高温高压条件下辉长岩的摩擦强度及其速率依赖性

在干燥条件下对辉长岩的摩擦本构参数进行了实验研究。结果表明 :1 )辉长岩模拟断层泥的摩擦速度依赖性参数 (a -b)基本为正或者接近于没有速度依赖性 ,表明在干燥条件下不具备不稳定滑动的成核条件 ,对下地壳地震成核的可能性有参考意义 ;2 )摩擦强度在干燥条件下与Byerlee定律高度一致 ,表明在下地壳的高温环境下Byerlee定律仍可给出适当的强度估计 ,至少在干燥条件下如此 ;3)Byerlee定律给出的剪应力强度与正应力的关系中有一个截距 ,但是本研究中关于模拟断层泥的结果却没有明显的截距 ,表明断层物质的有无在摩擦强度的表现上存在重要差异     

岩石高速摩擦实验与地震物理过程

简述了最近20年来国内外岩石高速摩擦实验研究领域的进展和动态:岩石高速摩擦实验技术的发展实现了对高滑动速率、大位移的地震过程的实验模拟;其结果揭示了岩石和断层泥在地震滑动速率下的力学性状,深化了对断层滑动弱化机制、临界滑动距离、以及地震发生过程的认识和理解;实验在假玄武玻璃成因方面取得了重要进展,并提出了断层发生地震滑动可能留下的其它地质证据,可望为研究断层滑动性状与地震物理过程提供新的思路和信息.岩石高速摩擦实验今后的发展方向主要包括:发展具有加温系统和孔隙压系统的岩石高速摩擦实验装置,研究水热作用下岩石和断层泥的高速摩擦性状;室内实验和地震资料分析相结合研究断层滑动和地震机制;室内实验和野外地质调查相结合探索断层发生地震错动的地质证据等等.     

热水条件下斜长石和辉石断层泥的摩擦滑动研究

在热水条件下对辉长岩的2种主要组成矿物斜长石和辉石进行了摩擦滑动实验研究。结果表明:1)斜长石在整个实验温度范围内(<607℃)显示速度弱化,而辉石除了在200℃附近表现出微弱的速度强化外,在其他温度范围也都表现为速度弱化;2)斜长石在低温时强度随温度的升高而略有增加,高温时强度则随温度的升高而降低。辉石的摩擦强度随着温度的增加没有系统性的变化,在0.74上下波动;3)在热水条件下辉长岩的摩擦性质并不是这2种主要矿物的叠加,有可能是辉长岩中的次要矿物的存在导致了辉长岩的速度强化;4)本实验所得热水条件下的实验结果与干燥条件下的结果有很大差异,再一次表明水的存在极大地影响了岩石的摩擦稳定性     

砂岩变形方式和变形机制的实验研究

在温度为200°—700℃,围压为200—700MPa,恒定应变速率(1×10~(-4)/s)条件下,笔者对长石砂岩和石英砂岩完整的和带预切口的试样进行了变形实验。应力-应变曲线表明,完整砂岩发生了脆性的、脆延性过渡状态的和延性的变形;而带预切口的砂岩在整个实验条件下都发生了稳定摩擦滑动。显微观测表明,岩石变形的主要机制是晶内和穿晶微裂隙的产生和发展。根据实验结果笔者推测,砂岩组成的地壳在地下10km左右的深度有最大破坏强度和摩擦强度;而发育在岩石中的断层的活动一般以稳定摩擦滑动为主。     

地震滑动加速和减速过程中的摩擦作用

在地震滑动过程中,断层动态摩擦是地壳内控制地震破裂的决定性因素。天然地震的脆性裂纹理论[1-3]使得以下观点被普遍接受:在地震断层快速滑动的过程中,断层摩擦力减弱,即所谓的滑动弱化[1]。高速断层泥实验[4-5],以及最近关于热增压[6-7]和摩擦熔化[8]的试验都支持该理论。但是,这些研究均仅针对固定的断层滑动速率。在本文中,我们的实验展示了不同滑动速率下断层物质的摩擦行为——这一模型的设置更接近天然地震的特征。实验结果表明,在断层滑动加速和减速的过程中,断层摩擦经历了增长、弱化和再增长。这种摩擦变化可能可以由低滑动速率下和更现实的滑动速率之下的速率-状态摩擦行为[9-10]来解释,但包含了不同的物理机制和不同的规模。最初的摩擦增强可能会阻碍小破裂向大地震的发展。断层滑动减速过程中的摩擦增强可能导致地震破裂呈脉冲状[11-14],并使得静态应力下降到与动态应力变化相比较低的水平[15]。     

白云母对岩盐断层带摩擦速度依赖性影响的实验研究

为更好地理解层状硅酸盐对断层强度、滑动速度依赖性及地震活动特征的影响,利用双轴摩擦实验对含白云母岩盐断层带在干燥及含水条件下摩擦的速度依赖性进行了实验研究,并观测了摩擦滑动过程中的声发射,分析了断层带的微观结构.实验结果表明,干燥条件下含白云母岩盐断层带在0.1 ～ 100μm/s的速度范围内表现为黏滑和速度弱化,增大σ2会使断层带从速度弱化向速度强化转化,速度依赖性转换出现在0.1 μm/s,其中断层滑动表现为稳滑或应力释放时间较长的黏滑事件;含水条件下含白云母岩盐断层带在0.05 ～0.01μm/s的速度范围内表现为速度强化,0.1 ～10μm/s的速度范围内表现为速度弱化,50～100μm/s的速度范围内又转换为速度强化行为.含白云母岩盐断层带在干燥条件下一次黏滑伴随一个或一丛声发射事件,而在含水条件下与稳滑相对应,滑动过程中并未记录到声发射事件.显微结构观察表明,速度弱化域的主要变形机制是岩盐颗粒的脆性破裂和局部化的滑动;干燥条件下,速度强化域的主要变形机制是岩盐颗粒的均匀破裂;含水条件下2个速度强化域对应不同的微观机制,高速域的速度强化受控于岩盐颗粒在白云母相互连结形成的网状结构上的滑动及其均匀碎裂作用,而低速域的速度强化还受岩盐的压溶作用控制.通过与岩盐断层带摩擦实验结果对比可知,白云母的存在对于燥岩盐断层带摩擦滑动方式和速度依赖性没有显著影响,而在含水条件下白云母的存在使得岩盐断层带滑动趋于稳定.实验结果为分析含层状硅酸盐断层的强度和稳定性提供了依据.此外,在速度依赖性转换域上观察到的应力缓慢释放的现象进一步证实了在岩盐断层带摩擦滑动过程中观察到的现象,这对慢地震机制研究具有参考意义.     

岩石高速摩擦实验的进展

文中简述了地震动力学国家重点实验室近年来在岩石高速摩擦实验方面的进展。为了深化断层与地震力学研究,实验室建设了一套旋转剪切低速-高速摩擦实验装置,可开展滑动速率介于板块运动速率(cm/a量级)至地震滑动速率(m/s量级)的岩石摩擦实验,其中高速摩擦性能填补了实验室的技术空白。以此为依托,围绕汶川地震断层带力学性质研究,开展了一系列高速摩擦实验。结果表明,龙门山断裂带断层泥的高速摩擦性质具有一致性,其高速滑动下显著的滑动弱化必定在汶川地震中极大地促进了破裂的扩展;断层弱化的主导机制是与摩擦生热相关的过程,包括凹凸体急速加热弱化和热压作用;断层泥在经历高速滑动弱化之后摩擦系数可在5~10s内恢复0.4,断层强度的快速恢复是同震主破裂带余震减少的原因之一。基于对实验装置现状和现有成果的分析,展望了近期实验室岩石高速摩擦的发展方向。     

孔隙压变化对岩石错动面滑动行为影响的实验研究

应用摩擦实验装置，在法向压力σ＿ｎ＝１０～１２０ＭＰａ下研究了孔隙压变化速率对岩石错动面滑动行为的影响。当孔隙压增压速率较大时，具粘滑振荡特性的岩石错动面仍将发生粘滑振荡，当孔隙压增压速率较小时，错动面发生稳定滑动，当增压速率介于上述两者之间时，错动面则呈粘滑－稳滑转化。以上结果对地震前兆和地震控制研究有重要意义     

汶川地震区的流变结构与发震高角度逆断层滑动的力学条件

本文利用龙门山地区的地质、地球物理剖面、弹性波速和流变实验数据等,建立了汶川地震相关构造单元的地壳流变结构.川西高原和龙门山构造带的地壳流变结构中存在多个塑性流变层,而四川盆地地壳基本没有出现塑性流变层,这种复杂的流变结构是汶川地震孕育和发生的基础.岩石破裂-黏滑-摩擦实验表明,以二长花岗岩为代表的震源区岩石具有很高的破裂强度和摩擦强度,能够承受极大的差应力和积累巨大的能量,这是高角度逆断层能够滑动和汶川地震强度大的原因之一.高流体压力是高角度逆断层滑动和触发汶川地震的另一个必要条件,而龙门山断层带内可能存在这种比较高的流体压力.     

我国实验岩石力学与构造物理学研究的若干新进展

简述了近年来我国学者在与地震学和地球内部物理学相关的实验岩石力学和构造物理学研究方面的进展．在此领域的进展主要体现在:大量实验以及数学模拟结果丰富了对岩石脆性破裂过程，特别是结构和介质非均匀条件下破裂过程的认识；在非均匀断层的摩擦行为与失稳成核方面取得了一些新结果，揭示了断层滑动行为的复杂性；在岩石脆塑性转换和塑性流变方面取得了一些新结果，特别是在下地壳和上地幔物质的流变性质方面取得了重要进展；在高温高压岩石物理方面取得了一批实验结果, 并应用于地球内部物质的组成和状态的研究．这些结果为深入理解地球内部物质的物理性质、变形机制及地震物理过程提供了有价值的参考资料.      

REPRESENTATIONS OF COULOMB FRICTION FOR DYNAMIC ANALYSIS

In many engineering problems involving friction, the friction is treated as Coulomb friction, where the magnitude of the friction force is constant but its direction is always opposite to that of the sliding velocity. In dynamic problems, the direction of the sliding velocity can change quite often. The many changes of the velocity direction cause many discontinuities in the friction force, complicating the process of evaluating the response of systems involving friction. In this paper, it is shown that the discontinuous Coulomb friction force can be represented by at least four different continuous functions. Each of these functions involves one constant that controls the level of accuracy of that function's representation of the friction force. The accuracy of the various representations is verified by comparing the response of a single degree freedom system, obtained through numerical solutions utilizing these representations, with an exact analytical solution. © 1997 by John Wiley & Sons, Ltd.     

Effects of vertical excitation on the seismic performance of a seismically isolated bridge with sliding friction bearings

A finite element model is constructed for a sliding friction bearing in a seismically isolated bridge under vertical excitation with contact/friction elements. The effects of vertical excitation on the seismic performance of a seismically isolated bridge with sliding friction bearings and different bearing friction coefficients and different stiffness levels (pier diameter) are discussed using example calculations, and the effects of excitation direction for vertical excitation on the analysis results are explored. The analysis results shows that vertical excitation has a relatively large impact on seismic performance for a seismically isolated bridge with sliding friction bearings, which should be considered when designing a seismically isolated bridge with sliding friction bearings where vertical excitation dominates.     

断层滑动速率变化对滑动稳定性的影响

在与主压应力方向斜交的断层上,正应力与剪应力之间存在线性相关关系,以此为基础导出了小扰动条件下决定稳定性的临界刚度与滑动速率的关系。由于这一关系具有临界刚度随滑动速率增加而减小的特点,因此速率增加可能导致周期性粘滑向稳定滑动转化,而速率减小可能使本来稳定的滑动转化为周期性粘滑过程。在这种斜交断层中,速率增加虽然可能抑制周期性粘滑,但是稳滑时超过一定限度的速率增加会导致一次性不稳定滑动。三轴摩擦实验提供了关于粘滑与稳滑可相互转化的支持证据     

Impact of the equivalent center of mass separating from the sliding surface on the isolation performance of friction pendulum bearings

A new equivalent center of mass model of FPBs(friction pendulum bearings) is introduced, and based on this model, coefficient j of the equivalent center of mass separating from the sliding surface is defined. It is thought in theory that j has a significant impact on the isolation parameter of FPBs, since the equivalent post-yielding stiffness and friction coefficients are not simply determined by sliding radius and sliding friction pairs. The results of numerical simulation analysis using ABAQUS conducted on two groups of FPBs support this viewpoint. For FPBs with the same sliding radius and sliding friction pairs, the FPB modules of structural analysis software such as ETABS could only distinguish the equivalent transformation using j one by one. The seismic response data obtained in a base isolation calculation example of FPBs are very different, which reveals that j's impact on the isolation effectiveness of FPBs cannot be ignored. The introduction of j will help improve the classical structural theory of FPBs and the weak points of structural analysis software based on this theory, which is important in achieving more accurate analyses in structural design.     

A model of triple friction pendulum bearing for general geometric and frictional parameters

Current models describing the behavior for the triple friction pendulum (TFP) bearing are based on the assumption that the resultant force of the contact pressure acts at the center of each sliding surface. Accordingly, these models only rely on equilibrium in the horizontal direction to arrive at the equations describing its behavior. This is sufficient for most practical applications where certain constraints on the friction coefficient values apply as a direct consequence of equilibrium. This paper presents a revised model of behavior of the TFP bearing in which no assumptions are made on the location of the resultant forces at each sliding surface and no constraints on the values of the coefficient of friction are required, provided that all sliding surfaces are in full contact. To accomplish this, the number of degrees of freedom describing the behavior of the bearing is increased to include the location of the resultant force at each sliding surface and equations of moment equilibrium are introduced to relate these degrees of freedom to forces. Moreover, the inertia effects of each of the moving parts of the bearing are accounted for in the derivation of the equations describing its behavior. The model explicitly calculates the motion of each of the components of friction pendulum bearings so that any dependence of the coefficient of friction on the sliding velocity and temperature can be explicitly accounted for and calculations of heat flux and temperature increase at each sliding surface can be made. This paper presents (a) the development of the revised TFP bearing model, (b) the analytic solution for the force–displacement relations of two configurations of the TFP bearing, (c) a model that incorporates inertia effects of the TFP bearing components and other effects that are useful in advanced response history analysis, and (d) examples of implementation of the features of the presented model. Copyright © 2016 John Wiley & Sons, Ltd.     

Acoustic emission processes occurring during high-pressure sand compaction

Granular materials submitted to uniaxial compression undergo pore space reduction due to mechanisms such as particle rearrangement and grain crushing. These changes in the internal structure of the material release energy in the form of elastic waves that can be detected by sensors sensitive to acoustic emission. In this study, Acoustic emission monitoring with a wavelet-based signal processing technique is used to identify the various mechanisms occurring during high-pressure sand compaction. Particle movement, grain failure, friction between grains and the surface of the compression cell and intergranular friction are studied. Acoustic emission data recorded during these simplified tests are used to characterize each phenomenon. Wavelet transform analyses allow the identification of useful features, making possible frequency discrimination among sliding, rolling, friction and grain fragmentation processes. For instance, we observe that at low stress, grain flow is characterized by the lowest centroid and peak frequencies, while at greater stresses, intergranular friction and grain fragmentation have the higher values. In the tests performed, the stress–strain evolution and final condition of the tested sand are broadly consistent, irrespective of the condition employed: continuous, stepwise or even variable loading rate or temperature. However, Acoustic emission data manifest much more complex behaviour (including thermal, load-rate dependency and delayed fragmentation phenomena) than that suggested by stress–strain relationships. At low stress levels, grain flow (sliding/rolling) is a relevant strain-accommodation mechanism, but so is crushing due to the effect of concentrated forces at the grain contact level. At high stresses, when crushing is generalized, intergranular friction is also a relevant phenomenon due to the increase in the coordination number produced by previous fragmentation.     

Characterizing friction in sliding isolation bearings

The force–displacement behavior of the Friction Pendulum? (FP) bearing is a function of the coefficient of sliding friction, axial load on the bearing and effective radius of the sliding surface. The coefficient of friction varies during the course of an earthquake with sliding velocity, axial pressure and temperature at the sliding surface. The velocity and axial pressure on the bearing depend on the response of the superstructure to the earthquake shaking. The temperature at an instant in time during earthquake shaking is a function of the histories of the coefficient of friction, sliding velocity and axial pressure, and the travel path of the slider on the sliding surface. A unified framework accommodating the complex interdependence of the coefficient of friction, sliding velocity, axial pressure and temperature is presented for implementation in nonlinear response‐history analysis. Expressions to define the relationship between the coefficient of friction and sliding velocity, axial pressure, and temperature are proposed, based on available experimental data. Response‐history analyses are performed on FP bearings with a range of geometrical and liner mechanical properties and static axial pressure. Friction is described using five different models that consider the dependence of the coefficient of friction on axial pressure, sliding velocity and temperature. Frictional heating is the most important factor that influences the maximum displacement of the isolation system and floor spectral demands if the static axial pressure is high. Isolation system displacements are not significantly affected by considerations of the influence of axial pressure and velocity on the coefficient of friction. Copyright © 2014 John Wiley & Sons, Ltd.     

Dynamic analysis of sliding structures with unsynchronized support motions

The dynamic analysis of sliding structures is complicated due to the presence of friction. Synchronization of the kinematics of all the isolation bearings is often granted to simplify the task. This, however, may lead to inaccurate prediction of the structural responses under certain circumstances. Stepped structures or continuous bridges with seismic isolation are notable examples where unsynchronized bearing motions are expected. In this paper, a logically simple and numerically efficient procedure is proposed to solve the dynamic problem of sliding systems with unsynchronized support motions. The motion equations for the sliding and non‐sliding modes of the isolated structure are unified into a single equation that is represented as a difference equation in a discrete‐time state‐space form and the base shear forces between the sliding interfaces can be determined through simple matrix algebraic analysis. The responses of the sliding structure can be obtained recursively from the discrete‐time version of the motion equation with constant integration time step even during the transitions between the non‐sliding and sliding phases. Therefore, both accuracy and efficiency in the dynamic analysis of the highly non‐linear system can be enhanced to a large extent. Rigorous assessment of seismic structures with unsynchronized support motions has been carried out for both a stepped structure and a continuous bridge. Effectiveness of friction pendulum bearings for earthquake protection of such structures has been verified. Moreover, evident unsynchronized sliding motions of the friction bearings have been observed, confirming the necessity to deal with each of the bearings independently in the analytical model. Copyright © 2000 John Wiley & Sons, Ltd.     

剪切破裂与粘滑——浅源强震发震机制的研究

周口店花岗闪长岩的高温高压三轴实验和理论分析表明,剪切破裂和摩擦滑移具有类似的孕育过程和发生机制。剪切破裂贯通强度就是一种摩擦强度。剪切破裂和摩擦滑移各自都有渐进式和突发式之分。突发式摩擦滑移是已有断层的粘滑滑移。突发式剪切破裂则是完整岩石的初始粘滑滑移。考虑到地壳温度随深度增加,完整岩石剪裂强震要求较高的围压,因此,多数浅源强震的发震方式很可能是已有断层的粘滑