鲁西地块中、新生界裂缝发育特征及构造应力场分析

鲁西地块是华北克拉通东部重要的构造单元,经历了多期构造演化,裂缝十分发育,是研究裂缝的有利场所。通过野外地质观测和室内研究,对鲁西地块部分地区的裂缝的产状、类型、开度、间距、填充物等参数进行了统计分析,得出裂缝优势方向主要为NNW向、SEE向、NEE向、NE向和NW向。在野外分期配套的基础上,结合区域构造应力场,用过滤法对鲁西地块中、新生界的裂缝进行了分期配套,初步分为NNW和SEE向,NNW和NEE向,NNW、NE、NWW和NEE向3期,并分别指示了早白垩世晚期至晚白垩世、古新世至始新世早期、始新世中期至渐新世区域构造应力场。     

江西大湖塘矿田两期岩浆作用与钨成矿的关系: 来自锆石矿物地球化学的证据

大湖塘矿田是我国新发现的世界级钨多金属矿产资源基地,位于江南造山带中段,地处九岭山脉北部的武宁、修水、靖安三县交界区域,面积约500km²,储藏着近二百万吨WO₃资源（伴生Cu和Mo）。该区以晋宁期花岗岩类的大面积出露为特色,而燕山期花岗岩为全隐伏,前者作为矿田最主要的细脉-浸染型白钨矿的赋存载体,后者则在成岩时代上与钨成矿时间基本一致。两期岩浆岩对区内大规模钨成矿作用的贡献问题,及其内在成因联系问题具有重要的研究意义。本文在矿田地质和岩石地球化学研究基础上,以锆石的矿物地球化学研究为切入点,对晋宁期和燕山期花岗岩类的年代学、Hf同位素、微量元素特征进行系统的对比研究。结果显示,大湖塘矿田石门寺花岗岩成岩时代为147.7Ma、靖安钨矿成矿时代为134.9Ma、赋矿花岗岩成岩时代为815.8Ma,两个时代的岩浆岩均为过铝质S型花岗岩系列;更有意义的是,燕山期花岗岩（石门寺）中发现多颗继承锆石,且继承锆石与晋宁期岩浆锆石具有相近的Hf同位素和微量元素组成,这指示燕山期花岗岩与晋宁期花岗岩具有亲缘关系,包括晋宁期花岗岩在内的中新元古代基底岩石可能参与了该区中生代花岗岩的源区重熔。锆石微量元素特征表明,这两期重熔的岩浆结晶温度都在700℃左右,经历了低氧逸度、水近饱和条件下的熔融。晋宁期花岗岩富含W、Ca等成矿所需元素,在中生代华南岩石圈地幔上涌导致的中上地壳大规模熔融的背景下,燕山期岩浆期后含矿热液与晋宁期花岗岩围岩发生交代,成为本区大型白钨矿为主的钨多金属矿床形成的必要条件。

     

X线及CT检查在外伤性骨质疏松中的应用及讨论

目的 讨论CT及X线检查在外伤性骨质疏松中的应用。方法 1998~2000年200例外伤复查病人行CT及X光检查。结果 2~3个月后出现骨疏松的病人113例,3~4个月后出现骨疏松的66例,未见骨疏松的21例。结论 骨折2~3个月后复查病人,应适量降低CT的窗宽、窗位和X线的照射剂量。     

CT长骨测量在骨折髓内钉固定术中的应用

目的:探讨CT在长骨测量中的应用价值。方法:经X线检查证实的肱骨、股骨、胫骨骨折患者600多例,其中302例临床行髓内钉固定术,并在术前进行了健侧骨的CT定位扫描,测量其两点之间骨干长度及骨髓腔最窄处的宽度。结果:依据术前CT定位测量数据而选择的髓内钉在手术中完全适用。结论:此方法操作简便测量数据准确为临床提供可靠依据。     

嵌岩桩水平承载性能影响因素模拟分析

嵌岩桩目前广泛应用于岩土工程中来承受水平荷载,但如何准确分析其水平承载性能仍是工程难题。本文采用FLAC^3D软件建立水平受荷嵌岩桩数值模拟模型,将模拟结果与实测结果进行对比。在验证了数值模拟方法及结果正确的基础上,分析岩体参数（岩体弹性模量E、黏聚力c、内摩擦角φ）、桩径、露头高度、嵌岩深度和桩身混凝土强度对其水平承载性能的影响。结果表明,岩体E、c、φ的增加可提高桩的水平承载力,E在桩体受力开始时便影响其水平承载能力,c、φ则在岩体进入塑性阶段后产生影响;桩径对桩的水平承载性能影响显著;桩身嵌岩深度的影响存在临界值,本次模拟中当嵌岩深度超过3倍桩径后,其水平承载能力的提高缓慢;桩身混凝土强度的提高可增强桩的水平承载能力,但效果不明显。露头高度的增加会降低桩的水平承载性能。本文从岩体和桩体两个方面出发,克服了以往影响因素选择不够全面的不足,其研究成果可为今后工程中嵌岩桩的设计提供参考。     

储集层中高压流体引爆强地震的机理——以5.12汶川地震为例

目前产生地震的机制仍以弹性回跳说为主：地震是因为断层错断使岩层的弹性能释放而引发。但越来越多的学者开始质疑,仅断层错断后的弹性能,是否真能达到实际地震所释放的巨大能量。因此,有必要探讨地震初动后破坏性强震的性质及其真正的能量来源。文章根据沉积地层中的储集层及其压力的特点分析得出,储集层内含有大量的高压流体,其压力在一定条件下可以释放出来,产生流体物理爆炸,有可能是强震能量的重要组成部分。通过计算得出,当断层破裂并刺穿面积较大的储集层时,其压力释放所产生的弹性能可以达到震级8.0以上地震所释放的能量;人为的工程活动也可引发小规模的流体压力的释放现象,如钻井时的井喷、水力压裂会诱发有感地震等。同时,文章根据对距离震中较近的地震台的波形及传播射线路径分析认为,强震波动可能不是横波S波,而是涨缩波P波,据此不能排除强震是由爆炸所致。综合汶川地震多个台站记录到的地震波的时间域和频率域特征、地面观测到的爆炸现象、地震后科学钻探获得的岩心等大量直接或间接证据,说明了这种流体爆炸能量释放的可能性。最后,文章提出了地震活动可分为三个阶段：微破裂阶段Ⅰ,该阶段有流体活动,并可产生动电效应,但未触发地震初动;地震初动后的断裂破裂阶段Ⅱ;由流体压力释放产生地震强震阶段Ⅲ。     

岩体质量分级的风险分析方法

提出了基于RMR岩体质量分级系统的岩体质量研究风险分析方法。该方法分析步骤如下 :(1)通过岩芯样品的现场观测和实验室试验获得分类所需的变量 ;(2 )统计分析拟合得出各变量的分布函数及参数 ;(3)运用Monte Carlo模拟方法获得 2万个RMR值 ,并将结果绘成岩体质量描述图 ;(4)利用以上结果作出岩体质量风险分析评价。该方法用于润扬长江公路大桥岩体质量评价研究获得良好效果     

Validating the ability of the discontinuous deformation analysis method to model normal P‐wave propagation across rock fractures

The effects of fractures on wave propagation problems are increasingly abstracting the attention of scholars and engineers in rock engineering field. This study aims to fully validate the ability of discontinuous deformation analysis (DDA) to model normal P‐wave propagation across rock fractures. The effects of a single fracture and multiple parallel fractures are all tested. The results indicate that DDA can accurately reflect the fracture effects, including the fractures stiffness, the fracture spacing and the fracture number, and the effects of incident wave frequency on one‐dimensional P‐wave propagation problems. Thus, DDA is able to deal well with normal incident P‐wave propagation problems. Copyright © 2017 John Wiley & Sons, Ltd.     

Discrete element model for crack propagation in brittle materials

We propose a discrete element model for brittle rupture. The material consists of a bidimensional set of closed‐packed particles in contact. We explore the isotropic elastic behavior of this regular structure to derive a rupture criterion compatible to continuum mechanics. We introduce a classical criterion of mixed mode crack propagation based on the value of the stress intensity factors, obtained by the analysis of two adjacent contacts near a crack tip. Hence, the toughness becomes a direct parameter of the model, without any calibration procedure. We verify the consistency of the formulation as well as its convergence by comparison with theoretical solutions of tensile cracks, a pre‐cracked beam, and an inclined crack under biaxial stress. Copyright © 2015 John Wiley & Sons, Ltd.     

Computational model coupling mode II discrete fracture propagation with continuum damage zone evolution

We propose a numerical method that couples a cohesive zone model (CZM) and a finite element‐based continuum damage mechanics (CDM) model. The CZM represents a mode II macro‐fracture, and CDM finite elements (FE) represent the damage zone of the CZM. The coupled CZM/CDM model can capture the flow of energy that takes place between the bulk material that forms the matrix and the macroscopic fracture surfaces. The CDM model, which does not account for micro‐crack interaction, is calibrated against triaxial compression tests performed on Bakken shale, so as to reproduce the stress/strain curve before the failure peak. Based on a comparison with Kachanov's micro‐mechanical model, we confirm that the critical micro‐crack density value equal to 0.3 reflects the point at which crack interaction cannot be neglected. The CZM is assigned a pure mode II cohesive law that accounts for the dependence of the shear strength and energy release rate on confining pressure. The cohesive shear strength of the CZM is calibrated by calculating the shear stress necessary to reach a CDM damage of 0.3 during a direct shear test. We find that the shear cohesive strength of the CZM depends linearly on the confining pressure. Triaxial compression tests are simulated, in which the shale sample is modeled as an FE CDM continuum that contains a predefined thin cohesive zone representing the idealized shear fracture plane. The shear energy release rate of the CZM is fitted in order to match to the post‐peak stress/strain curves obtained during experimental tests performed on Bakken shale. We find that the energy release rate depends linearly on the shear cohesive strength. We then use the calibrated shale rheology to simulate the propagation of a meter‐scale mode II fracture. Under low confining pressure, the macroscopic crack (CZM) and its damaged zone (CDM) propagate simultaneously (i.e., during the same loading increments). Under high confining pressure, the fracture propagates in slip‐friction, that is, the debonding of the cohesive zone alternates with the propagation of continuum damage. The computational method is applicable to a range of geological injection problems including hydraulic fracturing and fluid storage and should be further enhanced by the addition of mode I and mixed mode (I+II+III) propagation. Copyright © 2016 John Wiley & Sons, Ltd.