Austrian Tunneling Method Research Articles

The effectiveness of new austrian tunnelling method (NATM) for hydro power plant construction: lau gunung power plant, north sumatera, indonesia

Hydro Electric Power Plant is a power generating system using gravity fall of water as the main force to move the turbine and generate electricity. The construction purpose of Lau Gunung hydropower (2×7. 5 MW) that is located in Dairi, North Sumatra, is to Supply power to 14,000 house of the surrounding region. The river run-off system, where the water is immediately contained and then flowed through a tunnel considering the discharge flowing river, where it is constant and does not occur in the fluctuating water level. The Lau Gunung river has the minimum flow that can exceed from 15 to 25 m 3 /s with a high tunnel dimensions of 4 metres long, 3,9 metres wide and a length of 1,6 kilometres. In terms of the analysis of the time effectiveness of the NATM can be saved because of the continuous work of 24 hours, without any obstacles in which the sub methods used include the drilling & blasting. The tunnel then use the form of steel reinforcement rib and Safety shotcrete lining. The general review may show that using NATM result a tremendous savings, also the use of horse shape conduce small displacement which is effective for the construction.

Tunneling in lesser Himalaya, Jammu and Kashmir, India with special emphasis on tectonic mélange

Himalayan fold belt has full of geological surprises, ‘melange’ is one of them which create difficulties during tunneling. Such melange completely went unnoticed during surface mapping and geotechnical investigation preceding the construction of the Udhampur railway tunnel (URT). During the construction, the melange zone has encountered across the tunnel, which occurs along the Tanhal thrust (equivalent to MBT) that separates the Murree Group and the Shiwalik Group. The melange was characterized by a chaotic, heterogeneous geological mixture of stronger blocks (scale independence) and weaker sheared fine-grained matrix, often termed as “block-in-matrix rocks” or bimrocks, which enforced mixed face tunneling. The heterogeneity in a tectonic melange led to stress concentrations in the rock blocks, and there were relatively high deformations within the matrix also. Release of stress from the blocks due to excavation, with unfavorable joint and thrust orientations enforced brittle failure of the blocks (face and crown collapses) while matrix deformation (time dependent) caused convergence of primary support later. Additionally, the clay minerals with high swelling potential within the matrix swelled and created pressure on the primary support. Due to the geomechanical heterogeneity in melange, homogenizing the rock-mass by the commonly used quantitative systems might have lead to an inappropriate design and construction. The adopted New Austrian Tunneling Method (NATM) proved to be an useful tool for tunneling.

Excavation-Damaged Zone around Tunnel Surface under Different Release Ratios of Displacement

AbstractA tunnel excavation-damaged zone (EDZ) will gradually form with increasing release ratios of displacement (RRD) in the rock mass surrounding a tunnel. This paper presents a study of the longest subway tunnel in China, constructed with tunnel-boring machines (TBM) and the new Austrian tunneling method (NATM) in soft and weak rock ground. On the basis of the damage constitutive model, some studies are conducted using the FEM. The spatial distribution rules of EDZ and RRD are studied with a three-dimensional (3D) numerical simulation. The results show that the spatial support effect of the tunnel face is concentered in the range of approximately two times that of the tunnel diameter. A two-dimensional numerical simulation is carried out to study the relationship between the EDZ and RRD. The results show that the EDZ initiates when the RRD is more than 0.5, and the EDZ suddenly increases when RRD is more than 0.9.

3D NUMERICAL MODELLING OF SHALLOW TUNNEL IN WEATHERED GRANITE INCORPORATING MULTI-STAGE EXCAVATION AND PRE-SUPPORT

Generally tunnelling in urban ground condition is not always favourable due to the tunnels’ susceptibility to major displacement especially when excavated in the soft soil and/or weak weathered rock formation. Apart from conventional support systems, pre-support measure like forepoling umbrella arch is frequently used to reinforce the ground. Modern computational tools allows the inclusion of multi-stage excavations and pre-support which was not possible in two dimensional (2D) plane strain. This paper demonstrates the three dimensional (3D) finite element analysis of Pahang-Selangor raw water transfer tunnel, as a reference case, where multi-stage excavation and pre-support are incorporated as intrinsic part of the model. The New Austrian Tunnelling Method (NATM)-3 segments which encountered Grade III weathered granite, having shallow overburden cover, was selected for numerical analysis using RS3 software. Comparison between simulated and observed data has shown good agreement during verification

Shotcreting in Tunnels

Since the development of New Austrian Tunneling Method (NATM), shotcrete in tunnels has been widely applied. It’s most important features are durability, speed of application and cost effectiveness. The New Austrian Tunnelling Method (NATM) is characterized by the continuous adaption of driving parameters, such as unsupported length (i.e., the distance between the tunnel face and the shotcrete lining, excavation rate, etc.) to the observed response of the already-excavated part of the tunnel. In order to devise such tables, two different arch sections, together with three different overburden types, were considered. Some Geotechnical parameters such as apparent cohesion and angle of internal friction of surrounding rocks were chosen, based on the five-category classification of Bieniawski. Two K0 factors (the ratio of horizontal stress to vertical stress) and an average rock density were utilized. Using numerical methods, 60 models were then devised in this way.

Proposed soil classification based on the experiences of soft-ground tunneling in Iran

An essential step in successful mechanized and conventional tunneling operations is a thorough characterization of ground conditions and identification of geological and geotechnical risks. In bored tunneling, this and other information is needed in order to select the appropriate tunnel boring machine (TBM) and to determine its technical specifications for proper soil conditioning and optimal TBM performance. In conventional tunneling, this information is also important for ensuring the correct choice of drilling method and minimizing drilling risk. The major geological risks in tunneling (New Austrian Tunneling Method [NATM] or mechanized) are stickiness and clogging of soils, soil abrasi veness, soils with low fine content or oversized grains, tunnel collapse and instability, groundwater fluctuation, mixed-face conditions, liquefaction, and soil movement. Experiences from both conventional and mechanized tunneling in Iran show that the potential for each geological hazard is higher in certain types of soils. As such, knowledge of the various soil types is important for predicting soil behavior and possible geological hazards. In this study, we present a simple and practical classification of soil types for the prediction of soil behavior and geological hazards in both conventional and mechanized tunneling. With this method, soils are classified based on two parameters. The first is soil grain distribution. For this purpose, tests were conducted on soil samples from the test pit and geotechnical boreholes, and the percentage of particles remaining above a no. 4 sieve and those passing through a no. 200 sieve were calculated for each sample. The second parameter is the consistency index, which is estimated from the Atterberg limits. The soils were classified into ten groups based on these two parameters, and soil behavior and geological hazards for each class were then predicted based on Iranian tunneling experiences. Finally, the real soil behavior and geological hazards in the Qom tunnel were analyzed to determine the accuracy of the predictions. The results showed that the predictions were largely comparable to actual conditions. These results were then directly used for preliminary and permanent lining design and recommendations for soil conditioning, as well as for structural design of the different stations.

Analytical‐numerical solution for stress distribution around tunnel reinforced by radial fully grouted rockbolts

SummaryThis paper presents an analytical‐numerical approach to obtain the distribution of stresses and deformations around a reinforced tunnel. The increase in the radial stress of the reinforced tunnel, based on the performance of a bolt, is modeled by a function, which its maximum value is in the vicinity of the bolt periphery and it exponentially decreases in the far distance from the bolt. On the basis of this approach, the shear stiffness between the bolt and the rock mass and the shear stress distribution around the bolt within the rock mass are also analytically obtained. The results are compared with those obtained by the assumption of ‘uniform increase of radial stress’ method, which is made by the previous studies. The analyses show when the bolts' spacing is large, the safety factor must be increased if the ‘uniform increase of radial stress’ method is used for the design.Finally, a procedure is introduced to calculate the non‐equal deformation of the rock mass between the bolts at any radius that can be useful to compute the bending moment in shotcrete layer in New Austrian Tunnelling Method (NATM) approach. Copyright © 2016 John Wiley & Sons, Ltd.

Non-destructive evaluation of the grouted ratio of a pipe roof support system in tunneling

The pipe roof system is widely used in the New Austrian Tunneling Method (NATM) as the main support system. Thus, the integrity of the pipe roof system influences the tunnel stability. The purpose of this study is to evaluate the grouted ratio of a pipe roof system using a non-destructive method in the laboratory and in the field. In the laboratory tests, four specimens embedded in soils and five non-embedded specimens are prepared with different grouted ratios of 0%, 25%, 50%, 75%, and 100%. The steel pipes are 6m in length, 60.5mm in external diameter, and 3.8mm in thickness. Field tests are conducted with two fully grouted pipes with dimensions of 12m in length, 60.5mm in external diameter, and 3.8mm in thickness. The reflection method of guided waves, which are generated by a hammer impact and are measured using an acoustic emission sensor, is used for the non-destructive testing. Experimental studies demonstrate that the group velocities and the main frequencies of the guided waves decrease as the grouted ratio increases for embedded and non-embedded specimen in soils. The variation of the main frequency, however, is more significant than the variation of the group velocity. In addition, the group velocities and main frequencies of the field specimens are lower than those of the embedded specimens. This study demonstrates that the variations of the group velocity and main frequency may be used effectively to estimate the grout ratio of a pipe roof system in tunneling.

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

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

Development of an IFC-based data schema for the design information representation of the NATM tunnel

A tunnel data schema employing the New Austrian Tunneling Method (NATM) is proposed to efficiently manage and exchange the design information of road tunnels between different computer environments. The data schema was developed by extending the Industry Foundation Classes (IFC) used as standards in Building Information Modeling/Model (BIM) projects. The design guidelines and tunnel drawings were analyzed in order to apply the design information of the NATM road tunnels. From the analysis results, the applicable IFC elements were identified through a comparative analysis with the existing IFC data schema, and new items were defined for the additional necessary elements. The newly defined elements were classified into the parts representing the information of the space occupied by the tunnel and that representing the information on components such as shotcrete, steel ribs, and concrete linings. The applicability of the developed schema was examined by using it to construct an experimental environment, in which information modeling was possible.

REDUCING BUG-HOLES ON TUNNEL LINING CONCRETE BY USING COVERING SHEETS

This study focused on bug-holes on sidewalls of tunnel lining concrete. The bug-holes of lining concrete may negatively affect aesthetics and durability of NATM (New Austrian Tunneling Method) tunnels. Most bug-holes appeared on concrete surface are generated from entrapped air during consolidating concrete. In particular, the sidewall of tunnel lining is constructed with negative angles, so bug-holes are often observed on the sidewall. Seven concrete specimens were prepared to simulate conventional tunnel lining. In the experimental investigation, breathable-waterproof material sheets and permeable sheets were used. The primary experimental parameters are (a) covering-sheet materials and (b) form surfaces such as ceramic-coated steel with grooves. The study examined bug-hole distributions in the concrete specimens using the various sheets. The bug-hole distributions were quantified by using an image analysis developed in this study. The test results show that quantity of bug-holes of concrete using the sheets is lower than the quantity of concrete without sheets. It was noteworthy that the bug-holes were hardly observed in the test using the form covered with the permeable sheets.

Probabilistic analysis of tunnel loads using variance reduction

The selection of input parameters for the numerical modelling of geotechnical structures is problematic due to their variability and uncertainty. Generally, parametric studies are required to evaluate the impact of input parameters on the modelling results. The utilisation of various statistical methods can bring significant benefits, such as probabilistic distributions of the modelling outputs and the probability of failure. This paper presents a variance reduction method known as ‘Latin hypercube sampling'. Special attention is paid to the Latin hypercube sampling mean, which represents a more efficient sampling scheme within the method's framework. The performance of the mean method is evaluated by comparison with the standard median method, and the necessary number of simulations is recommended. To take the statistical dependency of input variables into consideration the method mean is combined with the simulated annealing method. The effectiveness of Latin hypercube sampling methods and their practical application is demonstrated by static calculations for the Brusnice tunnel in the Czech Republic. The tunnel is a part of the Blanka tunnel complex on the Prague City Circle Road excavated by the new Austrian tunnelling method. The two-dimensional numerical model was prepared using the finite-element method. The modelling results were evaluated in terms of confidence intervals.

Criteria for the selection of construction method at the Ovit Mountain Tunnel (Turkey)

The Ovit Mountain Tunnel (OMT) is an highway tunnel under construction at Mount Ovit between Ikizdere (Rize) and Ispir (Erzurum) in NE Turkey. It will be the country's longest tunnel about 14700 m long in twin tubes. This paper compares and assesses tunnel excavation by Tunnel Boring Machine (TBM) excavation or drill and blast method for the OMT. Rock mass and material characteristics were evaluated to identify the excavation method. The rock mass classification of the tunnel grounds was performed by utilizing the Rock Mass Rating (RMR), Q system and New Austrian Tunnelling Method (NATM) which was followed by a geotechnical investigation along the tunnel. Twelve boreholes with a total length of 1116.5 m were drilled to assist and verify rock mass classifications. Seventy five rock samples were obtained for mechanical test. TBM method was selected at preliminary design stage of the OMT. But now, the OMT is driven by drill and blast method, using hydraulic excavators and the support is based on the principles of the NATM. The selection of this tunnelling excavation method was decided by morphological site conditions, geological, geotechnical site conditions, time and economic criteria.

COMPARISON OF TUNNELLING METHODS NATM AND ADECO-RS

The New Austrian Tunnelling Method (NATM) has been often used in the CzechRepublic in last two decades. One of the methods, without application in the Czech Republic,is an Italian method called ADECO-RS, which has reached significant use in Italy and someother countries. It is the method of controlled deformation, which uses mainly the horizontalanchoring of the tunnel face to reinforce the area in front of the face (advance core). Thistechnology is especially important in weak and soft rocks where is necessary to excavatequickly and smoothly with minimum disruption of initial stress state of the rock mass in thevicinity of the excavation. The use of NATM can be in some cases uneconomical andtechnically inadequately challenging and in such cases would be appropriate to chooseanother technology.Given the facts above, in the Czech environment there is no data available forcomparison of these methods not only in terms of numerical modelling, but also in terms offeasibility and usability.The paper summarizes history of the tunnelling methods and it is closer devoted toNATM and ADECO-RS tunnelling approaches. The basic principles of both methods are setand further the comparison of these methods is made on a theoretical level.The paper hereinafter includes the analysis of fibreglass face anchors applicationduring the construction of three-aisled Veleslavín Station and the impact assessment of tunnelface anchoring during the excavation of ventilation tunnel on the newly built part of the PragueMetro „V.A“.The paper also deals with practical knowledge gained during the technical visit of ItalianVal di Sambro Tunnel which is built according to ADECO-RS approach. These findings areessential for the correct interpretation of Lunardi method.

Two-dimensional numerical tunnel model using a Winkler-based beam element and its application into tunnel monitoring systems

Infrastructure including public facilities has become ubiquitous. Remote measurement instruments based on automatic or real-time-oriented methods also substitute for the conventional tunnel measurement approach, and thereupon the requirements for efficient measurement and analysis processes on examining civil structures are increasingly needed. With the New Austrian Tunneling Method, in particular, huge amounts of measurement data are processed to estimate the safety of a tunnel support system under construction and operation. Therefore, the analysis model for a tunnel monitoring system ought to be lighter and faster. For this reason, this study developed a two-dimensional tunnel analysis model to substitute for the conventional model (the beam-spring model), and proposed an application of the model to a tunnel monitoring system. In the proposed model, Winkler-based beam elements were applied as an alternative to beam and spring elements. A process is also proposed to determine the ground state of the Winkler-based beam element. This process is related to simulation of the ground resistance loss in tensile ground areas. Four examples were examined to verify the model: one finite beam on tensionless foundation (Example 1); two circular tunnels (Examples 2 and 3); and one horseshoe-shape tunnel (Example 4). Numerical analysis was implemented with a specific code which developed using finite element method. Comparing the numerical results with those of the corresponding beam-spring models, in Example 1, the convergence rate of the proposed model was at least fourth times. In other examples, the results of the proposed model showed a nearly perfect agreement with those of the beam-spring model, whereas the computational efficiency of the proposed model was superior by twofold. Thus, our results suggest that the use of Winkler-based elements in a tunnel model could help enhance the performance of tunnel measurement systems.

Finding Best Model to Forecast Construction Duration of Road Tunnels with New Austrian Tunneling Method Using Bayesian Inference

Forecasting project final duration (i.e., time at completion) is crucial to project risk management and is always sought by project managers during the construction period. Because of a strong correlation between past and future performances in linear projects, past progress data are the best source of information to forecast final duration of this type of project, including tunneling projects constructed by the new Austrian tunneling method (NATM). Bayesian inference is a robust probabilistic approach that can provide accurate forecasts of final duration based on a project's past performance. However, results of research in this field have shown that selecting an appropriate model, which represents the unknown pattern of the project's actual progress well, is the most challenging and subjective part of this approach. Effective risk management necessitates looking for the best model that can forecast project final duration accurately and precisely, especially early in the project. This research was aimed at finding a best progress model for NATM tunneling projects by conducting Bayesian analysis on available data of a massive project, the Niayesh highway tunnel in Iran. The analysis showed that the dual Gompertz function (with flexible lower asymptote) was the most reliable model for this purpose. The results of this research bring advantages to the planning and risk management of NATM tunneling projects, which are discussed in this paper, and can be very useful for future NATM tunnel constructions.

Analysis of labour accidents in tunnel construction and introduction of prevention measures.

At present, almost all mountain tunnels in Japan are excavated and constructed utilizing the New Austrian Tunneling Method (NATM), which was advocated by Prof. Rabcewicz of Austria in 1964. In Japan, this method has been applied to tunnel construction since around 1978, after which there has been a subsequent decrease in the number of casualties during tunnel construction. However, there is still a relatively high incidence of labour accidents during tunnel construction when compared to incidence rates in the construction industry in general. During tunnel construction, rock fall events at the cutting face are a particularly characteristic of the type of accident that occurs. In this study, we analysed labour accidents that possess the characteristics of a rock fall event at a work site. We also introduced accident prevention measures against rock fall events.

Useful concepts for application of new Austrian tunnelling method in tunnel construction (NATM)

Useful concepts for application of new Austrian tunnelling method in tunnel construction (NATM)

A case study on Tunneling using NATM

The new Austrian tunneling method (NATM) is widely applied in design and construction of underground engineering projects. The NATM is also known as sequential excavation method (SEM). The NATM is a construction method, which is very adaptive according to changing subsoil conditions and changing shapes of cross-sections. NATM/SEM enhances the self-supporting capacity of the rock or soil by mobilizing the strength of the surrounding ground. It is today by far the most resistant tunnel support system in earthquake endangered zones. Experience from past projects has helped to identify several critical success factors for safe and cost effective NATM/SEM tunneling. According to actual site conditions the design of NATM is with a certain degree of flexibility for adjustments. Unit price contracts to support flexibility, adaptability and balance risk sharing - a proven way to a cost effective and state-of-the-art product. Skilled contractors are familiar with the principles of NATM/SEM and the utilization of the ground support measures. Basic idea behind NATM is that immediate rocks are self-supporting and this method is economical. Here the cycle time achieved is 12 hrs. for class I, II and III but for the rock classes IV and V the cycle time achieved normally is 16–18 hrs. The NATM is most appropriate support system for tunneling in soft ground i.e. rock class IV and below. The installation of reinforced lattice girder with wire mesh, shotcrete and rock bolting provides a uniform load bearing structure in soft rocks.

Temperature Monitoring on the Final Tunnel Lining

Modern tunnel structures are presently implemented primarily by conventional excavation, using the New Austrian Tunneling Method. Two linings are usually used to support the excavated area. The primary tunnel lining serves for consolidation of the extracting during tunneling and the secondary tunnel lining ensures the safe use of the structure during its life time. The design and evaluation of the tunnel lining is a comprehensive process that involves a lot of input conditions. We are not always able to define these inputs exactly. In order to specify the amount of secondary lining load, we must know not only the load by the rock but also e.g. the hydrostatic load and deformation behavior of concrete during its aging. The lining is also influenced by local climatic conditions. It is necessary to include effects of various temperatures on the lining in our design. The measurements carried out in the already completed structures serve us for a more exact determination of these temperatures. Based on the results from these measurements, we can determine the distribution of temperatures in the profile and the behavior of the construction versus the climate change more exactly. Monitoring the temperature development takes a long time. The specification of this behavior should lead to a material saving when new constructions are designed.