Austrian Tunneling Method Research Articles

Problems Encountered during a Railway Tunnel Excavation in Squeezing and Swelling Materials and Possible Engineering Measures: A Case Study from Turkey

The T3 railway tunnel—under construction within the scope of the Bursa-Yenişehir high-speed train project—is located in northwestern Turkey and has a length of 1250 m. The tunnel is being constructed entirely in silty clay/clayey silt, sand, and clay units, and it is designed in accordance with the principles of weak ground tunneling described by the new Austrian tunneling method (NATM). When the tunnel excavations began in 2013, during and after portal excavations, a failure occurred at the entrance of the tunnel; thus, a revision of the support systems became mandatory. While the excavation works proceeded after the revision phase, a collapse occurred again at the tunnel face where the overburden thickness was low. This study presents the mechanisms of the collapse that took place at the portal location and in the middle of the tunnel. The proposed tunnel support systems and their numerical analyses are also discussed, because the case is interesting for the tunnel community and will inform future tunnel construction work. For this reason, the relationship between portal excavation and tunnel excavation stability is described. Consequently, tunnels excavated through weak ground conditions are considered, and the importance of considering the face stability of tunnels in tunneling studies is underlined.

On discrepancies between time-dependent nonlinear 3D and 2D finite element simulations of deep tunnel advance: A numerical study on the Brenner Base Tunnel

A numerical study on a stretch of the Brenner Base Tunnel, characterized by high overburden and driven according to the New Austrian Tunneling Method, is presented. At first, a 3D time-dependent nonlinear finite element model is developed, taking into account the construction process, nonlinear material behavior of the surrounding rock mass, and the time-dependent nonlinear material behavior of shotcrete. Next, the prognosis capabilities of a simplified time-dependent 2D model are investigated, since in engineering practice 3D computations are often not feasible due to their computational expense. For this model, a thorough calibration of a particular stress release scheme based on the 3D model is performed, aiming at a good fit of the displacements. Hence, the remaining discrepancies of the response of the two models can be attributed to the simplifying assumptions inherent in the 2D model. The computed displacements are validated by comparison with in situ measurement data. It will be demonstrated that both the 3D model and the calibrated 2D model together with the nonlinear constitutive models allow a good correspondence of the predicted displacements with the measured ones at the tunnel site. However, striking discrepancies are observed for the predicted evolution of the stress state in the shotcrete shell.

Evaluation of twin tunnel-induced surface ground deformation by empirical and numerical analyses (NATM part of Eurasia tunnel, Turkey)

Pre-support systems are very important for inner-city shallow tunnels in order to minimize twin tunnel-induced surface deformations. However, previous studies concerning the assessment of the magnitude of surface displacements caused by twin tunneling have not considered the effects of a pre-support system and stress release by deformation. The aim of this study is to introduce a procedure for obtaining modification factor including the effects of a pre-support system and the rock mass quality that can be used as a reduction ratio in the prediction methods used for twin tunnel-induced surface settlement. The data comes from Asian side of the Eurasia Tunnel excavated by the New Austrian Tunneling Method and supported by the forepoling and umbrella arch method. In this study, numerical analyses were performed on 12 cross-section lines along the tunnel route to update the geological profile, in which a parametric study with variable distance between pipes in the pre-support systems was conducted, and a statistical formula that presents the decreasing effect of pre-support system on maximum surface settlement was obtained. It is concluded that twin tunnel-induced surface settlement mainly depends on deformation modulus of the geo-materials around the tunnel. A new formula predicting twin tunnel-induced ground deformation is proposed as a modification factor of Herzog’s equation.

Effects of different empirical tunnel design approaches on rock mass behaviour during tunnel widening

Empirical based approaches play an important role in tunnel excavation and support system design. These approaches are considered to be very effective in optimising the process of tunnel excavation and particularly tunnel widening. Several reliable empirical approaches have been developed, however the selection or utilisation of an appropriate empirical method for designing the widening of a tunnel is still a challenging task. Therefore, in this work, the analysis of seven different empirical design approaches was carried out to determine the rock mass behaviour during tunnel widening in high in-situ stress state. These approaches include New Austrian Tunnelling Method, Rock Mass Rating, Rock Mass Quality, Rock Mass Index, Rock Structure Rating, Geological Strength Index and Basic Quality Index. On the basis of simulated statistical results obtained from the said empirical approaches, it was found that the application of Rock Mass Quality approach is highly effective in the tunnel widening since it can satisfactorily incorporate the equivalent dimensions and in-situ stress condition of widened tunnel. The method furnishes optimised reinforcement and support design. Additionally, this study also produces reliable data related to the initial excavation of tunnel which can be helpful in defining precise rock mass parameters during tunnel widening.

A Gene Expression Programming Model for Predicting Tunnel Convergence

Underground spaces have become increasingly important in recent decades in metropolises. In this regard, the demand for the use of underground spaces and, consequently, the excavation of these spaces has increased significantly. Excavation of an underground space is accompanied by risks and many uncertainties. Tunnel convergence, as the tendency for reduction of the excavated area due to change in the initial stresses, is frequently observed, in order to monitor the safety of construction and to evaluate the design and performance of the tunnel. This paper presents a model/equation obtained by a gene expression programming (GEP) algorithm, aiming to predict convergence of tunnels excavated in accordance to the New Austrian Tunneling Method (NATM). To obtain this goal, a database was prepared based on experimental datasets, consisting of six input and one output parameter. Namely, tunnel depth, cohesion, frictional angle, unit weight, Poisson’s ratio, and elasticity modulus were considered as model inputs, while the cumulative convergence was utilized as the model’s output. Configurations of the GEP model were determined through the trial-error technique and finally an optimum model is developed and presented. In addition, an equation has been extracted from the proposed GEP model. The comparison of the GEP-derived results with the experimental findings, which are in very good agreement, demonstrates the ability of GEP modeling to estimate the tunnel convergence in a reliable, robust, and practical manner.

Frame structure analysis model of tunnel lining using nonlinear ground reaction curve

The new Austrian tunneling method (NATM) and the shield tunneling method can be applied to Diluvial and Neogene deposits, on which megacities are located in Japan. However, because the lining design techniques differ between the two tunneling methods, a unified concept for tunnel lining design is needed. To this end, in this study, a frame structure analysis model for tunnel lining design, developed based on the nonlinear ground reaction curve, is proposed. The proposed model can consider the passive and active earth pressure due to excavated surface displacement, including the effect of ground self-stabilization, and the excavated surface displacement before lining installation. In the evaluations of the model’s performance, the measured earth pressure acting on the lining at the site of a Diluvial deposit was compared with the earth pressures calculated by the proposed model and the conventional linear model. The results verify that the proposed model can reasonably represent the earth pressure acting on the lining, lining displacement, and lining sectional force for various ground types, ranging from soft ground to stiff ground.

Failures Inspire Progress: Protecting Sensitive Buildings from Tunnelling

Tunnelling in urban areas is always a challenge, and it’s especially so when construction is proximate to densely populated districts. Such was the case on January 25, 2005, when a 10-m length of a Barcelona Metro tunnel under construction (6.5 m wide × 6.85 m high) collapsed. The Carmel Tunnel is 32 m deep and was excavated using the New Austrian Tunnelling Method (NATM), whereby the strength of the surrounding ground is engaged to strengthen the tunnel structure. The rock into which the tunnel was cut is a series of alternating layers of sandstone and shales. Despite the high cover ratio, (32 m/6.5 m ≈ 5), the failure progressed upward, and two days later a large sinkhole, 30 m in diameter, developed. The sinkhole engulfed an entire building, damaged dozens more, and required evacuation of 1,000 people. Economic losses amounted to 100 million euros, with 30 percent of the payout devoted to building rehabilitation and 70 percent to monetary compensation to the affected people. Fortunately, there were no casualties or injuries.

Innovative design modification during construction of a twin tunnel using real-time field data

Abstract Tunnels are vital substructures that are strongly influenced by the surrounding soil, especially when using the New Austrian Tunneling Method (NATM) in which the soil surrounding the tunnel displaces under part of the applied load and the remaining load is borne by the tunnel initial lining. Displacement monitoring is of great importance in this method and designers should monitor data during construction in addition to a choosing an initial design based on primary soil parameters. The method should be a performance-based approach that is required to meet a target. This paper reports on a case study on an urban twin tunnel constructed using NATM. The construction method is compatible with existing geological conditions and space constraints caused by the high traffic congestion on Valiasr Street in Tehran. The twin tunnel is composed of asymmetric sections and has an overburden of about 12.5 m, height of 8 m and width of 18.3 m with three lanes. In other words, it is composed of a two-lane and a one-lane tunnel with connected initial linings and separate final linings. The numerical modeling was based on a 2D finite element program (PLAXIS version 8). Performance was evaluated by inducing settlement during and after excavation and initial and final stabilization. The model was analyzed statically. During construction, limiting settlement to the regulation values required strategies such as reducing the length of excavation, partial construction of the final lining on one side and reinforcement with micropiles and compensation grouting. The numerical results show that the length of excavation resulted in low efficiency of about 13%, but the micropile elements reduced the resultant surface settlement 30% and the induced total strain 46% over the critical value. In other words, the displacement trend line decreased with a dip of 30%. In comparison with field observations and field data, the numerically estimated settlement at the ground surface was approximately twice that of the measured value and, interestingly, the recorded convergence was fixed during tunneling, suggesting that unknown conditions like a cavity or deep soil with filling material exists above the tunnel. Comparison of the back-analyzed results with the field data showed a decrease in the real values of the geotechnical parameters for the soil layer of more than 20%. This confirms that the existence of local unknown conditions can cause a difference of up to 50% in surface settlement. It was found that the loose soil properties decreased the efficiency of soil improvement to less than 15%.

Upper-bound solutions for the face stability of a non-circular NATM tunnel in clays with a linearly increasing undrained shear strength with depth

The face stability of the NATM tunnels (the New Austrian Tunneling Method) in undrained clays with a linearly increasing strength is numerically and analytically investigated by defining two types of the safety factors F in this paper. Based on the kinematic approach of the limit analysis, a continuous velocity field for an open-face tunnel is proposed. Moreover, the calculated solutions are compared with the results obtained from the numerical simulation and other existing literatures to validate its effectivity and superiority. The stability charts for different influence factors are also provided. Finally, an improved velocity field is presented, which provides a closer result to the real situation of the face collapse.

Geological assessment for tunnel excavation under river with shallow overburden using surface site investigation data and electrical resistivity tomography

Tunnelling is a challenging task as many geotechnical uncertainties involved during construction, especially under a river crossing with shallow overburden. This study focussed on geological assessment for the New Austrian Tunneling Method excavation that crosses under Kerau River with shallow overburden. 3D filtered tunnel models using Boolean filter for rock mass weathering grade, rock quality designation, and Lugeon value are developed. Results predict that 53.3% of the tunnel excavation under the Kerau River crossing are highly weathered rocks (Grades III and IV), and 64.51% are in the moderately to highly fractured zone (0%–75% RQD) along the roof of the tunnel granitic bedrock. The Lugeon value models show that 71.64% of the excavating rocks possess a Lugeon value of 5–50 (6–60 × 10−5 cm/s), which denotes considerably high permeability. 2D electrical resistivity tomography is used to verify the permeability results from the Lugeon test.

Construction Monitoring and Numerical Simulation Analysis of the Yangwujian Soft Rock Tunnel

Tunnel construction monitoring plays a key role in excavation construction of soft surrounding rock tunnel, it can be accurately judged stability of surrounding rock, its provide more priority information to design and construction. This paper adopts to construction of New Austrian Tunnel-ling Method (NATM), by strengthening the supporting and actual measurement on the spot, obtained displacement curve above vault settlement and clearance convergence. Selection parameter of supporting structure property by using Midas-GTS finite element analysis software, as well it has obtained both upper guide and down guide clearance convergence displacement-excavation step curve and valut settlement-excavation step curve. It’s found that: the faster stage of changing velocity is the first 10 days; the optimal execution time of the secondary lining is that the tunnel was excavated 30 days. It’s almost anastomosis both numerical simulation analysis and actual monitoring, it is better confirmed correctnass to establish the tunnel model, which provide reference for design and construction.

Cover Picture: Geomechanics and Tunnelling 2/2019

Abstract2our stations of the new light transit rail line Eglinton Crosstown in Toronto are driven according to the NATM (New Austrian Tunnelling Method). To secure the stations in soft ground conditions under densely built‐up urban areas the AT‐pipe umbrella system, 139.7 × 6.3mm, with squeezed connection is used as forepoling means over a total drilling length of approx. 120,000 m. (DSI Underground)

Utilization of crumb rubber and FBC-based ternary binder in shotcrete lining

This paper describes the early-age properties of shotcrete modified by i) up to 12.5% by volume crumb rubber as a replacement for aggregates and ii) substitution of ordinary Portland cement (OPC) by a fluidized bed combustion-based ternary binder (FBC-TB) up to 80% of mass. For the tests conducted, an increase in the crumb rubber volumetric fraction of the mixture always led to a decrease in uniaxial compressive strength. Replacing OPC with FBC-TB up to 20% enhanced the development of the early-age compressive strengths; however, a larger substitution resulted in the reduction in the concrete’s final compressive strength. In a full-size experimental mock-up test, the highest-performing mixture—in terms of acceptable mechanical properties and a reasonable amount of reused by-products—was subjected to full deployment in a concrete batching plant. Two batches (6 m3 in total) of concrete with crumb rubber and FBC-TB replacement were sprayed onto a full-scale model of a tunnel for the mock-up test. Evaluation of shotcrete performance included an analysis of the development of compressive strength and a comparison of results with criteria from the relevant code of practice, the New Austrian Tunnelling Method. Based on laboratory experiments, optimization, and in-situ measurements, the mock-up tests proved shotcrete containing crumb rubber and FBC-TC is applicable for full-scale use.

Ground load on tunnels built using new Austrian tunneling method: study of a tunnel passing through highly weathered sandstone

The ground load acting on a tunnel is an important issue in tunnel design, especially when the tunnel passes through highly weathered sandstone. A systematic field-monitoring campaign was performed to investigate the ground loads on a tunnel structure, the behavior of the composite support system, and the deformation of the tunnel boundaries. The monitoring results were analyzed and compared with those of various theories, such as the whole-soil column theory and those of Terzaghi, Bierbaumer, Xie Jiaxiu, and Protodyakonov. The ground load on a highway tunnel in highly weathered sandstone does not conform to current theoretical methodologies. It was confirmed that Terzaghi’s theory is suitable for estimating the peak magnitude of the vertical ground load, but differs from the field-monitoring results for ground load distribution profile. To facilitate tunnel design, a potential profile for ground loads is proposed, in which the vertical load component is ‘mountain’-shaped and the horizontal component adopts a ‘folded-line’ pattern. The roof rockbolts are subjected to compression and should be replaced by pipe grouting that is capable of providing enhanced reinforcement and accelerating the construction schedule. The bending moments acting on the lining were found to form a ‘butterfly’ shape. Supplementary finite-element modeling was undertaken to explore the mechanical behavior of the tunnel lining. These results indicated that steel rebar needs to be pre-installed in both the intrados of the lining roof and extrados of the spandrels to improve the lining tensile strength.

Numerical analysis of changing the force factors in temporary lining at the tunnel construction by the NATM

The paper presents the results of a numerical analysis of force factors in temporary lining at the tunnel construction by New Austrian Tunneling Method (NATM). The relevance of the performed research is substantiated by the complexity of the temporary lining operation in the form of arches combination, anchors, and shotcrete that arose during construction of the Beskydskyi tunnel in Ukraine. NATM, used in construction, is associated with a change in the sectional area of the working and a staged installation of temporary lining, which leads to a gradual change in the stress-strain state of the “temporary lining – surrounding massif” system. In turn, this leads to a change in the force factors (bending moments and normal forces) in temporary lining. In this study, a series of finite-element models simulating the stages of rock excavation and installation of lining elements have been developed and analyzed. The obtained results allowed to determine the cardinal change of force factors in temporary lining, depending on the stage of construction. Changing the force factors at different stages of the tunnel construction by the NATM makes it possible to perform an optimal selection for temporary lining location.

Selection of Optimal Tunnel Route and Tunneling Method based on AHP Technique.

Selection of optimal tunnel route and tunnelling methods for head raise tunnel of a hydropower project is one of the most critical and complicated steps in its design stage. Since factors involved are highly diversified, the decision making process is quite complicated. In this study, the Analytical Hierarchy Process (AHP), a multi criterion decision making tool was employed to establish the optimal tunnel route and the most appropriate tunnelling method for the established optimal tunnel route. The optimal tunnel route was established by evaluating two tunnel route options with ten factor criterion. Four tunnelling alternatives were evaluated against relevant ten factor criterion in selecting the most suitable tunnelling method for the selected optimal tunnel route. Criterion were limited to geotechnical, geological, geomorphological, safety, technical, economical and socioenvironmental aspects. Analysis reveals that, route B, which is having the overall composite weight of 0.513 (51.30%) is the optimal tunnel route and combination of Drill & Blast method (section III of route B) and New Austrian Tunnelling Method (sections I and II of route B) is the most appropriate tunnelling criteria along the selected tunnel route.

Tunnelling 4.0 – Construction‐related future trends

AbstractThe digitalisation of construction‐related processes will increasingly penetrate the individual development phases of tunnel construction projects (design, construction and operation). The digital transformation will affect all tunnelling processes through its four key levers: ”digital data, automation, networks and digital access“. Topics such as Industry 4.0, digital twins, Building Information Modelling or Lean Management will lead to a rethink in the construction industry. The constant use of data sources and the storage of data in independent databases is already possible. This makes it possible for the project participants to analyse collected construction‐related data, to process it and to make it available through an online portal. This results in the possibility to evaluate, optimize and document construction processes on a well‐founded data base. Complex construction management systems will be described with digital models, and the use of digital knowledge systems will support the decision‐making process for stakeholders. The fundamental philosophy of the New Austrian Tunnelling Method should not be called into question by standardised calculation algorithms and tunnelling software. In this contribution, visionary future trends are outlined for cyclical and continuous tunnelling methods, which should stimulate a controversial discussion.

Gradient‐Enhancement of a Rock Model Applied to Numerical Simulations of Tunnel Advance

AbstractRock is classified as a frictional cohesive material characterized by nonlinear stress‐strain relations including softening leading to structural failure. To describe the mechanical behavior of rock comprising the accumulation of irreversible strains, strain hardening, and the degradation of stiffness and strength, an isotropic damage plasticity model for intact rock and rock mass was proposed in [1]. In the context of numerical simulations of tunneling, considering strain softening of rock allows to predict the formation of shear bands emanating from the tunnel surface due to the excavation process, which is crucial for engineers to forecast potentially dangerous situations related to failure. To ensure objective results in the softening regime upon mesh refinement, in the aforementioned rock model the concept of the crack band approach by Bažant and Oh was adopted. As a remedy of known deficiencies related to this regularization approach, the rock model is extended by the over‐nonlocal implicit gradient‐enhancement proposed in [2]. Accordingly, a nonlocal field of the damage‐driving variable, implicitly defined as the solution of a Helmholtz‐like partial differential equation, is introduced yielding a fully coupled system of second‐order PDEs. In the present contribution, the over‐nonlocal gradient enhancement of the rock model is presented and applied together with a linear‐elastic material model for shotcrete to finite element simulations of a deep tunnel constructed by the New Austrian Tunneling Method. Based on this real example, objectivity of the results with respect to the finite element discretization is discussed.

Research on influences of fly ash content on mechanical properties of shotcrete

Shotcrete technology is a key technology of the New Austrian tunnelling method. Owing to advantages of simple and quick process of construction and strong adaptability, it is an indispensable means of modern tunnel construction. Mixing shotcrete with appropriate amount fly ash not only can reduce the generation of cracks and compensate the shrinkage, but also can improve the shotcrete peace ability and reduce the cost of project construction. Through a given number of tests, we study on the influences of fly ash content on the mechanical properties of shotcrete, i.e., tensile, compressive, flexural strength. The results of experiments show that: the strength indexes of shotcrete decrease gradually with the increase mixing content of fly ash. When the fly ash content is more than 28%, the concrete strength has serious loss. For ordinary shotcrete, it is suggested that the optimum dosage of fly ash should be about 9%.

Performance of New Austrian Tunneling Method (NATM) in Weak Rock Case Study

The decline in the over ground utilizable space and increment in development of metro structures, cut and cover structures are winding up fairly difficult to conceptualize and build. In this examination, a nonlinear two dimensional limited component investigation was completed to show the New Austrian Tunneling Method (NATM) burrow developed in frail shake utilizing the business limited component with joint programming PHASE 2.The validity of the numerical modeling procedure performed by the author was checked by making back-analysis for an actual case study of Strengen Tunnel which is one of the biggest expressways in western Austria. A comprehensive parametric study was performed on a hypothetical circle tunnel. Two dimensional numerical simulations with the finite element with joint software PHASE 2 have been performed to ground behaviour with the results of the numerical analysis are presented and discussed for recommendations for future work. In general the tangential stress at side wall and crown obtained from finite element with joints are nearly equal or higher than the closed form solution and equivalent continuum.