Rock Mass Classification Systems Research Articles

Comparisons of Evaluation Factors and Application Effects of the New [BQ]GSI System with International Rock Mass Classification Systems

The basic quality (BQ) system is regarded as the national rock mass classification system that can be appropriate for use in most types of rock engineering in China. Two underlying parameters that the uniaxial compressive strength (UCS) and the rock intactness index (KV) are taken into account to access the basic BQ value. However, The KV was usually measured by an indirect acoustic wave approach which often cannot reflected the actual conditions. In this study, a direct measured parameter KGSI is recommended to obtain by means of the GSI system to replace the original KV, and a new method [BQ]GSI expressed by the new parameter KGSI is proposed. In particular, a graphic method is also presented to determine rapidly and rationally the rock mass classification by the X, Y coordinates of the UCS and the KGSI. In order to further compare the evaluation results and application effects between the [BQ]GSI and the international rock mass classification systems, a comprehensive solution is carried out. First, the evaluation factors of rock mass qualities from all these system are classified according to three groups: the rock mass inherent parameters, external parameters, and construction parameters. Second, the correlations among these evaluation factors in the new [BQ]GSI system and the common international systems (i.e. RMR, Q, and RMi) were compared. And the formulas or charts among the three groups are presented. Finally, five hydropower underground excavations are chosen to analysis the comparison results of the [BQ]GSI system and the international common RMR, Q, or RMi systems. The applicability scope of these international RMR, Q, or RMi systems is also discussed in the context of China’s rock characteristics and geological stress conditions.

A Study on Rock Mass Classifications and Tunnel Support Systems in Unconsolidated Sedimentary Rock

This paper presents new valuable field data and a comprehensive approach to the determination of the rock mass classification and tunnel support systems for tunnels in unconsolidated sedimentary rocks as a special soil condition. The main objective of this study is to investigate and present the characteristics of the unconsolidated sedimentary rock by using the point load tests and slake durability tests. In addition, the appropriate rock mass classification and tunnel support system for the unconsolidated sedimentary rock tunnel are proposed, based on the results of experimental tests. The proposed rock mass classification and tunnel support system are validated through comparison against results from measuring the convergence of a tunnel under the construction. The proposed tunnel support system is appropriate for the unconsolidated sedimentary rocks, since the convergence factors, such as the maximum displacement and velocity of displacement, satisfy the criteria.

Applying rock mass classifications to carbonate rocks for engineering purposes with a new approach using the rock engineering system

Classical rock mass classification systems are not applicable to carbonate rocks, especially when these are affected by karst processes. Their applications to such settings could therefore result in outcomes not representative of the real stress–strain behavior. In this study, we propose a new classification of carbonate rock masses for engineering purposes, by adapting the rock engineering system (RES) method by Hudson for fractured and karstified rock masses, in order to highlight the problems of implementation of geomechanical models to carbonate rocks. This new approach allows a less rigid classification for carbonate rock masses, taking into account the local properties of the outcrops, the site conditions and the type of engineering work as well.

Geotechnical Characterization of Bukov Underground Research Facility

Bukov Underground Research Facility (Bukov URF) is designed to operate as a test site to assess the properties and behavior of the rock mass analogous to selected seven candidate sites in the Czech Republic. It is situated at a depth of about 600 m beneath Earth's surface, which corresponds with the proposed storage depth of the final locality for the national deep repository of high-level radioactive waste. Bukov URF, the construction of which has started in 2013, is situated in the southern part of the Rožná uranium deposit, about 40km NNW from Brno. The rock mass is composed of relatively monotonous rock sequences mainly represented by migmatized biotite paragneisses up to stromatic migmatites, amphibole-biotite to biotite-amphibole gneisses, and amphibolites. Based on the analysis of physical and mechanical properties, intact rocks in the studied area exhibit a high to very high strength and may be only locally affected by metasomatic alterations. The research activities focus on a complex geological and geotechnical characterization of the rock mass of interest, which is necessary for further in situ research. This paper briefly describes the main results of the current stage of geotechnical exploration and research works made there by the Institute of Geonics of the CAS. These works especially include: determination and evaluation of physical and mechanical properties of the rocks taken from the drift walls and from the boreholes during driving, calculation of rock mass quality based on selected index rock mass classification systems, determination of stress and strain state of the rock mass using the methods of hydrofracturing, Goodman Jack, strain gauge probe measurements, long-term periodical tensometric and convergence measurements, and evaluation of the effects of technical and mining-induced seismicity on the rock mass of interest.

Evaluating the Suitability of Existing Rock Mass Classification Systems for TBM Performance Prediction by using a Regression Tree

Existing rock mass classification systems, such as rock mass rating (RMR) are often used in many empirical design practices in rock engineering contrasting with their original application, i.e. estimation of TBM performance in various ground conditions. However, the use of RMR or similar classification systems in providing an accurate estimation of TBM penetration rate has had limited success due to the nature of the weights assigned to the input parameters. The results of many investigations on this topic have shown a weak correlation between TBM penetration rate and RMR. This limitation can be addressed by performing regression tree analysis which revises the weights assigned to input parameters to better represent influence of rock mass properties on TBM performance. This paper offers an overview of the impact of rock mass classification on TBM performance and introduces a new model based on regression tree using the input parameters of RMR system to predict the performance of hard rock TBMs. The results of the preliminary analysis show that the use of the proposed model can improve the accuracy of TBM performance estimates in various rock masses. This is based on the comparison between the estimated and actual rate of penetration of TBMs in two tunneling projects in igneous and sedimentary rocks. This study shows the potential of regression tree approach to offer more suitable rating of input parameters for this application, if sufficiently diverse database of machine performance is used in the analysis.

Rock Mass Classification System in terms of Practical Tunneling

Rock Mass Classification System in terms of Practical Tunneling

The effect of rock mass gradual deterioration on the mechanism of post-mining subsidence over shallow abandoned coal mines

In this study, the effect of gradual deterioration on the long-term stability of shallow abandoned room and pillar coal mines is investigated. The conventional Tributary Area Method is adopted and modified to take into account the rate of deterioration on the lifetime of pillars. Moreover, a simple quantitative approach is proposed to incorporate the effects of deterioration in numerical modelling. The suggested methods are then used to assess the stability of the shallow abandoned room and pillar coal mines around Dolphingstone village, UK. Results of this study indicate that the gradual deterioration plays a significant role in the long-term stability of shallow abandoned coal mines. The stand-up time of a room and pillar mining panel is also estimated based on the modified Q-system. A good agreement is observed between the results of numerical modelling and the rock mass classification system.

Correlation of the Rock Mass Rating (RMR) System with the Unified Soil Classification System (USCS): Introduction of the Weak Rock Mass Rating System (W-RMR)

Underground gold mines in Nevada are exploiting increasingly deeper ore bodies comprised of weak to very weak rock masses. The Rock Mass Rating (RMR) classification system is widely used at underground gold mines in Nevada and is applicable in fair to good-quality rock masses, but is difficult to apply and loses reliability in very weak rock mass to soil-like material. Because very weak rock masses are transition materials that border engineering rock mass and soil classification systems, soil classification may sometimes be easier and more appropriate to provide insight into material behavior and properties. The Unified Soil Classification System (USCS) is the most likely choice for the classification of very weak rock mass to soil-like material because of its accepted use in tunnel engineering projects and its ability to predict soil-like material behavior underground. A correlation between the RMR and USCS systems was developed by comparing underground geotechnical RMR mapping to laboratory testing of bulk samples from the same locations, thereby assigning a numeric RMR value to the USCS classification that can be used in spreadsheet calculations and geostatistical analyses. The geotechnical classification system presented in this paper including a USCS–RMR correlation, RMR rating equations, and the Geo-Pick Strike Index is collectively introduced as the Weak Rock Mass Rating System (W-RMR). It is the authors’ hope that this system will aid in the classification of weak rock masses and more usable design tools based on the RMR system. More broadly, the RMR–USCS correlation and the W-RMR system help define the transition between engineering soil and rock mass classification systems and may provide insight for geotechnical design in very weak rock masses.

Empirical rock mechanical site-descriptive modeling (RMSDM) for the Korea Atomic Energy Research Institute Underground Research Tunnel (KURT)

As part of master plan, when preparing to construct the second stage of the Korea Atomic Energy Research Institute Underground Research Tunnel (KURT-2), site investigations were carried out to characterize the rock mass and its related geophysical nature. The rock mass at the study site was divided into rock units depending on a rock type and fracture developments in rock. The rock mass quality for each rock unit was evaluated, using rock mass classification systems, such as Q, rock mass rating (RMR), and rock mass index (RMi). The mechanical properties of rock units were empirically estimated with associated rock mass classification systems, including deformation modulus, uniaxial compressive strength, and cohesion and friction angles. Ultimately, a rock mechanical site-descriptive model (RMSDM) covering the block size of 85 m × 120 m × 80 m was developed by combining the analysis of rock units. Rock block consists of granite, dike, and fault, being divided into six rock units, such as G1, G2, G3, D1, D3, and F3. G1 and D1 rock units were classified as good rock masses, and the rock mass quality of G2 is fair. G3 and D3 rock units were classified as poor rock masses, and the F3 rock unit was very poor. The mechanical properties of rock unit G1 and D1 were almost considered similar and best, and those of G2 were considered middle class. G3 and D3 rock units had poor mechanical properties and those of F3 were the worst. G1 occupies most of block volume, but other rock units were distributed as small portions. Two-dimensional distributions of rock mass from modeling and face mapping at the elevation of the tunnel excavation exhibited that predicted distributions well fit to those observed. Therefore, RMSDM will be of help with the geoscientific understanding of site investigation and designing of a site and construction of a site, similar to KURT-2, and ultimately, it will become a scientific base to future-related research and development projects of the Korea Atomic Energy Research Institute (KAERI).

해저터널 주변 그라우팅 보강암반의 탄성파 전달특성 평가

해저터널 시공 중 단층, 파쇄대 및 미고결층 등의 취약한 지반조건에서 일어나는 문제점을 극복하기 위해 시공 중 그라우팅을 진행한다. 암반에서 그라우팅은 주로 불연속면을 따라 주입되므로 절리의 분포, 거칠기 또는 폭과 같은 절리 인자들이 그라우팅 보강암반의 물성에 지대한 영향을 미친다. 해저터널 주변의 그라우팅 보강암반은 해저환경에서 정수압을 다 부담하여 장기적인 열화와 미세구조변화 및 균열 등이 발생하며 암반물성이 시간에 따라 변하므로 그라우팅으로 인한 해저터널 주변암반의 장기적인 거동평가가 요구된다. 본 연구에서는 실내실험을 통해 다양한 축 응력, 양생기간 및 절리조건에서 그라우팅 보강암반의 탄성파 전달특성을 분석하였고 국내에서 사용되는 다양한 암반분류법들의 탄성파 기준을 고려하여 그라우팅 보강암반의 보강정도를 탄성파 속도로 추론하였다. Grouting is frequently used before the construction of subsea tunnels to mitigate problems that can occur in weak ground zones such as joints, faults or unconsolidated settlements during construction. The grout material injected into rock mass often flows through the discontinuities present in the host rock and hence, joint properties such as its distribution, roughness and thickness greatly affect the properties of grouting-improved rocks. The grouting-improved zones near subsea tunnels are also subjected to high water pressures that can cause long-term weathering in the form of changes in grout microstructure and crack formation and lead to subsequent changes in ground properties. Therefore, an assessment method is needed to accurately measure changes in the grouting-improved zones near subsea tunnels. In this study, the elastic wave propagation characteristics in grouting-improved rocks were tested for various axial stress levels, curing time, joint roughness and thickness conditions under laboratory conditions and the results were compared with wave velocity standards in different Korean rock mass classification systems to provide a basis for inferring improvement in grouted rock-mass.

A discussion on the adjustment parameters of the Slope Mass Rating (SMR) system for rock slopes

Rock mass classification systems are common tools used in the design and construction of rock engineering. Numerous classification systems have been developed for rock slopes, of which the Slope Mass Rating (SMR) system is the most popular. Consequently, many rock slope classification systems have been derived from the SMR system. However, these systems are not good at determining the values of the two adjustment parameters F1 and F3, implying that the original SMR system may contain theory defects. In this paper, we propose some corrected methods for determining F1 and F3 and perform a series of analyses considering the three failure modes of rock slopes: plane, wedge, and toppling failures. The results of the discrepancy analysis from F1 illustrate that, with respect to each of the aforementioned three failure modes the calculated original SMR index is larger than, or equal to, the real value, and the designed slope is possibly in danger. The results of the discrepancy caused by the F3 illustrate that for each of the aforementioned three failure modes, the calculated original SMR index is smaller than, or equal to, the real value, and the designed slope might be conservative and not economical.

Assessing the ability of rock masses to support block breakage at the TBM cutter face

In order for tunnel boring machines to efficiently cut or break rock, it is necessary that the block of rock in contact with the cutter be adequately supported by the surrounding rock mass. This support is provided by the interlocking of blocks and the friction of the surfaces. If blocks are inadequately supported or become free without breakage the result can be jamming at the TBM face. Such blocky ground conditions are typically assessed according to the spacing and orientation of discontinuities (including joints) within the rock mass, typically using a rock mass classification system. In laboratory tests on cuttability or abrasivity of rocks, test samples are typically supported securely in a frame or jig. Numerical models of rock breakage also assume boundary conditions in which the sample is completely supported. Therefore the applicability of the results from laboratory and numerical studies depends on the same degree of support of blocks in the ground. The conditions required to adequately support a block for breakage are investigated and related to rock mass parameters, in particular, the three-dimensional patterns of discontinuities. A rock mass can be capable of providing adequate support to a block of rock such that the cuttability is adequately described by conventional methods. However, there are some rock mass conditions where support of blocks is not well developed, potentially resulting in otherwise unexpected poor TBM progress or jamming of TBM with loose blocks. Three-dimensional discontinuity patterns can be assessed using stereographic methods or borehole (α–β) methods. It is proposed that problematic conditions may occur where: two or more oblique (α between 20° and 70°) discontinuity sets are present (and over-represented relative to a uniform distribution); one or more of these discontinuity sets are dipping into the opening (β=180°±90°) and additional discontinuities (in sets or randomly oriented) are present to form complete tetrahedral wedge blocks.

Characterization of rock slopes through slope mass rating using 3D point clouds

Rock mass classification systems are widely used tools for assessing the stability of rock slopes. Their calculation requires the prior quantification of several parameters during conventional fieldwork campaigns, such as the orientation of the discontinuity sets, the main properties of the existing discontinuities and the geo-mechanical characterization of the intact rock mass, which can be time-consuming and an often risky task. Conversely, the use of relatively new remote sensing data for modelling the rock mass surface by means of 3D point clouds is changing the current investigation strategies in different rock slope engineering applications. In this paper, the main practical issues affecting the application of Slope Mass Rating (SMR) for the characterization of rock slopes from 3D point clouds are reviewed, using three case studies from an end-user point of view. To this end, the SMR adjustment factors, which were calculated from different sources of information and processes, using the different softwares, are compared with those calculated using conventional fieldwork data. In the presented analysis, special attention is paid to the differences between the SMR indexes derived from the 3D point cloud and conventional field work approaches, the main factors that determine the quality of the data and some recognized practical issues. Finally, the reliability of Slope Mass Rating for the characterization of rocky slopes is highlighted.

Empirical methods of calculating the mechanical parameters of the rock mass

The knowledge of the main mechanical constants of a rock mass (such as strength, deformability and the Poisson’s ratio) is one of the most important for rock engineering design on or in rock mass. Until now, several empirical relationships were determined for calculating these material constants based on both the quality of the studied rock mass (ie. RMR or GSI values) and the mechanical parameters of an intact rock. The goal of this paper is to review the empirical relationships between the mechanical properties of rock masses and the rock mass classification systems. The engineering properties involve not only the uniaxial compressive strength and deformation modulus of rock masses, but also Poisson’s ratio and tensile strength, among the others, which are of crucial for designing rock engineering structures. These different methods are compared and a general equation is determined in this paper. The presented expressions are yet to be tested with experimental data and empirical relationships should not replace in situ tests for final design.

Numerical Analysis for a Realistic Support Design: Case Study of the Komurhan Tunnel in Eastern Turkey

AbstractThe aim of this study was to highlight the importance of the numerical approach in realistic support design for tunneling. The Komurhan Tunnel, which is to be constructed between the Elazig–Malatya highway, located east of Elazig City in eastern Turkey, was selected as the application site of this study. The lithology of this area consists of Late Cretaceous–age ophiolitic rocks, known as Komurhan ophiolites. Field and laboratory studies were performed to determine the geotechnical properties of rock mass and intact rock materials. Empirical and numerical approaches were used, and the results were compared, focusing on tunnel design safety. The rock mass was classified in terms of the rock mass rating (RMR), rock mass index (RMi), Austrian tunneling method, and geological strength index rock mass classification systems, and then the support systems for the tunnel were determined accordingly. The support systems obtained from the classification systems were also analyzed using software based on the...

Assessment of a Modified Rock Mass Classification System for Rock Slope Stability Analysis in the Q-system

<p>This paper explores the applicability of a modified Q classification system and its component parameters for analysis and conclusion of site investigation data to estimate rock slope stability. Based on the literature, Q classification system has high applicable potential for evaluation of rock mass quality. Therefore, in this study, it was used with RMR and SMR rock mass classification systems to assess stability or instability of different rock slopes along the Hamedan-Ganjnameh-Tuyserkan road, Hamedan province west of Iran. Furthermore, a modified rock mass classification system namely Slope Quality Rating (SQR) was proposed based on the correction of the Q classification parameters and calculating some new parameters such as dip and strike of discontinuities and the method of rock excavation or blasting. For this purpose, the SMR and RMR rock mass classifications were also needed. By measuring SQR for different rock slopes, it will be possible to measure Slope Mass Rating (SMR).</p><p> </p><p><strong>Evaluación del sistema Q modificado de clasificación del macizo rocoso para el análisis de estabilidad de pendiente de roca</strong></p><p> </p><p><strong>Resumen</strong></p>Este artículo explora la aplicabilidad del sistema de clasificación Q modificado y sus parámetros para analizar y determinar la información estimada de estabilidad de pendiente de roca en el sitio determinado de estudio. Según la literatura, el sistema de clasificación Q tiene un alto potencial de aplicabilidad paral a evaluación de la calidad del macizo rocoso. En este estudio además se utilizó el sistema Q junto con los sistemas Índice de Masa de Pendiente (SMR) y Clasificación Geomecánica de Bienawski (RMR) para evaluar la estabilidad e inestabilidad de diferentes pendientes rocosas en la carretera Hamedan-Ganjnameh-Tuyserkan, de la provincia de Hamedan, en el Oeste de Irán. Además, se propone el Índice de Calidad de Pendiente (SQR), un sistema de clasificación de macizo rocoso modificado, a partir de la corrección de los parámetros de clasificación Q y el cálculo de nuevos parámetros como pendiente y caída de las discontinuidades y el método de excavación o explosión de la roca. Para esta propuesta también se utilizaron las clasificaciones SMR y RMR. La medición SQR en diferentes pendientes hizo posible el cálculo del sistema SMR.</p>

Application of the SSPC method in the stability assessment of highway rock slopes in the Yunnan province of China

Assessing the stability of rock slopes is an important and difficult problem. Rock mass classification systems have become a suitable tool for fast assessment of rock slope stability. In contrast to other slope stability classification systems, the slope stability probability classification (SSPC) method has made obvious progress. In this study, numerous excavation slopes were surveyed along the Wentian and Xiaolan highways in the Yunnan province, China and their basic data were collected in the field. From the slopes, we choose some typical excavation slopes with different structure types, such as cataclastic, granular, layered and blocked structures. According to the three-step analysis method in the SSPC system, failure probability of the excavation slopes were assessed based on the possible failure mechanisms and modes of the slopes. The results show that the SSPC method exhibited an accuracy of 70 % in the stability assessment of the highway slopes in the Yunnan province.

Estimation of rock block size distribution for determination of Geological Strength Index (GSI) using discrete fracture networks (DFNs)

Rock mass classification provides fundamental data for a numerical stability analysis of rock structures. Among rock mass classification systems, the RMR and Q systems often are used for rock support system selection and the Geological Strength Index (GSI) system for estimating rock mass strength and deformation parameters. Moreover, the GSI system is the only rock mass classification that is directly linked to engineering design parameters such as the Mohr–Coulomb or Hoek–Brown strength parameters or the rock mass modulus. However, the original application of the GSI system requires long-term experience and a careful approach because of the fact that its use is a subjective decision. A quantitative approach to assist a less experienced engineer in assigning representative GSI values was presented. It employed the rock block volume and joint conditions as quantitative characterisation factors. Their approach is founded on the linkage between descriptive geological terms and measurable field parameters, such as joint spacing and joint roughness. In this study, a discrete fracture network (DFN) model incorporated with stochastic simulation is applied to characterise rock block size distribution for determination of the GSI. The fracture frequency obtained from the core logging data is analysed and provided to the DFN model as input data. Realisation of the DFN and its verification are conducted to establish the joint systems corresponding to the original fracture frequency. As a result, the stochastic simulation can successfully provide the information on the rock block size distribution to the procedure of the GSI determination.

Practical Investigations on Use of Weighted Joint Density to Decrease the Limitations of RQD Measurements

Various techniques have been established in geotechnical engineering to determine the quality of rock drilled out from a borehole. These simple and inexpensive methods include total core recovery (TCR), solid core recovery (SCR), and rock quality designation (RQD). Among these, RQD provides a general indication of rock mass quality and is widely used as an index to evaluate rock quality by expressing the degree of fracturing in drill cores. The RQD was modified from the TCR method by Deere (1963) to indirectly measure the number of fractures and amount of softening or/and alteration in rock mass for engineering applications. Its simplicity, low cost, and reproducibility generally resulted in quick development of the RQD for a wide variety of rock engineering applications, such as tunnels, mining engineering, and large caverns. Nowadays, this method is considered as a standard method in drill core logging and forms a basic element of the most widely used rock mass classification systems, such as the rock mass rating (RMR) and Q-system (Bieniawski 1989; Barton 1995). However, a number of limitations such as dependence on borehole orientation and the selected threshold value for the minimum intact core length restrict the consistency of the measured values. Accordingly, several methods have been established to overcome these limitations, such as the corrected rock quality designation (RQDc) (Li et al. 2009), volumetric joint density (Jv) (Palmstrom 1982, 1985, 1986; Sen and Eissa 1992), cumulative core index (Sen 1990), and weighted joint density (WJD) (Palmstrom 1995, 2005). Although such new methods have been developed, the RQD is still used with the initial definition, without correction, in many geotechnical engineering applications, e.g., rock mass classification, rock mass strength, and modulus of elasticity. This paper reviews the conventional RQD measurement techniques by Deere (1963) and RQD measurements from the WJD (hereafter called RQDWJD) by Palmstrom (2005) using rock cores drilled out from directional boreholes at the Bakhtiary Dam site. In this way, the RQD values from different methods were compared, and a new modification is proposed, called RQDM-WJD.

A simple regression based approach to estimate deformation modulus of rock masses

Rock mass characterization has a crucial importance in rock engineering applications including foundation design, slope design, support design and others. For these purposes, it is necessary to determine some input parameters for design, such as deformation modulus (Em), uniaxial compressive strength (σci) and Poisson ratio (υ). The Em is an important input parameter and the practical and economical way to determine this parameter is to apply a rock mass classification system and estimate using the rock mass properties. Data from four different sites were used in the study. The values of Em were calculated using the existing empirical equations based on the Rock Mass Rating (RMR89) system. Furthermore, pressuremeter tests were carried out to determine the Em in one of the sites. The relationship between the RMR89 and the Em was obtained via simple regression analysis using the Em calculated from empirical equations based on RMR89 system. Afterwards, performance of the equation obtained from regression analyses was examined and compared the predicted Em values with experimental values with respect to the R2 values using the data of fourth site. Overall R2 value was found to be as 0.75.