加筋土挡墙变形特性研究进展

从理论研究、模型试验、数值模拟和实地调查四方面评述了国内外加筋土挡墙变形特性的研究成果。理论研究方面分析并归纳了研究方法和挡墙变形计算公式;模型试验和数值模拟介绍了已有的静、动力模型试验成果和常用的数值模拟方法。实地调查介绍了现有调查结论及部分规范、标准规定的位移限值。通过4种方式的研究情况介绍,指出了当前加筋土挡墙变形特性研究中存在的一些不足,并进一步阐述了今后的研究方向。     

Equilibrium thallium isotope fractionation and its constraint on Earth’s late veneer

Equilibrium isotope fractionation of thallium(Tl) includes the traditional mass-dependent isotope fractionation effect and the nuclear volume effect(NVE). The NVE dominates the overall isotope fractionation, especially at high temperatures. Heavy Tl isotopes tend to be enriched in oxidized Tl^3+-bearing species. Our NVE fractionation results of oxidizing Tl^+ to Tl^3+ can explain the positive enrichments observed in ferromanganese sediments. Experimental results indicate that there could be0.2–0.3 e-unit fractionation between sulfides and silicates at 1650 ℃. It is consistent with our calculation results,which are in the range of 0.17–0.38 e-unit. Importantly,Tl’s concentration in the bulk silicate Earth(BSE) can be used to constrain the amount of materials delivered to Earth during the late veneer accretion stage. Because the Tl concentration in BSE is very low and its Tl isotope composition is similar with that of chondrites, suggesting either no Tl isotope fractionation occurred during numerous evaporation events, or the Tl in current BSE was totally delivered by late veneer. If it is the latter, the Tl-contentbased estimation could challenge the magnitude of late veneer which had been constrained by the amount of highly siderophile elements in BSE. Our results show that the lateaccreted mass is at least five-times larger than the previously suggested magnitude, i.e., 0.5 wt% of current Earth’s mass. The slightly lighter 205 Tl composition of BSE relative to chondrites is probable a sign of occurrence of Tlbearing sulfides, which probably were removed from the mantle in the last accretion stage of the Earth.     

时域有限差分法在地质雷达二维正演模拟中的应用

本文从地质雷达正演原理着手,分析了差分格式中半空间步长与半时间步长的实现方法,同时通过分析数值频散的产生,进而推导出了理想频散关系和超吸收边界条件．最后文中还对比了有无边界条件的雷达正演模拟效果和精度．     

不同掏蚀深度下古城墙的稳定性数值分析

以浙江良渚古城的宽顶古场面墙稳定性问题为研究对象,本文针对古城墙可能出现的不同深度的风沙掏蚀的实际工况,通过有限差分软件FLAC3D,建立计算模型进行了稳定性分析,探讨了不同掏蚀深度下城墙破坏机理和规律.研究表明:当城墙墙根掏蚀深度不是很大时,城墙整体稳定,土体开始出现比较小的位移量,掏蚀部位及其周围出现局部塑性破坏现象.随着掏蚀深度的增加,城墙塑性破坏区域不断向城墙体内部、顶部及顶部后缘范围发展,城墙上的土体位移量随着掏蚀深度的增加而呈数量级的增加,直至城墙出现整体崩塌破坏.掏蚀作用加剧了地震作用下城墙体的破坏,在掏蚀部位形成潜在破坏口,内部形成塑性贯通区,造成墙体整体崩塌.     

A 3D gravity data interpretation of the Matagami mining camp, Abitibi Subprovince, Superior Province, Québec, Canada: Application to VMS deposit exploration

Two inversions, unconstrained and constrained, of a gravity survey of the Matagami mining camp (Abitibi Archaean Subprovince, Canada) have been performed in order to identify the downward extension of a rhyolitic horizon hosting VMS-type base metals deposit and the morphologies of the major felsic plutons. A comparative study exhibits the similarities between measured and calculated densities from chemical compositions of the Matagami lithologies. This allows building an initial 3D geodensity model which integrates densities and available structural and geological surface mapping data. This model is integrated during the iteration process of the constrained inversion in the objective function. The resulting true density model and two derived cross-sections upgrade the 3D imaging of this area. Also, the model gives new insight for regional geological interpretation exposing possible shapes of the main geological units at depth and suggests the potential existence of deep fertile geological bodies.     

基于二次场的海洋可控源电磁法三维有限元正演

根据库伦规范势的定义,推导出关于磁矢量势和电标量势的偏微分方程,为了克服由电流源引起的奇异性和数值模拟计算困难,将电磁总场分解为一次场和二次场,一次场由基于Schelkunoff势函数的一维正演算法得到,二次场由有限元法计算得到,实现了海洋可控源电磁法三维有限元正演算法。通过一维数值模拟实例,验证该算法的计算精度。然后,利用该算法对带海底地形的三层储层模型进行正演,分析了海底地形对海洋控源电磁场各分量产生的影响。     

小台站的大数据和云计算设想

地球科学是一门观测科学,相关科学研究及公益服务,如气象、地震等,都依赖于野外台站的观测。目前,由于多种因素的作用,导致台站观测和后续分析应用严重脱节。本文基于大数据和云计算的思想,将台站工作和目前后续研究中心的工作进行有机结合,提出了一套新的工作思路,即将数据计算分析和区域监测预报的工作由台站来完成,然后由一个综合的数据中心负责存储和管理台站提供的"大数据"信息,并根据台站需要和反馈情况研发相关软件,为台站的分析计算提供云计算的平台。     

微型抗滑桩单桩设计计算模型及算法研究

考虑微型桩与周围岩土体间摩擦力的作用,提出了一种新的微型抗滑桩单桩设计计算模型,并给出了具体算法。由微型桩加固滑坡体的变形特点,分析微型桩与岩土体之间的相互作用机制,将微型桩与周围岩土体的摩擦作用引入其受力分析中;根据微型桩上各部分受力特点的不同,将微型桩分成上部摩擦受拉段、中部滑坡推力作用段和下部锚固段3段进行分析,推导了微型桩总的变形控制方程及各分段的变形控制方程;采用初参数法对控制方程进行求解,得到了微型抗滑桩上的内力分布及变形规律。计算结果表明,在滑坡推力作用下,微型桩的变形主要发生在滑面附近及以上桩段,滑面附近桩段将产生较大的内力和弯曲变形,受拉段弯曲变形较小,近似水平移动;桩与岩土体间的摩擦力是微型桩与周围岩土体相互作用的重要组成部分,摩擦力的作用能显著减小微型桩的弯曲变形,有效控制滑坡体的位移。     

核安全相关边坡与一般边坡挡土墙抗震稳定性验算对比分析

在挡土墙稳定性计算基本原理基础上, 引入《核电厂抗震设计规范》(GB 50267-97) 关于地震系数的规定, 重新建立了安全相关边坡挡土墙土压力和地震角计算公式, 并应用到实际工程中。对比分析显示, 挡土墙按核安全边坡和一般边坡进行抗震验算时, 地震系数、地震角的取值相差较大; 由于按核安全边坡计算时地震力远大于一般边坡, 因此稳定系数远小于一般边坡。     

Nature of the Ore-Forming Fluid at the Quaternary Noya Gold Deposit in Kyushu,Japan

We discuss the nature of the ore-forming hydrothermal fluid in the Noya gold-bearing calcite-quartz-adularia veins of central Kyushu, Japan on the basis of oxygen, carbon, and strontium isotope ratios, and aqueous speciation calculations for the present-day geothermal fluid. The isotopic values of the Noya ore-forming fluid were estimated to be −6.5‰ for δ¹³C and −7.5‰ for δ¹⁸O. The oxygen isotopic equilibrium temperatures for vein calcite are more than 180°C at the bottom of the Noya mineralization zone, and decrease with increasing elevation. As the temperature decreased, the dominant carbon species in the fluid changed from H₂CO₃ to HCO₃^- at about 120°C. The equilibrium temperatures for vein quartz are consistent with the calcite calculations. The carbon and oxygen isotope trends of the Noya vein calcite and the isotope ratios of strontium suggest that the fluids that precipitated the Noya veins were controlled by an andesite-dominated geology. Chondrite-normalized REE patterns for the white-colored veins from wells 51-WT-1 and 51-WT-2 displayed a light REE-rich pattern with positive Eu anomalies, suggesting the existence of a reducing environment for the fluid. The pyrite-rich gray-colored veins and a silicified rock from well 51-WT-2 showed higher REE concentrations than did the white veins. Altered host andesitic rocks have similar REE patterns to that of the silicified rock, and have higher REE contents than the others in the drill cores. Aqueous speciation calculations showed that the fluid in the hydrothermal reservoir is currently in muscovite stability. The fluid at the ore-mineralization stage may have contained more potassium or have had a higher pH, so that adularia precipitated with calcite and quartz, as well as gold. Fluid boiling at depth in the system produced the gold-bearing calcite-quartz-adularia veins.