至碱性过渡系列花岗岩;稀土元素丰度中等,呈轻稀土富集、重稀土亏损的右倾海鸥状。微量元素特征表现为大离子亲石元素(LILE)Rb、Th、U、K相对较为富集,高场强元素(HFSE)Nd、Ta、Zr和Hf相对富集,而Ba、Sr、P、Ti强烈亏损。上述特征与A_1型花岗岩相似,成因可能为在拉张构造体制下软流圈物质上涌与地壳混染而成。  相似文献   

基于IFA的组合分析算法及其在矿产预测中的应用     

姚旺  卞姗姗  余先川 《江苏地质》2018,42(4):623-631

矿产预测是寻找潜在矿产资源、增加后备储量的主要手段。地球化学信息作为直接找矿信息,在矿产预测中占据重要地位,对地球化学数据进行矿致异常的识别和评价是关键环节之一。地球化学数据分析的目的是从杂乱无章的原始数据中寻找并有效圈定化探组合异常。针对目前常用于组合异常分析的R型聚类分析和因子分析等传统算法对数据源限制较多、预测效果不理想等问题,将信号处理领域的盲源分离算法——独立因子分析(IFA)引入到矿产预测中,提出了基于IFA的组合分析算法,并选取广东汕头澄海区鸿沟山锡金多金属矿区地球化学数据作为研究对象。验证结果表明,基于IFA的组合分析结果更有利于解释矿产分布规律,圈定的化探组合异常更符合实际勘查结果。依据分析结果进行矿产预测,成功圈定出3个找矿靶区。  相似文献   

鄂尔多斯盆地南缘铜川地区三叠系延长组油页岩中“钙质结核”的成因初探          下载免费PDF全文

马　瑶李文厚  刘江斌李智超 《地质科学》2018,(2):458-469

在鄂尔多斯盆地南缘铜川地区野外露头三叠系延长组长7段油页岩中发现了一些“钙质结核”,野外露头中呈层状发育于长7段油页岩中,形态为“透镜状”、“椭球状”、“飞碟状”,直径大小约为10～70 cm。为探明其岩石类型和主要岩石组分,运用显微镜薄片鉴定、电子探针实验、能谱分析等方法,对结核体进行岩石学特征分析。在此基础上,对其成因进行初步探讨。岩石学特征显示,霸王庄和宜君套滩剖面的“钙质结核”主要成分为重结晶方解石和晶粒方解石,具“球粒状”结构,岩石类型为灰岩;瑶曲聂家河剖面结核体主要岩石类型为泥-粉晶白云岩。分析认为这些“钙质结核”其野外产状和岩石成分,符合热水沉积碳酸盐岩和受热液活动影响的特征,并且铜川地区在长7期具备热液活动的条件。初步认为这些“钙质结核”为湖底热液活动成因的湖相碳酸盐岩。  相似文献   

巴布亚新几内亚陆缘火山岛弧成矿带铜金成矿规律     

姚仲友 《地质与勘探》2018,54(6):1187-1201

巴布亚新几内亚陆缘火山岛弧成矿带形成于印澳板块与太平洋板块的边界带,其演化涉及俯冲与火山岛弧（岩浆弧）的形成、弧陆碰撞与造山、俯冲陆壳折返、岩浆侵入、成矿作用等多种地质作用。该成矿带的铜金成矿时代比较年轻,成矿集中于23～12（Ma）、7～1（Ma）及0.5～0（Ma）三个成矿高潮期。空间上可以分为6个成矿亚带,分别为奥克泰迪-波尔盖拉成矿亚带、弗里达河-拉穆成矿亚带、海登山谷-凯利门戈成矿亚带、托鲁库玛-比尼山成矿亚带、瓦普鲁-伍德拉克成矿亚带、利希尔-潘古纳成矿亚带。成矿带主要铜金矿床类型为斑岩型、浅成低温热液型和矽卡岩-斑岩型。成矿受控于俯冲作用、弧陆碰撞造山作用、侵入杂岩体、褶皱和断裂、破火山口等因素。  相似文献