Tunnel Support System Research Articles

Fire-induced damage in tunnels: Thermo-mechanical modeling incorporating support system and geological conditions

The thermo-mechanical response of underground tunnels to fire loads is governed by interactions between the tunnel structure and the surrounding geological formation. Accordingly, for accurate prediction of damages in the tunnel structure subsequent to a fire event, it is critical to incorporate the state of the support system as well as in-situ conditions in the surrounding geology at the time of the fire event. Current tunnel-fire studies are mainly developed adopting beam-spring elements, thus disregarding the intricacies of the surrounding geological formation, its true constitutive behavior, as well as realistic tunnel-rock interactions. Another limitation in current tunnel-fire studies is assuming uniform temperature loads within the tunnel interface using time–temperature curves obtained from design codes, therefore ignoring the spatial nature of fire-induced temperatures along the tunnel interior. Temperature gradients can generate additional damage to the tunnel structure. This paper presents a comprehensive integrated numerical framework aimed to predict fire-induced damages in underground tunnels, incorporating four novel components: (i) detailed design of the tunnel support system and in-situ conditions; (ii) degradation of the original tunnel support system over the years due to presence of chloride and sulfates in nearby environment; (iii) thermal gradients generated along tunnel cross section due to real fire events; (iv) and thermo-mechanical interactions between the tunnel structure and the surrounding geological medium, incorporating thermal-induced strength degradation in the concrete and in the steel support elements following design standards from Eurocode. The numerical framework consists of fire simulation using computational fluid dynamics, and thermo-mechanical modeling of the tunnel response to fire. The proposed numerical framework has been utilized to simulate the Caldecott tunnel fire as the case study in this paper, and to evaluate the impacts from the in-situ stress regime and rock strength parameters on the thermo-mechanical behavior response of tunnel to fire events. Results provide a novel insight into the geomechanical response of horseshoe tunnels to fire. Findings reveal the critical zones prone to damage during a fire event to be highly governed by the in-situ stress field and the strength parameters of the surrounding geological strata.

Determination of Support Systems According to Rock Classes-Tlemcen-Akkid Abbas High Speed Railway Project-Algeria

Tüneller için yapılan kaya kütle sınıflamalarında karşılaşılan en büyük sorunlardan birisi, tünel kesitinde farklı birimler geçilmesi durumunda hangi desteklerin uygulanacağıdır. Tünel kesitinde üst yarıda zayıf birim ile karşılaşılırken alt yarı ve invert kesimi ise sağlam birimde yer alabilmektedir. Bu durumlarda ise kaya kütlesi en kötü koşullara göre belirlenirken, destek sisteminde ise farklılıklar olabilmektedir. Üst yarıda ağır destek sistemi gerekirken invert kesiminin sağlam birimde kalması durumunda invert kazısı yapılmayabilir. Ayrıca zayıf zeminlerde açılan tünellerde karşılaşılan sorunlar genelde sıkışma mekanizmasına bağlı olarak tünel destek sistemlerinde yenilmeler ile tünel aynasında karşılaşılan stabilite sorunları olarak karşımıza çıkmaktadır. Zayıf zeminlerde genelde destek sistemlerinin tamamlanmasından sonra uzun dönemde yenilmeler meydana gelmektedir. Sığ tünellerde ise, tünel çevresinde kemerlenme sağlanamaması sebebi ile destek sistemlerimin tasarımı daha kritiktir. Zira deformasyonlara müsaade edilmesi tünel çevresinde yüzeye kadar etkileyecek deformasyonları tetikleyebilecektir. Ayrıca tünel aynasında kazı esnasında oluşabilecek bir yenilmenin etkisi yüzeye kadar obruk şekilde yansıması olacak ve tüm tünel destek sistemlerini etkileyecektir. Bu sebeple sığ örtü altında zayıf zeminlerde açılan tünellerde deformasyonlara müsaade edilmeden destek sistemleri tamamlanmalıdır. Ayrıca tünel aynasında herhangi bir göçüğün oluşmaması için ayna destek sistemlerinin yapılması zorunludur. Bu çalışma kapsamında Telmcen Akkid Abbas Yüksekl Hızlı Demıryolu Projesinde açılan T10 tüneli destek sistemleri ve tünel tasarımı incelenmekedir. Yapılan çalışma sonucunda zayıf zeminlerde tünel destek sistemlerinin belirlenmesinde ayna ve tavan stabilitesinin son derece önemli olduğu görülmüştür. Ayrıca uzun dönemde sıkışma sorunlarının önüne geçmek için tünel destek sistemi basıncı belirlenirken, kritik destek sistemi basıncından en az 2-3 kat yüksek olması gerektiği görülmüştür.

An Overview of Tunnel Support Systems under Squeezing Rock Condition in Arun Hydroelectric Project, Stage-III, Eastern Nepal

An Overview of Tunnel Support Systems under Squeezing Rock Condition in Arun Hydroelectric Project, Stage-III, Eastern Nepal

Stability Evaluation of Bener Dam Diversion Tunnel During Construction

Bener Dam Diversion Tunnel is located in two rock units such as andesite and andesite breccia. Based on the engineering geology investigation, the subsurface tunnel will penetrate andesite breccia with good rock mass quality (fresh-moderately weathered), while surrounding the tunnel consist of andesite breccias with moderate and poor rock mass quality. Geological and engineering geology conditions are used as the basis for stability analysis of excavation methods and determining primary tunnel support systems. Geological Strength Index is used for determining rock mass parameters. The stability analysis of the openings and tunnel supports was carried out using an empirical and numerical method approach. The results of the empirical analysis of support system stability were then evaluated using the finite element method. The most suitable excavation method is applied by blasting. Evaluation of the support system based on rock mass rating with the finite element method modeling shows that the lowest safety score in the tunnel geomechanical zone is in zone 2 with a safety factor value at the final support is 1.786, however in general they are in a good condition which are safe from the initial excavation until the installation of supports stage.

Zayıf zeminlerde açılan büyük çaplı çift tüp tünellerde tünellerin birbirine olan etkisinin 3 boyutlu sayısal analizler ile incelenmesine bir örnek, Bolu Tüneli destek sistemlerinin değerlendirilmesi

Bolu Tüneli Ankara İstanbul Otoyolu üzerinde yer almaktadır. Bolu Tüneli proje çalışmalarına 1993 yılında başlanmış olup 2007 yılında trafiğe açılmıştır. 3 şeritli çift tünel olarak inşa edilmiştir. Tünel uzunlukları sağ tünel 2788 m sol tünel ise 2954 m’dir. Bolu Tüneli inşası sırasında 2 kez sel ve 2 kez depreme maruz kalmış ve tünelin Ankara girişinde yeralan Elmalık kesiminde 12 Kasım 1999 Düzce Depremi sonrası göçük yaşanmıştır. Bu göçük sonrasında tünel güzergahı değiştirilmiştir. Bolu Tüneli jeolojik olarak Kuzey Anadolu Fay Hattı ana kolu ile Düzce Fayı arasındaki tektonik bloktan geçmektedir. Tünelin İstanbul tarafı (Asarsuyu girişi) metakristalin temel kayaları içerisinde yer almakta iken Ankara tarafı (Elmalık girişi) sedimanter kayaçlar içerisinde bulınmaktadır. Tünel bu iki birimi Bakacak fayı ile kesilmektedir. Tünelde kazı aşamasında en büyük sorunların meydana geldiği Elmalık girişinde Elmalık fayı bulunmakta olup, tünelin bu bölümlerinde 1.2 m’ye varan deformasyonlar ile karşılaşılmıştır. Ayrıca Elmalık sağ tünelde fay geçişi sırasında 1996 yılında göçük meydana gelmiş, 12 Kasım 1999 Düzce Depreminde ise Elmalık sol tünel tamamen kapanarak göçük oluşmuştur. Yeni Avusturya Tünelcilik Yöntemi ile projelendirilen Bolu Tünellerinde yaşanan sorunlar ve geliştirilen destek sistemleri tünelcilik açısından çok değerli bilgiler içermektedir. Bu çalışma kapsamında Bolu Tünel destek sistemleri Flac3d programı ile 3 boyutlu olarak incelenmiş, iki tünelin birbirine olan etkisi, üst yarı, alt yarı ve invert kazılarında meydana gelen değişimler ortaya konmuştur.

Mechanical performance of shotcrete shell accompanied with steel sets

The appropriate support system for tunnels in squeezing conditions is the hybrid supporting system consisting of steel sets and a shotcrete layer. The stiffness of this hybrid supporting system is variable between two consecutive steel sets, i.e., a greater value in the vicinity of the steel sets than in other locations. This is because, the contribution of steel sets to confine tunnel convergence is not uniform, but depends upon the distance to each steel frame. Accordingly, the tunnel convergence becomes non-uniform between two consecutive steel sets, and a bending moment is developed on the shotcrete layer, which may influence its design.In this paper, an analytical model is presented to simulate the shotcrete performance between two consecutive steel sets. For this purpose, the shotcrete layer is considered a shell fastened by consecutive steel rings. Using the principles of the theory of shells in the axisymmetric condition, it is assumed that the shotcrete is composed of longitudinal elements glued together from their sides. Therefore, the problem is simplified to analyzing continuous beams leaned on consecutive supports but subjected to loading from the radial and tangential directions. By employing the convergence confinement method, the non-uniform displacements are found.The results obtained with this theoretical simulation well agree with those of numerical modeling by FLAC3D. Therefore, the presented theoretical solution can provide a tool for the preliminary design of the shotcrete layer and an initial estimate of its performance to be used in more complicated numerical models. The results show that the non-uniform radial displacement and bending moment enhance by increasing the tunnel depth and decreasing the rock mass quality. As well, as the thickness of the shotcrete increases, the bending moment reduces.

Tunnel support practice in small hydropower tunnels in the Himalayas through observational approach

With the high mountains, steep terrain and fast flowing river, the Himalayan region has a great opportunity and potential for hydropower development. In Nepal, many hydropower projects have been constructed and many are under construction among which majority of the project are small to medium scale project. For such project, medium size tunnel provides an economic and safe route for water convergence. Squeezing and collapse have been observed in most of the hydropower tunnels, which have resulted in support failure, as the tunnel passes through weak rock mass under high in-situ stress during construction. Due to insufficient tunnel closure measurements, field-based observation has been conducted to study the installed support at different tunnels in the Himalayas. The observational approach is used for analysis and recommendations have been made for designing a stable and safe support system for tunnels. Through an analysis of a case study from Nepal, comparison has been made on the design and practiced support systems, and description of supports used in various case histories from Nepal have been provided.

Numerical modelling for geotechnical assessment of rock mass behaviour and performance of support system for diversion tunnels using optimized Hoek-Brown parameters

Purpose. Empirical and numerical methods play a vital role in assessing rock mass behaviour quantitatively and qualitatively to design underground structures/caverns and support systems. This research aims to assess and evaluate the rock mass be-haviour for safe, stable, efficient, and economical design of support system for underground structures especially tunnels in diverse rock mass conditions. Methods. In this research, such empirical design methods as Rock Mass Rating (RMR), Q-system and GSI were used to characterize and classify the rock mass environment along the tunnel for the preliminary design of twin tunnels and support systems. The geomechanical parameters, Hoek-Brown failure criterion, and its variants for assessing rock mass behaviour were optimized using multiple regression of Stewart, generalized and globalized variant of nonlinear regression method. The rock mass was classified for the selected section A-A. The excavation method and support system for the said section were designed based on the results obtained from empirical modelling. 2D elasto-plastic finite element method (FEM) was used for numerical analysis of rock mass behaviour and performance of the designed supports in section A-A. Findings. The major rock type encountered in the diversion scheme comprises gabbronorite (GN) and Ultramafic Association (UMA). Based on the quantification of RMR, Q-system, and GSI, section A-A’s rock mass ranges from very poor to poor. From the numerical analysis for the said rock mass environment both RMR and Q system support recommendations are equally efficient to support the rock mass surrounding the tunnel. However, keeping in view the yield zone, especially in the crown, the rock bolt’s length should not be less than 5 meters. Based on the analysis of results, both the tunnels are at a safe distance from each other. Originality. In this research, the design input parameters for numerical modeling were optimized by using different techniques to eliminate the chances of error in evaluating rock mass behaviour and designing an optimum support system in the said rock mass environment. Practical implications. The assessment of rock mass behaviour and the design of optimum support systems in heterogenous conditions is quite challenging and requires thorough investigation through different design techniques. This research provides a refined meth-od to be used for the safe, stable, and economical design of tunnels.

Prediction of Final Displacement of Tunnels in Time-Dependent Rock Mass Based on the Nonequidistant Grey Verhulst Model

Time-dependent deformations of rock are important factors for the design and construction of tunnels in the rock masses with time-dependent strength and deformation properties. Therefore, determination displacement and stable time of tunnel are an indispensable task in geotechnical engineering, especially during the design and construction of underground structures. However, in some types of rock masses, the tunnel displacement may increase for months or years after the excavation owing to the rheological behavior of the surrounding rock masses, which greatly influences the selection of the initial tunnel support system, the excavation layout, and the determination of its load-carrying capacity. In this paper, we present a method to quickly predict the final displacement and stable time of tunnels in time-dependent rock mass using the improved nonequidistant grey Verhulst model (INGVM) with Fourier series, which is used to reduce the periodic residual error. The proposed method is validated fairly via a test for a newly excavated roadway of −600 m level in a coal mine, Democratic People’s Republic of Korea. These results are useful references for similar projects in the future.

Physical model simulation of rock-support interaction for the tunnel in squeezing ground

The existence of squeezing ground conditions can lead to significant challenges in designing an adequate support system for tunnels. Numerous empirical, observational and analytical methods have been suggested over the years to design support systems in squeezing ground conditions, but all of them have some limitations. In this study, a novel experimental setup having physical model for simulating the tunnel boring machine (TBM) excavation and support installation process in squeezing clay-rich rocks is developed. The observations are made to understand better the interaction between the support and the squeezing ground. The physical model included a large true-triaxial cell, a miniature TBM, laboratory-prepared synthetic test specimen with properties similar to natural mudstone, and an instrumented cylindrical aluminum support system. Experiments were conducted at realistic in situ stress levels to study the time-dependent three-dimensional tunnel support convergence. The tunnel was excavated using the miniature TBM in the cubical rock specimen loaded in the true-triaxial cell, after which the support was installed. The confining stress was then increased in stages to values greater than the rock's unconfined compressive strength. A model for the time-dependent longitudinal displacement profile (LDP) for the supported tunnel was proposed using the tunnel convergence measurements at different times and stress levels. The LDP formulation was then compared with the unsupported model to calculate the squeezing amount carried by the support. The increase in thrust in the support was back-calculated from an analytical solution with the assumption of linear elastic support. Based on the test results and case studies, a recommendation to optimize the support requirement for tunnels in squeezing ground is proposed.

Global Sensitivity Analysis for a Tunnel-Support System in Weak Rock Mass for Both—Uncorrelated and Correlated Input Parameters

Global Sensitivity Analysis for a Tunnel-Support System in Weak Rock Mass for Both—Uncorrelated and Correlated Input Parameters

Engineering Geological Investigation of the Kırık Tunnel Route

Engineering structures are of great importance in the comfort and safe travel of people who prefer the highway in the existing transportation networks. Highway tunnels are one of the most important engineering structures that easily overcome transportation problems. This study investigates the geological and geotechnical structures of the Kırık tunnel on the Erzurum-Rize highway route, makes the rock mass classification required for tunnel excavation according to the New Austrian Tunneling Method and determines the tunnel support systems. Geological mapping, drillings, geological- geotechnical investigation based on in-situ and laboratory tests were carried out in order to reveal the physical and mechanical properties of the geological formations on the tunnel and to determine the basic data required by the project. It is divided into 4 classes on the basis of NATM Rock Classification along the tunnel axis. Rock support types related to rock classes defined as B1, B2, B3 and C2.

Weak rock mass characterization for determination of support system of the DK99-DK100 Jakarta – Bandung speed railway tunnel, Indonesia

Rock mass characterization is a crucial factor in determining a safe design of a tunnel support system. This research is carried out in constructing tunnel DK 99 – DK 100 high-speed railway Jakarta-Bandung, Indonesia. The research includes determining surface and subsurface quality of rock masses based on rock mass classifications of Geological Strength Index (GSI) and the Basic Quality (BQ-System). Both rock mass classifications were then correlated to the Rock Mass Rating (RMR) for the tunnel support system determination. Another support system determination based on the Japanese Society of Civil Engineers (JSCE, 2007) method was also compared. The result showed that the rock masses at the tunnel elevation had very poor to poor quality according to GSI, RMR, and BQ. The rock masses were classified as category class E and DII according to the JSCE competence factor. The recommended tunnel support system based on the RMR are shotcrete, rockbolt, steel set, while those based on the JSCE are shotcrete, rockbolt, steel support, and lining. This paper is expected to provide a better understanding of tunnel construction in weak rock masses, particularly in Indonesia.

Construction of twin tunnel in weak and blocky rock mass by using arch supporting method

Design of tunnel excavation and support system in weathered and blocky rock mass is usually a principal challenge in tunneling. In this study, the excavation method of twin tunnel was newly taken into consideration in the condition of weak rock mass, the section size of tunnel was reasonably determined, and new supporting method was established. Firstly, the mechanical characteristics of the project rock mass were determined in each section of tunnel using in-situ point load test (PLT) and RocLab software. Then, design of twin tunnel excavation from mono-tunnel excavation in the weak parts of rock mass was proposed and section of twin tunnel joint was reasonably determined based on the safety and stability of the twin tunnel joint by FLAC3D. Finally, the sequential excavation method of combining top heading and benching with arch supporting method (ASM) was newly proposed and the validity of this method was determined by the numerical simulation modeling. Introducing ASM for the support system ensured the support strength in the excavation tunnel. Advanced excavation scheme and the support system have been successfully applied to ensure the safety and conveniency of the target tunnel construction, with about twice reduction of construction time and 1.5 times raising of stability factor. As a result, proposed method in this paper can be used to all manual tunnelling and underground structures in weak and blocky rock mass.

Assessment of collapse mechanism of a High Speed Railway Tunnel (T341 Tunnel, Turkey)

Excavation and implementation of tunnel support system of T341 tunnel of Ankara-Sivas High Speed Train Project were completed recently. Throughout the tunnel excavation, serious stability problems occurred both in the entrance portal section and tunnel. The purposes of this study are to explain the failure mechanism and to propose a suitable support system for the section between Km: 341 + 040 - 341 + 114. Tunnel works were interrupted after the collapse, which occurred in a section of approximately 74 m between Km: 341 + 040 - 341 + 114. As a result of the collapse in the tunnel, local settlements emerged on the surface and it was observed that the effects of the collapse on the surface, as well. To surpass the collapsed section, extra reinforcements were performed by grouting taking place both at the surface and inside the tunnel. Afterwards, tunnel excavation was completed in relatively short stages by applying double umbrella system and rigid support system. Consequently, the causes of the failure, excavation and support system design and results of the numerical analyses are discussed.

Numerical Analysis of Tunnel Support System at Pune Metro

Pune has witnessed enormous industrial growth, rapid urbanization in the recent past and has put the city's travel infrastructure to stress. Being a densely populated area, Pune's traffic needs cannot be met by road-based transportation systems and additional flyovers. Considering this, the Pune Metro project a strong public transport system partly elevated, and partly underground Line 1 and the completely elevated Line 2 has been discussed and undertaken by Maha Metro Rail Corporation. With the rise in demand, the responsibility for a safe and efficient public transport system also increases hence proper planning, designing, and execution play a vital role. The underground tunnel stretch of the Pune Metro Line 1 project is carried out by TBM and by segmental lining as a support system. By geotechnical parameters and FEM, RS2 software author analyses the ground behaviour and support system and conveys a basic understanding of ground behaviour and results in guidelines for designing the underground tunnel.

Empirical Support Design for Proposed Diversion Tunnels at Dasu Dam Site Pakistan


 This research work presents the rock mass characteristics and tunnel support system recommendations for hydroelectric power tunnels at Dasu dam site Pakistan. Two inverted U-shaped tunnels are proposed at the left bank of Indus river. The tunnels have inlet portals at an elevation of 773.00 m and outlet portals at an elevation of 758.00 m. The thickness of rock cover above the tunnels is between 100 and 200 m. Three types of rock are encountered at project site including Granulite, Amphibolite and Gabbronorite. Granulite rocks are encountered along the alignment of tunnels. Rock mass is classified using Rock mass rating (RMR) and Tunneling quality index (Q system). Support system is suggested based on values of Q and RMR. Correlation between Q-index and RMR is also derived.
 

Three-Dimensional Finite Difference Analysis on the Ground-Sequential Tunneling-Superstructure Interaction

In this paper, a three-dimensional finite difference analysis is presented to investigate the interactive effects of sequential tunneling and the superstructure on the settlement profile of the ground. To simulate the practical sequential tunneling procedure, tunnel excavation is conducted in a step-by-step framework; tunnel excavation starts from the beginning of the model and is updated in a continuous manner, and the installation of the tunnel support system is done with a delay step compared to tunnel excavation. The numerical modeling accuracy is validated using the available analytical and numerical solutions for both two-dimensional and three-dimensional simplified cases. The well-validated modeling procedure is adopted to investigate effects of tunnel diameter, depth of tunneling, and number of superstructure stories on the profile of occurring settlements. Two cases of free-field and three-dimensional superstructural modeling are compared with regard to the effect of tunneling. In addition, the effect of tunneling advancement on the generation of excess structural forces and moments are studied as another important factor in the soil-tunneling-superstructure interaction problem. It is observed that, in the free-field case, with advancing the tunnel face, the longitudinal settlement profiles approach the steady-state condition and the maximum ground settlement tends to converge to a specific value, whereas as the tunnel passes under a structure, the settlement increases steadily as the tunnel progresses. There is a direct relationship between the depth and diameter of the tunnel and the settlement. In addition, the effect of the number of superstructure stories on the maximum settlement is more considerable compared to the free-field condition. According to the results, when the tunnel passes under 8-story and 12-story structures, the maximum settlement increases by 40% and 70%, respectively, compared to the free-field condition. It is also shown that tunneling-induced settlements result in the regeneration of structural forces.

Effects of Portal Failure on Tunnel Support Systems in a Highway Tunnel

Effects of Portal Failure on Tunnel Support Systems in a Highway Tunnel

Probabilistic stability assessment of tunnel-support system considering spatial variability in weak rock mass

Analysis of tunnel-support system stability with uncertain rock mass properties is conducted in this paper. A horseshoe shaped tunnel driven in weak rock mass is analyzed through deterministic, random variable and random field approaches. Performance of the tunnel in probabilistic analysis was assessed by defining three limit states which ensure that tunnel convergence remained below a safe threshold level, the rock bolts installed are embedded sufficiently beyond the depth of yielded rock mass and load induced on liner support does not exceed its capacity. Both unsupported and supported tunnels were analyzed with deterministic, random variable and random field approaches. Fourier series method was applied to discretize the random fields, and random finite difference analysis was conducted using Monte Carlo simulations. Scale of fluctuation (SOF) for isotropic random fields and horizontal and vertical SOF ratios for anisotropic random fields were varied to study their effect on performance of the tunnel and failure mechanisms involved. It was found that SOF significantly influences the output statistics and Pf of the limit states. It was observed that, random variable approach underestimates the performance of the tunnel-support system; however, it can be adopted as conservative option in absence of data required for random field characterization.