Mechanism on progressive failure of a faulted rock slope due to slip-weakening

1 Introduction The damage or failure of faulted rock slope is a quite difficult problem in geotechni- cal engineering, and attention has been drawn from researchers for a long time. Apart from the toppling damage of steep slopes, most of the failure pattern of faulted rockslopes is shear-typed. The failure process of such a slope includes: initiation and devel- opment of a single micro-crack, breakthrough of two or more cracks, formation of fail- ure zones, and even shear damage in large scale…     

干湿循环作用下滑带土的变形演化和强度

干湿循环是一种常见的水—土相互作用方式,对岩土体的变形和强度以及库岸滑坡的稳定性有着重要影响。本文在分析粉土和粉质黏土两种滑带土基本特征的基础上,通过室内干湿循环试验和直接剪切试验,对不同类型的滑带土在干湿循环作用下的变形演化和强度弱化特征进行了试验研究。结果表明：在干湿循环变化下,粉土滑带土的变形表现为风干时土样内部产生裂隙,且随着干湿循环次数的增加,裂隙不断扩展贯穿和增宽,饱和后裂隙又闭合;粉质黏土滑带土变形则为风干时体积收缩,饱和后体积膨胀;两种滑带土在干湿循环条件下的强度弱化规律基本相同,第一次干湿循环造成滑带土强度弱化程度最大,第二次后强度基本趋于稳定值;两种滑带土的黏聚力与干湿循环次数呈对数曲线形式降低,内摩擦角呈线性降低;干湿循环过程中滑带土抗剪强度的降低主要是由于其黏聚力的降低引起的,同时黏聚力受干湿循环的影响较为显著。     

Mechanism of action of cracks water on rock landslide in rainfall

In worldwide, the most common triggering factor of rock landslides is extended and intense rainfall. However, different from the soil slope failure caused by softening action of infiltration rainwater, the mechanism of rock landslide in rainfall is not clear. From the view of fracture mechanics, the propagation of cracks on rock slope and the development of sliding surface were researched. Then based on hydraulics formulas and using Sweden arc method, the influence of crack water on stability of rock slope was quantitatively studied. Finally, an example was given to check the theoretical approach. The result shows that the development of sliding surface of rock slope is mainly caused by crack propagation under hydrostatic pressure when the stress intensity factor K _I at crack tip is bigger than the toughness index of rock fractures K _IC, and the failure of slope is the result of hydraulic action of crack water and the softening of materials on sliding surface when the depth of crack water is bigger than a minimum value h _min.     

幂软化材料动态裂纹尖端的弹塑性场

采用塑性动力学方程,对应变损伤材料平而应力动态裂纹尖端场进行了渐近分析。假定材料服从J_2流动理论,且损伤规律以幂律应变软化的规律给出,其结果表明:在裂纹尖端附近,应力和应变分别具有如下的奇异性:σ/(1n R/r)~(-n/n+1),∈～(1n R/r)~(1/n+1),并且通过数值计算给出了裂纹尖端附近的应力分布。而对于n=1情况下,即损伤规律服从反比例关系,本文对平面应变问题和Ⅲ型反平面剪切问题进行了研究。给出了动态弹塑性场的渐近解,揭示了场的渐近特性。     

三点弯曲-剪切试样的应力强度因子

利用一种边界元法研究具有偏移边裂纹的三点弯曲-剪切试样.该边界元方法由Crouch与Starfield提出的常位移不连续单元和笔者最近提出的裂尖位移不连续单元构成.在该边界元方法实施过程中,左、右裂尖位移不连续单元分别置于裂纹的左、右裂尖处,而常位移不连续单元则分布于除了裂尖位移不连续单元占据的位置之外的整个裂纹面及其他边界.算例说明这种边界元法不论对无限大还是对有限大平面弹性复杂裂纹问题的应力强度因子的计算都是非常有效的.对具有偏移边裂纹的三点弯曲-剪切试样的应力强度因子进行了详细的研究,给出了数值结果.     

Rock fracture under anti-plane shear (Mode III) loading

Anti-plane punch-through shear test and anti-plane four-point bending test are used to study the crack initiation and propagation under anti-plane shear (Mode III) loading. The tensile and shear stresses at the crack tip are calcualted by finite element method. The results show that under Mode III loading the maximum principal stress σ₁ at crack tip is smaller or a little larger than the maximum shear stress τ_max. Since the tensile strength of brittle rock is much lower than its shear strength, σ₁ is easy to reach its critical value before τ_max reaches its critical value and thus results in Mode I fracture. The fracture trajectory is helicoid and the normal direction of tangential plane with the fractured helicoid is along the predicted direction of the maximum principal stress at the notch tip. It is further proved that Mode I instead of Mode III fracture occurs in brittle rock under Mode III loading. The fracture mode depending on the fracture mechanism must be distinguished from the loading form. Foundation item: Project (50374073) supported by the National Natural Science Foundation of China; project (2002032256) supported by the Postdoctor Science Foundation of China     

Study on fault induced rock bursts

In order to study the rules of rock bursts caused by faults by means of mechanical analysis of a roof rock-mass balanced structure and numerical simulation about fault slip destabilization, the effect of coal mining operation on fault plane stresses and slip displacement were studied. The results indicate that the slip displacement sharply increases due to the decrease of normal stress and the increase of shear stress at the fault plane when the working face advances from the footwall to the fault itself, which may induce a fault rock burst. However, this slip displacement will be very small due to the increase of normal stress and the decrease of shear stress when the working face advances from the hanging wall to the fault itself, which results in a very small risk of a fault rock burst.     

Dynamic analysis of fault rockburst based on gradient-dependent plasticity and energy criterion

Fault rockburst is treated as a strain localization problem under dynamic loading condition considering strain gradient and strain rate. As a kind of dynamic fracture phenomena, rockburst has characteristics of strain localization, which is considered as a one-dimensional shear problem subjected to normal compressive stress and tangential shear stress. The constitutive relation of rock material is bilinear (elastic and strain softening) and sensitive to shear strain rate. The solutions proposed based on gradientdependent plasticity show that intense plastic strain is concentrated in fault band and the thickness of the band depends on the characteristic length of rock material. The post-peak stiffness of the fault band was determined according to the constitutive parameters of rock material and shear strain rate. Fault band undergoing strain softening and elastic rock mass outside the band constitute a system and the instability criterion of the system was proposed based on energy theory. The criterion depends on the constitutive relation of rock material, the structural size and the strain rate. The static result regardless of the strain rate is the special case of the present analytical solution. High strain rate can lead to instability of the system.     

不同速率下单双钎头破岩声发射数值分析

选用脆性花岗岩为研究对象,利用岩石破裂过程分析软件RFPA2D,分别对其进行单、双钎头在不同加载速率下的数值模拟试验,得到RFPA2D应力图及相对应同一加载步下的声发射图。结果表明:较单钎头相比,岩石在双钎头协同作用下将会形成应力叠加,且钎头下面的裂纹会对相邻裂纹产生影响,裂纹尖端会产生应力集中,试件破坏释放出的声发射能量和声发射计数更大;随着加载速率的增大,试件释放的声发射总能量增大,且所得竖向载荷增大。     

Microscopic study of mode I crack tip deformation

By simulating edge dislocation emissions from a mode I crack tip along multiple inclined slip planes, the plastic zone and dislocation-free zone around the crack tip are obtained. It is found that the shape of the mode I plastic zone consists of two leaning forward loops which is better agreement with experimental observations. Except at the crack tip there are also stress peaks in front of the crack tip. A formula of the maximum peak stress as a function of the applied stress intensity factor and the friction stress has been regressed.     

法向压缩载荷对II型裂纹扩展的影响规律研究

压剪共同作用下裂纹是地下岩体中广泛存在的,为了研究法向压缩载荷对剪切型即II型裂纹扩展的影响规律,利用砂岩制作了单边裂纹试件,通过岩石剪切实验系统对不同法向压缩载荷作用下的裂纹进行了剪切实验研究,结果表明法向压缩载荷对裂纹的起裂及扩展起到抑制作用,随着裂纹法线压缩载荷的增大,裂纹起裂角逐渐减小;同时,得出法向压缩载荷与II型裂纹极限应力强度因子之间的关系,随着法向压缩载荷增大,岩石II型裂纹极限应力强度因子也随之增大。运用ABAQUS模拟软件,对不同压缩载荷作用下压剪裂纹的扩展进行模拟研究,得出了裂纹尖端II型应力强度因子随压缩载荷的变化规律。     

岩质边坡稳定分析三维与二维的比较

提出岩质边坡沿软弱结构面滑移一剪切的三维稳定分析方法。在分析模型中,下滑体沿滑动面下滑,在其他的面上则产生剪切破坏。在结构面上满足莫尔库伦破坏准则,把剪切面上的摩阻力向下滑方向投影,由下滑体的力学平衡条件求解出未知力,通过迭代可以求得稳定系数。同时推导了摩阻力倾向与倾角的计算式,编制了相应的程序,并利用这个程序,研究了边坡长度、岩层与坡面夹角等因素对边坡稳定系数的影响,比较了三雏分析与二维分析的差别。     

Simulation of failure process of jointed rock

A modified discontinuous deformation analysis (DDA) algorithm was proposed to simulate the failure behavior of jointed rock.In the proposed algorithm,by using the Monte-Carlo technique,random joint network was generated in the domain of interest.Based on the joint network,the triangular DDA block system was automatically generated by adopting the advanced front method.In the process of generating blocks,numerous artificial joints came into being,and once the stress states at some artificial joints satisfy the failure criterion given beforehand,artificial joints will turn into real joints.In this way,the whole fragmentation process of rock mass can be replicated.The algorithm logic was described in detail,and several numerical examples were carried out to obtain some insight into the failure behavior of rock mass containing random joints.From the numerical results,it can be found that the crack initiates from the crack tip,the growth direction of the crack depends upon the loading and constraint conditions,and the proposed method can reproduce some complicated phenomena in the whole process of rock failure.     

含裂隙无腹筋梁的抗剪承载能力

分析混凝土梁内部既有裂隙的位置及角度对无腹筋梁抗剪承载力的影响, 制作多组含既有裂隙的试验梁, 进行梁的三点弯曲试验, 研究位于梁跨中和梁侧基本拱体范围内既有裂隙对无腹筋梁抗剪承载力的影响及裂缝扩展规律。结果表明: 梁上的既有裂隙对梁的抗剪承载力有削弱作用; 在其他条件相同的情况下, 梁跨中既有裂隙的裂尖距离梁底中部越近, 对无腹筋梁抗剪承载力的削弱作用越大; 梁侧既有裂隙的角度与基本拱体重合度越高, 对无腹筋梁抗剪承载力的削弱作用越大;梁侧既有裂隙的角度与基本拱体重合度越高, 梁底裂缝越容易扩展通过既有裂隙的两个裂尖, 反之, 梁底裂缝可扩展至既有裂隙中部。     

无限长条功能梯度材料的反平面裂纹问题

研究了无限长条正交各向异性功能梯度材料在平面剪切作用下的Yoffe裂纹的动力学问题，材料的两上方向的剪切模量假定为指数模型，通过采用积分变换-积分方程方法，求得了裂纹尖端的动态应力场和动态应力强度因子，并研究了裂纹运动速度、几何尺寸、梯度参数和不均匀系数对动态应力强度因子的影响，结果表明，裂纹尖端应力具有的奇异性，裂纹的运动速度越大，应力强度因子越大；材料的模量梯度越大，应力强度因子越低；不均匀系数越大，应力强度因子越小。     

尺寸效应对结构面抗剪强度影响研究

岩体中存在的结构面对岩体的物理力学性质有着重要的影响,而尺寸效应是结构面的物理力学性质的重要影响因素。为研究尺寸效应对岩体结构面强度与变形的影响,对岩芯岩样进行扫描,根据数据建立模型,对不同尺寸岩样进行直剪试验的数值模拟,同时进行法向应力下的直剪试验,对结构面在剪切应力作用下的抗剪强度曲线以及不同尺寸结构面的剪切特性进行深入研究,得出结构面抗剪强度与结构面尺寸之间的关系,并建立抗剪强度经验公式。结果表明:随着结构面尺寸的增大,结构面抗剪强度也随之增大,当达到一定尺寸后,抗剪强度开始稳定,定义此临界尺寸为表征单元面,在确定结构面抗剪强度时,结构面尺寸不得低于表征单元面面积, 本文中岩样表征单元面面积为0.384 8 m2。       

Quantitative calculation for the dissipated energy of fault rock burst based on gradient-dependent plasticity

The capacity of energy absorption by fault bands after rock burst was calculated quantitatively according to shear stressshear deformation curves considering the interactions and interplaying among microstructures due to the heterogeneity of strain softening rock materials. The post~peak stiffness of rock specimens subjected to direct shear was derived strictly based on gradientdependent plasticity, which can not be obtained from the classical elastoplastic theory. Analytical solutions for the dissipated energy of rock burst were proposed whether the slope of the post-peak shear stress-shear deformation curve is positive or not. The analytical solutions show that shear stress level, confining pressure, shear strength, brittleness, strain rate and heterogeneity of rock materials have important influence on the dissipated energy. The larger value of the dissipated energy means that the capacity of energy dissipation in the form of shear bands is superior and a lower magnitude of rock burst is expected under the condition of the same work done by external shear force. The possibility of rock burst is reduced for a lower softening modulus or a larger thickness of shear bands.     

公路隧道二次衬砌裂损病害机理研究

公路隧道二次衬砌裂损病害对隧道结构的稳定性有着很大影响,为研究公路隧道二次衬砌裂损病害发生的机理,首先划分了衬砌裂损病害的3种类型,并对每种裂损类型展开了力学行为分析.以断裂力学作为切入点,研究了在围岩荷载及结构自身作用下衬砌产生的裂缝的发展规律,通过获取应力强度因子K、J积分、以及裂纹面的最大张开位移δ求得裂纹尖端应力和应变值,在此基础上,通过最大周向应力理论分析了Ⅰ型＋Ⅱ型复合裂纹发生的临界条件.根据最大周向应力σθ所对应的应力强度因子值来对比临界强度因子值KIC,判断二次衬砌裂纹是否会发生扩展以及分析衬砌裂损病害发生的可能.获得了一系列有益的结论,能够对公路隧道二次衬砌裂损病害机理的理论研究和工程应用提供一定的参考和借鉴.     

高速远程滑坡动力学研究进展

高速远程滑坡动力学机理研究一直是国际地质灾害领域长期关注的热点与前沿性科学。通过对已有研究成果的系统性梳理,对高速远程滑坡动力学研究现状进行了概略性述评,厘定了本文所讨论的高速远程滑坡的定义,阐述了高速远程滑坡的典型沉积学特征,并对国内外学者提出的最有影响、最有地质证据支持的高速滑坡远程运动机理——摩擦生热减阻、滑带液化减阻、动力破碎减阻、底部裹挟减阻、剪切振动减阻、动量传递远程进行了论述。在此基础上,分析与讨论了高速远程滑坡动力学研究的发展趋势,提出今后研究所面临的深层次科学问题,并提出未来应进一步重点研究的关键科学问题在于速率相依摩阻弱化机理、破碎渐进相变耗能机理、过程相依波动减阻机理等。     

表面涂层材料终止于界面裂纹尖端弹塑性奇异应力场

针对涂层材料分析了终止于界面的裂纹尖端弹塑性应力场奇异性。由线性硬化全量理论并考虑到裂纹尖端应力奇异特征,建立了相关的本构方程。利用Goursat应力函数求得了裂纹尖端弹塑性奇异应力场。分析结果表明,所得应力场奇异性可以通过两个与硬化系数相关的Dundurs参数进行描述。当硬化系数远小于弹性模量时,奇异应力场仅需要一个Dun-durs参数来表征。对于涂层为陶瓷基体为金属的情形,奇异性取决于裂纹方向。