Modification of rock failure criteria considering the RMR caused by joints

The aim of this study is to present a modification of the failure criteria of rock masses, separately considering the effect that the Bieniawski’s rock mass rating (RMR) has due to joints, as well as the RMR linked to compressive strength of the mass rock. This modification can be applied to three of the already existing criteria: that of Bieniawski–Yudhbir–Kalamaras, that of Sheorey, and that of Hoek–Brown, comparatively analysing the effects of the three modifications that have been proposed. The new, modified criterion will be validated with new data obtained in a marble mine exploited by means of rooms and pillars. The values observed and measured in the mine are compared to those obtained through numerical modelling of the pillars, using the Análisis Lagrangiano de Medios Continuos, Lagrangian Analysis of Continuous Media (ALMEC) program. Finally, several conclusions related to the application of these rock failure criteria to the analysis of mining excavation of rooms and pillars will be proposed.     

一种基于块体化程度理论的裂隙岩体巷道顶板稳定性分级方法研究

岩体完整性是进行巷道顶板稳定性分级的一个重要指标,当前分级方法均是从一维角度对岩体结构进行描述,不能全面刻画出三维空间上顶板围岩的完整性。针对这一缺陷,引入裂隙岩体块体化程度理论,以块体化程度代替常规标准中表征岩体完整性的岩体质量RQD值和节理间距两项子指标,开展裂隙岩体巷道顶板稳定性分级研究,创新形成了一种适用于裂隙岩体顶板稳定性分级的BT分级方法。以块体百分比和块体体积曲线为基本依据,构建出裂隙岩体巷道顶板围岩块体化程度的解算流程;运用AHP法对稳定性影响因素权重进行了排序,制定出稳定性分级方法与标准。以铜坑矿92号矿体裂隙岩体试验区巷道顶板结构面调查数据和岩石力学参数为基础,运用传统分级方法RMR法和BT法分别对各试验区巷道顶板稳定性进行评价,对两种分级结果进行比较分析,结果表明：与传统的RMR法相比,BT法在稳定性描述、分级准确性和安全管理指导作用等方面更为优越,更能够客观真实地反映出裂隙岩体巷道顶板稳定性。研究成果可为复杂裂隙岩体条件下的巷道顶板安全分级与管理提供更为可靠的科学依据。     

基于修正RMR法评价体系的滨海深部开采矿山岩体质量评价

对深部开采矿山岩体进行质量评价时, RMR体系在考虑深部岩体质量影响因素以及评价指标评分值确定等方面存在不足之处。首先利用连续性细化计算方法对传统RMR法中岩石单轴抗压强度、RQD、节理间距、地应力等指标进行了修正, 得到了评价指标与其评分值之间的拟合回归曲线以及连续性方程, 其次, 在深入分析不良地质因素、深部采矿工艺及其对岩体质量影响机制的基础上, 提出爆破震动影响系数及采场暴露面积两个新评分项并建立了M-IRMR体系, 最后, 借助该体系对三山岛金矿深部采掘工程岩体质量进行了评价。研究对于深部矿山岩体工程的稳定性评价具有一定的指导与借鉴意义。     

Estimation of the rock mass deformation modulus using a rock classification system

It is often difficult to directly obtain specific design parameters of interest. In these situations, estimation based on empirical correlations is an alternative. The deformation modulus of a rock mass, which is important to know for engineering projects, is measured by in situ tests, such as plate bearing, flat jack, pressure chamber, borehole jacking and dilatometer tests. Nevertheless, these in situ tests are expensive, time consuming and sometimes even impossible. Many attempts have been made to estimate the E modulus using easy-to-obtain parameters of a rock mass. This paper reviews previous studies and the equations that have been developed. In addition, this study presents a new relation developed using a database of 82 dilatometer test results gathered from two dam sites and a tunnel site. Statistical analyses were performed to correlate accessible rock parameters with measured E modulus values from in situ tests. Knowing that discontinuity characteristics and the strength of rock materials are the most important contributors to rock deformability, the focus was on identifying parameters that are affected by the mentioned properties. Among the tested parameters, RMR (Rock Mass Rating) showed the best correlation with the E modulus. Statistical analyses resulted in a new empirical equation that has an acceptable estimation ability.     

Empirical and numerical analyses of support requirements for a diversion tunnel at the Boztepe dam site, eastern Turkey

This paper presents the engineering geological properties and support design of a planned diversion tunnel at the Boztepe dam site that contains units of basalt and tuffites. Empirical, theoretical and numerical approaches were used and compared in this study focusing on tunnel design safety. Rock masses at the site were characterized using three empirical methods, namely rock mass rating (RMR), rock mass quality (Q) and geological strength index (GSI). The RMR, Q and GSI ratings were determined by using field data and the mechanical properties of intact rock samples were evaluated in the laboratory. Support requirements were proposed accordingly in terms of different rock mass classification systems. The convergence–confinement method was used as the theoretical approach. Support systems were also analyzed using a commercial software based on the finite element method (FEM). The parameters calculated by empirical methods were used as input parameters for the FEM analysis. The results from the two methods were compared with each other. This comparison suggests that a more reliable and safe design could be achieved by using a combination of empirical, analytical and numerical approaches.     

高放废物处置北山预选区地表岩体结构与岩体质量相关性及其应用研究

岩体工程质量是影响高放废物地质处置（HLW）工程长期稳定性和安全性的关键因素,也是处置库场址比选的重要依据。在地表岩体节理调查统计的基础上,采用RMR(relative metabolic rate)分级方案,探讨北山高放废物处置预选区内以花岗岩为主体围岩的岩体质量与岩体结构的对应特征,建立结构面间距D与RMR岩体质量总评分值之间的定量关系,对北山预选区芨芨槽地表岩体质量分布进行研究。研究结果表明,RMR与D值的点群分布具有扇形发散的正相关特征,随D值的增大,RMR亦呈增长趋势,但低级序岩体结构与岩体质量比高级序岩体表现出更好的对应关系。研究认为,选用RMR与D的点群中心线对应的线性方程评价花岗岩候选区的岩体质量可达到快速评价岩体质量、查明各级岩体空间分布特征的目的,同时也便于对不同候选场区进行大范围岩体质量对比。分析结果显示,北山芨芨槽预选地段BS16钻孔周边3 km2范围内主要以Ⅰ、Ⅱ级岩体为主,岩体质量总体较好且分布相对较为均匀。     

Strain-dependent Fluid Flow Defined Through Rock Mass Classification Schemes

Summary ?Strain-dependent hydraulic conductivities are uniquely defined by an environmental factor, representing applied normal and shear strains, combined with intrinsic material parameters representing mass and component deformation moduli, initial conductivities, and mass structure. The components representing mass moduli and structure are defined in terms of RQD (rock quality designation) and RMR (rock mass rating) to represent the response of a whole spectrum of rock masses, varying from highly fractured (crushed) rock to intact rock. These two empirical parameters determine the hydraulic response of a fractured medium to the induced-deformations. The constitutive relations are verified against available published data and applied to study one-dimensional, strain-dependent fluid flow. Analytical results indicate that both normal and shear strains exert a significant influence on the processes of fluid flow and that the magnitude of this influence is regulated by the values of RQD and RMR.     

隧洞围岩分类与洞径和超欠挖之间的关系研究

岩体的地质结构特征是影响隧洞围岩超欠挖的主要因素,正确评价岩体的质量,对岩体进行分类,并研究岩体质量与隧洞超欠挖之间的关系对分析和预测隧洞超欠挖具有重要的意义。对隧洞围岩的RMR分类和Q分类与超欠挖之间的关系进行了详细研究,研究了在同类岩体条件下不同开挖洞径与隧洞超欠挖之间的关系,并由此建立了RMR分类和Q分类之间的关系,得出围岩的RMR分类和Q分类与隧洞超欠挖呈线性关系和对数线性关系,根据超欠挖建立起来的RMR分类和Q分类之间的关系比较符合工程实际。最后研究了超欠挖与围岩分类及洞径之间的复相关关系。     

Improved RMR Rock Mass Classification Using Artificial Intelligence Algorithms

Rock mass classification systems such as rock mass rating (RMR) are very reliable means to provide information about the quality of rocks surrounding a structure as well as to propose suitable support systems for unstable regions. Many correlations have been proposed to relate measured quantities such as wave velocity to rock mass classification systems to limit the associated time and cost of conducting the sampling and mechanical tests conventionally used to calculate RMR values. However, these empirical correlations have been found to be unreliable, as they usually overestimate or underestimate the RMR value. The aim of this paper is to compare the results of RMR classification obtained from the use of empirical correlations versus machine-learning methodologies based on artificial intelligence algorithms. The proposed methods were verified based on two case studies located in northern Iran. Relevance vector regression (RVR) and support vector regression (SVR), as two robust machine-learning methodologies, were used to predict the RMR for tunnel host rocks. RMR values already obtained by sampling and site investigation at one tunnel were taken into account as the output of the artificial networks during training and testing phases. The results reveal that use of empirical correlations overestimates the predicted RMR values. RVR and SVR, however, showed more reliable results, and are therefore suggested for use in RMR classification for design purposes of rock structures.     

矿柱安全留设尺寸的宽度折减法与应用

从岩石强度理论出发,提出房柱式开采中矿柱安全留设尺寸的宽度折减法思想,通过不断折减矿柱宽度,研究矿柱由稳定状态向临界失稳状态演化过程,从而得到矿柱的临界宽度,引入矿柱安全系数,获得矿柱安全留设尺寸。采用宽度折减法对磨坊矿3#井房柱法开采矿柱安全留设尺寸进行研究,获得不同矿房跨度下矿柱的安全留设宽度。将宽度折减法得到的安全矿柱宽度与Lunder经验公式比较,研究发现,宽度折减法得到的安全矿柱宽度和Lunder经验公式的计算结果较为吻合且偏安全。结合磨坊矿3#井的开采条件和矿柱宽度折减法分析结果,确定矿房基本参数为：矿房跨度为13 m左右,矿柱宽度为5.0～5.5 m。通过对磨坊矿3#井采空区上覆岩层移动规律的监测,发现岩层相对稳定,地表沉降量控制在120～150 mm之间,用宽度折减法分析得到的矿房基本参数是合理的。     

A hybridized numerical and regression method for estimating the minimum rock pillar width of twin circular tunnels

Twin tunnels can be used for many applications. Interaction between two tunnels is an important problem in tunnel engineering that should be studied specially. Numerical investigations are well adapted to field data and numerical methods can be used in design of rock pillar of twin circular tunnels. So far, no relationship has been provided to estimate the minimum stable rock pillar width. In this paper, the interaction between twin circular tunnels has been studied using 2D finite element analysis. To do this, a great number of twin tunnels were modeled in Phase2 software with different conditions of rock mass (RMR value) and depth of tunnel. Models were analyzed and minimum stable rock pillar width was determined. This process was repeated for three different ratios of K (ratio of horizontal stress to vertical stress, 0.5, 1, and 1.5). Finally, according to the linear and nonlinear regression methods, the best merit function was fitted to result of numerical analysis. Then, new approximate formula was proposed to estimate the minimum rock pillar width according to RMR value and depth of twin circular tunnels with different K values. The formulae are very accurate (coefficient of correlation equals to minimum 0.96) that can be used for estimating the minimum rock pillar width of twin circular tunnels.     

某电站地下厂房围岩质量综合分级

在大量现场调查、统计资料基础上，利用国际上通用的RMR分类、Q系统分类及我国的水电围岩分类方案，对某电站地下厂房围岩进行了岩体质量分级。三种围岩分类结果具有良好的一致性，围岩质量较好。     

会泽铅锌矿6号矿体稳定性工程地质研究

为查明会泽铅锌矿的岩体工程地质条件,评价各岩组的稳定性,在收集和整理原有资料的基础上,对6号矿体回采区段的岩体工程地质条件进行了详细调查和测试,采用RMR和Q系统分级方法确定了各岩组的级别,根据试验参数分析了钻孔岩芯饼化现象产生的原因,系统地论证了采区的岩体工程地质条件,为选择合理的采矿方法提供了依据.     

玲珑金矿深部应力分析及岩爆防治措施研究

通过对玲珑金矿深部岩石的循环加卸载试验、单轴和三轴刚性试验以及三维数值模拟计算,从整体上揭示了玲珑金矿岩石内聚集较高弹性应变能和深部岩体中分布较大弹性能的现象,并且这些弹性能释放具有很高的冲击特性。结合多种理论判断岩爆准则,得出玲珑金矿深部开采具有潜在的强岩爆可能性,并且岩爆总体上讲是可以预测的。同时,根据现场实际施工情况,提出了相应地防止岩爆发生的对策和安全措施。     

某水电站地下厂房岩体质量分级研究

根据某水电站地下厂房各勘探平硐现场统计的基础数据,采用RMR分类、Q系统法、水电系统分类法(HC法)、BQ法对地下厂区围岩岩体质量进行了分析评价,然后综合4种方法的评价结果,得到了各硐段的综合岩体质量类别,使这4种分类法相互补充、相互验证,达到综合确定围岩类别的目的,以此作为围岩稳定性分类的基础.此外,还对不同方法所得的评价结果进行了相关性分析.     

Prediction of surface crown pillar stability using artificial neural networks

A relatively novel technique, artificial neural networks (ANN), is used in predicting the stability of crown pillars left over large excavations. Data for the training and verification of the networks were obtained from the literature. Four artificial networks, based on two different architectures, were used. The networks used different numbers of input parameters to predict the stability or failure of crown pillars. Multi‐layer perceptron networks using mine type, dip of orebody, overburden thickness, pillar thickness, pillar length, stope height, backfill height, Rock Mass Rating (RMR) of the host rock and RMR of the orebody showed excellent performance in training and verification. Adding three more variables, namely pillar width, rock density and pillar thickness to width ratio, showed symptoms of over‐learning without degrading performance significantly. Radial basis function networks were capable of predicting crown pillar behaviour on the basis of few input functions. It was shown that mine type, dip and pillar thickness to width ratio can be used for a preliminary estimation of stability. Copyright © 2006 John Wiley & Sons, Ltd.     

Influence of Rock Mass Parameters on the Performance of a TBM in a Gneissic Formation (Varzo Tunnel)

Summary The paper analyses the influence of rock mass quality on the performance of a double shield TBM in the excavation of a tunnel in a gneiss formation which is characterized by high strength and low fracture intensity.As full observation of the rock conditions was prevented by the use of segmental lining, a geomechanical survey of the face was performed during maintenance downtime and the observed conditions were correlated with the machine performance parameters for that same day. A statistical analysis of the data shows that penetration rate correlates well with a slightly modified RMR index (in which the influence of the water conditions and joint orientation were discounted), but the most important factor is by far the partial rating of the RMR classification related to joint spacing only. However in tunnels characterized by greater variability in rock strength and joint conditions, it could be worthwhile using the complete RMR index.Given the toughness of the rock, failure of the cutter bearings and supports were a frequent occurrence during excavation. Owing to this factor the influence of rock quality on the rate of advance was found to be weak and the correlation more scattered.The results obtained for the Varzo tunnel were compared with those relative to other tunnels in granitic rocks and found to be in good agreement. However the relationships obtained should be considered valid only for this type of rock; machine behaviour could be found to be markedly different in other rock types, even where rock material strength and joint frequency are the same.     

基于Hoek-Brown经验公式的岩体稳定性可靠度分析

为消除因用Hoek-Brown经验公式的中间变量而导致评估的稳定性概率产生累积误差,提出岩体稳定性可靠度应直接由基本变量入手来评估.简要介绍Hoek-Brown经验公式评估力学参数方法后,根据微元体应力定义了单元安全系数,建立了包含Hoek-Brown经验公式基本变量在内的功能函数.选用了Rosenbleuth点估计法评估单元安全系数的概率特征值,介绍了与有限元法结合计算稳定性可靠度的基本流程.对一开挖边坡稳定性可靠度计算分析表明,计算结果与边坡实际发生的破坏特征一致.建议的方法可方便地用于边坡、地基和地下洞室中岩体稳定性的可靠度评价.     

基于广义Hoek-Brown准则的岩体等效强度

为了更方便地求出岩体的等价粘聚力C和摩擦角φ,基于Hoek-Brown准则与RMR法岩体质量分级,求出不同RMR值下的C和φ,拟合出C和φ的折减系数关于RMR值的变化曲线。结果表明:对于质量等级较好的岩体,根据RMR值可以分别求得岩体的C和φ的折减系数,对已知岩石的C和φ值进行折减,求得岩体的C和φ值。岩体的C值随岩石单轴抗压强度成线性正相关,岩体的φ值不随单轴抗压强度变化而变化。C和φ的折减系数不随岩石的单轴抗压强度变化而变化,只与岩体RMR值有关。     

应用RMi法估算岩体变形模量

RMR法与Q法是国内外八、九十年代岩体质量和参数估算的常用方法,然而RMR法和Q法对质量较差的岩体不太实用,而RMi法是一种既适用于软岩又适用于硬岩的岩体质量评价和参数估算方法。本文在介绍RMi法基本原理的基础上,对贵州省鱼简河水库坝基岩体变形模量进行确定。