Rock Mass Classification Research Articles

Estimation of the Poisson's Ratio of the Rock Mass

The value of Poisson's ratio is a crucial parameter in rock mechanics and engineering for both intact rock and rock mass. Poisson's ratio has not gotten the attention it merits compared to other essential mechanical characteristics of intact rock and rock mass. Limited relationships exist between rock mass classification systems (such as RMR, RMQR, Q, and GSI) and Poisson's ratio. This paper provides a comprehensive review of models proposed by various researchers for estimating Poisson's ratio for rock mass. The different methods are compared, and new general equations are derived. The results indicate that the Poisson's ratio value of rock mass is inversely proportional to its quality and strength and depends on the Poisson's ratio value of the intact rock. Specifically, a linear equation is obtained using the RMR or GSI system, showing that the Poisson's ratio increases as the quality and strength of the rock mass decrease. The Q system has a logarithmic link between the rock mass quality and Poisson's ratio. It should be noted that the derived equations are applicable only under the assumption of a homogeneous isotropic rock mass.

Developing rock mass classification method using precise description of joints

Developing rock mass classification method using precise description of joints

Prediction of uniaxial compressive strength of rock based on lithology using stacking models

Uniaxial compressive strength (UCS) of rock is an essential parameter in geotechnical engineering. Point load strength (PLS), P-wave velocity, and Schmidt hammer rebound number (SH) are more easily obtained than UCS and are extensively applied for the indirect estimation of UCS. This study collected 1080 datasets consisting of SH, P-wave velocity, PLS, and UCS. All datasets were integrated into three categories (sedimentary, igneous, and metamorphic rocks) according to lithology. Stacking models combined with tree-based models and linear regression were developed based on the datasets of three rock types. Model evaluation showed that the stacking model combined with random forest and linear regression was the optimal model for three rock types. UCS of metamorphic rocks was less predictable than that of sedimentary and igneous rocks. Nonetheless, the proposed stacking models can improve the predictive performance for UCS of metamorphic rocks. The developed predictive models can be applied to quickly predict UCS at engineering sites, which benefits the rapid and intelligent classification of rock masses. Moreover, the importance of SH, P-wave velocity, and PLS were analyzed for the estimation of UCS. SH was a reliable indicator for UCS evaluation across various rock types. P-wave velocity was a valid parameter for evaluating the UCS of igneous rocks, but it was not reliable for assessing the UCS of metamorphic rocks.

A quantitative assessment method for the correlation between rock mass basic quality and Protodyakonov coefficient

With the implementation of the “Belt and Road” initiative, tunnel projects were designed in accordance with Russian design specifications and constructed by Chinese companies in countries along the route. Design companies and construction companies use different rock classification methods, which will increase the safety risk and cost of the tunnels. Therefore, it is necessary to study the correlation between Chinese engineering rock mass classification and Russian rock mass classification. The goal was to establish the correlation between rock mass basic quality (BQ) and Protodyakonov coefficient (f) for rock mass classification. Firstly, based on the equivalence principle of uniaxial compressive strength (UCS), the relationship between BQ and f containing the velocity index of rock mass (Kv) was established by comparing the relationship between f and BQ in the empirical formula of UCS. Secondly, through the equivalent principle of volumetric joint count of rock mass (Jv), we compared the empirical formula between the intactness index of Kv and rock quality designation (RQD) and conducted linear regression analysis on a large amount of data. The relationship between Kv and RQD was established. Finally, the relationship between BQ and f is quantitatively expressed and a classification table corresponding to the Russian rock classification and the Chinese engineering rock classification is obtained. The method is applied to Kyrgyzstan mountain tunnels.

Tunnel Stability Analysis Under Seismic Load Using Finite Element Method: A Case Study of Spillway Tunnel, Sidan Dam, Bali, Indonesia

The location of the Sidan Spillway Tunnel, as shown on the Earthquake Hazard Zone Map of Bali Island, is in a moderate hazard zone. The support system of the spillway tunnel of the Sidan Dam, Indonesia, was empirically designed based on rock mass classification systems. The objective of this research was to verify the performance of the proposed support system by a numerical method considering the uncertainty in using rock mass classification systems for designing a tunnel support system. In addition, being located in an active seismic region, the seismic load was not considered in the empirical tunnel support design. The proposed tunnel support design was numerically modeled in two dimensions using a finite element method and subjected to a seismic load obtained from probabilistic seismic hazard analysis. A numerical analysis without seismic load was also conducted for comparison. Phase2 software was used for the tunnel stability analysis. The input parameters in the numerical analysis were derived from field investigations (surface engineering geological mapping and evaluation of drilling cores) and laboratory tests. The spillway tunnel area consists of pyroclastic rocks, and the Generalized Hoek-Brown Failure Criterion was selected for the strength parameter of rocks. The suggested support designs are systematic rock bolts (20 mm diameter fully grouted), wired mesh, shotcrete, and steel ribs at specific locations. The numerical models determined that applying the proposed tunnel support system recommended based on the empirical method resulted in a roof strength factor of more than 1.5 under static load & 1.1 under seismic load and roof displacements lower than a 10 cm maximum displacement at every stage of construction. The results verify that the tunnel construction will be stable and fulfill the required safety standard, both under and without seismic loads.

Stability assessment for proposed Hemja-Patichaur road tunnel using empirical and analytical methods, western Nepal

Stability assessment is an important aspect for the safety and proper design of underground structures. This paper aims to analyze the stability issues for the proposed 13 km long road tunnel alignment along the Pokhara-Baglung Highway which stretches from the southeast Hemja (Kaski District) to the northwest Patichaur (Parbat District), Gandaki Province, Nepal. For this purpose, initially, an engineering geological mapping in the field was conducted followed by comprehensive analysis of stability. The study has shown that rock mass class within the proposed tunnel stretch ranges from good to extremely poor as per Q and RMR systems of rock mass classification. In this study, stability assessment was carried out by empirical methods and analytical methods. The sections along tunnel alignment were selected for stability study according to the overburden, rock class and presence of weakness zones. The study concluded that empirical methods has shown squeezing conditions at four sections and non-squeezing conditions at four sections as per Q-values. Similarly, analytical methods have shown the rock bursting condition as stable at the roof at most of the sections except minor spalling at some sections. However, the tunnel wall may suffer severe rock bursting with increased in-situ stress conditions of the rock mass. Further, the instantaneous and final deformation of the tunnel was obtained by Panthi and Shrestha’s approach as less than one percent which is negligible.

Stability assessment of desander cut slope of Seti Khola Hydropower Project

Due to steep topography in the Himalaya, opening space for the development of infrastructures involves excavation of hillside slopes which possesses certain degree of risk associated with failure. This paper aims to assess the stability of the rock slope excavated for the placement of desander basin of the Seti Khola Hydropower Project (22 MW) located in Lekhnath, Kaski district of Gandaki Province. The height of the cut slope is about 60 m and is the challenging part of the construction work of this project. The slope is cut in the rock mass belonging to highly schistose graphitic phyllite intercalated with meta-sandstone at the upper part of the slope. To conduct a detailed stability assessment, the discontinuities, and geometric characteristics have been evaluated by field mapping. A three dimensional (3D) geological model has been generated to represent the geometric properties of discontinuities and the cut slope incorporating failure plane. The mechanical characteristic of the intact rock is established through literature review whereas the rock mass properties have been assessed using different equations. Rock mass quality has been assessed by using Rock Mass Rating (RMR) method of rock mass classification. RMR values are then correlated into Slope Mass Rating (SMR) incorporating different factors of slopes as per the site conditions. Further, kinematic analysis has been carried out using geometric and discontinuity properties to evaluate the structurally controlled failure. The influence of groundwater and earthquake has been considered while determining the shear strength of sliding surface. Finally, stability assessments have been carried out empirically, analytically and two dimensional (2D) numerical modelling.

A LightGBM-based strategy to predict tunnel rockmass class from TBM construction data for building control

Identification of rockmass class before construction is crucial to the safe and high-efficiency building of underground tunnels and has been a challenge for long water diversion tunnels. This paper is devoted to developing the LightGBM-based strategy for on-site rockmass class prediction in long tunnels from TBM construction data. The LightGBM-based strategy optimizes the input features and hyperparameters automatically by combining the tree-structured Parzen estimator (TPE), the light gradient boosting machine (LightGBM), and Shapley Additive exPlanations (SHAP) and establishes rockmass prediction models with data of various structures in 7505 TBM tunneling cycles in the Yinsong tunnel of 17.488 km long. The LightGBM-based strategy has an accuracy of 92% on the testing set, outperforms the random forest and support vector machines on the Yinsong tunnel data, and shows good generalization ability in the TBM7 tunnel in Xingjiang. The work contributes to the intelligent and efficient construction of long TBM tunnels.

EXCASS system and Rock Mass Rating (RMR) classification for determining excavation method and tunnel support at Pelosika Dam Spillway Tunnel

Pelosika dam spillway tunnel was designed to drainage flood discharge and prevent overtopping. In recent investigations, the rock mass classification has not been done specifically in the spillway tunnel. This research aims to obtain technical geological data and information to define excavation methods and tunnel support. For more comprehensive research, engineering geological investigations were carried out regarding the Geological Strength Index (GSI), selecting excavation methods using EXCASS system and Rock Mass Rating (RMR) for tunnel support. The geological mapping showed that the study site was composed of 2 lithological units: quartz muscovite phyllite and pebblely sand deposits. The GSI value in the tunnel is between 14-25, indicating poor and very poor quality. Adopting the EXCASS system, the optimum method of excavation (EPIopt) in the Pelosika dam spillway tunnel are ripper easy and digger. While RMR values of 9 – 25 are classified as poor quality. Consequently, the appropriate method for the excavation sequence is using the top heading and bench and multiple drifts. And the recommended support system is a systematic rock bolt with wire mesh and shotcrete in the crown and walls with medium to light steel rib.

Rock Mass Classification for Support System Design and Stand-up Time of Asahan 3 Hydroelectric Power Plant Tunnel (STA 7+085 - STA 7+717)

This Engineering geology research on rock mass classification to determine the support system’s design and stand-up time at the Asahan 3 hydroelectric tunnel STA 7+085 – STA 7+717 has not been thoroughly carried out in detail. This study aims to estimate the support requirements. Rock mass classification is determined through core drill observations and then analyzed by Q-system and RMR methods. The results show that the rock mass at the tunnel depth elevation consists of sandstone with good quality based on RMR and Q-system. Based on the Q system classification, good quality sandstone is obtained. Based on RMR, the suggested support system is shotcrete in the crown and rockbolt. Meanwhile, a rock bolt is the appropriate support system based on the Q-system. The use of an RMR based support system is recommended because it provides a higher level of security with the addition of shotcrete. The tunnel stand-up time is 2,200 - 2,700 hours based on RMR. The result of this research is expected to be applied in other tunnel construction having similar engineering geological condition.

Empirical Approach For Preliminary Support and Excavation Method Design Based On Engineering Geological Study Of Mbay Dam Diversion Tunnel

This paper presents excavation methods and support systems in the diversion tunnel of the Mbay Dam, East Nusa Tenggara, Indonesia, based on rock mass quality ratings. The rock mass quality was classified through geological surveys, core drilling evaluations, and laboratory tests. The results showed that the lithology along the tunnel alignment was pyroclastic breccia. Using the Rock Mass Rating (RMR) classification system, which was the single classification at the time of designing the Mbay Dam Diversion Tunnel, the pyroclastic breccia rock mass was classified III and IV (fair and poor). Meanwhile, according to the Q-System classification, the second classification used, pyroclastic breccias were also classified as fair and poor. Therefore, according to the RMR classification, the recommended excavation methods were top heading and bench. Support systems suitable for rock mass quality in the Mbay Dam diversion tunnel were rock bolt, wire mesh, shotcrete, and steel sets, with different variations and types depending on the rock mass class and classification used.

Surface and Subsurface Engineering Geological Characterization for Empirical Design Excavation Method and Support System of Jragung Dam Diversion Tunnel, Indonesia

The diversion tunnel of Jragung Dam was initially designed using the New Austrian Tunnelling Method (NATM) based on assessment of limited drill cores. Due to the uncertainty in the use of single empirical tunneling method and limited data for the tunnel design, this research was conducted to better characterize the rock masses and provide design alternatives for the tunnel construction. In addition to drill core evaluation, surface engineering geological mapping was carried out to obtain complete parameters of Rock Mass Rating (RMR) and Q rock mass classifications for designs of the tunnel excavation method and support system. The results show that the tunnel area consists of highly weathered sandstone and claystone layers with extremely poor to fair rock mass quality. The rock masses have very favorable and fair discontinuity strike and dip orientations with respect to the tunneling direction. The recommended excavation methods are top heading and bench and multiple drifts. The tunnel mostly requires rock bolt and shotcrete support system and the tunnel sections with poor rock mass quality require additional installation of steel sets. This research highlights potential collapse of the extremely poor quality rock masses near the tunnel portals during excavation of the diversion tunnel.

Empirical Designs of Excavation Method and Support System of the Intake Tunnel of Meninting Dam, West Nusa Tenggara, Indonesia

The intake tunnel of Meninting Dam has been designed based on RMR but with less detailed drill core evaluation in the tunnel area, which will lead to less accuracy in the design. The objective of this study was to evaluate the tunnel’s excavation method and support system using the latest data based on rock mass classification of RMR, GSI, and Q–system. The investigation was conducted by surface geological mapping and core drilling evaluation. The results showed that the tunnel area consists of pyroclastic breccia intercalated with lapilli stone. Based on the rock mass quality, the tunnel can be divided into two sections: Section A has fair quality rock, and Section B has poor quality rock. Based on the empirical designs, the recommended rock and tunnel excavation in Section A by hammer and top heading bench, and Section B by ripping and top heading bench. The recommended supports in all sections were using a combination of rockbolts, shotcrete, and wire-mesh. Even though the empirical approach is helpful in the preliminary design, a numerical study is needed to verify the empirical design so the recommended excavation and support system can be safely applied.

Slope Stability Analysis of Alterated Dasit Rock on Ponorogo Pacitan Road Using Hoek-Brown Failure Criteria

To mitigate landslide on rock slopes the information on adequate safety factors is needed. The strength of rock and soil is one of the important parameters on a slope stability analysis. This paper discussed the stability of the altered and dissected dacite rock. To make it easier to determine the Hoek-Brown failure criteria, the GSI rock mass classification is used. By using the Hoek-Brown failure criterion and supporting by the Rocsience software the analysis of safety factor of rockslide has been conducted. From field and laboratory observations of the rock masses that make up the slopes at the study site, a Geological Strength Index value of 25 was obtained. Base on GSI and some field condition can be obtained the Hoek-Brown parameter are γ = 2.6 t/m3, mi = 25, Disturbance Factor (D) = 1.0, mb = 0.118, s = 3.73e-6, 𝑎 = 0.531. The rock mass strength of the sample was brittle so that it can easily collapse. The purpose of this analysis is to do further study to overcome the problems that occur in most rocks, especially those related to transportation routes next to the slope.

RMR y tipo de explosivo: incidencia en las voladuras subterráneas

La clasificación de masas rocosas de Bieniawski, RMR -Rock Mass Classifications, junto con la Q de Barton y el GSI de Hoek, los tres sistemas de clasificación más frecuentemente utilizados en muchos países incluyendo a Colombia como ayuda para determinar un sinnúmero de propiedades del macizo rocoso, que de otra forma serían muy tediosas y costosas de determinar. Estas características permiten prever los tiempos de autosoporte de una excavación subterránea, así como su tipo de sostenimiento, velocidad de avance y complejidad de construcción y con base en ellos determinar costos y tiempos de excavación bastante aproximados de estas estructuras, y aunque se recomienda utilizar el método de avance de perforación y voladura para macizos rocosos con RMR de I, II y III, en la bibliografía no se encuentra ninguna relación directa entre el RMR y las dimensiones del burden, del espaciamiento ni del retaque. También es cierto que la mayoría de las expresiones propuestas para determinar estos parámetros (burden, espaciamiento y retaque) solo contemplan la densidad de la roca y del explosivo; algunas pocas, la velocidad de las ondas en el medio y otras más, la resistencia a la compresión o a la tracción. Por otro lado, las excavaciones subterráneas se caracterizan por su estado de confinamiento debido a la profundidad, por la forma y tamaño del área a excavar, así como por parámetros geométricos inherentes al proceso de perforación tales como el diámetro, la longitud, la dirección y la ausencia de una cara libre. Estas condiciones insinúan que, en los diseños de la malla de perforación y voladura subterránea, debería reflejarse la influencia de estos parámetros. Los resultados de la investigación que venimos realizando nos permite proponer una expresión que conlleva las propiedades dinámicas a tracción del macizo rocoso para estar acorde con las características dinámicas generadas por el explosivo, el cual también ingresa como una variable importante; además, estamos considerando el nivel de acoplamiento de las cargas, las dimensiones de la sección del túnel, sus condiciones de confinamiento y el RMR en el que se encuentra inmerso.

Rockmass Characteristics and its Influence on TBM Penetration Rate in Archeans and Meta-sedimentary Rocks of India

TBM penetration rate prediction models were developed for the hard Archean granites, granite gneisses and Meta-sedimentary rock groups comprising of quartzites, quartz arenites and sandstone of peninsular India.Construction stage engineering geological mapping comprising of face logging resulted in rockmass characterisation of Archeans and Meta-sedimentary rock groups. Statistical correlation of TBM penetration rate (PR) with Rock quality designation (RQD), unconfined compressive strength (UCS), volumetric joint count (Jv) and rockmass class was carried out. The prediction model provides good correlation only in the Meta sedimentary rock group for RQD, UCS and rockmass class and good correlation only for RQD and rockmass class in the Archean group but poor correlation with UCS. There is an exponential increase of penetration rate with Jv in both the rock groups. Keywords: TBM Penetration Rate, Rockmass Characteristics, Geological Mapping, Rockmass Classification, Rock Tunnel

Rock mass quality classification based on deep learning: A feasibility study for stacked autoencoders

Objective and accurate evaluation of rock mass quality classification is the prerequisite for reliable stability assessment. To develop a tool that can deliver quick and accurate evaluation of rock mass quality, a deep learning approach is developed, which uses stacked autoencoders (SAEs) with several autoencoders and a softmax net layer. Ten rock parameters of rock mass rating (RMR) system are calibrated in this model. The model is trained using 75% of the total database for training sample data. The SAEs trained model achieves a nearly 100% prediction accuracy. For comparison, other different models are also trained with the same dataset, using artificial neural network (ANN) and radial basis function (RBF). The results show that the SAEs classify all test samples correctly while the rating accuracies of ANN and RBF are 97.5% and 98.7%, repectively, which are calculated from the confusion matrix. Moreover, this model is further employed to predict the slope risk level of an abandoned quarry. The proposed approach using SAEs, or deep learning in general, is more objective and more accurate and requires less human intervention. The findings presented here shall shed light for engineers/researchers interested in analyzing rock mass classification criteria or performing field investigation.

Rock mass classification in highway tunnel engineering during exploration phase and case study

Rock mass classification in highway tunnel engineering during exploration phase and case study

Assessment of Foundation Rocks of the Proposed Makhol Dam in the Northern Salah- Alddin, Iraq

This study was done as an assessment of the foundation rocks of the proposed Makhol dam in the northern Salah- Aiddin Governorate, Iraq. This study consists of field, laboratory, and office work. It was noticed in the field that the thirteen (13) different rock mass units comprised along the dam axis. Three rock mass classification systems were adopted (used) in the evaluation: Rock Mass Rating, Dam Mass Rating, and Geological Strength Index. The DMRSTA (RMR related to dam stability) values for the right bank range between 36.97- 73.8. These values indicate good stability of foundation rocks of the right part with the presence of some instability of primary effect (not serious effect) in unit no.3 (Fatha Formation), and the DMRSTA values of the left bank range between 44.97– 61.7 These values indicate no instability for the foundation rocks on the left bank for all rock mass units. The RMRBD89 values range between 37– 73.3. These values reveal that the foundation rocks are desirable and can be excavated for rockfill and earth fill dams, but for the gravity dam, the rock mass unit 3, must be excavated to the desirable RMRBD89 value in the case of a gravity dam, and indicate that the foundation rocks do not require grouting when the type of dam is earth fill. Some rock mass units require grouting (spot grouting), especially for the rock mass unit 3 when the type of dam is Rockfill, and require systematic grouting, especially when the type of dam is Gravity. The Roc Lab software was used for the purpose of determining the mechanical properties of all rock units through the Hook-Brown failure criterion.

Analisis Sistem Penyangga pada Terowongan Pengelak Proyek Bendungan Lau Simeme Kec. Sibiru-biru Kabupaten Deli Serdang, Sumatera Utara

This tunnel is an alternative structure used to divert river water during construction of the dam body. Location The tunnel is located in Kuala Deca Village, Civilville District, Deli Serdang District, North Sumatra. Since this tunnel is located under a hill, a buffer system is required within the tunnel for the tunnel to be considered safe. The purpose of this study is to analyze the entrance side stress and calculate the safety factor of the tunnel. Rock mass classification (RMR) is currently used to determine the service life of tunnels. Analysis of the upstream support system "Inlet" shows that at STA 0+ 043.000 the support system used on the upstream side of the tunnel is I conclude that it is bedrock bolts and shotcrete. A geologist gives him an RMR value between RMR 41 and 60. Mathematically, the inlet stress is 11,758 MPa and the maximum stiffness is 41.221,137 MPa/m, so the inlet safety factor is 301,14. 51,50 for roofs and walls. The Lau-Simeme Dam Tunnel is considered safe because the overall tunnel safety factor is 1,5.