考虑初始损伤和蠕变损伤的岩石蠕变全过程本构模型

考虑到天然岩石存在不同程度初始损伤以及蠕变过程中岩石受载后裂隙扩展而导致的新损伤,对具有初始损伤的岩石蠕变特性进行全面描述。根据不闭合结构面应力与法向变形之间的关系,提出裂隙岩石塑性变形体元件,描述岩石蠕变过程中的瞬时塑性变形。引入初始损伤影响因子,建立具有初始损伤的岩石损伤变量演化方程,构建模拟岩石加速蠕变的蠕变损伤体元件。将裂隙岩石塑性变形体和蠕变损伤体与描述瞬时弹性变形和黏弹性变形的广义开尔文模型进行串联组合,形成能够反映具有初始损伤的岩石瞬时弹-塑性变形、稳定蠕变和加速蠕变的蠕变全过程本构模型,提出了进行少量蠕变试验既能解析模型参数的方法,在不同应力水平下模型理论曲线与蠕变试验曲线吻合。     

Spatial variations in damage zone width along strike-slip faults: An example from active faults in southwest Japan

Field investigations reveal spatial variations in fault zone width along strike-slip active faults of the Arima–Takatsuki Tectonic Line (ATTL) and the Rokko–Awaji Fault Zone (RAFZ) of southwest Japan, which together form a left-stepping geometric pattern. The fault zones are composed of damage zones dominated by fractured host rocks, non-foliated and foliated cataclasites, and a fault core zone that consists of cataclastic rocks including fault gouge and fault breccia. The fault damage zones of the ATTL are characterized by subsidiary faults and fractures that are asymmetrically developed on each side of the main fault. The width of the damage zone varies along faults developed within granitic rocks of the ATTL and RAFZ, from ∼50 to ∼1000 m. In contrast, the width of the damage zone within rhyolitic tuff on the northwestern side of the ATTL varies from ∼30 to ∼100 m. The fault core zone is generally concentrated in a narrow zone of ∼0.5–∼5 m in width, consisting mainly of pulverized cataclastic rocks that lack the primary cohesion of the host rocks, including a narrow zone of fault gouge (<0.5 m) and fault-breccia zones either side of the fault. The present results indicate that spatial variations in the width of damage zone and the asymmetric distribution of damage zones across the studied strike-slip faults are mainly caused by local concentrations in compressive stress within an overstep area between left-stepping strike-slip faults of the ATTL and RAFZ. The findings demonstrate that fault zone structures and the spatial distribution in the width of damage zone are strongly affected by the geometric patterns of strike-slip faults.     

Displacement variation along thrust faults: implications for the development of large faults

Displacement analyses along thrust faults of different maturity (or size) reveal maxima and minima, often associated with minor folding of the adjacent beds, between the tip points. The results show that these faults are segmented, and that they formed through the linkage of smaller (previously independent) faults, and (or) by propagation of a single fault affected by the existence of barriers. Points of potential linkage (marked by displacement minima) are fault bends or distinct fault breaks. Fault nucleation (marked by displacement maxima) occurs within the planar segments of a fault; only in one of eight examples is the nucleation point seen to occur at a fault bend.Displacement variations along inferred or extrapolated regional-scale thrust faults show a variety of patterns, most of which involve constant displacement or a monotonic increase or decrease away from the basal décollement. These data are not considered to be as reliable as those from observed thrusts due to the necessary subjectivity involved in the extrapolation process.In general, displacement variation appears to be a reflection of the symmetry of the thrust fault system, such that, for example, a flat-ramp geometry ending in a steep tip will show an asymmetrical displacement function skewed toward the surface, with a nucleation point above the basal décollement.     

The initiation of brittle faults in crystalline rock

Faults in the upper crust initiate from pre-existing (inherited) or precursory (early-formed) structures and typically grow by the mechanical interaction and linkage of these structures. In crystalline rock, rock architecture, composition, cooling, and exhumation influence the initiation of faults, with contrasting styles observed in plutonic rocks, extrusive igneous rocks, and foliated metamorphic rocks. Brittle fault growth in granitic rock is commonly controlled by the architecture of inherited joints or preexisting dikes. In basalt, abundant joints control the surface expression of faulting, and enhanced compliance due to abundant joints leads to folding and deformation asymmetry in the fault zone. Highly reactive mafic minerals likely become rapidly evolving fault rocks. In foliated metamorphic rocks, fault initiation style is strongly influenced by strength anisotropy relative to the principal stress directions, with fracturing favored when the foliation is aligned with the directions of principal stress. The continuity of micas within the foliation also influences the micromechanics of fault initiation. Brittle kink bands are an example of a strain-hardening precursory structure unique to foliated rock. Each of these fault initiation processes produces different initial fault geometry and spatial heterogeneity that influence such properties as fault permeability and seismogenesis.     

Contemporaneous movement along crossing conjugate normal faults

A sandbox experiment is described in which conjugate normal faults cut each other in an ‘X’ configuration. Detailed measurements, using a stereoscopic technique, demonstrate synchronous movement along these opposing faults. Their mutual offset leads to generation of new fault segments, and finally to a complex but systematic interference structure. Since similar structures can be observed in the field, it is argued that contemporaneous operation of conjugate normal faults is also possible in large-scale crestal-extension structures over salt domes and deltaic rollover anticlines.     

小尺度断裂沿层曲率敏感性研究

沿层曲率作为地震属性的一种,不仅有数学几何意义更有着重要的地质意义。和相干体相比,沿层曲率在油气勘探中常被用于刻画地质构造形态及断裂精细解释,特别是在小尺度断裂发育的地区更为有效。而在实际工作中,有时利用沿层曲率所描述的断裂效果不太明显。为进一步明确对于刻画断裂结果的影响因素及其适用条件,以鄂尔多斯盆地Q区Tj9为研究对象,基于Geoeast软件对该区小尺度断裂系统从选取属性、方位角、频带三个方面展开分析。结果表明：（1）曲率比相干体更适用于刻画较小尺度的断层;（2）平面上从平行断裂的方位观测,断裂识别不清晰;从垂直断裂的方位观测,易于识别;（3）在反射层同相轴较强时,中高频段对断裂识别更清楚;在反射层同相轴较弱时,中频段对断裂识别更清楚。因此可以根据不同属性、不同方位角、不同频带对断裂的敏感程度,用不同的数据体解释小尺度断裂,提高对断层刻画的精度,为复杂油气勘探寻找有利区奠定基础。     

场地和断层对埋地管道破坏的影响分析

场地条件和断层活动是埋地管道破坏的主要原因,避免因为场地岩土和断层的影响而造成管道破坏,是城市地下生命线工程建设中急需解决的问题。采用ADINA软件的Parasolid建模方式,通过定义合适的体类型和布尔操作,建立了埋地管道破坏分析的几何模型,实现了土体－断层－管道破坏有限元建模。借助模型参数选择,确定了基岩与岩土性质、管道特性等模型参数;定义了管-土摩擦和约束条件、地震波和断层位移荷载等。依据计算结果,分析了场地条件和断层参数对地下管道地震破坏的影响;结果表明：管道埋藏越深,断层断距越大,管道的变形越大,破坏越严重。给出了管-土摩擦系数和断层与管道交角的最优值,并给出了几点工程建议。     

地表剥蚀作用对地应力场反演的影响

岩体自重和剥蚀作用都是形成岩体初始应力场的重要因素。在地应力回归分析中，反演所得岩体重度往往大于实测重度。通过算例说明，地表剥蚀作用因素是导致该结果的主要原因，并分析了由此产生的一些工程应用问题。     

脉动孔隙水压下三轴加压对煤岩损伤变形的影响

为研究脉动孔隙水压作用下低透性松软煤岩在不同三轴加压条件下的损伤变形规律,采用RLW-2000M煤岩流变仪进行了不同轴压和围压系列下的试验研究。结果表明：煤岩破坏的应变曲线具有先疏后密再疏的变化规律,且累积应变和残余应变随着围压的增加而减小,而随着轴压的增加而增大;平均单次耗散能随着围压的增加而减小,随着轴压的增加而增加,其关系符合指数函数变化特征;采用累积耗散能计算了煤岩破坏过程中的损伤变化特征,并采用Logistic方程逆函数对其进行了拟合分析,得到了煤岩损伤演化模型,为预测煤岩破坏周期提供了依据。研究结果为具有不同地应力条件下的低透气性松软煤层施工脉动水力压裂提供了一定的理论依据。     

基于新型损伤定义的岩石损伤统计本构模型探讨

针对几何损伤理论中损伤定义的局限性与不足,对岩石损伤定义进行了改进;在此基础上,将在应力作用下的岩石材料抽象为破坏与未破坏两部分,并根据这两部分不同的受力情况,建立出新型损伤模型;其次,利用统计损伤理论,建立出岩石统计损伤演化方程,进而建立起基于特定围压下的岩石损伤统计本构模型;然后,通过探讨模型参数与围压的经验关系,对模型进行合理修正,从而建立了反映不同围压条件下的岩石损伤统计本构模型,并通过探讨模型参数的物理意义,初步建立了反映岩石软化与硬化特性相互转化的临界物理力学参数的确定方法。该模型能够反映岩石软化与硬化特性相互转化的特征,与试验结果进行比较分析表明,该模型与实测结果吻合良好。     

断层影响下隧道围岩变形监测与特征分析

断层等软弱结构面是隧道工程中经常遇到而又必须有效处理的不良地质体.诸多工程实践和有关研究均表明,隧道围岩的变形与破坏一般受断层等软弱结构面控制;而断层对于隧道围岩变形与破坏的影响程度及其机理仍是一个模糊问题.因此,对于断层影响下隧道围岩变形与破坏的研究具有重要的理论意义和实用价值.黄河大柳树水利枢纽地处青藏褶皱系与阿拉善地块过渡带,区域断层发育,工程中的隧道大多为受断层影响的隧道.本文以黄河大柳树水利枢纽1号导流隧洞为例,对不同地段(根据断层的发育状况)在开挖过程中围岩变形的现场监测,试图对断层影响下隧道围岩变形特征与机理进行定量地深入分析.此外,为更准确监测隧道围岩变形,作者根据对该隧道变形特点的初步分析自行设计了监测仪器,即分点锚固式多点伸长计.这也是隧道工程监测技术的积极探索.     

基于岩石统一能量屈服准则的硬岩损伤模型

为了更准确、便捷地确定深埋地下工程中硬岩的力学行为,开展了如下研究：根据损伤与塑性演化存在相似机制,假设损伤阈值与初始屈服采用相同的确定方法,将岩石统一能量屈服准则作为损伤阈值的判定准则;基于Rabotnov对损伤变量的定义和Lemaitre应变等效性假设,并考虑未损伤部分的应力-应变关系符合广义虎克定律,提出了简化形式的硬岩损伤本构方程;为了更好地表达硬岩从低围压到高围压条件下的脆-延转化特性,提出了改进的Mazars损伤演化方程;基于锦屏T2b大理岩常规三轴压缩试验结果,对损伤模型参数进行求解,并分别与基于Mazars损伤演化方程和Mohr-Coulomb准则为损伤阈值判定准则的损伤模型进行对比,结果表明：提出的损伤模型可更好地表达硬岩从低围压的脆性到高围压的延性转变过程,特别是对损伤阈值后岩石的损伤演化过程的模拟更为精确,对硬脆性岩石的工程计算有一定的借鉴意义。     

Electric currents along earthquake faults and the magnetization of pseudotachylite veins

Pseudotachylites occur in the form of thin glassy veins quenched from frictional melts along the fault planes of major earthquakes. They contain finely grained magnetite and often exhibit a high natural remanent magnetization (NRM). High NRM values imply strong local electric currents. These currents must persist for some time, while the pseudotachylite veins cool through the Curie temperature of magnetite around 580 °C. There is no generally accepted theory explaining how such powerful, persistent currents may be generated along the fault plane. Data presented here suggest the activation of electronic charge carriers, which are present in igneous rocks in a dormant, inactive form. These charge carriers can be “awakened” by the application of stress. They are electrons and defect electrons, also known as positive holes or p-holes for short. While p-holes are capable of spreading out of the stressed rock volume into adjacent p-type conductive unstressed rocks, electrons require a connection to the hot, n-type conductive lower crust. However, as long as the (downward) electron flow is not connected, the circuit is not closed. Hence, with the outflow of p-holes impeded, no current can be sustained. This situation is comparable to that of a charged battery where one pole remains unconnected. The friction melt that forms coseismically during rupture, provides a conductive path downward, which closes the circuit. This allows a current to flow along the fault plane. Extrapolating from laboratory data, every km³ of stressed igneous rocks adjacent to the fault plane can deliver 10³–10⁵ A. Hence, the current along the fault plane will not be limited by the number of charge carriers but more likely by the (electronic) conductivity of the cooling pseudotachylite vein. The sheet current will produce a magnetic field, whose vectors will lie in the fault plane and perpendicular to the flow direction.     

岩体初始地应力场分析方法研究

初始地应力场是影响岩土工程稳定性的重要因素之一,如何合理地模拟初始地应力场一直是岩体力学中的重要研究课题。以国内某大型水利水电工程构筑区域实测空间地应力资料为基础,以边界位移为控制对象,采用有限元（无界元）方法对工程区大范围内的岩体初始地应力场进行了分析和研究。尝试在实际边界上满足无穷远处位移为0的模型边界上引入了无界单元,实测点上的应力拟合结果有较明显的改善,这表明所采用的方法是切实可行和有效的。     

渗透压力对裂隙岩体损伤破坏的研究

基于Betti能量互易定理推导了含水裂隙岩体初始损伤柔度张量和损伤演化方程,建立了考虑渗透压力的裂隙岩体脆弹性断裂损伤本构模型。并提出采用渗透压力附加柔度张量的概念来定义渗透压力对岩体力学特性的影响。工程算例结果表明：当岩体中有地下水活动时,考虑渗透压力对损伤区的影响是十分必要的。     

巷道软岩蠕变损伤模型

介绍了西原及修正西原模型的蠕变特性、物理机制和优点。根据软岩加速蠕变的力学特性,指出西原模型不能较好的描述蠕变加速阶段,并引入损伤变量,认为蠕变引起的应变是由无损材料及已损材料蠕变应变之和,推导出材料非稳定蠕变阶段的蠕变方程。同时,利用有限元方法,建立了带有损伤变量蠕变单元方程,可以此编制有限元程序,进行蠕变分析。     

岩石低周疲劳损伤模型与损伤变量表达方法

在岩石（体）工程领域,周期荷载作用下岩石的疲劳破坏特性与岩体的长期稳定性密切相关。针对目前对混凝土疲劳损伤研究较多,但对岩石疲劳损伤研究相对较少这一现状,运用损伤力学方法对以累积塑性应变表达的损伤变量进行了分析,指出了目前常用的以累积塑性应变表达的损伤变量表达式存在的理论上的缺点,建立了一种新的岩石疲劳损伤变量表达方法。为研究岩石在疲劳荷载作用下力学性能不断劣化的过程,从连续介质损伤力学的基本理论出发,分析岩石在疲劳荷载下的损伤发展和变形规律,并考虑岩石材料的硬化特性,推导了低周疲劳损伤演化方程,经低周疲劳试验数据分析,所建模型可以较好地反映岩石的疲劳损伤演化规律,可用于岩石在低周疲劳荷载作用下的有限元分析。     

岩石爆破的相对损伤与损伤累积计算

为了便于工程应用,利用损伤变量定义,确定既真实反映力学作用过程,又易于获取和进行客观度量损伤变量的一种方法。通过提出的相对损伤概念,用相对损伤变量表示含损伤材料在载荷作用下损伤扩展程度和不同部位的相对损伤程度,使衡量受力作用程度的损伤变量确定更易实现。同时,提出了一种基于裂纹扩展的损伤累积计算方法,并用实例计算说明了其合理可行。