逆断层地裂缝在黄土中破裂扩展的数值模拟

隐伏地裂缝在黄土中的扩展机理,其影响的范围、程度等问题,都是城市工作者所广泛关注和亟待解决的重要问题。为了研究黄土中逆断层地裂缝的扩展机理和扩展特征,参照正断层大型物理模型试验,利用数值模拟的方法,建立了三维数值分析模型,进行了黄土中逆断层的扩展机理研究。研究表明,隐伏逆断层地裂缝活动时,在地裂缝的上端,土体单元受到拉、压、剪的共同作用,裂缝很快被贯通,因而在其上端形成了破裂区,但向两侧的扩展有限;地裂缝的下盘在地裂缝活动时,受到的影响较小,即逆断层主要影响地裂缝的上盘,而对下盘影响甚微;同时,逆断层的影响范围和深度都明显小于正断层。由此可见,逆断层地裂缝活动特征明显区别于正断层,在黄土中的扩展有其独特之处。     

用数值模拟研究西安地裂缝

本文在分析总结西安地缝基本特征的基础上,采用二维有限元法,对西安地裂缝进行了数值模拟。     

隐伏地裂缝破裂扩展物理模型试验边界效应

物理模型试验是研究地质灾害变形破裂特征、动力学过程和成因机制的有效手段,受制于模型箱尺寸,试验过程中边界效应问题显著,如何减弱边界效应影响一直是研究者所关注的焦点问题。本文以隐伏地裂缝破裂扩展物理模型试验为研究对象,通过物理模型试验现象分析以及数值模拟验证等手段,对物理模型箱体边界效应进行了系统分析。结果表明,模型箱体边界效应的主要控制因素为箱体边壁阻尼与箱体尺寸比,其中：边壁阻尼与边界效应幅值呈正相关,边壁摩擦角小于土体内摩擦角时,黏聚力是边界效应影响的主要因素,边壁摩擦角大于土体内摩擦角时,摩擦力是边界效应影响的主要因素;箱体尺寸比影响边界效应幅值,长宽比与边界效应幅值呈正相关,并确定试验模型箱设计最优尺寸比为5∶3∶2.2。箱体边界效应对隐伏地裂缝破裂扩展物理模型试验结果存在显著影响。     

隐伏地裂缝破裂扩展研究综述

日益增多的地裂缝灾害受到人们的普遍关注,而隐伏地裂缝数量更加巨大,其破裂扩展的随机性及潜在的灾害效应是我们必须面临和解决的问题。隐伏地裂缝的破裂扩展方式受多种因素影响,包括地裂缝的位错量、倾角和活动速率,上覆土层的性质、厚度和地层结构,以及表水下渗、开采地下水、地震动和时间效应等,这些因素的组合和叠加,导致隐伏地裂缝的破裂力学机制复杂,破裂扩展过程难以再现。目前隐伏地裂缝的破裂扩展研究方法主要采用现场调查与勘探、模型试验、力学综合分析与解析和数值模拟等综合手段,研究内容包括地裂缝破裂扩展各种形成条件和诱发因素的影响效应。通过分析隐伏地裂缝破裂扩展在其形成的复杂环境地质条件、多期活动性、长期蠕动性和多种诱发因素共同作用下的综合效应与力学机制,研究其破裂扩展过程,追踪不同深度的破裂位置及影响带宽度,确定一定条件下隐伏地裂缝扩展引起的地表最大位错量和最小安全覆盖层厚度,制定统一的地裂缝影响带宽度确定方法和标准,可为解释实际地裂缝破裂现象和地裂缝灾害综合防治提供依据,也是今后的研究重点。     

频繁矿震作用下地裂缝扩展机理及数值模拟研究

频繁矿震诱发断层活化以及由此引起的地裂缝不仅对矿井生产构成威胁。同时对于城市安全、居民生活也构成严重危害。论文根据工程场地岩土体破裂的观点,以辽宁抚顺地裂缝为例,采用理论解析、数值模拟等手段,开展了矿震引发地裂缝扩展效应探讨。研究认为：地下开采对抚顺地区的地质环境造成了破坏,地表沉陷为地裂缝的发育提供了运移空间及应力条件。浑河断裂带为抚顺地区地裂缝发育提供了地质构造基础。频繁发生的矿震加剧了地表裂缝的扩展及破坏作用。     

临汾地面沉降数值模拟及其与地裂缝灾害关系研究

临汾市区是继西安、大同等地区之后又一地裂缝灾害比较严重的地区, 已经严重影响着临汾市经济的可持续性发展。经研究表明, 地下水超采为影响该区地裂缝灾害的第二大因子, 它是通过地面沉降来促使地裂缝的形成和发展。本文通过对临汾市区地面沉降进行数值模拟, 总结出了地面沉降的变化规律。分析认为, 地裂缝灾害的易出现部位为沉降梯度陡变带, 即沉降梯度最大处。     

基于黄土结构损伤的地裂缝局部化破裂发展机制

针对西安地裂缝活动条件下黄土覆盖层裂缝的发展与形成,依据黄土的构度和应力比结构性参数变化规律,分析了黄土构度和抗拉强度之间的关系,建立了黄土结构性演变的数学模型,抗拉强度与抗剪强度随结构性参数变化强度准则,以及反映黄土结构性演变的Mohr-Coulomb屈服面弹塑性模型.通过本构模型嵌入FLAC3D软件,数值模拟西安地裂缝活动边界条件,以及结构性黄土地层结构,进行了黄土结构损伤变化和地层破裂带形成发展分析研究.表明地裂缝错动位移作用条件下,黄土地层塑形区域破裂带发展分为初始剪切破坏、初始拉伸破坏、剪切与拉伸破坏发展、破裂带贯通四个阶段;地层破裂带黄土的结构性损伤衰减变化突出,黄土应力比结构性参数等值线与地层塑性破裂带分布一致.揭示的黄土地层局部化破裂发展过程机制,对于认识地裂缝造成地面建筑物与地下工程灾害有重要的理论和实际意义.     

先存断裂对抽水沉降及地裂缝活动影响的数值模拟

过度抽取地下水对断层构造型地裂缝的加剧作用是很明显的,但具体的作用机制却很复杂,过去的研究多是简单的定性分析,数值模拟和定量计算少有报道。笔者采用比奥(Biot)固结渗流理论和基于A、B面接触判断的库仑滑动和张裂的接触面单元,对抽水作用下地裂缝的活动进行了数值模拟,初步探讨了抽水活动引发和加剧地裂缝活动的机制。结果表明:抽水作用下抽水井周围水平应力场发生近井区挤压、远井区拉张的变化,当拉张区内的拉应力超过土体抗拉强度时将会出现自上而下的张裂缝;先存断裂的存在将影响应力变化的模式,同时由于断裂的软弱性,使得地层容易沿其发生滑动或拉裂,从而加剧地裂缝的活动;先存断裂对地面沉降和地裂缝具有诱导、隔离和放大的作用。     

页岩气封存顶板变形破裂的机理与数值模拟

由于页岩气赋存机理的特殊性,页岩气成藏受保存条件及顶板类型的影响。封存顶板岩层对页岩气封盖影响极大。本文对页岩气藏封存顶板的破裂机理进行理论分析,并建立模型对顶板进行数值模拟。顶板岩层破裂与注水压力、岩石抗拉强度、地应力有关。封存顶板的破裂机理为压裂初始阶段,储层膨胀变形,封存顶板受压产生剪切裂纹,压裂液进入顶板,当注水压力小于最小主应力时,岩层发生剪切破裂,注水压力达到最小主应力和地应力之和时,岩石发生剪切破裂和张性破裂,裂缝增加并扩展,形成网状体系。数值模拟结果显示,压裂注水会在储层产生水力破坏区域,注水压力升高,水力破坏区域扩大并相互叠加影响,使得水力破坏集中于中间注水口的上部,当顶板岩层内部出现水力破坏区域时,岩石会发生破裂产生裂缝。在储层压裂的整个过程中,开始1h内,裂缝在储层内发展,顶板保持稳定,空隙水压力和变形很小,顶板岩层底部有少量裂纹。压裂2h,顶板底部裂缝增多,岩石空隙水压力上升,且顶板发生变形,中间变形最为明显。压裂3h,裂缝从顶板底部延伸到上部,岩层内部裂缝快速发育,空隙水压力持续升高,变形加大。数值模拟的结果与破裂机理的分析结果相吻合。     

西安典型段地面沉降分层标观测及数值模拟

根据西安地下水监测和详细的地层剖面资料,采用比奥固结理论和不连续面的接触分析,建立了含2条地裂缝的典型地段的二维抽水沉降计算模型,对先存断裂存在时抽水作用下的地面沉降进行了尽可能精细地模拟计算。结合该计算段的监测资料,分析了西安市抽水作用下地层压缩量垂向上的分布特点及地面沉降水平位置上存在差异的原因。研究认为,西安市的地面沉降量主要由100～300 m深度范围内土层的压缩量组成,地裂缝的出现不单是地层厚度不同产生的差异沉降引起的,先存断裂面的作用也很大。由于断裂的存在以及其正断层的特点,沉降过程中上盘（南盘）的沉降得到了放大,而下盘（北盘）沉降缩小,不同结果导致地面沉降在断裂位置出现差异放大现象,导致地裂缝越来越严重。研究成果很好地解释西安地裂缝附近地面沉降的反常差异现象,对于进一步确定地裂缝的成因、预测其发展变化规律具有一定的作用。     

西安市地裂缝对长安路立交桥致灾机理调查研究

西安地裂缝作为一种特殊的城市地质灾害,已经对基础设施造成很大的危害。长安路立交的破坏最为严重和典型,文章结合西安地裂缝的分布及活动特点,详细分析了地裂缝活动引起的长安路立交的破坏形式和特点。并对引起长安路立交破坏的原因做了进一步分析,得出了由于长安立交没有很好的排水措施导致地裂缝的异常活动从而引起桥梁破坏的结论。同时,文章还结合长安路立交的结构措施给出了在地裂缝带修建立交的结构措施建议。并最终得出了在地裂缝带修建城市立交等基础设施,应从采取措施减少地裂缝活动和采取合理的结构措施以适应地裂缝活动两方面进行综合考虑的结论。     

考虑卸荷效应的深埋隧洞围岩分区破坏数值模拟

基于卸荷岩体力学基本理论,运用三维有限差分软件,提出以塑性体积应变增量变化区间与不同卸荷区域岩体力学参数相对应的卸荷模拟方法,模拟了不同侧压系数条件下开挖洞周附近围岩最大体积应变增量以及围岩损伤范围的变化情况。数值模拟结果表明：当侧压系数较低时,洞周附近围岩的塑性体积应变增量区域的外边界近似为竖向椭圆形,随着侧压系数的增大,其外边界逐渐向圆形变化,最后变为横向椭圆形。侧压系数越大,围岩的卸载效应越显著,洞周附近围岩的塑性体积应变增量就越大,其所产生的围岩损伤范围也相应越大。利用所获得的结果,可以为深埋隧洞的稳定性分析以及支护设计提供依据。     

Numerical simulation on the cracking and failure law of compacted clay lining in landfill closure cover system

According to the mass conservation equation of solid phase, water transport, air migration and enthalpy balance equations in a deformable and unsaturated porous medium, and the mechanics model, a thermal‐hydro‐mechanical (THM) coupling mathematical model is developed in order to accurately predict the crack propagation of the compacted clay lining (CCL) in a landfill closure cover system. Numerical simulation analysis of the cracking and failure of the CCL in a landfill closure cover system under complex conditions (landfill gas pressure, variation of soil surface temperature, moisture loss of coverage soil, and uneven settlement of landfilled MSW (municipal solid waste)) is performed. The results show that the cracks are discovered firstly on the soil surface and then extend to the deeper cover system and became bigger. The cracks had broken through the closure cover system at 30 days. Over the depth range of 0.06 m, the change rate of settlement is found to be the highest because of the strong influence of temperature. The rise of temperature around the cracks is fast when the CCL is broken through by the cracks. There is a hollow area near the cracks over the depth range from 0.15 to 0.7 m, and the temperature stabilize at around 11°C without any obvious reduction. Under the condition of evaporation, the main crack in the CCL is similar to a pumping well, which causes more rapid moisture content reduction around the cracks. Vertical deformation increases linearly with depth in the process of deformation and cracking of CCL induced by uneven settlement of landfilled MSW. Copyright © 2014 John Wiley & Sons, Ltd.     

Numerical modelling of desiccation cracking

The ability to model and predict the formation of desiccation cracks is potentially beneficial in many applications such as clay liner design, earth dam construction, and crop science, etc. However, most studies have focused on statistical analysis of crack patterns and qualitative study of contributing factors to crack development rather than prediction. Because it is exceedingly difficult to capture the nonlinear processes during desiccation in analytical modelling, most such models handle crack formation without considering variation of material properties with time, and are unattractive to use in realistic modelling. The data obtained from laboratory experiments on clay soil desiccating in moulds were used as a basis to develop a more refined model of desiccation cracking. In this study, the properties, such as matric suction, stiffness and tensile strength of soil, and base adhesion, could be expressed approximately as functions of moisture content. The initial conditions and the development of suction due to desiccation and the varying material properties were inputted to UDEC, a distinct element code, using its internal programming language FISH. The model was able to capture some essential physical aspects of crack evolution in soil contained in moulds with varying lengths, heights, and materials of construction. Extension of this methodology is potentially beneficial not only for modelling desiccation cracking in clay, but also in other systems with evolving material properties such as concrete structures and road pavements. Copyright © 2010 John Wiley & Sons, Ltd.     

Numerical simulation of desiccation cracking in a thin clay layer using 3D discrete element modeling

Desiccation cracking of clay soil is of critical importance in many applications, such as industrial waste containment, hydraulic barriers, road embankments, and agricultural operations. The factors that influence cracking are known qualitatively, but it is not clear how to predict the initiation and propagation of cracks. This study presents a discrete element approach to modeling desiccation cracking in thin clay layers, considering material property changes. First, an aggregate shrinkage model based on the aggregate structure of clay was proposed, and the drying shrinkage of clay soil was modeled by imposing drying shrinkage kinetics for each aggregate at the micro-scale. Second, the clay soil was represented by an assembly of aggregates linked by bonds, and desiccation cracking of the clay layer was modeled using a three-dimensional discrete element code (PFC3D), with the aid of the embedded programming language FISH. When the clay layer is sufficiently thin, the water content gradient along the section can be neglected; thus, the shrinkage kinetics are the same for all of the grains of clay. In the model based on the discrete element method (DEM), the bond strength and contact stiffness changed during drying. Their changes were determined by matching the simulation results with the experimental data. Third, the DEM approach was validated by reproducing experimental desiccation tests performed on a thin clay layer in a disk shape. The geometric parameters of surface cracks were quantified using image analysis techniques and were compared with experimental observations. Fourth, some factors of influence, such as the sample thickness, the properties of the soil–base interface, micro-mechanical parameters, and shrinkage parameters, were investigated using the DEM model. The results obtained from the DEM analyses were compared with the results of prior research in this field of study. The approach used in this study is very promising for simulating desiccation cracking in thin clay soil because the model captures the initiation and propagation mechanism of desiccation cracks. Although this study was carried out on surface cracking in a thin clay layer, the extension of this methodology is of potential benefit not only for predicting three-dimensional desiccation cracking in real clay liners but also for modeling cracking in other materials with properties that vary with water content or temperature, such as concrete and rock.     

北山花岗岩热破裂室内模拟试验研究

岩石热破裂是高放废物地质处置工程中需深入研究的课题。对我国高放废物重点预选场址甘肃北山的花岗岩开展室内热破裂模拟试验研究,采用多通道温度测试仪、声发射、波速层析成像和数码显微镜等手段研究了该花岗岩热破裂过程。试验表明,（1）热破裂从试件端部开始产生,逐步向内缓慢扩展,表现出分段性和独立性;（2）根据声发射撞击率可将热破裂可分为稳定热损伤、宏观裂纹形成、宏观裂纹扩展、裂纹冷却闭合4个阶段,声发射定位的时空演化规律清楚地揭示了裂纹从试件上端部向内部扩展的规律;（3）波速层析成像指示了宏观裂纹位置及高温对岩石造成显著损伤的区域,热应力产生的损伤集中在试件边界,范围小,损伤严重,高温造成的损伤集中在钻孔附近高温区,范围较大,损伤略轻微;（4）监测多通道温度,获得了试件内的温度场并为数值模拟参数选取提供验证,采用有限元程序进行了热力耦合数值模拟,从机制上初步解释了热破裂现象,研究认为综合声发射实时监测热破裂过程和波速层析成像能实现对热损伤的量化的特性可实现岩石热破裂的动态监测和损伤量化,为今后地下实验室相关试验的开展和认识高放废物处置长期稳定性做了有意义的探索。     

波生沿岸流数值模拟

为了更好地研究近岸海域波生沿岸流,建立了基于高阶Boussinesq水波方程的波生沿岸流时域数值模型。控制方程在中等水深范围内具有较好的色散性和变浅作用性能,同时具有二阶完全非线性特征,适合描述近岸区域波浪强非线性运动。通过采用松弛造波方法实现了非线性波浪的无反射入射,采用周期性侧边界条件模拟开敞边界。通过数值试验,讨论了模型中主要参数对数值结果的影响。利用率定后的参数模拟了均匀坡度海岸上产生的沿岸流,通过和实验数据的对比验证了模型的准确性和适用性。利用模型数值模拟了不同波浪入射条件(包括周期、波高和波浪入射角度)对波生沿岸流的影响。     

区域地下水动态数值模拟

在系统综述区域地下水数值模拟的基础上,运用有限差分和有限体积法,结合济南泉域裂隙岩溶地下水含水介质系统,采用二维非稳定流数学模型进行了数值模拟,对泉域地下水动态变化进行了评价,为泉域地下水资源评价与管理提供了一种有效的分析手段,为区域地下水资源的科学管理提供了有意义的参考。