Mechanism of anomalous low friction phenomenon in deep block rock mass

Deep rock mass has the unique "self-stressed" block-hierarchical structure,anomalous low friction(ALF) was one of the typical nonlinear geo-mechanical and dynamic responses in deep block rock mass,which occurred as the result of movements of large-scale geo-blocks under the impact of external pulses(such as a deep confined explosion,earthquakes,rock bursts and etc.).ALF phenomenon obtained its name to describe the curious phenomenon that the friction between interacting geo-blocks quasi-periodically disappears at some discrete points in time along the direction orthogonal to the direction of the external pulse.With the objective to confirm the existence of the ALF phenomenon and study the geo-mechanical conditions for its occurrence experimentally and theoretically,laboratory tests on granite and cement mortar block models were carried out on a multipurpose testing system developed independently.The ALF phenomenon was realized under two loading schemes,i.e.,blocks model and a working block were acted upon jointly by the action of a vertical impact and a horizontal static force,as well as the joint action of both vertical and horizontal impacts with differently delayed time intervals.We obtained the rules on variation of horizontal displacements of working blocks when the ALF phenomenon was realized in two tests.The discrete time delay intervals,corresponding to local maxima and minima of the horizontal displacement amplitudes and residual horizontal displacements of the working block,satisfied canonical sequences multiplied by(2～(1/2))i.Some of these time intervals satisfied the quantitative expression(2～(1/2))i Δ /Vp.At last,1D dynamic theoretical model was established,the analytical results agreed better with the test data,while the quantitative expression drawn from test data was not validated well in theoretical analyses.

Mechanism of Pendulum-type wave phenomenon in deep block rock mass

Pendulum-type ( μ wave) wave is a new type of elastic wave propagated with low frequency and low velocity in deep block rock masses. The μ wave is sharply different from the traditional longitudinal and transverse waves propagated in continuum media and is also a phenomenon of the sign-variable reaction of deep block rock masses to dynamic actions, besides the Anomalous Low Friction (ALF) phenomenon. In order to confirm the existence of the μ wave and study the rule of variation of this μ wave experimentally and theoretically, we first carried out one-dimensional low-speed impact experiments on granite and cement mortar blocks and continuum block models with different characteristic dimensions, based on the multipurpose testing system developed by us independently. The effects of model material and dimensions of models on the propagation properties of 1D stress wave in blocks medium are discussed. Based on a comparison and analysis of the propagation properties (acceleration amplitudes and Fourier spectra) of stress wave in these models, we conclude that the fractures in rock mass have considerable effect on the attenuation of the stress wave and retardarce of high frequency waves. We compared our model test data with the data of in-situ measurements from deep mines in Russia and their conclusions. The low-frequency waves occurring in blocks models were validated as Pendulum-type wave. The frequencies corresponding to local maxima of spectral density curves of three-directional acceleration satisfied several canonical sequences with the multiple of 2～(1/2), most of those frequencies satisfied the quantitative expression (2～(1/2))i V p/2△ .

GREY CLASSIFICATION FOR EVALUATING THE STABILITY OF DANGEROUS ROCK-BLOCK MASSES

This paper introduces a grey classifica- tion method forevaluating the stability of dangerous rock- block masses according tothe Grey System Theory. This method is applied to the stability ofthe V~# dangerous rock- block masses of Qingjiang water conservancyproject, and better results are abtained. The method which isadvanced in the article is very single and practical, and it can meetall kinds of project's demands.

Development of 2D computer program to determine geometry of rock mass blocks

Due to various geological processes such as tectonic activities fractures might be created in rock mass body which causes creation of blocks with different shapes and sizes in the rock body. Exact understanding of these blocks geometry is an essential issue concerned in different domains of rock engineering such as support system of underground spaces built in jointed rock masses, design of blasting pattern, optimization of fragmentation, determination of cube blocks in quarry mines, blocks stability, etc. The aim of this paper is to develop a computer program to determine geometry of rock mass blocks in two dimensional spaces. In this article, the geometry of jointed rock mass is programmed in MATLABTM.

Dynamic Instability of Tunnel in Blocky Rock Mass

The displacements and geometry of the rock blocks and the properties of the rock struc-ture play an important role in the stability of tunnels.Based on the key block model,the dynamic instability analysis of underground tunnel subjected to intensive short-time compressional wave was conducted.The instability of the tunnel caused by the spallation and the inertial effect was distin-guished.And the influence of the roof contour curvature of tunnel was also determined.

Zonal disintegration phenomenon in rock mass surrounding deep tunnels

Zonal disintegration is a typical static phenomenon of deep rock masses. It has been defined as alternating regions of fractured and relatively intact rock mass that appear around or in front of the working stope during excavation of a deep tunnel. Zonal disintegration phenomenon was successfully demonstrated in the laboratory with 3D tests on analogous gypsum models, two circular cracked zones were observed in the test. The linear Mohr-Coulomb yield criterion was used with a constitutive model that showed linear softening and ideal residual plastic to analyze the elasto-plastic field of the enclosing rock mass around a deep tunnel. The results show that tunneling causes a maximum stress zone to appear between an elastic and plastic zone in the surrounding rock. The zonal disintegration phenomenon is analyzed by considering the stress-strain state of the rock mass in the vicinity of the maximum stress zone. Creep instability failure of the rock due to the development of the plastic zone, and transfer of the maximum stress zone into the rock mass, are the cause of zonal disintegration. An analytical criterion for the critical depth at which zonal disintegration can occur is derived. This depth depends mainly on the character and stress concentration coefficient of the rock mass.

Investigation of block foundations resting on soil-rock and rock-rock media under coupled vibrations

In the present study,the dynamic response of block foundations of different equivalent radius to mass（R;/m） ratios under coupled vibrations is investigated for various homogeneous and layered systems.The frequency-dependent stiffness and damping of foundation resting on homogeneous soils and rocks are determined using the half-space theory.The dynamic response characteristics of foundation resting on the layered system considering rock-rock combination are evaluated using finite element program with transmitting boundaries.Frequencies versus amplitude responses of block foundation are obtained for both translational and rotational motion.A new methodology is proposed for determination of dynamic response of block foundations resting on soil-rock and weathered rock-rock system in the form of equations and graphs.The variations of dimensionless natural frequency and dimensionless resonant amplitude with shear wave velocity ratio are investigated for different thicknesses of top soil/weathered rock layer.The dynamic behaviors of block foundations are also analyzed for different rock-rock systems by considering sandstone,shale and limestone underlain by basalt.The variations of stiffness,damping and amplitudes of block foundations with frequency are shown in this study for various rock—rock combinations.In the analysis,two resonant peaks are observed at two different frequencies for both translational and rotational motion.It is observed that the dimensionless resonant amplitudes decrease and natural frequencies increase with increase in shear wave velocity ratio.Finally,the parametric study is performed for block foundations with dimensions of 4 m × 3 m × 2 m and 8m×5m×2m by using generalized graphs.The variations of natural frequency and peak displacement amplitude are also studied for different top layer thicknesses and eccentric moments.

岩体临空面块体振动响应规律研究

结构面是控制岩体工程局部稳定的关键因素之一,查明结构面赋存及组合状态是岩体稳定性分析的前提条件,目前常采用地质调察的方法,由于勘察手段的局限性,存在遗漏时常需要补充勘察,成本耗费高。通过开展室内试验,对结构面模型的表面振动响应规律进行了研究,研究表明:对于单结构面模型,结构面前方的质点振幅存在增幅效应,对于由两条结构面切割的块体模型,仅在远离动力输入侧的结构面前方存在振幅放大效应。在试验成果的基础上开展了数值模拟分析,分别对不同结构面倾角的岩体模型进行计算,结果表明:相对于萨道夫斯基经验公式得到的振动衰减规律,当结构面与爆源方向地面夹角θ值小于90°时,结构面前方的振动波入射区域质点振幅存在明显放大效应,结构面后方质点振动幅值则显著衰减。随着结构面与边界面夹角θ的减小,结构面前质点峰值振速增幅率逐渐增大,并在θ=20°时波幅放大2.8倍。通过合理布置爆破振动监测测点,这一规律为爆破工程中识别结构面及块体提供判据。

无人机技术在超高陡边坡危岩体半自动识别中的应用

在新疆山区开展危岩体勘察时,由于工程区存在复杂且陡峭的山体,传统人工勘察危岩体的方案往往受限。为了有效地提高危岩体调查的效率与自动化程度,本研究提出了一种基于无人机的高陡边坡危岩体半自动勘察技术。将无人机贴近摄影测量技术与精确的仿地飞行路线规划相结合,获取超高边坡精确三维点云模型;应用CloudCompare软件点云剖分工具结合危岩体突出于边坡表面的形态特征对异型滑移式块体进行语义分割;并通过分析异型滑移式块体的三维特征,实现对危岩体的定性分析。将上述理论方法应用于玉龙喀什水利工程左岸超高边坡坝址,在试验区提取出了4块危岩体。所有危岩体稳定性系数(K)均低于0.9,平均体积均在2000 m3左右,最大高差在7~11 m。危岩体的空间位置分布和三维特征与现场人工勘测的基本一致。试验表明,结合危岩体特征的高精度边坡点云模型能有效识别危岩体,提高调查效率并解决人工数据模糊的问题,对高陡边坡的危岩体评估具有实际应用价值。

Influence of stress wave-induced disturbance on ultra-low friction in broken blocks

Deep rock mass tends to be broken into blocks when mining for materials deep below the surface.The rock layer of the roof of the mine can be regarded as a system of blocks of fractured rock mass.When subjected to high ground stress and mining-induced disturbance,the efect of the ultra-low friction of the block system easily becomes apparent,and can induce rock burst and other accidents.By taking the block of rock mass as research object,this study developed a test system for ultra-low friction to experimentally examine its efects on the broken blocks under stress wave-induced disturbance.We used the horizontal displacement of the working block as the characteristic parameter refecting the efect of ultra-low friction,and examine its characteristic laws of horizontal displacement,acceleration,and energy when subjected to the efects of ultra-low friction by changing the frequency and amplitude of the stress wave-induced disturbance.The results show that the frequency of stress wave-induced disturbance is related to the generation of ultra-low friction in the broken block.The frequency of disturbance of the stress wave is within 1–3 Hz,and signifcantly increases the maximum acceleration and horizontal displacement of the broken blocks.The greater the intensity of the stress wave-induced disturbance is,the higher is the degree of block fragmentation,and the more likely are efects of ultra-low friction to occur between the blocks.The greater the intensity of the horizontal impact load is,the higher is the degree of fragmentation of the rock mass,and the easier it is for the efects of ultra-low friction to occur.Stress wave-induced disturbance and horizontal impact are the main causes of sliding instability of the broken blocks.When the dominant frequency of the kinetic energy of the broken block is within 20 Hz,the efects of ultra-low friction are more likely.

浮放运输货物在冲击载荷下倾覆风险研究

目的对浮放运输货物在车辆冲击载荷下摇摆特性进行分析和其倾覆风险评价。方法将浮放运输的货物或包装件简化为刚性质量块,载运车辆建模为具有一定水平加速度载荷的刚性支座,推导出刚性质量块在加速度载荷下的摇摆运动控制方程,通过试验设计测取车辆减速制动工况下冲击载荷波形,建立冲击载荷波数学表达式,采用理论分析方法在近似线性化范围内分析冲击载荷下刚性质量块的动态摇摆特性与倾覆风险。结果刚性质量块在正向加速度载荷下进入摇摆,响应初始摇摆角度小于0并且倾覆是发生在自由振动状态下;绘制了刚性质量块在半正弦波冲击载荷下最小倾覆加速度频谱,存在一条边界线将频谱划分为安全区和倾覆区;刚性质量块的宽高比和稳定性呈正相关。结论通过转变为刚性质量块摇摆响应系统问题线性近似研究了浮放运输货物的摇摆特性和倾覆风险。

渗流力和结构面水弱化作用下裂隙岩体边坡块体的稳定性

裂隙岩体渗流是影响岩体稳定性的重要因素之一。裂隙中的流体流动不仅会产生渗流力,而且会降低裂隙面的强度,致使边坡失稳、隧道塌方等事故频发。为揭示渗流作用对裂隙岩体边坡块体稳定性的作用机理,基于关键块体理论,提出一种同时考虑渗流力和结构面水弱化作用的稳定性分析方法,其中,渗流力基于渗流理论和统一管网法计算,结构面水弱化根据经验公式确定。以某岩质边坡为例,采用该方法对边坡在渗流作用下的块体稳定性开展研究。研究结果表明,渗流力与结构面水弱化作用对裂隙岩体边坡块体稳定性的作用方式不同,渗流力既会改变块体的抗滑力又会改变块体的滑动力,对块体稳定性的影响较为复杂,包括改变块体的稳定状态、滑移面、失稳形式;结构面水弱化只降低块体的抗滑力,进而降低块体的稳定性,不改变块体的失稳形式。此外,对于裂隙边坡工程,通常存在一个最危险渗流压力值。

铜矿峪矿深部矿岩赋存特征研究对自然崩落法开采的指导意义

本文通过对铜矿峪矿深部矿岩赋存特征及其物理力学特性研究,探讨深部矿岩可崩性,为矿山深部自然崩落法开采提供重要的指导意义。研究表明:4^(#)、5^(#)矿体岩体中存在倾向为北西向和南东向的两组优势节理组,节理面陡倾;岩石坚固程度属坚硬岩~较坚硬岩;岩体质量属Ⅱ~Ⅲ级,破碎特性为中等大块~大块较多,可崩性属难崩~中等可崩。为改善深部矿岩可崩性,在深部开采时还应积极引用水压预裂矿岩预处理技术,合理规划首采区拉底部位、确定拉底推进方向、控制拉底速率,并辅以适当的预裂、割帮等诱导工程,以实现自然崩落法的成功开采。

CAVABILITY CLASSIFICATION MODEL IN BLOCK CAVING

ＣＡＶＡＢＩＬＩＴＹＣＬＡＳＳＩＦＩＣＡＴＩＯＮＭＯＤＥＬＩＮＢＬＯＣＫＣＡＶＩＮＧ￥ＷａｎｇＬｉｇｕａｎ（ＤｅｐｏｒｔｍｅｎｔｏｆＲｅｓｏｕｒｃｅｓＥｘｐｌｏｉｔａｔｉｏｎＥｎｇｉｎｅｅｒｉｎｇ，ＣｅｎｔｒａｌＳｏｕｔｈＵｎｉｖｅｒｓｉｔｙｏｆＴｅ...

A method to determine relevant geomechanical parameters for evaluating the hydraulic erodibility of rock

Among the methods used for evaluating the potential hydraulic erodibility of rock,the most common methods are those based on the correlation between the force of flowing water and the capacity of a rock to resist erosion,such as Annandale’s and Pells’methods.The capacity of a rock to resist erosion is evaluated based on erodibility indices that are determined from specific geomechanical parameters of a rock mass.These indices include unconfined compressive strength(UCS)of rock,rock block size,joint shear strength,a block’s shape and orientation relative to the direction of flow,joint openings,and the nature of the surface to be potentially eroded.However,it is difficult to determine the relevant geomechanical parameters for evaluating the hydraulic erodibility of rock.The assessment of eroded unlined spillways of dams has shown that the capacity of a rock to resist erosion is not accurately evaluated.Using more than 100 case studies,we develop a method to determine the relevant geomechanical parameters for evaluating the hydraulic erodibility of rock in unlined spillways.The UCS of rock is found not to be a relevant parameter for evaluating the hydraulic erodibility of rock.On the other hand,we find that the use of three-dimensional(3D)block volume measurements,instead of the block size factor used in Annandale’s method,improves the rock block size estimation.Furthermore,the parameter representing the effect of a rock block’s shape and orientation relative to the direction of flow,as considered in Pells’method,is more accurate than the parameter adopted by Annandale’s method.

煤表面粗糙度对煤岩超低摩擦效应影响试验研究

超低摩擦型冲击地压本质是煤岩界面发生超低摩擦效应诱发的一种新型煤矿动力灾害,以沈阳红阳三矿顶板-煤层-底板为研究对象,利用自主研发的试验装置进行了轴压、垂直扰动和水平冲击共同作用下砂岩-煤-砂岩叠加块体超低摩擦效应模拟试验,以煤块为工作块体,分析了煤表面粗糙度对工作块体水平位移幅值、水平位移突变时间、水平加速度幅值、水平加速度突变时间的影响,得到了煤表面粗糙度对超低摩擦效应影响规律。结果表明:(1)砂岩表面粗糙度系数一定时,随煤表面粗糙度系数增大,工作块体水平位移和水平加速度时间历程曲线存在三阶段特征,即孕育阶段、激发阶段、稳定阶段;(2)煤表面粗糙度系数存在拐点为3.98,当煤表面粗糙度小于拐点3.98时,随煤表面粗糙度增大,激发阶段水平位移大于稳定阶段水平位移,位移差线性减小,超低摩擦效应减弱;(3)当煤表面粗糙度大于拐点3.98时,随煤表面粗糙度增加,激发阶段水平位移小于稳定阶段水平位移,此时工作块体水平位移出现二次增加,随位移差绝对值不断增大,超低摩擦效应越显著;(4)水平位移幅值和水平加速度幅值随煤表面粗糙度增大,呈先线性递减后线性递增规律;(5)水平位移突变时间和水平加速度突变时间随煤表面粗糙度增加,呈先线性增加后线性递减规律。

动态扰动下顶板块体失稳冒落研究综述

巷道、采场等地下开挖空间周边围岩的次生结构面发育,岩体极易被切割成多个独立岩块,并在准静态地应力或外界动力扰动作用下发生滑动冒落.针对准静态条件下的顶板失稳冒落问题,研究的重点在于结构面的扩展分析以及块体系统的受力平衡条件分析.对于动态扰动条件下的顶板岩块滑动失稳问题,不仅涉及到应力波促进下的裂隙扩展问题,还与块体系统中应力波的传播规律和应力波影响下岩块动态受力条件有关.本文分别从静态条件下与动态扰动条件下两个方面总结了顶板岩块稳定性相关研究.目前针对静态条件下的顶板块体稳定性研究已经形成了诸多较为成熟的理论体系;而对于动态扰动条件下的块体稳定性的研究主要还是集中于块体系统内部应力波传播过程的分析,忽略了对顶板岩体受扰过程中裂隙扩展和应力失衡的分析.因此,针对顶板岩块动态失稳问题的研究尚不能揭示冒落机理,而该研究的难点在于“揭示动态扰动诱发块体失稳的本质机理”.最后,介绍了课题组针对动态扰动下顶板块体滑动失稳问题开展的一系列实验与数值模拟研究,揭示了不同方向动态扰动作用诱发顶板块体滑动失稳的机理,为地下矿山冒顶灾害的防控提供一定的理论参考.

改进的岩质凸块的超载储备极限平衡法

脱离模式是块体理论提出的有限可动块体的失稳模式之一。虽然直接塌落是地下工程中最常见的失稳现象,但是目前依然缺少适用的定量分析方法,这使得地下工程的开挖和加固设计缺乏必要的理论支撑。为此,提出了一种改进的考虑渐进破坏的岩块稳定分析方法。主要改进了3处:(1)引入超载基数和超载方向两个参数来量化描述储备荷载;(2)提出了Tan和Scal两种超载基数设定方式;(3)超载方向设定在节理锥的边界扇面上。算例验证结果表明,改进方法完全兼容现有双面滑模式的安全系数算法,实现了脱离模式的定量稳定性分析。最后,讨论了改进方法的刚度参数取值方法及其敏感性。

缓倾层状岩体隧道底部结构变形和裂缝发展规律

以渝黔铁路(重庆—贵阳)老周岩隧道为工程背景,采用三维离散元数值模拟方法,分别研究了不同岩层层理倾角和侧压力系数条件下隧道底部结构变形特征和裂缝发展规律。结果表明:隧道底部结构隆起量和中轴线两侧隆起不对称程度均随倾角、侧压力系数的增大而增大,底部结构隆起量最大值出现在层理方向与隧道底部相切位置;底部结构裂缝张开量、剪切滑移量和分布范围均随倾角、侧压力系数的增大而增大;随倾角增大裂缝发展最显著位置由仰拱中心向右墙脚移动,随侧压力系数增大裂缝向深部扩展程度增大,底部结构三角形破裂区域范围也逐渐增大。

Identifying rock blocks based on hierarchical rock-mass structure model

Rock-masses are divided into many closed blocks by deterministic and stochastic discontinuities and engineering interfaces in complex rock-mass engineering. Determining the sizes, shapes, and adjacent relations of blocks is important for stability analysis of fractured rock masses. Here we propose an algorithm for identifying spatial blocks based on a hierarchical 3D Rock-mass Structure Model (RSM). First, a model is built composed of deterministic discontinuities, engineering interfaces, and the earth's surface, and the deterministic blocks surrounded by these interfaces are traced. Then, in each deter-ministic block, a network model of stochastic discontinuities is built and the stochastic blocks are traced. Building a unitary wire frame that connects all interfaces seamlessly is the key for our algorithm to identify the above two kinds of blocks. Using this algorithm, geometric models can be built for block theory, discrete element method, and discontinuous deformation analysis.