动态应力追踪方法识别采动裂隙带发育研究

煤层开采过程中,开采工作面围岩一定范围内的岩体会产生卸荷裂缝或新裂隙,其中有一部分裂缝和裂隙存在张开的经历。由于张开的裂隙和缝隙内没有力的传递介质,在这些裂缝、裂隙附近区域的应力会从因重力引起的应力大值降低到一个很小的值,但不一定会达到应力为0值。裂缝、裂隙附近区域的应力由于之后的应力重分布可以发生调整而振荡,裂缝、裂隙相应地可以闭合,甚至可以承受很大的剪应力。基于一部分采动张开裂隙附近区域的应力大值曾经历过大幅度卸载到一个很小值这一动态过程,提出了一种识别采动裂隙带发育的动态应力追踪方法。以宁夏石嘴山矿区三号煤层为工程背景,利用离散元UDEC软件包计算确定煤层开采过程中覆岩内部不同开采阶段的应力分布。借助于后处理软件TechPlot,利用提出的动态应力追踪方法,识别该矿采动裂隙带的范围和高度;研究结果表明,所提出的动态应力追逐方法具有可行性和很好的适用性。     

Jurassic septarian concretions from NW Scotland record interdependent bacterial, physical and chemical processes of marine mudrock diagenesis

Septarian concretions in the Staffin Shales Formation (Kimmeridgian, Isle of Skye) allow controls on concretion rheology and septarian cracking to be investigated. Stratabound concretions consist of anhedral ferroan calcite microspar enclosing clay and minor pyrite. Intergranular volumes range from 77% to 88%, and calcite δ¹³C and δ¹⁸O values in most concretion bodies range from ?10·0‰ to ?17·3‰ and +0·3‰ to ?0·6‰ respectively, consistent with rapid and pervasive cementation in marine pore fluids. Septarian rupture occurred during incipient cementation, with a sediment volume reduction of up to 43%. Crack‐lining brown fibrous calcite records pore fluid re‐oxygenation during a depositional hiatus, followed by increasing Fe content and δ¹³C related to bacterial methanogenesis. Brown colouration results from an included gel‐like polar organic fraction that probably represents bacterially degraded biomass. A new hypothesis for concretion growth and septarian cracking argues that quasi‐rigid ‘proto‐concretions’ formed via binding of flocculated clays by bacterial extracellular polysaccharide substances (EPS). This provided rheological and chemical conditions for tensional failure, subcritical crack growth, volume contraction, calcite nucleation, and incorporation of degraded products into crack‐lining cements. Bacterial decay of EPS and syneresis of host muds provided internal stresses to initiate rupture at shallow burial. Development of septarian (shrinkage) cracks in muds is envisaged to require pervasive in situ bacterial colonization, and to depend on rates of carbonate precipitation versus EPS degradation and syneresis. Subsequent modification of septarian concretions included envelopment by siderite and calcite microspar, hydraulic fracturing associated with Cretaceous shallow burial or Palaeogene uplift; and cementation by strongly ferroan, yellow sparry calcite that records meteoric water invasion of the host mudrocks. An abundance of fatty acids in these spars indicates aqueous transport of organic breakdown products, and δ¹³C data suggest a predominantly methanogenic bicarbonate source. However, the wide δ¹⁸O range for petrographically identical cement (?1·3‰ to ?15·6‰) is difficult to explain.     

花山谜窟景区2号、35号洞窟稳定性分析研究

花山谜窟景区2号、35号洞窟位于安徽省黄山市的新安江畔,其所处的地质环境条件复杂,洞窟区岩石力学的强度差异大,洞窟顶板裂隙较发育,顶板渗水较严重,加之,洞窟内部分支撑柱的间距过大,洞窟开发过程中忽略了对洞窟地质环境的保护等,引发了片状剥落、块状坠落、新生裂缝(顶板及支撑柱)三类洞窟变形失稳问题,这三类问题不仅破坏了洞窟内的地质环境,同时,也给洞窟的科学保护带来了隐患。为此,对洞窟稳定性问题产生的条件进行分析研究,并在此基础上提出了加强洞窟地质环境保护的对策。     

关于恐龙化石在发掘过程中因应力释放造成风化破坏的研究

在恐龙化石发掘过程中不仅机械扰动会直接导致化石或围岩的破碎,应力释放也会导致化石及围岩表面裂隙的产生及扩张,这些节理裂隙又为水和空气的活动提供了通道,使风化破坏作用更加迅速。作者以分层开挖理论为基础,建立了模拟化石开挖过程的数值模型。通过计算机模拟开挖过程中0m、11m、14m、19m四个深度的等效应力变化过程和XZ方向应力的变化过程发现:开挖前后化石表面的最大等效应力差达到0.34MPa,围岩表面的最大等效应力差达0.3MPa;埋深越大的化石,在开挖露出地面后等效应力的回弹现象越明显,即应力释放越严重;虽然化石表面所受剪应力不大,但其对化石风化的影响比在压应力条件下要大的多,这是导致卸载裂隙产生的主要原因。因此,恐龙化石发掘要逐层缓慢开挖,使化石逐渐达到新的应力平衡,以便减少应力快速释放对化石造成的风化破坏,特别是要做好护坡,最大限度地防止剪应力的产生。     

单轴压缩载荷作用下双裂隙扩展的CT扫描试验

由于精选后的陶瓷材料与岩石性质相似,因此选择陶瓷作为基本材料制作中部含2条圆币状裂隙的试件,进行单轴压缩荷载作用下的CT实时扫描试验,研究试件内双裂隙的扩展和损伤演化规律。采用3种不同区域划分方案,通过CT数、CT方差和CT图像的对比,分析上、下裂隙及岩桥区域不同的扩展状况。分析表明,上裂隙区域一直以压密为主,扩展很小,对试件破坏影响较小;下裂隙区域扩展剧烈,最终形成了宏观裂纹,对试件的破坏影响较大;当上下裂隙之间的中心距离等于4倍的裂隙半径时,裂隙的扩展过程将与裂隙自身参数有关,几乎看不出裂隙之间的相互作用。     

无人机遥感技术在采煤地面塌陷监测中的应用

为研究无人机遥感技术在采煤地面塌陷监测中的应用,以宁东煤炭基地金凤煤矿011805综采工作面为例,探讨了利用无人机遥感技术进行地表裂缝解译、地面沉降量计算和地面塌陷规律研究的方法。结果表明：无人机飞行航高可根据需要识别的地表裂缝宽度确定,地形平坦地区识别2 cm地表裂缝的飞行航高一般应不超过143 m;地表裂缝宜于采用基于光谱、延长度和紧密度规则的面向对象的信息提取方法进行自动识别,在采用这种方法发现地表塌陷裂缝时宜采用基于边缘检测的图像分割模型和基于Full Lambda Schedule的图像融合模型;对无人机遥感地表高程值进行拟合校正可近似获得采煤工作面地表下沉量和下沉系数,说明无人机遥感技术可应用于采煤地面沉降量监测;综采工作面内地表裂缝数量多,总体垂直回采方向排列,切眼和顺槽附近地表裂缝数量少,总体平行顺槽和切眼展布。     

Crack Coalescence in Molded Gypsum and Carrara Marble: Part 2—Microscopic Observations and Interpretation

Experimental uniaxial compression loading tests were conducted on molded gypsum and Carrara marble prismatic specimens to study the cracking and coalescence processes between pre-existing artificial flaws. The study showed that material had an influence on the cracking and coalescence processes (see the companion paper in this issue). As reported in the companion paper, one of the pronounced features as observed in the high-speed video recordings was the development of macroscopic white patches prior to the development of observable cracks in marble, but not in gypsum. This paper (part 2) deals with the microscopic aspects of the study. Specifically, the scanning electron microscope (SEM) and the environmental scanning electron microscope (ESEM) imaging techniques were used to study the microscopic development of white patches and their evolution into macroscopic tensile cracks and shear cracks in marble, and the microscopic initiation of hair-line tensile cracks and their evolution into macroscopic tensile cracks in gypsum. The microscopic imaging study in marble showed that the white patches were associated with extensive microcracking zones (process zones), while the extent of process zone development in gypsum was limited. The comparison of the macroscopic and microscopic results indicates that the different extent of microcracking zone development, related to the material textural properties, is a key factor leading to different macroscopic cracking behavior in gypsum and marble.

Experiment and analysis of the formation,expansion and dissipation of gasbag in fine sediments based on pore water pressure survey

Deep-seated gas in seabed sediments migrates upwards from effect of external factors, which easily accumulates to form gasbags at interface of shallow coarse-fine sediments. Real-time monitoring of this process is important to predict disaster. However, there is still a lack of effective monitoring methods, so we attempt to apply multi-points pore water pressure monitoring technology when simulating forming and dissipation of gasbags in sediments through laboratory experiment. This study focuses...     

淮河大堤土体工程地质特性及采动裂缝研究

淮河下采煤,使地面大堤土体中出现了许多采动裂缝,普遍认为裂缝的存在对大堤与河下采煤安全构成很大威胁。以土体工程地质特性研究为基础,采用试验和力学分析方法,分析论证了大堤土体采动裂缝的形成条件及其发育深度,得出几点结论:1)目前,淮南淮河大堤在粘土堤土体拉应变超过8～12mm/m、砂土堤超过3～5mm/m时,堤体就会出现裂缝;2)土中裂缝发育深度不会超过与土的力学特性有关的某一极限值。目前淮河大堤粘土堤约为4.0m、砂土堤约为2.0m;3)采取粘土注浆、铺设防渗膜等措施处理后,淮河大堤采动裂缝的存在就不会对河下采煤与大堤安全构成威胁。     

裂隙各向异性介质横波双折射特性研究

借助于有限元方法,对裂隙各向异性介质一雏四分量弹性波场中横波双折射的有关问题进行了研究。它们是裂隙方位与相速度,双折射与震源主频,双折射与裂隙丰度,双折射与能量分配,双折射与延迟时,双折射及其振幅谱等。这些问题对深入认识横波双折射特性,对理论和实际工作都有一定帮助。