Rock Mass Classification Research Articles

Estimating the Hydraulic Conductivity of jointed rock mass using Genetic Programming

Ground engineering through injection of cementitious grouts or polymer resins is an integral part of fractured rock mass stabilisation by improving its maximum load carrying capacity, stiffness, cohesiveness and reduction in permeability. To optimise product delivery and achieve a high penetrability of product into the rock mass, it is imperative to understand the permeability characteristics or hydraulic conductivity of the rock mass. The hydraulic conductivity of the rock mass also dictates the type of polyurethane (PU) or cement-based products to be injected. For this purpose, a Packer test has to be conducted to measure the hydraulic conductivity of a rock formation which is an expensive and time-consuming process. Alternatively, a number of empirical methods that use rock mass classifications and rock joint properties Rock Quality Designation (RQD), Q-system (Q), Geological Strength Index (GSI), Joint Spacing (JS), Joint Aperture (a) proposed by a number of researchers that are capable of predicting hydraulic conductivity (HC). In this research, a predictive model between rock mass properties and HC is proposed using new approach - genetic programming (GP). For this purpose, a database of rock mass parameters including RQD, Q, GSI, JS, Joint Aperture (a), Second Permeability Index (SPI) and Packer test results available in the literature is established. The database is split into randomly selected training and testing sets. To assess the fitting quality, the sum of the absolute difference is used, while maximum depth on trees is set to control the bloat of the model. The performance is assessed with four statistical criteria and three GP models using different input combinations are proposed. These models have been converted into simple mathematical equations to calculate HC based on collected input data. In summary, two out of three models have successfully predicted HC with high correlation to the actual HC (R2 of testing sets ≈ 0.92). Therefore, this study has shown the feasibility of applying GP models into future prediction of HC for the initial phase of rock grouting design.

Rock Mass Characterizations and Kinematic Analysis for Construction Design Method of Diversion Tunnel of Dolok Dam, Central Java

Investigation of slope stability in the design of the tunnel portal is important to minimize slope failure. This research aims to describe the rock mass characterizations and classifications using Geological Strength Index (GSI) and Rock Mass Rating (RMR), along with the kinematic analysis and Slope Mass Rating (SMR) to define the risk of slope failure and the recommended support at the tunnel portal. Geological mapping and core evaluation were conducted to analyse the slope stability. The results show that the rock masses consist of intercalated rudstone with mudstone, typically have disintegrated, moderately disturbed, and blocky structures with slightly to highly weathered. The discontinuities have 3 – 4 sets consisting of bedding and joint, have medium to high persistence, close spacing, and dominantly have no infillings. These rock masses are classified as poor-fair rock in the upper part of the sequence, and good rock in the bottom part of the sequence. The kinematic analysis predicts the risk of toppling failure both in the inlet and outlet portal. The recommended support in the inlet portal is the combination of shotcrete, beams, and bolts, whilst in the outlet portal is the combination of surface drainage, shotcrete, dental concrete, beams, and bolts.

THE SIZE CORRECTION AND CORRELATION OF POINT LOAD INDEX WITH COMPRESSIVE STRENGTH OF SOME DIMENSION STONES OF TECTONIC ZONES, NORTH PAKISTAN

The Uniaxial compressive strength (UCS) is an important geotechnical property of rock used in tunnel design, rock mass classification and other surface and underground mining projects. It is the Key parameter of rock mass rating (RMR) and the RMR is the basic of all the slope stability analyses methods. This key parameter of slope stability analyses and tunneling can be determine easily by axial and diametral point load test (PLI/Is50). In the past irregular lumps PLI is also correlated with UCS but the data is limited particularly the rocks along Karakoram High Way (KKH), North Pakistan. In this study the diametral, axial and the irregular lumps PLI is correlated with UCS using dimension stones of tectonic regions along KKH. A methodology of size correction of irregular lumps have been set. Using regression analyses the PLI of cores and lumps have been correlated with UCS. The significance of the correlation were developed by correlations coefficients. It is found that the Is(50) of irregular lump of white marble is 1.8MPa. For pink and white granite the Is(50) value is recorded as 3.2MPa and 2.4MPa respectively. In the size correction factor (F) the power n for irregular lump is corrected as 0.8 for marble lumps and the n value for pink and white granite is 0.9 and 1.4 respectively. For diametral and axial PLI the power n is used as 0.45. The correction factor F=(De/50)0.8 is suggested for marble irregular lumps while for axial and diametral specimens of marble the correction factor is F=(De/50)0.45 is recommended. In the case of pink and white granite the correction factors are F=(De/50)0.9 and F=(De/50)1.4 respectively.

The technique for extrapolation of rock mass initial parameters during the construction of the tunnel

It is important to perform research to the degree that it is adequate to identify the features of the terrain composition, before, during, and after the building of facilities since predicting the behaviour of rock mass during tunnel construction is a complicated engineering challenge. Engineering research works in laboratories and in the field are of different scope and methodology during testing. In this paper, the established interdependencies of some of the basic parameters obtained during the testing of rock mass are presented: Edyn = f(Vp), Edyn = f(RMR) i Edyn = f(Q). Also, the relations between the engineering systems of rock mass classification and seismic primary waves are derived. RMR = f(Vp), Q = f(Vp). The relations were based on the examination of the rock mass for the construction needs of the tunnel on the Nis-Merdare highway. The results obtained in this study can be applied in environments that have similar lithological and structural characteristics.

SLOPE STABILITY TECHNICAL STUDY USING SLOPE MASS RATING (SMR) METHOD AT PT. KARYA SUMBER ALAM PERKASA, SANGGAU REGENCY, KALIMANTAN BARAT

Soil (topsoil and overburden) above the granite quarry in pit 2 (two) PT. Karya Sumber Alam Perkasa has experienced a landslide. It is probably caused by the condition of pit 2 (two) slopes at PT. Karya Sumber Alam Perkasa, which is currently being mined, is quite steep. External factors that can trigger the movement of rock masses are vibrations due to breakers. This condition has the potential to increase the risk of slope stability. Slope stability is influenced by geological conditions, joints, slope geometry, water conditions below the soil surface, physical and mechanical properties, and vibrations due to blasting and mechanical equipment. Therefore, it is necessary to conduct a technical study of slope stability. The research aims to study rock mass class, potential type of landslide, and potential slope stability. The technical study of slope stability uses the Slope Mass Rating (SMR) method. Data processing using software Rocscience Dips 7.016. Analysis of potential types of landslides based on stereographic projections. The result of the RMR calculation is 78, so the rock mass class is number II, which is included in the excellent category. The results analysis of the potential for the type of failure indicates t tends to lead to the toppling failure, but after the study, there is no failure because it does not meet the landslide requirements. The result of the analysis of potential slope stability is that the slope in pit 2 (two) is safe or stable because the SMR value is 78 and the safety factor value is 2,458.

SLOPE STABILITY TECHNICAL STUDY USING SLOPE MASS RATING (SMR) METHOD AT PT. KARYA SUMBER ALAM PERKASA, SANGGAU REGENCY, KALIMANTAN BARAT

Soil (topsoil and overburden) above the granite quarry in pit 2 (two) PT. Karya Sumber Alam Perkasa has experienced a landslide. It is probably caused by the condition of pit 2 (two) slopes at PT. Karya Sumber Alam Perkasa, which is currently being mined, is quite steep. External factors that can trigger the movement of rock masses are vibrations due to breakers. This condition has the potential to increase the risk of slope stability. Slope stability is influenced by geological conditions, joints, slope geometry, water conditions below the soil surface, physical and mechanical properties, and vibrations due to blasting and mechanical equipment. Therefore, it is necessary to conduct a technical study of slope stability. The research aims to study rock mass class, potential type of landslide, and potential slope stability. The technical study of slope stability uses the Slope Mass Rating (SMR) method. Data processing using software Rocscience Dips 7.016. Analysis of potential types of landslides based on stereographic projections. The result of the RMR calculation is 78, so the rock mass class is number II, which is included in the excellent category. The results analysis of the potential for the type of failure indicates t tends to lead to the toppling failure, but after the study, there is no failure because it does not meet the landslide requirements. The result of the analysis of potential slope stability is that the slope in pit 2 (two) is safe or stable because the SMR value is 78 and the safety factor value is 2,458.

A comprehensive investigation of engineering geological characteristics of interlayer shear weakness zones embedded within Baihetan hydropower station

The interlayer shear weakness zones (ISWZs), which are a kind of large-scale infilled discontinuity, are frequently considered the most hazardous potential slip surface in the rock masses. Based on laboratory and field investigations, the engineering characteristics of ISWZs (i.e., genesis, fabric, structure, mineral composition, water-physical properties, shear strength properties, and engineering classification) embedded in and around the Baihetan hydropower station area are systematically examined.The results of the laboratory and field show that ISWZs have complex occurrence features, undulating and spatial inconsistency in thickness, and variation in mineral composition, fabrics, and structures. Moreover, based on variabilities in various features and extend, ISWZs are categorized into single-layer structures (Type-A) and multilayer structures (Type-B). An engineering geological classification approach for large-scale ISWZs is developed based on the two essential index such as clay proportion and infilled ratio. This classification method not only involves the influence of the undulating state of ISWZs on their shear properties but also considers the physical and mechanical properties of weak interlayer materials. The results of this investigation contribute to a proper understanding of mechanical properties and rock mass classification, especially for large-scale ISWZs.

Load-bearing Behavior of Offshore Rock Socketed Monopile Foundation Regarding Different Rock Mass Classification

With the increasing electricity demand in China, wind power has been heavily developed in recent years. It is important to stabilize the wind turbine foundations in rock bedded near the sea area while installation. Based on different rock classification standards (GB 50218 and GSI), this paper numerically analyzed the load capacity of rock socketed monopile. When the rock class is high (class III and above), under effective socketed depth, the rock-socket effect is important, and the pile tip deflection is nearly 0, which could be considered as a clamping constraint. In this case, even if the rock quality around the pile tip decreases a little or becomes a little weakened, the pile deformation and internal force will not change a lot. However, when the rock mass class is lower than IV, the pile tip load capacity will largely decrease. The definition of rock mass parameters is also important when analyzing rock socketed monopile. In conclusion, it is suggested to take GB 50218 as a reference. BQ engineering rock mass classification and its corresponding rock mass parameters could be applied. Also, the M-C model is suggested to be used for some related work.

A comparison of slope stability assessment techniques using different rock mass classification systems and finite element method (FEM): A case study from the Garhwal Himalayas, India

A comparison of slope stability assessment techniques using different rock mass classification systems and finite element method (FEM): A case study from the Garhwal Himalayas, India

Modified RMR Rock Mass Classification System for Preliminary Selection of Potential Sites of High-Level Radioactive Waste Disposal Engineering

This paper proposed a modified Rock Mass Rating (RMR) system, the RMRHLW system, for evaluating the rock quality of High-level Radioactive Waste (HLW) geological disposal engineering. Some salient factors, including the weakening of groundwater and temperature on the uniaxial compressive strength, the continuity of index values, the geostress, the rock permeability, and the groundwater chemical properties, were further incorporated based on the widely used RMR system. The proposed RMRHLW system was then verified by the case study of selection of nine candidate sites for HLW disposal engineering in China. The results indicated that the rock quality of the Xinchang site was the best and ranked as the most appropriate site, while the Jiujing site ranked the worst. Compared with the traditional RMR system, the proposed RMRHLW system can further consider crucial factors related to the long-term safety of HLW disposal and better reflect the differences between the potential sites. It can facilitate engineers to preliminarily evaluate the rock quality of the potential sites for High-level Radioactive Waste geological disposal engineering.

Prediction of geology condition for slurry pressure balanced shield tunnel with super-large diameter by machine learning algorithms

Real-time and precise prediction of geological conditions is extremely beneficial to the safe and efficient construction of slurry pressure balanced shield machines (SPBMs), especially for super-large diameter tunnels. Machine learning algorithms provide an effective way to predict geological conditions and have been successful in hard-rock tunnel boring machine (hard-rock TBM) tunnels or earth pressure balance shield machine (EPBM) tunnels. However, the effectiveness of machine learning in predicting geological conditions for super-large diameter SPBM tunnels is still unknown. This study systematically demonstrated the application of machine learning algorithms to the prediction of geological conditions in super-large diameter SPBM tunnels based on field data from the Heyan Road crossing river tunnel. The relationship between SPBM parameters and geological conditions was first evaluated, and subsequently, an adaptive model was proposed to determine the number of input variables. The performance of three algorithms, random forest (RF), AdaBoost, and support vector machine (SVM), in rock mass classification, and seven algorithms, multi-objective random forest (MORF), single-target-RF, regressor chain-RF, single-target-AdaBoost, regressor chain-AdaBoost, single-target-SVM, and regressor chain-SVM, in formation percentage prediction, were compared. The results showed that machine learning algorithms can effectively predict the geological conditions in super-large diameter SPBM tunnels. Specifically, RF had the best performance in rock classification compared with AdaBoost and SVM. MORF outperforms the other six algorithms in terms of formation percentage prediction. Additionally, sensitivity analysis indicates that the newly proposed parameters, including slurry system parameters and cutter type, have a clear positive effect on the performance of geological condition prediction.

Why Engineers Should Not Attempt to Quantify GSI

In the past decade, there has been an increasing trend of digitalizing rock engineering processes. However, this process has not been accompanied by a critical analysis of the very same empirical methods that many complex numerical and digital methods are founded upon. As engineers, we are taught to use and trust numbers. Indeed, we would not be able to define the factor of the safety of a structure without numbers. However, what happens when those numbers are nothing but numerical descriptions of qualitative assessments? In this paper we present a critical review of the many attempts presented in the literature to quantify GSI (geological strength index). To the authors’ knowledge, this paper represents the first time that all the different GSI tables and quantification methods that have been proposed over the past two decades are collated and compared critically. In our critique, we argue against the paradigm whereby the quantification process adds the experience factor for inexperienced engineers. Furthermore, we discuss the limitations of the notion that GSI quantification methods could transform subjectivity into objectivity since the parameters under considerations are not quantitative measurements. Relying on empirically defined quantitative equivalences raises important questions, particularly when these quantitative equivalences are being used to define so-called accurate rock mass classification input for design purposes.

Mixture distribution model for three-dimensional geometric attributes of multiple discontinuity sets based on trace data of rock mass

The geometric attributes of discontinuities are critical to an accurate discrete fracture network (DFN) model of rock mass. It is difficult to estimate three-dimensional (3D) geometric parameters of multiple groups of discontinuities by observation data. The study proposes a mixture distribution model for the 3D geometric attributes of multiple discontinuity sets. The method of estimating the mixture distributions of 3D geometric attributes of all discontinuity sets from the two-dimensional (2D) trace data in a sampling window is established and modified, including discontinuity diameter distribution estimation, volume density estimation, orientation distribution estimation, and distribution mixing. Discontinuities are assumed to be thin disks uniformly distributed in space, and their roughness and aperture are ignored. Discontinuity diameter and orientation follow lognormal distribution and bivariate normal distribution, respectively. Orientation distributions defined on the definitional domain of the geological coordinate system are derived to represent the real frequency distributions of orientation measurements in 3D rock mass space. The mixture distribution model is verified by using Monte Carlo method to generate DFNs with different volume densities, and distribution parameters of orientation and diameter. The maximum error of volume density is <0.5 m−3. The estimated distributions of diameter and orientation are in good agreement with the true distributions, while there are limited symmetry estimation errors of the discontinuity sets with orientation samples covering both sides of the 0° or 180° polar axis. The model is applied to Sejilashan tunnel, and the result indicates that the surrounding rock of two excavation faces have a high probability to be rated as the V classification according to the engineering classification of rock mass in China, which is in good agreement with the reality according to the geological survey and field observation.

Application of the NATM Methodology for the Excavation of Rail Tunnel in Difficult Geological Conditions: A Case from Garhwal Himalaya, Uttarakhand

Abstract The documentation of excavation method and support design based on rock mass classification systems i.e. rock mass rating (RMR), Q-system and New Austrian tunneling method (NATM) for adit-7 tunnel being constructed in Garhwal Himalaya, India is discussed in this paper. The New Austrian tunneling method classes of rock units have been developed by using correlations with the RMR and Q systems, according to the ONORM B 2203. NATM principles were used because the geological conditions were continually changing. The study indicated that the RMR-based rock mass estimation was overstated, but the qualitative assessment was right. The NATM technique is more adaptable for Garhwal Himalayan rocks having various uncertainties in rock mass evaluation. The current adit investigations indicate that there are numerous unanswered concerns, concerning rock mass quality evaluation, tunnel behavior during construction and usability. Results of the analysis are considered to be useful for the design of the new tunnels constructed in the similar type of the terrain.

Obtaining initial data for forecast engineering geological model construction

Objective and relevance. Technologies in mining and geology are intensely developing making the present research particularly relevant. The research considers the problems of obtaining reliable and high-quality data on the degree and nature of rock mass fracturing in a solid mineral deposit. These are fundamental data required to construct a forecast engineering geological model of a deposit. The engineering geological model is usually based on a structural geological model with the addition of various geomechanical parameters used in generally accepted international classifications for rock stability analysis, in particular, RMR (Bieniawski), MRMR (Laubscher), and Q-system (Barton). Methods of research. The authors describe the procedure for obtaining classification geomechanical parameters of a rock mass according to the data from oriented and non-oriented core drilling of special engineering geological (geomechanical) boreholes. Research results. The main factors and conditions for reliable data acquisition are given. Among the most important ones are: economic feasibility and validity of geomechanical boreholes drilling as well as their number; features of the geological and structural composition of a deposit as a condition for borehole location selection; proper organization of the drilling process aimed at obtaining high-quality core material; characteristics of geomechanical description of the core, depending on the rating system of rock mass classification applied. Scope of results. By way of example, deposits with different geological and structural conditions are listed where the described procedure was applied. High-quality and reliable information about the structural and tectonic features of the rock mass allows to create and fill the engineering geological model with data and solve the problems of stability analysis for almost any area of the future mine working.

Stability Analysis of Lava Tunnels on Santa Cruz Island (Galapagos Islands, Ecuador) Using Rock Mass Classifications: Empirical Approach and Numerical Modeling

The cavities or lava tubes in the Galapagos Islands were formed by the differential cooling of the basaltic flow of the volcanoes surrounding these islands. In this article, a stability analysis was carried out to determine the degree of safety of different lava tubes using three methods: two empirical ones based on geomechanical classifications and one strain–strain (Hoek–Brown failure criterion). The methodology used consisted of the following phases: (i) compilation of information based on existing geomechanical mapping; (ii) geomechanical classification of the rock mass using Barton’s Q index and rock mass rating; (iii) steady state qualification using the geotechnical index of cavities (GCI); (iv) numerical modeling applying the Hoek–Brown criterion; (v) comparison of methodology and discussion of the results. The data obtained indicate that the methodologies used to evaluate the stability of the lava tubes have high reliability since they allowed the characterization of the different lava tubes. As the final “product” of the investigation, a graph was drawn up in which the empirical observations and the safety factors obtained with the numerical analysis (stress–strain) were superimposed, classifying the lava tubes as stable and non-stable. It can be concluded that the characterization methodologies used in this article can be applied to similar cases and fill a gap in rapid preliminary analyses of the degree of stability and risk of cave collapse.

Stability Analysis of Evasion Tunnels Using the Rock Tunneling Quality Index (Q-System) Method On the Construction of the Bagong Dam Trenggalek, East Java

The Bagong Dam evasion tunnel is part of the dam construction which functions to drain the water flow so that the dam work can be done. In planning the construction of evasive tunnels, it is necessary to study the geological, geotechnical and structural conditions of the tunnel. This study is intended to provide an overview of the subsurface and engineering geological conditions of the research area, so as to determine the stability of the evasion tunnel and then provide recommendations for the support to be used. The method used is the Rock Tunneling Quality Index (Q-System) method to determine the buffer to be used in the construction process. Based on the analysis of the subsurface geological conditions of the study area, there are three rock layers, namely: sandstone, breccia and limestone. In the Q-System analysis, the rock mass class value ranges from 0.451 to 0.651 with Very Poor quality and the rock mass class value is 1.162 with Poor quality. At the four drill points BH-09, BH-03, BH-10 and BH-11, the recommendation for support is obtained with the type of support (B+5) and SRF+B

Optimization Drift Support Design Based on Engineering Geological and Geotechnical Analysis in Deep Hard-Rock Mine: A Case Study

Geotechnical issues due to inappropriate support designs of underground drift will affect mining developments and production. The aim of this study was to provide a systematic support design method for deep hard-rock drifts in China. Field investigations and laboratory studies were carried out on the engineering geological properties of the rock masses along drifts in the Sanshandao Gold Mine. Potential wedge analysis and safety factors were determined using Unwedge software. The rock mass properties and support requirements were analyzed accordingly using different rock mass classification systems; then, an updated combined support system including rock bolts, wire mesh, and shotcrete was proposed. Numerical methods were used to quantify the plastic zone and principal stress of the drift, the plastic zone was reduced, and the rock stress state was improved after installing the support systems. Field monitoring data also confirmed that the updated support system prevented excessive rock mass deformation in drift. This study provides a reliable method for deep hard-rock drift support at Sanshandao Gold Mine and will also be helpful for the optimization of subsequent support.

Estimation of rock mass deformability based on empirical relations for Ghezel Ozan dam site in the north of Iran

Rock mass deformability modulus is one of the most important parameters for underground structures and dam site design. The current methods for determining this parameter are in situ tests and empirical equations. In situ tests are the best and most accurate methods and include plate bearing, flat jack and dilatometer tests. However, these in situ tests are difficult, time-consuming, expensive and sometimes even impossible. Therefore, many empirical equations have been developed to determine the rock mass deformability indirectly based on various parameters. In this study, the correlation between the deformation modulus values, rock mass rating (RMR) and tunnelling quality index ( Q ) classification has been studied for the Ghezel Ozan dam site in NW Iran. Then, empirical equations are used to calculate the rock mass deformation modulus ( E m ) based on dilatometer in situ tests and rock mass classifications as mentioned above are defined. Finally, the correlation between the equations given in this study and the empirical equations presented by other researchers based on RMR and TQI ( Q ) are also investigated using statistical indicators. According to this analysis, the equation estimated based on RMR has a good compliance with the equations presented by earlier researchers. Supplementary material: Supplementary datasets and figures are available at https://doi.org/10.6084/m9.figshare.c.6139108

Upscaling the Mechanical Properties of a Fractured Rock Mass Using the Lattice-Spring-Based Synthetic Rock Mass (LS-SRM) Modeling Approach—Comparison of Discontinuum, Continuum and Empirical Approaches

A numerical characterization of a fractured rock mass and its mechanical behavior using a discontinuum approach was carried out utilizing lattice-spring-based synthetic rock mass (LS-SRM) models. First, LS-SRM models on a laboratory scale were created to reproduce standard rock mechanical tests on Triassic sandstone samples from a quarry in Germany. Subsequently, the intact rock properties were upscaled to an element volume representative for geotechnical applications, recalibrated and combined with a Discrete Fracture Network (DFN) model. The resulting fractured rock mass properties are compared to predictions from empirical relationships based on rock mass classification schemes and the DFN-Oda-Geomechanics approach. Modeling results reveal a significant reduction in the strength of the fractured rock mass compared to the intact rock, showing a high agreement with empirically calculated values. Results for the deformation modulus reveal a significant reduction induced by the fracture network and a good agreement compared to the results obtained by other approaches. It is shown that the LS-SRM allows analyzing the complex mechanical behavior during failure of rock masses, including crack initiation, propagation and coalescence. The resulting rock mass properties are key parameters for a wide range of geotechnical applications and can be used for large-scale numerical modeling as well.