Preliminary Support Design Research Articles

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.

Evaluation of a Preliminary Support Design of Railway Tunnel Adit in Inner Lesser Himalaya India: An Empirical Analysis

This article addresses the excavation method and support design for the adit tunnel in the Rudraprayag District, Lesser Himalayas of India, using Rock Mass Rating (RMR), Tunneling Quality Index (Q), and New Austrian Tunneling Method (NATM). Based on ONORM B 2203 correlations with RMR and Q systems, the New Austrian Tunneling Method rock structure classes were developed. Because the geology was constantly changing, NATM concepts were applied. The RMR-based rock mass estimates were overestimated, but the qualitative investigation was correct. The NATM method is more appropriate for a Garhwal Himalayan rock with varying rock mass uncertainty. The present adit research reveals several outstanding questions about rock mass quality, tunnel behavior during construction, and use. The analysis results might be used to build new tunnels in comparable terrain in other parts of the world.

Analytical and numerical assessment of a preliminary support design – a case study

Underground tunneling results in redistribution of the in-situ stress state. This process can create unstable underground conditions. Tunnel instability can result in fatalities, property damages, project delays, high rehabilitation cost, and can compromise the overall functionality of the excavation. This study assesses the efficiency of the empirically recommended support design of the Pahang-Selangor Water Transfer Tunnel in Peninsular, Malaysia using convergence-confinement (CV-CF) and 2-Dimensional two-dimensional Finite Element Method (FEM). To reduce the effect of subjective uncertainties associated with the rock mass rating system, the lump rating system was replaced with the continuous rating system to classify the rock masses and provide empirical support design for the tunnel. The maximum capacity and stiffness of the support systems were analytically determined using the CV-CF method. The results of the maximum elastic deformation of the support systems were compared to the actual critical internal pressures which show that the empirically recommended support systems can satisfactorily stabilize the underground excavation. The Reliability of the support design, the plastic zones, and total deformations were determined using Phase2. The radius of plastic zones and the maximum total deformations were significantly reduced after the supports were installed. The plastic zones that remained were restricted within the reinforced zones, signifying the effectiveness of the recommended support systems.

Preliminary support design for underground mine adit, Artana mine, Kosovo

1. BAŞARIR H., 2006, Engineering geological studies and tunnel support design at Sulakyurt dam site, Turkey, Engineering Geology, Vol. 86, pp. 225–237. Google Scholar

Preliminary support design for underground mine adit, Artana mine, Kosovo

1. BAŞARIR H., 2006, Engineering geological studies and tunnel support design at Sulakyurt dam site, Turkey, Engineering Geology, Vol. 86, pp. 225–237. Google Scholar

Displacement monitoring, displacement verification and stability assessment of the critical sections of the Konak tunnel, İzmir, Turkey

The main focus of this study is vertical displacement monitoring and verification along with preliminary support design for the four geotechnical sectors of the twin tube Konak tunnel that was constructed in a highly populated area in İzmir. The displacements of the tunnel that were obtained through numerical analysis were verified by comparing them with the displacements obtained by construction monitoring. In the study area, volcanics, pyroclastics and some sedimentary deposits (sandstone, mudstone and conglomerate) often intertongue with each other especially in the exit portal area. The accurate estimation of the shear strength and deformation parameters of these units is important for the displacement predictions and for the assessment of tunnel stability. Rock mass classification systems, namely, RMR, Q system and GSI have been employed to obtain the rock mass shear strength and deformation parameters along with performing empirical tunnel support design. Numerical analysis has been performed by using the finite element analysis for assessing tunnel support design and for predicting the vertical displacements at five different measurement points around the tunnel periphery and in the four geotechnical sectors of the tunnel.An evaluation of the results revealed that about 70% of the predicted displacements matched the measured displacements while only about 12.5% of the displacement predictions exceeded the measured displacements by more than about 50%. Moreover, it was observed that neither the support system elements nor the rock mass have yielded due to the redistribution of the stresses imposed by the disturbance related with the tunnel excavation.

An Empirical Approach for Tunnel Support Design through Q and RMi Systems in Fractured Rock Mass

Empirical systems for the classification of rock mass are used primarily for preliminary support design in tunneling. When applying the existing acceptable international systems for tunnel preliminary supports in high-stress environments, the tunneling quality index (Q) and the rock mass index (RMi) systems that are preferred over geomechanical classification due to the stress characterization parameters that are incorporated into the two systems. However, these two systems are not appropriate when applied in a location where the rock is jointed and experiencing high stresses. This paper empirically extends the application of the two systems to tunnel support design in excavations in such locations. Here, the rock mass characterizations and installed support data of six tunnel projects are used. The back-calculation approach is used to determine the Q value using the Q-system support chart, and these values are then used to develop the equations and charts to characterize the stress reduction factor (SRF), which is also numerically evaluated. These equations and charts reveal that the SRF is a function of relative block size, strength–stress ratio, and intact rock compressive strength. Furthermore, the RMi-suggested supports were heavier than the actual installed ones. If the approximate inverse relation between stress level (SL) and SRF is used, the difference between the actual and the recommended supports increases when using the RMi-recommended rock support chart for blocky ground. An alternate system is made for support recommendation using a Q-system support chart. In this system, the ground condition factor is modified from the available parameters, and a correlation is developed with a modified Q system.

Extension of tunneling quality index and rock mass rating systems for tunnel support design through back calculations in highly stressed jointed rock mass: An empirical approach based on tunneling data from Himalaya

A preliminary support design is the basic output of an empirical rock mass classification system. Tunneling quality index (Q) and rock mass rating (RMR) systems are used specifically for tunnel support in moderately jointed and massive rocks; however, they do not provide any information/guidance for jointed rock masses in a highly stressed environment. Hence, this study focuses on the already supported drill and blast tunnel sections mapping data of four tunneling projects in Pakistan. The study extends the application of these systems to the tunnel support design for highly stressed jointed rock mass through an empirical approach. In each empirical approach, the parameters for the stress condition are suggested. Rock mass quality (Q or Qc) is determined from back calculations using an installed support and tunnel span. Empirical equations and charts are proposed for the stress reduction factor (SRF) characterization. In the proposed equations and charts, the SRF is a function of intact rock strength, relative block size, and strength–stress ratio. In the case of the RMR system, approximately 90% of the sections show that the actual supports are heavier than the suggested supports by RMR89. The RMR was determined from the installed support for each tunnel section through the back calculations. To select the adjustment rating factor for stress, three hypotheses are considered based on the intact rock strength to the major principal stress ratio. The RMR14 suggested support revealed that all sections are heavily supported. A strong correlation exists between RMR89 and RMR14. Three hypotheses are considered for the stress adjustment factor rating selection for RMR14 based on the correlation equation between RMR89 and RMR14. For the evaluation, the application of modified Q and RMR systems are used in the tunnel support in a case study. The exploration reports show that the tunnel will pass through a jointed rock mass under high in-situ stress environments. The comparison shows that heavy support is recommended from the modified systems for tunnel stability.

Empirical Evaluation of Rock Mass Rating and Tunneling Quality Index System for Tunnel Support Design

The primary output of the rock mass rating (RMR) and tunneling quality index (Q) system is a preliminary tunnel support design, as these methods are empirically developed and updated for this purpose. In this study, these internationally accepted design tools are evaluated to improve results for tunnel support design. The rating system is simplified and improved for some parameters through the use of equations to replace the discrete/lump characterization with a continuous rating. Recent developments in characterization and support are used in proposing the back analysis approach of rock mass quality calculation from tunnel span and installed support. This approach is used for two tunnel projects which experience high stresses. Approximately 90% of the tunnel sections show that actual supports have rock bolt spacing and shotcrete thickness which are heavier than those indicated by RMR89, indicating a system limitation. Another assessment using RMR14 indicates that its rating is higher than that of RMR89. A strong correlation exists between them, as supported by the literature and data from analyses of 462 tunnel sections. Despite its new version, RMR89 still preserves its importance. Evaluating the different correlations between RMR and Q through published data indicates that the rock mass fabric index gives comparatively better results.

Engineering geological appraisal and preliminary support design for the Salarha Tunnel, Northeast Turkey

The purpose of this study is to determine the engineering geological properties of the rock masses and to recommend a convenient support design for the Salarha Tunnel located in northeast Turkey. The detailed geotechnical studies were performed in three phases as surface, subsurface and laboratory studies to assess the rock masses that mainly consist of sedimentary and volcanic rocks. Empirical, analytical and numerical methods were combined for safe tunnel design. The RMR, Q and NATM systems were used as empirical methods to define the rock masses and to determine the preliminary support design. The convergence-confinement analytical method was utilized. The performance of the suggested empirical support design, extent of the plastic zones and deformations were analyzed by means of the finite element method (FEM)-based 2D and 3D numerical modeling. According to analytical and numerical analyses results, the empirical support design was sufficient to prevent stability problems developing around the rock masses surrounding the tunnel. The interpretations of results demonstrate that the 3D numerical method seems to fit even better with the respective outcomes from the analytical method. Thus, it is suggested that the empirical, analytical and numerical methods should be combined for a more reliable support design.

Designing Tunnel Support in Jointed Rock Masses Via the DEM

A systematic approach of using the distinct element method (DEM) to provide useful insights for tunnel support in moderately jointed rock masses is illustrated. This is preceded by a systematic study of common failure patterns for unsupported openings in a rock mass intersected by three independent sets of joints. The results of our simulations show that a qualitative description of the failure patterns using specific descriptors is unattainable. Then, it is shown that DEM analyses can be employed in the preliminary design phase of tunnel supports to determine the main parameters of a support consisting of rock bolts or one lining or a combination of both. A comprehensive parametric analysis investigating the effect of bolt bonded length, bolt spacing, bolt length, bolt pretension, bolt stiffness and lining thickness on the tunnel convergence is illustrated. The highlight of the proposed approach of preliminary support design is the use of a rock bolt and lining interaction diagram to evaluate the relative effectiveness of rock bolts and lining thickness in the design of the tunnel support. The concept of interaction diagram can be used to assist the engineer in making preliminary design decisions given a target maximum allowable convergence. In addition, DEM simulations were validated against available elastic solutions. To the authors’ knowledge, this is the first verification of DEM calculations for supported openings against elastic solutions. The methodologies presented in this article are illustrated through 2-D plane strain analyses for the preliminary design stage. More rigorous analyses incorporating 3-D effects have not been attempted in this article because the longitudinal displacement profile is highly sensitive to the joint orientations with respect to the tunnel axis, and cannot be established accurately in 2-D. The methodologies and concepts discussed in this article, however, have the potential to be extended to 3-D analyses.

Geotechnical investigations and preliminary support design for the Geçilmez tunnel: A case study along the Black Sea coastal highway, Giresun, northern Turkey

This study encompasses geotechnical investigations, stability assessments and design of the preliminary support systems for the Geçilmez tunnel which is constructed in Giresun for the improvement of the highway along the Black Sea coast. During the study, a detailed geological map of the study area was prepared and the geotechnical characteristics of the rock masses were determined. The rock mass classification of the tunnel grounds was performed by utilizing the RMR method, Q system, NATM and the Geological Strength Index (GSI) classification which was followed by performing a geotechnical investigation along the tunnel grounds in order to obtain the geotechnical parameters for the stability analyses of the portals and of the tunnel. Lugeon (water pressure) tests were performed in order to determine the permeability of the rock mass along the tunnel. The appropriate geotechnical parameters were utilized in order to perform rock slope stability kinematic and limit equilibrium analyses at the portals of the tunnel. Empirical preliminary tunnel support systems according to the RMR method, Q-system and NATM were determined. The structurally controlled instabilities within the tunnel sections were identified and the required preliminary tunnel support systems were determined to overcome these instabilities. Regarding the structurally controlled rock failures along the probable weak zones and lineaments (i.e., inactive probable faults or shear zones) during tunneling, wedge stability analysis was utilized to determine the potential wedge failures that could possibly occur during tunneling and to apply the necessary support systems for stabilizing any wedge failure in the tunnel. The induced stress distributions and deformations in the rock mass surrounding the tunnel grounds was investigated and the interaction of the support systems with the rock mass was analyzed by using numerical (finite element) modeling. In the finite element analyses it was assumed that the rock mass behaved as a fractured rock mass since the tunnel grounds were moderate to highly jointed. The objective of the numerical modeling was to check the validity of the empirical preliminary tunnel support requirements and also to compare the results with those obtained through assuming structurally controlled failures during tunneling. The performance of the preliminary tunnel support was also validated on the basis of thrust–moment interaction analyses. The results of the structurally controlled failure analyses, numerical analyses and thrust–moment analyses were compared in an attempt to determine the preliminary tunnel support systems to stabilize the Geçilmez tunnel.

Analysis of support requirements for a tunnel portal in weak rock: A case study from Turkey

In this paper, engineering geological properties of the entrance portal section of Konakonu Tunnel, located on Black Sea Coastal Highway, Turkey, is studied.Moderately weathered basaltic and andesitic tuffs orderly to be driven by the entrance portal section. Tunnel portal design in weak rock presents some special challenges to the designers, since misjudgements in the design of tunnel can lead to very costly failures. The entrance portal was analyzed by empirical and numerical methods. Both field and laboratory studies were carried out during this study. Field studies involved geological mapping, detailed discontinuity surveying and sampling. Laboratory tests were carried out to determine the physico-mechanical and elastical properties of rock units. For this purpose, tunnel stability analyses were performed at the entrance portal section. The RMR (rock mass rating), Q (rock mass quality), RMi (rock mass index), NATM (new Austrian tunnelling method) and GSI (geological strength index) systems were employed for empirical rock mass quality determination and preliminary tunnel portal support design. The parameters calculated by the empirical methods were used as input parameters for the FEM (finite element method) analysis. The results from the two methods were compared and preliminary support designs were carried out. This comparison suggests that for more reliable support design, empirical and finite element methods should be combined. Key words: Finite element method, rock mass classification systems, tunnel portal, weak rock.

Engineering geological evaluation and preliminary support design for the metro extension tunnel, Ankara, Turkey

The paper reports an assessment of the engineering geological characteristics of the rock mass to be encountered between Mecidiye and Gazino stations on the new extension of the Ankara metro and the determination of appropriate support and excavation methods. The rock mass quality was estimated using the rock mass rating (RMR), geological strength index (GSI) and rock mass quality (Q) systems and the tunnel divided into sections. The RMR, Q and NATM systems were used to determine the support and excavation methods in these areas. The deformations and stress concentrations around each tunnel section were investigated and the interaction of the support systems with the rock mass was analyzed using finite element software. It is concluded that rock mass classification systems should be used in tandem with numerical tools, although it is emphasized that the estimation of rock mass properties is not an exact science and both rock properties and numerical models should be refined based on observations and the results of instrumentation installed during the construction of a tunnel.

Numerical Analysis of a Tunnel Support Design in Conjunction with Empirical Methods

In this paper, preliminary support design of a tunnel was analyzed by numerical and empirical approaches. The case study for this analysis is a tunnel to be constructed on the Bilecik-Istanbul roadway in Turkey. The rock mass properties of the tunnel route and design support recommendations were obtained by using an empirical approach. The rock mass properties obtained from the empirical method were used as input parameters for the numerical analysis. The empirical and numerical results, in terms of support design, were evaluated. It was seen that the numerical analysis results supported by empirical values were logical and reliable.

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.

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.

Development of a back analysis algorithm using flac

The main focus of this study is vertical displacement monitoring and verification along with preliminary support design for the four geotechnical sectors of the twin tube Konak tunnel that was constructed in a highly populated area in İzmir. The displacements of the tunnel that were obtained through numerical analysis were verified by comparing them with the displacements obtained by construction monitoring. In the study area, volcanics, pyroclastics and some sedimentary deposits (sandstone, mudstone and conglomerate) often intertongue with each other especially in the exit portal area. The accurate estimation of the shear strength and deformation parameters of these units is important for the displacement predictions and for the assessment of tunnel stability. Rock mass classification systems, namely, RMR, Q system and GSI have been employed to obtain the rock mass shear strength and deformation parameters along with performing empirical tunnel support design. Numerical analysis has been performed by using the finite element analysis for assessing tunnel support design and for predicting the vertical displacements at five different measurement points around the tunnel periphery and in the four geotechnical sectors of the tunnel.An evaluation of the results revealed that about 70% of the predicted displacements matched the measured displacements while only about 12.5% of the displacement predictions exceeded the measured displacements by more than about 50%. Moreover, it was observed that neither the support system elements nor the rock mass have yielded due to the redistribution of the stresses imposed by the disturbance related with the tunnel excavation.

Proposed support design, Kaletepe tunnel, Turkey

In this paper, preliminary support design of Kaletepe tunnel, located on Bilecik-Istanbul highway, Turkey, was analyzed by empirical and numerical methods. The rock mass rating (RMR) and rock mass quality (Q) systems were employed for empirical rock mass quality determination. Numerical analysis for the stress–strain distribution of the tunnel excavation and support systems was also carried out. The applied support performance was investigated at different sections of the tunnel route. It was seen that empirical and numerical approaches showed similar results. This indicates that when the empirical method is supported by numerical method, the preliminary support design will be more reliable.

Preliminary support design for Ankara subway extension tunnel

This paper presents the results of preliminary support design of the subway tunnel for Ankara subway project in accordance with some empirical and numerical methods, using the phase 2D finite element method (FEM). The 5m diameter subway tunnel will advance through slightly to moderately weathered dacite and weak zones. Rock masses were characterized in terms of rock mass rating (RMR), geological strength index (GSI) and Q System. Core samples were tested in the rock mechanics laboratory to determine uniaxial compressive strength, deformability parameters, unit weight, tensile strength and triaxial compressive strength properties. Finally, rock mass strengths were determined by empirical and numerical methods. Required support system was suggested.