Determination of mechanical parameters for jointed rock masses

Combining with empirical method, laboratory test and numerical simulation, a comprehensive system was presented to determine the mechanical parameters of jointed rock masses. The system has the following four functions: (1) Based on the field investigation of joints, the system can consider rock mass structures, by using network simulation technology. (2) Rock samples are conducted by numerical simulation with the input engineering mechanical parameters of rocks and joints obtained from laboratory tests. (3) The whole stress-strain curve of jointed rock masses under certain normal stress can be plotted from numerical simulation, and then the shear strength parameters of jointed rock masses can be obtained from the whole stress-strain curves under different normal stresses. (4) The statistical values of mechanical parameters of jointed rock masses can be determined according to numerical simulation. Based on the statistical values, combining with engineering experiences and geological investigations, the comprehensive mechanical parameters of jointed rock masses can be achieved finally. Several cases are presented to prove the engineering feasibility and suitability of this system.     

节理岩体各向异性力学研究综述

对节理岩体各向异性力学研究的现状与进展进行了系统分析和阐述,分别探讨了节理本身的各项异性力学性质,岩石介质和节理综合(即整个节理岩体)的各向异性力学性质,并对节理岩体本构模型、各向异性力学参数和屈服准则研究进行了较为详细的描述和比较,以指导实践。     

Influence of degree of interlock on confined strength of jointed hard rock masses

The strength of jointed rock mass is strongly controlled by the degree of interlock between its constituent rock blocks. The degree of interlock constrains the kinematic freedom of individual rock blocks to rotate and slide along the block forming joints. The Hoek–Brown (HB) failure criterion and the geological strength index (GSI) were developed based on experiences from mine slopes and tunneling projects in moderately to poorly interlocked jointed rock masses. It has since then been demonstrated that the approach to estimate the HB strength parameters based on the GSI strength scaling equations (called the ‘GSI strength equations’) tends to underestimate the confined peak strength of highly interlocked jointed rock masses (i.e. GSI > 65), where the rock mass is often non-persistently jointed, and the intact rock blocks are strong and brittle. The estimation of the confined strength of such rock masses is relevant when designing mine pillars and abutments at great depths, where the confining pressure is high enough to prevent block rotation and free sliding on block boundaries. In this article, a grain-based distinct element modeling approach is used to simulate jointed rock masses of various degrees of interlock and to investigate the influences of block shape, joint persistence and joint surface condition on the confined peak strengths. The focus is on non-persistently jointed and blocky (persistently jointed) rock masses, consisting of hard and homogeneous rock blocks devoid of any strength degrading defects such as veins. The results from this investigation confirm that the GSI strength equations underestimate the confined strength of highly interlocked and non-persistently jointed rock masses. Moreover, the GSI strength equations are found to be valid to estimate the confined strength of persistently jointed rock masses with smooth and non-dilatant joint surfaces.     

围压卸载速度对岩石动力强度与破碎特性的影响

利用带轴向静压和围压装置的霍普金森压杆设备,对砂岩在不同围压卸载条件下的动态力学性能进行试验研究,即保持轴压和冲击条件不变,改变围压卸载速度的动静组合冲击试验,着重研究了围压卸载速率对岩石动态强度及损伤的影响。实验结果表明：在仅改变围压卸载速度条件下,当卸载速度在 0.5 ～ 10 MPa/s 范围内变化时,砂岩动态抗压强度、能耗密度随围压卸载速度增大而降低;破坏块度分维数则呈现出随围压卸载速度增大而增大。但当卸载速度增大到 200 MPa/s 时,其动态抗压强度、能耗密度反而增加,而破坏块度分维数则降低。     

Responses of jointed rock masses subjected to impact loading

Impact-induced damage to jointed rock masses has important consequences in various mining and civil engineering applications. This paper reports a numerical investigation to address the responses of jointed rock masses subjected to impact loading. It also focuses on the static and dynamic properties of an intact rock derived from a series of laboratory tests on meta-sandstone samples from a quarry in Nova Scotia, Canada. A distinct element code (PFC2D) was used to generate a bonded particle model (BPM) to simulate both the static and dynamic properties of the intact rock. The calibrated BPM was then used to construct large-scale jointed rock mass samples by incorporating discrete joint networks of multiple joint intensities into the intact rock matrix represented by the BPM. Finally, the impact-induced damage inflicted by a rigid projectile particle on the jointed rock mass samples was determined through the use of the numerical model. The simulation results show that joints play an important role in the impact-induced rock mass damage where higher joint intensity results in more damage to the rock mass. This is mainly attributed to variations of stress wave propagation in jointed rock masses as compared to intact rock devoid of joints.     

随机节理岩体变形与强度参数及其尺寸效应的数值模拟研究

节理岩体力学参数及其尺寸效应一直以来都是岩体研究的热点和难点,但对于基于结构面网络模型进行数值模拟的研究尚未见报道。笔者以小湾坝基卸荷岩体为例,在对现场节理进行大量统计的基础上,分析出节理特征值的分布函数,再运用蒙特卡罗方法建立了其结构面网络模型。在此基础上,利用编制的接口程序和现有的FLAC3D岩土分析软件,实现了对随机节理结构面网络模型的不连续位移数值模拟。模拟结果表明:小湾坝基卸荷岩体变形模量与岩体尺寸的关系服从负指数分布,而强度参数与岩体尺寸的关系基本服从负幂函数分布,其结果与现场斜面载荷试验及经验评估参数结果较为接近。     

岩体工程与岩体力学仿真分析——各向异性开挖卸荷岩体力学研究

概述了岩体工程与岩体力学研究现状 ,讨论了现理论研究成果与岩体工程实际监测资料不相吻合的问题。分析其主要原因 ,是现岩体力学研究理论模型与岩体工程实际力学模型不相吻合所致。故应严格根据岩体工程实际力学动态相应进行岩体力学仿真分析 ,方可得到正确的分析成果。笔者曾提出“卸荷岩体力学”的概念 ,以归纳开挖卸荷岩体力学研究内容 ,已经高边坡和地下工程实例所验证 ,开挖卸荷岩体力学研究是岩体工程及其力学仿真分析的重要组成部分。     

节理岩体卸荷非线性力学特性研究

工程岩体根据其受力特性可以分为加载岩体和卸荷岩体,结合三峡工程永久船闸高边坡岩体,利用自行开发的三轴试验设备进行研究,根据几何和重力相似、材料力学性能相似、岩体结构相似、边界力相似、开挖过程模拟相似,由重晶石粉、铁粉、石膏、水等制作尺寸为250 mm×250 mm×250 mm的试件,试件的几何比尺选择为CL=3,9,27,81;并对几何比尺为27的试件制作含有与船闸轴线相垂直的卸荷方向成8°,36°,52°,82°,90°的结构面。对节理岩体的加卸荷应力–应变关系、卸荷岩体(应力–应变关系、抗拉强度、变形模量)的各向异性、卸荷岩体(抗拉强度、抗压强度、泊松比、变形模量)的尺寸效应、卸荷岩体的流变特性、卸荷岩体的强度准则进行试验研究。研究结果表明,不同结构面方向对岩体的卸荷作用明显;岩体的抗压强度、抗拉强度、变形模量、泊松比以及岩体的各向异性等均随着尺寸的加大而降低;岩石受拉的流变特性与岩石所受的拉应力大小直接有关;得出Hoek-Brown准则所描述的岩体强度关系曲线中的岩体材料常数m,s值。     

节理岩体正交各向异性等效强度参数研究

将节理裂隙视为岩体的损伤,利用岩体裂隙网络模拟技术、损伤力学和节理张量理论对等效抗剪强度参数(即黏聚力和摩擦系数)进行了研究。在岩体损伤力学研究成果的基础上,研究了包含多组节理裂隙的岩体在空间任意截面上损伤变量的近似计算方法;以损伤变量作为加权系数,将岩块和结构面抗剪强度参数的加权平均值作为岩体等效强度参数;根据岩体在各空间截面上的等效抗剪强度参数计算成果,将岩体抗剪强度参数等效为正交各向异性变化的抗剪强度参数;编制相应的计算程序,通过计算实例验证了研究成果和计算程序的正确性。     

牙根水电站右岸1号松动体削坡减载方案研究

通过对松动体地质情况及滑移模式的研究,以蓄水＋地震工况来确定牙根水电站右岸1号松动体的削坡减载方案,结果表明,松动体开挖平台高程为2565m,开挖边坡最好选用预应力锚索支护。     

Flow analysis of jointed rock masses based on excavation-induced transmissivity change of rough joints

Underground excavation can induce significant deformation of pre-existing joints in rock mass. Due to the sliding and opening of the joints, consequent changes in the flow characteristics of a jointed rock mass would be anticipated. In the present work, a number of numerical techniques are employed and combined in order to evaluate the excavation-induced changes in the flow properties of a jointed rock mass. These are represented by the Micromechanics-Based Continuum (MBC) model analysis (FE excavation analysis in a jointed rock mass), and FracMan/Mafic package (FE flow and transport analysis in the discrete network of joints). A separate computational module connecting these two codes is incorporated to modify initially imposed transmissivities into the excavation-induced ones. The effect of excavation on the flow properties is evaluated by including these excavation-induced transmissivity changes of individual joints in the FE flow analysis. The excavation-induced transmissivities are calculated by the numerical and analytical techniques developed for flow through a single rock joint. The calculation of the excavation-induced transmissivity involves the distributions of shear displacements and normal stresses around the excavation, and implicitly takes into account the effect of surface geometric roughness. A test simulation for a deep underground repository is performed to illustrate the typical results predicted in the proposed approach.     

断续节理岩体动态疲劳损伤研究

分析了断续节理岩体动态疲劳损伤的复杂性,阐明了疲劳损伤研究的近似处理方法。基于剩余应变强度理论和线性退化准则讨论了断续节理岩体动态疲劳损伤累积过程。研究了岩体破裂概率与疲劳损伤的等效性,建立了疲劳损伤变量与分形维数间的定量关系。最后通过动态疲劳实验验证了结论的正确性。     

Strength of massive to moderately jointed hard rock masses

The Hoek-Brown(HB) failure criterion and the geological strength index(GSI) were developed for the estimation of rock mass strength in jointed and blocky ground where rock mass failure is dominated by sliding along open joints and rotation of rock blocks. In massive, veined and moderately jointed rock in which rock blocks cannot form without failure of intact rock, the approach to obtain HB parameters must be modified. Typical situations when these modifications are required include the design of pillars,excavation and cavern stability, strainburst potential assessment, and tunnel support in deep underground conditions(around s1/s ci 0.15, where s1 is the major principal compressive stress and s ciis the unconfined compressive strength of the homogeneous rock) in hard brittle rocks with GSI ! 65. In this article, the strength of massive to moderately jointed hard rock masses is investigated, and an approach is presented to estimate the rock mass strength envelope using laboratory data from uniaxial and triaxial compressive strength tests without reliance on the HB-GSI equations. The data from tests on specimens obtained from massive to moderately jointed heterogeneous(veined) rock masses are used to obtain the rock and rock mass strengths at confining stress ranges that are relevant for deep tunnelling and mining;and a methodology is presented for this purpose from laboratory data alone. By directly obtaining the equivalent HB rock mass strength envelope for massive to moderately jointed rock from laboratory tests,the HB-GSI rock mass strength estimation approach is complemented for conditions where the GSIequations are not applicable. Guidance is also provided on how to apply the proposed approach when laboratory test data are not or not yet available.     

裂隙岩体卸荷渗透规律试验研究

边坡开挖等岩体工程使得岩体形成卸荷作用,同时引起岩体中地下水性态的改变。水库蓄、放水使库岸边坡产生加载、卸荷效应,库岸边坡的稳定性受到影响。这都涉及到有关卸荷-渗流问题,因此研究裂隙岩体卸荷渗透规律具有重要意义。文章通过裂隙岩体的卸荷-渗流试验,探讨了裂隙岩体的渗透系数在卸荷过程中的变化规律,不仅揭示了裂隙岩体渗透系数与卸荷量的近似双曲线关系,还验证了裂隙岩体在加载、卸荷过程中渗透系数的迟滞现象。同时从理论上推导了裂隙岩体卸荷量与渗透系数之间的关系式,并对式中的试验系数进行了优化计算,其计算结果与试验结果吻合较好。     

船闸边坡节理岩体锚固效应的模型试验研究

通过室内相似材料模型块试验,研究了在不同的布锚参数下三峡船库高边坡节理岩体的抗压强度、弹性模量、泊松比及扩容特性等力学性质的变化规律,得出了一些有益的结果。     

高围压卸荷条件下横观各向同性岩体变形破坏与能量特征研究

 为揭示石英云母片岩变形及能量特征,针对平行片理和垂直片理方向的试件,基于MTS815岩石力学试验平台开展不同围压下的卸荷试验,分别从体积变形系数、能量比、能量变化率、能量应力增量比等方面系统研究高围压卸荷条件下石英云母片岩变形破坏特征及能量演化规律。结果表明：平行组试件径向变形发育能力及各特征应力量值均高于垂直组;其能量演化规律具有显著的围压效应,2组试件能量特性差异明显;与垂直组相比,平行组试件峰前、峰后应变能变化率较低且高围压下裂隙发育及塑性变形程度更高;提出能量应力增量比以表征试件能量变化对卸荷程度的敏感性,2组试件峰前能量应力增量比均随围压的增加而增加,但峰后弹性能应力增量比几乎不受初始围压的影响,垂直组峰前、峰后弹性能应力增量比和耗散能应力增量比量值均大于平行组。