Creep Properties of Altered Rock Subjected to Water Influx-Lost Cycles

Geotechnical and Geological Engineering - Creep properties of altered granite were changed due to water level rise and fall in the tailings ponds. In this paper, the effects of water influx-lost...     

Numerical Simulation Study on Crack Evolution Characteristics of Coal Specimen Subjected to Conventional Compression Loading

Geotechnical and Geological Engineering - The paper represents a simulation investigation about the crack evolution and acoustic emission characteristics of coal specimen subjected to conventional...     

青藏粉质黏土冻融循环试验研究

以青藏公路沿线常遇到的青藏粉质黏土作为研究对象, 在室内分别进行了1、 2、 3、 4次冻融循环试验, 分析了冻融前后试样的温度分布特征、 水分分布特征、 冻融位移变化特征. 结果表明: 多次冻融循环的冻结过程中, 温度场分布更趋向均衡和平稳, 0 ℃等温线和低温等温线趋向深部发展; 多次冻融循环后, 试样含水量可划分4个区域, 第1区域为表层冰晶聚集高含水量区, 第2区域为低温梯度含水量均衡区域, 第3区域为冷锋面冰透镜冰层积聚高含水量区域, 第4区域为高温低含水量区域; 青藏粉质黏土首次冻结的冻胀位移量和相对冻融位移量都比较大, 冻胀量可以达到几十毫米, 冻胀率可达8.3%, 伴随冻融次数增加, 相对冻胀量和相对冻融量幅值逐渐减少.     

冻融循环下加筋膨胀土边坡稳定性模型试验

控制边坡在冻融循环中的劣化作用,可保障季节冻土区域膨胀土边坡长期稳定。为确定土工格栅对膨胀土边坡在冻融循环过程中的稳定效果与工程意义,本文开展了膨胀土边坡模型试验,对比冻融过程中边坡内土压力、含水率、位移、温度变化。结果表明：土工格栅可约束膨胀土冻融裂缝,使裂缝发育更为均匀一致,同时减小边坡位移;加筋材料能抑制边坡水分迁移与热传导并减小土压力变化;对膨胀土边坡加筋处理可显著降低含水率波动幅值,从而减小膨胀土受含水率变化引发的胀缩劣化;不同于普通黏土,膨胀土边坡冻融循环中呈现冻缩融胀特点,而边坡加筋可有效提升冻土区膨胀土边坡的冻融稳定性,具有工程应用价值。     

Fatigue Behavior of Granite Subjected to Cyclic Loading Under Triaxial Compression Condition

A series of laboratory tests were performed to examine the fatigue behavior of granite subjected to cyclic loading under triaxial compression condition. In these tests, the influences of volumetric change and residual strain on the deformation modulus of granite under triaxial cyclic compression were investigated. It is shown that the fatigue behavior of granite varies with the tendency for volumetric change in triaxial cyclic compression tests. In the stress–strain space, there are three domains for fatigue behavior of rock subjected to cyclic loading, namely the volumetric compaction, volumetric dilation with strain-hardening behavior, and volumetric dilation with strain-softening behavior domains. In the different domains, the microscopic mechanisms for rock deformation are different. It was also found that the stress level corresponding to the transition from volumetric compaction to volumetric dilation could be considered as the threshold for fatigue failure. The potential of fatigue deformation was compared with that of plastic deformation. The comparison shows that rocks exhibit higher resistances to volumetric deformation under cyclic loading than under plastic loading. The influence of residual strain on the fatigue behavior of rock was also investigated. It was found that the axial residual strain could be a better option to describe the fatigue behavior of rock than the loading cycle number. A constitutive model for the fatigue behavior of rock subjected to cyclic loading is proposed according to the test results and discussion. In the model, the axial residual strain is considered as an internal state variable. The influences of confining pressure and peak deviatoric stress on the deformation modulus are considered in a term named the equivalent stress. Comparison of test results with model predictions shows that the proposed model is capable of describing the prepeak fatigue behavior of rock subjected to cyclic loading.     

反复冻融下黄土抗剪强度劣化的试验研究

以陕西杨凌黄土为研究对象,对不同初始含水率的重塑黄土进行了长期反复冻融循环,对经历不同冻融次数的试样进行了系列直剪试验.结果表明:在控制含水率不变的情况下,黄土的黏聚力和抗剪强度一般在3～5次冻融循环之后降到最低值,并趋于稳定;内摩擦角基本不变.探讨了长期冻融循环下黄土的强度劣化特性,采用插值法修正了含水率下降对强度的影响.由试验数据拟合出黄土抗剪强度和冻融循环次数之间的经验关系,推导出一种考虑冻融循环作用的黄土强度劣化模型.经试验验证,该模型可以较好描述黄土强度的劣化特性,为黄土工程力学性质的劣化研究提供了一种新的有效途径.     

A Review of the Influence of Microscopic Characteristics on the Progressively Brittle Failure of Foliated Rocks Subjected to Compression Loading

Geotechnical and Geological Engineering - The progressively brittle failure of foliated rocks involving the initiation, propagation, and aggregation modes is closely related to the microscopic...     

Dynamic Characteristics of Granite Subjected to Intermediate Loading Rate

Summary A large diameter split Hopkinson pressure bar (SHPB) has been developed. This equipment is briefly described, together with a shaped striker that initiates a half-sine incident waveform to obtain the complete stress-strain relationship of the Bukit Timah granite at medium strain rate. Good constant strain rate was derived, and the dynamic complete stress-strain curves and energy absorption of the granite were measured at a strain rate between 20 and 60 per second. Repeated impact between 60–90% of the static strength of the granite was also conducted. Results from the tests show that the cumulative damage of the granite depends on the peak stress of the dynamic loads with a fixed duration. The dynamic fracture strength of the granite loaded at medium strain rate is directly proportional to the cube root of the strain rate. For the granite loaded at this strain rate, Youngs modulus is unchanged. Energy absorption of the samples loading to fragmentation determined its fragmented size distribution. At high strain rate, the rock possesses large energy absorption and the particle size of the fragments is much smaller.     

Strength and Compressibility Characteristics of a Soft Clay Subjected to Ground Treatment

The compressibility properties, undrained shear strength, and stress history are essential for reliable calculations of settlement and bearing capacity of soft soils. However, it is sometimes a challenge to determine representative parameters for very soft and high plasticity clays, which are often found in Brazilian coastal areas. In this study an extensive site investigation was planned aiming to interpret the behaviour of a trial embankment on stabilized soft ground. The site investigation was carried out in a test area located in the west of city of Rio de Janeiro, consisted of three clusters in which standard penetration tests, vane shear tests, and piezocone tests (CPTu) were performed. A number of correlations was developed and compared with empirical equations in order to verify their reliability. The results of these tests made it possible to define geotechnical parameters of the soft clay to use in the numerical and analytical computations of the embankment on reinforced ground.     

Seasonal Variability of Mineral Formation in Microbial Mats Subjected to Drying and Wetting Cycles in Alkaline and Hypersaline Sedimentary Environments

Interactions of the microbial mat community with the sedimentary environment were evaluated in two shallow, ephemeral lakes with markedly different hydrochemistry and mineralogy. The characterization of growing and decaying microbial mats by light microscopy observations and fluorescence in situ hybridization was complemented with biogeochemical and mineralogical measurements. The lakes studied were Eras and Altillo Chica, both located in Central Spain and representing poly-extreme environments. Lake Eras is a highly alkaline, brackish to saline lake containing a high concentration of chloride, and in which the carbonate concentration exceeds the sulfate concentration. The presence of magnesium is crucial for the precipitation of hydromagnesite in microbialites of this lake. Altillo Chica is a mesosaline to hypersaline playa lake with high concentrations of sulfate and chloride, favoring the formation of gypsum microbialites. Differences in the microbial community composition and mineralogy of the microbialites between the two lakes were primarily controlled by alkalinity and salinity. Lake Eras was dominated by the cyanobacterial genus Oscillatoria, as well as Alphaproteobacteria, Gammaproteobacteria and Firmicutes. When the mat decayed, Alphaproteobacteria and Deltaproteobacteria increased and became the dominant heterotrophs, as opposed to Firmicutes. In contrast, Deltaproteobacteria was the most abundant group in Lake Altillo Chica, where desiccation led to mats decay during evaporite formation. In addition to Deltaproteobacteria, Cyanobacteria, Actinobacteria, Alphaproteobacteria and Gammaproteobacteria were found in Altillo Chica, mostly during microbial mats growth. At both sites, microbial mats favored the precipitation of sulfate and carbonate minerals. The precipitation of carbonate is higher in the soda lake due to a stronger alkalinity engine and probably a higher degradation rate of exopolymeric substances. Our findings clarify the distribution patterns of microbial community composition in ephemeral lakes at the levels of whole communities, which were subjected to environmental conditions similar to those that may have existed during early Earth.     

鹰峰环斑花岗岩地球化学特征及其构造意义

柴达木北缘鹰峰环斑花岗岩出露于柴达木地块与南祁连地体之间的柴北缘造山带,是我国发现的又一元古宙环斑花岗岩体.初步研究表明,鹰峰环斑花岗岩是具环斑结构和A-型花岗岩特征的典型的元古宙环斑花岗岩体,且属于A1亚型,岩浆组合具双峰式特征.环斑结构主要由几个钾长石斑晶颗粒形成聚斑,中心有一斜长石内核,斑晶表面具不均匀高岭土化,条纹构造明显且有规律,基质由细粒-微粒的石英组成,有明显重结晶及定向构造; 岩石化学组成以高钾为特征,A/ NKC < 1,A/NK > 1,属准铝质; 微量元素组成上富集Ba、U、Th、Ce、Hf、Sm,亏损Sr、Ta、Nb、Zr、Y,Rb/Sr (0.17~0.6)和Rb/Ba (0.03~0.24) 很低,岩石分异演化程度不高; 稀土元素: REE、Ce、Zr含量高,Ga含量高达25×10-6以上,远远高出其他类型花岗岩,但Eu (0.75~4.3) ×10-6轻度亏损,属轻稀土富集型.通过对微量元素和稀土元素的地球化学行为分析,鹰峰环斑花岗岩是发生在板内的一种岩浆作用,是下地壳的麻粒岩受底侵或拆沉作用地幔上涌影响,发生部分熔融,然后经过分异演化形成了碱性的“干”岩浆,并在后碰撞的区域拉伸构造环境下侵位.同时伴随温度的降低,钠质的斜长石从钾长石中出溶,并迁移到钾长石的边沿,形成了具环斑结构的A1型花岗岩.      

冻融循环对青藏高原腹地不同生态系统土壤细菌群落结构的影响

通过构建16S rRNA基因克隆文库,研究了冻融循环对青藏高原腹地北麓河的高寒沼泽草甸和高寒沙化草原两种不同生态系统土壤细菌群落结构的影响. 结果表明: α-、 β-、 γ- 和δ-变形菌门(α-、 β-、 γ- 和δ-Proteobacteria)、 酸杆菌门(Acidobacteria)、 放线菌门(Actinobacteria)、 拟杆菌门(Bacteroidetes)和浮霉菌门(Planctomycetes)为两个生态系统土壤共有的细菌类群, 其中, 变形菌门、 酸杆菌门及浮霉菌门细菌为研究区域优势菌, 而厚壁菌门(Firmicutes)为高寒沼泽草甸土壤所特有, 疣微菌门(Verrucomicrobia)和绿弯菌门(Chloroflexi)细菌是高寒沙化草原土壤特有的细菌类群, 表明青藏高原腹地两种生态系统土壤具有丰富的细菌多样性. 冻融循环会降低区域土壤的细菌多样性, 随冻融循环, 高寒沼泽草甸和高寒沙化草原生态系统土壤放线菌门丰度均呈现下降趋势, 但大部分细菌随冻融循环的变化在两种生态类型中呈现不同的变化规律, 结果说明冻融循环对于不同生态系统土壤细菌群落结构的影响既存在相似性, 也存在着较大的差异.     

诸广山岩体南部铀矿成矿特征

诸广山岩体南部是我国铀矿产的重要聚集地,文章从阐明决定该区铀矿床形成的有关地质因素入手,对诸广山岩体南部的四个铀矿田的矿床、矿体、矿点进行对比,分析其同位素年龄、矿体标高、物质成分、平均品位等方面的异同,找出不同地段的矿床特征差异和变化规律,总结铀成矿特征.研究认为诸广山岩体南部具有较好的成矿、控矿条件,是较好的产铀岩体.通过研究铀成矿单元、铀成矿条件的差异,综合物化探成果和以往工作程度,并进一步查明地质背景和加强对深部信息的分析、研究,可为下一步针对不同成矿前景的有利地区进行分类预测提供依据.     

循环冻融条件下安山岩和花岗岩的物理力学特性试验研究

结合青藏铁路块石护坡路基处于青藏高原特殊的气候条件,对用于青藏铁路护坡的两种主要岩石（花岗岩和安山岩）进行循环冻融试验.结果表明:两种岩石在经历了数次冻融循环后都出现了微细裂纹;声波监测表明,超声波速同冻融循环周期呈指数下降关系,显示了冻融循环对岩石风化的影响以及循环后岩石物理力学参数变化的趋势.结果说明,花岗岩的冻融...     

Fatigue-Damage Evolution Characteristics of Interbeded Marble Subjected to Dynamic Uniaxial Cyclic Loads

In this work, uniaxial fatigue tests combined with post-test X-ray computed tomography (CT) scanning were conducted on marble samples with different interbed orientations, in order to reveal the anisotropic damage evolution characteristics during rock failure. The dynamic elastic modulus, damping ratio, fatigue deformation, damage evolution, accumulative damage modeling and crack pattern were systematically analyzed. The testing results indicate that the interbed structure in marble affects the damage evolution and the associated dynamic mechanical behaviors. The damage curve in “S” style indicates three-stage trend, namely, initial damage stage, steady damage stage and the accelerated damage stage. The damage index during cyclic deformation for marble presents obvious discrepancy. In addition, a fatigue damage prediction models was employed numerically as double-term power equations based on the experimental data. It is found that the selected damage model is suitable in modeling the rapid damage growth in the early and final stage of rock fatigue lifetime. Moreover, post-test CT scanning further reveals the anisotropic damage characteristics of marble, the crack pattern in the fractured sample is controlled by the interbed structure. What is more, the most striking founding is that the fracture degree is in consistent with the damage accumulation within the steady damage stage. Through a series of damage mechanical behavior analysis, the internal mechanism of the effect of interbed orientation on damage evolution of marble is firstly documented.

     

延边—东宁地区晚三叠世花岗岩地球化学特征及其大地构造背景

U-Pb锆石测年结果表明,东宁地区太平岭岩体形成于201 Ma,与区域上七十二顶子、闹枝沟及珲春大荒沟等岩体形成时代一致,均为晚三叠世末.岩石类型以花岗闪长岩和二长花岗岩为主,地球化学特征表明该期花岗岩属于中钾钙碱性系列,并有向高钾钙碱性系列演化的趋势;富集大离子亲石元素Rb、Th、K、La,相对亏损Sr、P、Ti和高场强元素Nb、Ta、Zr、Hf等,Ba相对Rb、Th具有轻微的负异常.同位素地球化学研究表明,本区花岗岩具有低ISr、高εNd(t)、年轻Nd模式年龄的特点.综合研究表明,该期花岗岩的形成与大洋板块的俯冲作用有关,标志着古太平洋板块对东北地区俯冲作用的开始.     

Nitrogen Contents and Isotopic Characteristics of Mesozoic and Cenozoic Granites in Northeastern China

The method of determining the nitrogen isotopic composition of granites in the northeastern part of China is described.The content and isotopic values of nitrogen released from granite samples by stepwise heating were determined as well.The results showed that the diferent areas of northeastern China hae a great difference in nitrogen content and isotopic composition.Nitrogen released from the granites is 1.64-6.23μL/g ,with the maximum at about 600℃,from rhyolite and granophyre is 108.98-755.96μL/g,with the maximum at about 900℃,It is proved that fluid is characterized by heterogeneity in the deep crust of the different areas in northeastern China.The nitrogen isotopic compositions in different ranges of temperautes are wweighted.And the nitrogen isotopic compositions in different anges of temperatures are weighted.And the nitrogen isotopic values are 9.2‰ to 17.0‰,with a variation range of 7.8‰,The nitrogen isotopic ratios may have been fractionated during degassing and the fluid released from granites is the residual component.     

腾冲地区与锡矿床有关的花岗岩地球 化学特征及类型判别

腾冲地区自东向西依次发育早白垩世（K1）东河花岗岩带（143.0~111.7Ma）、晚白垩世（K2）古永花岗岩带（84.3~65.9Ma）和早第三纪（E1 2）槟榔江花岗岩带（66.4~41.2Ma）。通过对与锡成矿关系密切的槟榔江花岗岩带中来利山花岗岩和古永花岗岩带中小龙河、水城花岗岩的岩相学、元素地球化学研究发现：花岗岩SiO2含量高,全碱（ALK）＝8.17%~8.15%,K2O/Na2O＞1,修改后的钙碱指数（MALI）＝7.25~8.34,属高钾钙碱性 碱钙性系列;来利山花岗岩A/CNK＝1.02~1.04,为弱过铝质花岗岩,小龙河和水城花岗岩A/CNK≤1.0,为准铝质花岗岩;这些花岗岩的形成与腾冲地块和保山地块碰撞有关,其中来利山花岗岩FeO/(FeO＋MgO)＝0.61~0.67,相对富Mg,但铁镁含量低,源于（含）泥质岩石,为形成于后碰撞造山伸展阶段的S型花岗岩;小龙河和水城花岗岩FeO/(FeO＋MgO)＝0.88~0.94,相对富Fe,源于无水硅酸盐大陆地壳,为形成于后碰撞造山阶段A型花岗岩中的A2亚型花岗岩。研究确定了腾冲地区与锡矿床有关的来利山、小龙河、水城花岗岩的成因类型、源区特征和构造背景,并表明不同花岗岩带发育不同类型的花岗岩。     

REE Geochemistry and Mineralization Characteristics of the Zudong and Guanxi Granites,Jiangxi Province

Abstract The Zudong and Guanxi granites are original rocks of the ion adsorption-type HREE and LREE deposits in weathering crust of granites. The ∑REE ¹ ∑REE=REE+Y.
value and LREE ² LREE=∑(La-Eu) and HREE=∑(Gd-Lu)+Y.
/ HREE ratio of the Zudong granite are 264 ppm and 0.81-0.24 respectively, and the average Y/∑REE ratio is 35.8-54.5%. This is mainly due to magmatic crystallization and evolution and deuteric metasomatism (albitization, muscovitization and fluorite-doveritization). These alterations resulted in endogenic mineralizations of yttrium-group REE fluorine carbonates, silicates and arsenates. The Guanxi granite is characterized by LREE enrichment (the average LREE/HREE ratio is 2.43).     

广西花山花岗岩体地球化学特征及产铀潜力分析

广西花山花岗岩体为燕山期形成的中粗粒黑云母花岗岩。通过其主量元素、微量元素和稀土元素地球化学特征的研究表明：花山岩体具有富碱、高钾、低磷、高铁镁比值,富含U、Th、Pb、Nb、Ta等高场强元素（HFSE）和Rb、K等大离子亲石元素（LILE）,明显的Ti、Sr、P、Ba负异常等特征。稀土配分模式为右倾的轻稀土富集型,具...