On the formation of linear folds in regularly layered rock masses under biaxial loading

The piecewise-homogeneous model and the three-dimensional theory of stability for small and finite subcritical strains are used to study the formation of folds in layered rock masses of the Earth’s crust under biaxial loading. The general statement of the problem is given, and the governing characteristic equations are derived. Numerical results are presented for a layered rock mass composed of two alternating layers __________ Translated from Prikladnaya Mekhanika, Vol. 41, No. 12, pp. 26–34, December 2005.     

深部岩体变形破坏的特征能量因子与应用

深部岩体在高地应力作用下储存了大量的弹性应变能。在开挖或爆破扰动作用下,原有的平衡状态被打破,围岩中形成了有势场和不平衡应力场。在不平衡力场和扰动场的共同作用下,岩体的变形与破坏表现出了诸如分区破裂化、大变形、岩爆以及人工地震等非线性行为。传统的连续介质理论并不能考虑岩体的构造特性与含能特性,因此无法很好地解释深部岩体的特殊非线性力学现象。特征能量因子从能量的角度出发,结合统计物理学观点,为分析深部岩体在动静荷载组合作用下的变形和破坏过程提供了有效的理论支撑。本文主要对特征能量因子进行了简要介绍,并回顾了其在深部岩体分区破裂以及动力诱发围岩不可逆变形等非线性工程灾害现象中的应用。     

高地应力岩体多孔爆破破岩机制

深部岩体爆破破岩是爆炸荷载与高地应力共同作用的结果。基于一些简化假设,建立了一个高地应力岩体双孔爆破计算模型,采用光滑粒子流体力学-有限元方法耦合数值模拟方法,研究了高地应力作用下炮孔间裂纹的传播及贯通过程,分析了炮孔周围应力场动态演化过程与分布特征。研究结果表明：爆破引起的岩体开裂主要是环向动拉应力所致,地应力对岩体的压缩降低了炮孔周围环向动拉应力、缩短了环向动拉应力的作用时间,因而对爆炸致裂起抑制作用;静水地应力条件下多孔爆破时,垂直于炮孔连线方向传播的爆生裂纹更易受到地应力的抑制;对于高地应力岩体爆破,炮孔间的裂纹扩展长度随地应力水平的提高而减小,裂纹主要沿最大主应力方向扩展,因此沿最大主应力方向布置炮孔、缩短炮孔间距有利于炮孔间裂纹的连接贯通,形成良好的爆破开挖面。

     

A fracture damage model for Jointed rock masses and its application to the stability analysis of dam abutments

Based on continuum damage mechanics, for jointed rock masses, a fracture damage model is presented in this paper. First, the damage tensors are defined through the elastic-flexibility of intact rock and the equivalent elastic-damage flexibility for rock mass. Then, by the self-consistent principle of solid mechanics, the equivalent elastic-damage flexibility tensors involving the interaction between multicracks are deduced. The damage evolution law is proposed involving the mechanism of crack propagation process: frictional sliding, crack kinking, growing of branched tension cracks, interlinking of the microcracks near branched crack tips leading to the breakthrough of macro-cracks and finally the failure of rock mass. Thus the evolution of damage variables reasonably unified with the process of crack propagation is given. Finally, a plastic-brittle damage constitutive relation including brittle coupled strain rate, developed and applied to the stability analysis of complicated rock foundation of a dam in China, is described in this paper.     

Linear Mohr-Coulomb strength parameters from the non-linear Hoek-Brown rock masses

Most conventional computer codes, design practice and standards in rock engineering are formulated in terms of a linear Mohr-Coulomb (MC) failure criterion. However, experimental data shows that the failure of almost all types of rock masses follows a modified Hoek-Brown (HB) failure criterion that is non-linear. In order to avoid the difficulty resulting from the non-linearity of the strength envelope of rock masses in calculation of bearing capacity, the equivalent MC strength parameters from the modified HB failure criterion are developed for practical use in engineering. From the results, it is found that the equivalent strength parameters depend on not only the non-linear HB failure criterion but also the surcharge load and self-weight, which is different from the published results.     

非贯通裂隙岩体损伤演化率相关性及变形特征

含非贯通裂隙岩体是自然界中岩体的主要赋存形式,其裂隙几何特征对岩体的强度及变形均产生显著影响。应变率对岩体的损伤演化及黏滞效应也具有显著的率相关性。首先,运用模型元件的方法,将非贯通裂隙岩体动态破坏过程视为具复合损伤、静态弹性特性、动态黏滞特性的非均质点组成,对黏弹性响应的Maxwell体进行改进,将细观损伤体与裂隙损伤演化的宏观损伤体根据等效应变假设并联组成宏细观复合损伤体,构建综合考虑岩体宏细观缺陷的动态损伤模型;其次,基于断裂力学及应变能理论,对岩体宏观裂隙动态扩展的能量机制进行分析,综合考虑初始裂隙应变能、裂隙动态损伤演化过程应变能、裂隙闭合应变能,得到裂隙岩体宏观动态损伤变量计算公式;最后,将模型计算结果与实验结果进行比较,模型计算结果与实验结果吻合较好,证明了模型的合理性,同时利用模型讨论了裂隙倾角、应变率、岩石性质对岩体变形特征的影响规律。     

Local instability of horizontal elliptic excavations in elastoviscoplastic rock masses

In the framework of three-dimensional stability equations, we study the local instability of a horizontal excavation with elliptic cross-section under the assumption that the rock mass behaves like an elastoviscoplastic media. An estimate of the influence of the rock mass parameters on the value of the critical pressure is given.     

Zonal disintegration of deep crack-weakened rock masses: A non-Euclidean model

Rock masses are characterized by the existence of distributed joints and fractures. One of behaviors of the deep rock masses is high in situ stresses. The internal space of rock-like materials subjected to high in situ stresses after deformation is treated as a non-Euclidean one. The incompatible deformation of the deep rock masses is induced by high in situ stresses within the framework of non-Euclidean geometric space. A non-Euclidean model in which effects of cracks on zonal disintegration phenomenon of the deep crack-weakened rock masses is taken into account is established. Based on the non-Euclidean model, the elastic stress-field distribution of the deep surrounding rock masses induced by compatible deformation of non-fractured zones and incompatible deformation of fractured zones is determined. The stress intensity factors at the tips of cracks is given out. The strain energy density factor is applied to investigate the occurrence of disintegration zones. It is observed from the numerical results that the magnitude and site of fractured zones depend on the value of in situ stress, mesomechanical parameters and non-Euclidean parameters.     

损伤围岩中爆炸应力波动的数值模拟

应用有限元方法分析了硐室损伤围岩中爆炸应力波的传播和应力分布特征,通过引入JHC本构模型和岩石损伤变量D探讨了应力波作用下岩体的损伤演化模式。研究表明：围岩初始损伤对后续爆炸应力波的波动性质、作用范围和围岩应力分布具有不同程度的影响。当初始损伤超过某临界值后会显著地影响应力波的波动范围和围岩应力分布;在一定爆炸当量下,爆炸应力存在一个有效作用范围Lp,该范围塑性区以内,爆炸应力对岩体的损伤随围岩初始损伤增大而增大;有效作用范围Lp以外,围岩初始残余非弹性变形积累和单元残余拉应力可以平衡爆炸应力波动产生的损伤叠加效应,耗散了爆炸应力作用和波动能量。分析了产生在这种现象的原因。给出了有效作用范围Lp与围岩初始等效应力p之间的经验关系。     

轮廓爆破下柱状节理岩体开裂过程的数值模拟

以白鹤滩水电站柱状节理玄武岩为研究对象,根据现场的柱状节理分布统计资料生成数值模型,模拟边坡开挖轮廓爆破下柱状节理岩体的开裂过程。结果表明：轮廓爆破时,柱状节理面对岩体裂纹的发展起着导向和控制作用;爆炸荷载作用下炮孔周围的节理面首先张开,然后裂缝沿着炮孔连心线附近的节理面扩展,最后形成贯通的由大量柱状节理面连接而成的裂缝;预裂爆破条件下,预裂缝宽度先增大后减少,最后达到稳定的开度,而且预裂爆破在柱状节理岩体中产生的裂纹范围比光面爆破产生的大。

     

Stress-strain state near mine workings in anisotropic rock masses under the action of discontinuous waves

The ray-path method is used to analyze the stress-strain state near mine workings acted upon by discontinuous waves. A dynamic failure criterion is proposed for analyzing the stability of mine workings. The efficiency of the approach is demonstrated with a specific example __________ Translated from Prikladnaya Mekhanika, Vol. 44, No. 4, pp. 56–64, April 2008.     

Upper and lower bounds for constitutive relation of crack-weakened rock masses under dynamic compressive loads

A micro-mechanics-based model is proposed to investigate the rate-dependent constitutive relation for crack-weakened rock masses subjected to dynamic compressive loads. The present micro-mechanical model reveals that the nucleation, growth and coalescence of sliding cracks dominate the failure and macroscopic properties of crack-weakened rock masses subjected to dynamic compressive loads. The interactions among multiple parallel sliding cracks in crack-weakened rock masses subjected to dynamic compressive loads are examined asymptotically in an explicit and quantitative manner in order to reveal fully their so-called shielding and magnification effects on the stress–strain relation. Based on the micro-mechanical framework and the asymptotic analysis, analytical upper and lower bounds are proposed for the rate-relation for rock masses containing multiple rows of echelon cracks subjected to dynamic compressive loads. The factors that affect the rate-dependent properties of crack-weakened rock masses have been analyzed. The strain energy density factor approach, which is related to crack growth velocity and dynamic fracture toughness of rock material, is employed in the analysis. The rate-dependent constitutive relation of crack-weakened rock masses is derived from micro-mechanical framework and the asymptotic analysis. The closed-form explicit expression for the rate-dependent constitutive relation of rock masses containing echelon cracks subjected to dynamic compressive loads is obtained. Finally, the present model is used to analyze the complete stress–strain relation and strength for jointed rock masses at shiplock slope of the Three Gorges Dam.     

爆破开挖扰动下锚固节理岩质边坡位移突变特征与能量机理

针对白鹤滩水电站左岸坝基河谷底部边坡岩体爆破开挖,采用现场岩体位移监测、锚索轴力监测及数值模拟的手段,研究了爆破开挖扰动下锚固节理岩质边坡的位移突变特征及其能量机理。研究结果表明:对于深切河谷底部高地应力边坡岩体爆破开挖,爆炸荷载挤压及地应力作用下,岩体所积聚的应变能快速释放,导致了节理岩质边坡的位移突变,突变位移包括节理张开位移和岩体回弹位移两部分;地应力水平越高、岩体弹性模量越低,总的突变位移量越大;预应力锚索主要通过抑制节理张开位移来控制边坡岩体的位移突变,锚索预应力等级越高,其吸能和释能速率越高,对节理岩体位移突变的控制效果越好,当锚索的预应力等级高到一定程度后,节理岩体的突变位移不再随锚索预应力等级的升高而显著减小。     

结构阻尼时域本构模型及其应用

阻尼合金作为一种新型结构功能材料在不少领域已获应用,由于其阻尼值较大且随频率呈复杂交化关系,传统的线性粘性阻尼理论或经典的非频变结构阻尼理论难以精确地描述其耗能行为。本文应用粘弹性阻尼理论,根据阻尼合金储能模量和损耗因子在频域的实测数据．应用最优化方法拟合出标准线性体模型中的本构参数;根据积分形式的三参量本构关系和变形体虚功原理,推导出了有限元形式的动力学方程;讨论了三参数初值的选取;对包含卷积积分的有限元动力学方程通过数学推导将其化为三阶线性微分方程组,再转化为标准状态变量方程,应用数值求解。数值计算实例证明了所提方法的正确和有效性。     

近场动力学研究进展与岩石破裂过程模拟

近场动力学（Peridynamics,PD）作为一种新兴的非局部性理论,在非连续处不需要任何处理,能够很好表述模型从连续到非连续的过程。首先,在PD基本理论简介的基础上,系统回顾了PD的国内外研究现状。其次,采用键型PD理论对非均匀性的圆孔岩板单轴拉伸破裂过程进行了二维数值模拟,采用态型PD理论对单轴、常规三轴以及真三轴等不同压缩条件下的岩石破裂过程进行了三维数值模拟,并以加拿大Mine-by隧洞为例对现场岩体破裂过程进行了模拟,结果表明PD在岩石破裂过程模拟上具有较强适用性。最后,指出当前PD在岩石破裂过程模拟中存在的主要问题和未来值得开展的若干研究课题。