Rock Mass Classification Systems Research Articles

Combining the RMR, Q, and RMi classification systems

The main rockmass classification systems make use of similar rockmass parameters. Therefore, the input parameters in three of the systems can be combined into a set of common parameter tables. This enables the ground quality to be found directly in these systems from characterization of only one set of observations. Thus, the estimated rock support found in one system can easily be compared with and checked in the other systems.

An Integrated Numerical Modelling–Discrete Fracture Network Approach Applied to the Characterisation of Rock Mass Strength of Naturally Fractured Pillars

Naturally fractured mine pillars provide an excellent example of the importance of accurately determining rock mass strength. Failure in slender pillars is predominantly controlled by naturally occurring discontinuities, their influence diminishing with increasing pillar width, with wider pillars failing through a combination of brittle and shearing processes. To accurately simulate this behaviour by numerical modelling, the current analysis incorporates a more realistic representation of the mechanical behaviour of discrete fracture systems. This involves realistic simulation and representation of fracture networks, either as individual entities or as a collective system of fracture sets, or a combination of both. By using an integrated finite element/discrete element–discrete fracture network approach it is possible to study the failure of rock masses in tension and compression, along both existing pre-existing fractures and through intact rock bridges, and incorporating complex kinematic mechanisms. The proposed modelling approach fully captures the anisotropic and inhomogeneous effects of natural jointing and is considered to be more realistic than methods relying solely on continuum or discontinuum representation. The paper concludes with a discussion on the development of synthetic rock mass properties, with the intention of providing a more robust link between rock mass strength and rock mass classification systems.

Rock slope stability assessment through rock mass classification systems

Over the last several decades, rock mass classification systems have been proposed in order that cuttings at high risk for failure be identified, and preventive measures be effectively prioritized. The present paper attempts a review of the systems in question, illustrating the main differences and similarities among them, which are focused on the types of failures considered and the factors involved. The reliability of these systems is discussed as well. Relatively, these systems contain factors which raise queries about their suitability or the manner by which they are attributed into them. Moreover, although a rock cut failure event presupposes the action of a triggering factor (e.g., earthquake, precipitation), rock mass classification systems, by omitting it, do not classify cuttings according to their actual hazard (potentiality) for failure. Groundwater, when it is not erroneously ignored, is taken into account as instability factor with limited effect upon the systems (<15%) and not as a triggering factor for failure. Additionally, a number of suggestions regarding rock mass classification systems are given. Relatively, it is recommended rock cuttings to be classified according to their failure hazard taking into account both their condition and the influence of triggering factors upon stability. Moreover, each type of failure should be examined independently, as each one of them is governed by specific instability factors. Finally, some recommendations concerning amalgamation of factors, the possible ways that water may trigger a failure and the quantification of the most common triggering factors for failure (earthquake and precipitation) are provided.

Application of rock mass classification techniques to weak rock masses: A case study from the Ruahine Range, North Island, New Zealand

Rock mass classification systems were first generated for use in engineering applications, but their potential for utilization in geomorphic studies has since been recognized. These techniques were mostly developed for hard rock environments, and questions remain about their applicability to weak rocks. Here, the applicability of three rock mass classification techniques (rock mass strength (RMS), rock mass rating (RMR), and slope mass rating (SMR)) to weak rock masses was analyzed. Techniques incorporated parameters such as uniaxial compressive rock strength, discontinuity condition and orientation, and groundwater ratings. Rock mass classification values were determined from 14 profiles sited on recently excavated road cuttings on the Saddle Road, in the Ruahine Range, North Island, New Zealand. This is an important transport route across the North Island’s axial ranges, with the road excavated into weak late Pliocene – Early Pleistocene mudstone. Mean slope and minimum slope angle were measured at each profile in concert with the rock mass classification schemes. The three classification techniques all appear to have limited usefulness given the subaerial conditions prevalent at the study site. It would appear that the relative weightings of the different parameters within the RMR, RMS, and SMR classification schemes would need modifying for weak rock masses, but the precise details of this are difficult to determine.

Safe rapid drifting – Support selection

Abstract Current drift advance rates in mining fall short of expectations with advances in drilling and blasting technologies. Quick access to orebodies improves their net present value (NPV). This is critical for block cave mining where several kilometers of drift network is initially required at high capital cost. Many mining companies are now planning block caving because of its long-term low production cost. This paper critically reviews the developments in tunnelling and mine drift development rates with advances in drilling and explosives technologies. Current drift support practice during development is also critically reviewed together with the rock mass classification systems. These reviews show that, while drilling and explosive technologies have drastically improved since 1850, current drift advance rates in the Canadian metalliferrous mining industry have either remained stagnant or dropped below the1960 advance rate levels and in comparison to advance rates in civil tunnelling. It is also established that a major cause for this stagnation is the use of long-term support in good ground conditions where only temporary support is required near-face for worker safety in the short-term. Long-term support takes up 46% of development cycle time. The paper presents a methodology for drift support design for underground hard rock conditions typically found in current mining practice in the Canadian Shield and discusses the rationale for optimizing ground support systems installed near-face during drift development. An improved Q-system called Q-star (Q∗) that accounts for discontinuous joints (rock bridges) and roughness of short joints in the rock mass is developed to more reliably estimate the self-support capacities of rock masses. It is recommended that construction damage be accounted for in the rock mass rating for safe support selection during development. A procedure is developed for the adjustment of Q∗ to account for construction damage. Perimeter blasting is recommended as pre-requisite for rapid drift development in order to minimize construction damage, reduce support demand and scaling and mucking times. A support matrix is presented based on rock mass quality and stress level for safe rapid drift development. Two case histories in active mines are presented to validate the procedure. The methodology is applicable to stress-induced damage and may not apply where complete relaxation occurs. While the procedures presented are focused on typical conditions in the Canadian Shield underground mines, they may be applicable in civil engineering tunneling and other underground mines where drill-and-blast is used as the excavation method.

A specific upscaling theory of rock mass parameters exhibiting spatial variability: Analytical relations and computational scheme

In this paper the representation of geological conditions in a numerical simulation model is considered. By the expression “geological conditions” we mean the 3D volume geometry of the geological formations, the spatial variability exhibited by the rock parameters inside each of these geological volumes and the necessary upscaling of the rock deformability and strength parameters that are determined in the laboratory from cores collected in the field. A specific theory is outlined of how to go from laboratory tests, geological information and field measurements and observations to the full-scale numerical or “ground model” that includes, apart from initial and boundary conditions and ground water, the rock constitutive laws and associated material parameters for use in simulation models. The term “specific” used in the title of this paper stems from the fact that other possible approaches for the same problem may be applied; i.e. empirical rock mass classification systems, explicit modeling of joints in the rock by the distinct element or finite element methods, homogenization techniques, etc. The method used to take into account the spatial variability of rock mass properties by virtue of Geostatistical Theory and 3D modeling tools is also outlined, with an example case study.

Analysis of rock–support interaction using numerical and multiple regression modeling

This paper presents the results of performance analysis on the support systems recommended by the RMR (rock mass rating) rock mass classification system. Rock–support interaction is analyzed by means of both numerical and multiple regression modeling. Five different rock mass conditions were assumed from very poor to very good, each representing varied RMR. Extensive computer simulations were conducted to investigate the stresses, displacements, and yielded zones around a circular opening excavated at different depths, and under different rock conditions. The performances of the RMR recommended support systems were analyzed and the stability of excavation was evaluated. Multiple regression modeling was conducted to assess the relationship between support pressure, depth, and tunnel deformation for different rock conditions. Regression models were derived and the response surfaces were constructed, showing the interaction between tunnel depth, support pressure, and tunnel displacement. Using the derived models and the constructed response surfaces, engineers are able to describe the support performance and assess the practical range of expected deformation for their specific site conditions. Also, the approach presented can be used for any special case.

Engineering geological investigations and the preliminary support design for the proposed Ordu Peripheral Highway Tunnel, Ordu, Turkey

This paper presents engineering geological investigations and the tunnel support design for the Boztepe tunnel of the Ordu Peripheral Highway located in northeast Turkey. In order to characterize the rock masses in Boztepe Tunnel which mainly consist of flysch (mostly alternation of sandstone, marl and siltstone) and pyroclastics (agglomerate and tuff), engineering geological investigations have been carried out in three stages as surface, subsurface and laboratory investigations. Rock mass classification systems (Geomechanics Classification System, RMR; Norwegian Geotechnical Institution Q-system and Geological Strength Index, GSI) have been utilized through information obtained from engineering geological investigations. Sixteen boreholes with a total length of 1497 m have been drilled to assist and verify rock mass classifications. Approximately seventy five rock samples have been obtained for rock mechanics tests. The information provided from all the engineering geological investigation stages has been handled in the characterization of the rock masses at the tunnel elevation. In an attempt to check the validity of empirical tunnel supports of the various rock mass classification systems, stress analysis around the tunnel opening has been executed by the 2D finite element analysis program, Phase 2 where rock mass data obtained through the rock mass classification systems have been utilized as input data. In these analyses, the empirically proposed support systems have been found to be successful to prevent further deformations around the tunnel openings.

Discussion on article titled “Use and misuse of rock mass classification systems with particular reference to the Q-system” by Palmstrom and Broch [Tunnelling and Underground Space Technology, 21 (2006) 575–593

Discussion on article titled “Use and misuse of rock mass classification systems with particular reference to the Q-system” by Palmstrom and Broch [Tunnelling and Underground Space Technology, 21 (2006) 575–593

Comparison of rock mass classification systems

The paper presents the comparison of the most widely-applied rock-mass classifications RMR and Q and a system developed by VNIMI in Russia. It has been shown that the results obtained from using these systems for the forecast of rock mass stability and selection of support types enjoy a satisfactory conformity.

Engineering geological appraisal of the rock masses and preliminary support design, Dorukhan Tunnel, Zonguldak, Turkey

This paper presents the results of engineering geological studies of the rock masses along a road tunnel. Rock mass qualities of the rock units along the tunnel were determined by means of Rock Mass Rating (RMR), Geomechanic Classification ( Q) system, Geological Strength Index (GSI), Rock Mass Index (RMi) and New Australian Tunneling Method (NATM). In order to determine tunnel stability, necessary support types and categories RMR, Q, RMi and NATM systems were employed as empirical tunnel support design methods. However, these empirical design guidelines for tunnel support based on rock mass classification systems failed to analyze the support performance. The performances of the proposed support systems were analyzed by means of numerical analysis, described in this paper. A 2D finite element analysis program was used as numerical method. The necessary rock mass parameters were obtained by means of rock mass classification systems.

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.

A correlation of four rock mass classification systems through their fabric indices

Four classification systems are investigated in this work, RMR, Q, GSI and RMi. The common parameters of these systems, which concern and characterize solely the rock mass, are those used for rating the rock structure and the joint surface conditions. Rock structure is quantified by the block size or the discontinuity spacing ratings ( BS) and the joint surface conditions are quantified by the joint conditions ratings ( JC). A Rock Mass Fabric Index, denoted as F, may thus be defined as a scalar function of the components rock structure and joint conditions i.e., F = F ( BS , JC ) . All rock mass classification systems’ ratings are grouped together in a common Fabric Index chart. The validity of the chart is tested using data extracted from various projects. The use of the chart simplifies input, correlates rock mass classification systems and improves their utility.

A new approach for application of rock mass classification on rock slope stability assessment

The objective of this paper is to present a new rock mass classification system which can be appropriate for rock slope stability assessment. In this paper an evaluation model based on combining the Analytic Hierarchy Process (AHP) and the Fuzzy Delphi method (FDM) was presented for assessing slope rock mass quality estimates. This research treats the slope rock mass classification as a group decision problem, and applies the fuzzy logic theory as the criterion to calculate the weighting factors. In addition, several rock slopes of the Southern Cross-Island Highway in Taiwan were selected as the case study examples. After determining the slope rock mass quality estimates for each cases, the Linear Discriminant Analysis (LDA) model was used to classify those that are stable or not, and the discriminant functions which can determine failure probability of rock slopes were carried out by the LDA procedure. Afterward, the results may be compared with slope unstable hazards occurring actually, and then the relation and difference between them were discussed. Results show that the proposed method can be used to assess the stability of rock slopes according to the rock mass classification procedure and the failure probability in the early stage.

Rock support in hydropower projects of Nepal: case studies

The principal objective of rock support is to assist the rock mass to support itself. One common example is where the rock support system (e.g. rock bolts and shotcrete) actually becomes integrated with the rock mass. Rock support strengthens the rock mass surrounding an excavation by creating a reinforced zone, which maintains the integrity of the excavated surface, possesses sufficient flexibility to allow for the redistribution of stresses around the excavation, and has enough stiffness to minimise the dilation (opening) of discontinuities. Rock mass classification systems are used worldwide as a basis for tunnel support design. The Q and Rock Mass Rating systems have been extensively applied in rock support design on most of the hydropower projects in Nepal. Generic design guidelines based on rock mass classification systems cannot provide suitable rock support for every site. Therefore some modifications are necessary to suite the site-specific ground conditions including local rock mass and geological hazards.&#x0D; There are relatively few tunnels excavated in the tectonically active Nepal Himalaya. Large diameter tunnels in Nepal are commonly lined with concrete whereas recently smaller-diameter tunnels are either shotcrete-lined or left unsupported. "Leaky" lining has been used in most of the projects to avoid the heavy reinforcement needed to withstand the occasional very high external water pressures.

Rock Mass Classification Using Electrical Resistivity - an Analytical Study

Geophysical prospecting using electrical resistivity is one of the principal methods for subsurface exploration. However, the majority of such application methods are restricted to coarse descriptions of underground conditions. The Q-system is commonly used as a representative rock mass classification system in modern rock engineering. In this paper, electrical resistivity is related to the Q-system through theoretical analyses. The analyses are based on Coulomb's law and Gauss' law considering electrical characteristics of constituent parameters for rock mass classification such as joint thickness, joint condition, joint spacing, intact rock strength, and RQD. The results show that there is a strong correlation between electrical resistivity and rock mass classification.

Visualization of rock mass classification systems

A rock mass classification system is intended to classify and characterize the rock masses, provide a basis for estimating deformation and strength properties, supply quantitative data for mine support estimation, and present a platform for communication between exploration, design and construction groups. In most widely used rock mass classification systems, such as RMR and Q systems, up to six parameters are employed to classify the rock mass. Visualization of rock mass classification systems in multi-dimensional spaces is explored to assist engineers in identifying major controlling parameters in these rock mass classification systems. Different visualization methods are used to visualize the most widely used rock mass classification systems. The study reveals that all major rock mass classification systems tackle essentially two dominant factors in their scheme, i.e., block size and joint surface condition. Other sub-parameters, such as joint set number, joint space, joint surface roughness, alteration, etc., control these two dominant factors. A series two-dimensional, three-dimensional, and multi-dimensional visualizations are created for RMR, Q, Rock Mass index RMi and Geological Strength Index (GSI) systems using different techniques. In this manner, valuable insight into these rock mass classification systems is gained.

Estimation of Block Sizes for Rock Masses with Non-persistent Joints

Discontinuities or joints in the rock mass have various shapes and sizes. Along with the joint orientation and spacing, the joint persistence, or the relative size of the joint, is one of the most important factors in determining the block sizes of jointed rock masses. Although the importance of joint persistence on the overall rock mass strength has long been identified, the impact of persistence on rock strength is in most current rock mass classification systems underrepresented. If joints are assumed to be persistent, as is the case in most designs, the sizes of the rock blocks tend to be underestimated. This can lead to more removable blocks than actually exist in-situ. In addition, a poor understanding of the rock bridge strength may lead to lower rock mass strengths, and consequently, to excessive expenditure on rock support.

Electrical resistivity-based rock mass classification for tunnelling

Geophysical prospecting using electrical resistivity is one of the principal methods for subsurface exploration. However, the majority of such application methods are restricted to coarse descriptions of underground conditions. The Q-system is commonly used as a representative rock mass classification system in modern rock engineering because it properly captures the important characteristics of a rock mass. In this paper, electrical resistivity is related to the Q-system through theoretical analyses. The analyses are based on Coulomb's law and Gauss' law considering electrical characteristics of constituent parameters for rock mass classification such as joint thickness, joint condition, joint spacing, intact rock strength, and RQD. Analytical results are compared with experimental results. The comparison shows that the analytical results agree with the experimental results, and there is a strong correlation between electrical resistivity and rock mass classification. (A) This paper was presented at Safety in the underground space - Proceedings of the ITA-AITES 2006 World Tunnel Congress and the 32nd ITA General Assembly, Seoul, Korea, 22-27 April 2006. For the covering abstract see ITRD E129148. Reprinted with permission from Elsevier.

Use and misuse of rock mass classification systems with particular reference to the Q-system

Rock mass classification systems have gained wide attention and are frequently used in rock engineering and design. However, all of these systems have limitations, but applied appropriately and with care they are valuable tools. The paper describes the history of the Q-system that was introduced in 1974, and its later development. The individual parameters are analysed, and their relevance for the natural geological features they seek to simulate, is discussed. This applies to both the original application for assessing rock mass quality to estimate the extent of rock support, and the later attempts to make the method into a kind of general rock mass classification with many applications. This also includes the recently introduced Q TBM, which shall allow estimates of penetration and advance rate for TBM, and also the attempts to apply Q to express the effects of pre-grouting. It is concluded that the Q-system, used with full awareness of its limitations, may be applied for classification of the stability and support estimates of tunnels and rock caverns, preferably in jointed rocks. Applied here, it may be used for planning purposes. It is less useful for prescription of rock support during construction. It is not likely that Q is suitable to express the effects of pre-grouting. Q TBM is complex and partly misleading and is not recommended for use in its present form.