Gotthard Base Tunnel Research Articles

Effects of Creep on Shield Tunnelling Through Squeezing Ground

The present work aims to improve the reliability of shield jamming and lining damage risk assessment in squeezing ground by analysing the effects of creep on the evolution of rock pressure over time. The study is based on numerical simulations of typical mechanised tunnelling processes, generally consisting of shield advance phases alternating with shorter or longer standstills for lining installation, maintenance, etc. A linear elastic—viscous plastic constitutive model based upon Perzyna’s overstress theory is employed, which considers the time-dependency of plastic deformations via a single viscosity parameter. The investigations demonstrate the following: (i) shield loading during advance increases with increasing viscosity under certain conditions, which contradicts the common perception in many existing works that creep is thoroughly favourable for shield jamming; (ii) creep is thoroughly unfavourable for shield loading during long standstills and long-term lining loading, due to the additional viscoplastic ground deformations manifested over time; (iii) the commonly adopted simplifying assumption of continuous excavation with the gross advance rate is adequate only where standstills are very short (e.g., for lining erection during the stop-and-go shield tunnelling process), but otherwise underestimates the shield loading, even in cases of regular inspection and maintenance standstills lasting only a few hours. Two application examples, the Fréjus safety gallery and the Gotthard Base tunnel, demonstrate the need to consider creep and the accuracy of modelling tunnel construction by a semi-discrete approach, where only the very short standstills for lining erection are considered via an average advance rate, but longer standstills are explicitly simulated.

An estimation equation for the TBM thrust force in creeping rock

Shield jamming due to insufficient thrust force poses a critical hazard in mechanised tunnelling through squeezing ground. The time-dependency of squeezing due to creep can substantially alter the thrust force requirements, and the use of existing design tools that neglect it might therefore be misleading for the feasibility assessment of mechanised tunnelling or the design of the tunnel boring machine (TBM). This paper develops an equation for estimating the required thrust force in creeping rock under squeezing conditions during ongoing TBM advance, as well as during construction standstills. The method uses and extends the applicability of existing design nomograms through design equations established via multiparametric nonlinear regression, considering the results of 12,300 transient numerical simulations that cover a wide range of in-situ stresses and ground, TBM, and creep parameters relevant in tunnelling practice. The proposed method approximates the numerical results with sufficient accuracy to provide a reliable basis for decision-making during design and a valuable tool for fast assessments of the shield jamming risk. Its versatility and suitability in practical situations are demonstrated via two application examples from the Fréjus safety gallery and the Gotthard base tunnel.

Strength, deformability and permeability of kakiritic rocks from the Gotthard base tunnel

Strength, deformability and permeability of kakiritic rocks from the Gotthard base tunnel

Causal mechanism of Gotthard Base Tunnel-induced ground deformation: Insights from 3D fully-coupled hydro-mechanical simulation and comparison to field measurements

The Gotthard Base Tunnel (GBT), constructed between 2000 and 2011, is a 57 km long and up to 2.5 km deep high-speed railway tunnel located in the Swiss Alps. Significant ground surface displacements reaching about 10 cm were observed during and after the tunnel construction. To gain a better understanding of the causal mechanism of such conspicuous ground deformations, we develop a three-dimensional (3D) fully-coupled hydro-mechanical model to simulate GBT-induced groundwater drainage, stress redistribution, rock mass consolidation, and fault zone deformation at the regional scale. First, we construct a geological model with topographical features, lithological units, and natural faults realistically represented. We constrain the material properties of fault zones and rock masses based on available extensive laboratory testing results and site characterisation datasets. We then simulate the tunnelling process over time, with the resulting coupled hydro-mechanical responses of faulted rock masses well captured and ground surface/subsurface displacements quantitatively analysed. The simulation results in general show a good agreement with the field monitoring data of ground surface displacement, subsurface tunnel settlement, and groundwater inflow into the tunnel. Our model indicates that ground surface displacements originate from GBT-induced water drainage and rock mass consolidation in the deep subsurface. Our results also show that the GBT construction could trigger faults to shear via drainage-induced pressure diffusion and poroelastic stressing. The research findings from our work have important implications for many groundwater drainage-related geoengineering activities such as underground excavation in alpine mountains and fluid withdrawal in subsurface reservoirs.

A gravimetric assessment of the Gotthard Base Tunnel geological model: insights from a novel gravity terrain-adaptation correction and rock physics data

The Gotthard Base Tunnel (GBT) is a 57 km long railway tunnel, constructed in the Central Alps in Switzerland and extending mainly North–South across numerous geological units. We acquired 80 new gravity data points at the surface along the GBT profile and used 77 gravity measurements in the tunnel to test and constrain the shallow crustal, km-scale geological model established during the tunnel construction. To this end, we developed a novel processing scheme, which computes a fully 3D, density-dependent gravity terrain-adaptation correction (TAC), to consistently compare the gravity observations with the 2D geological model structure; the latter converted into a density model. This approach allowed to explore and quantify candidate rock density distributions along the GBT modelled profile in a computationally-efficient manner, and to test whether a reasonable fit can be found without structural modification of the geological model. The tested density data for the various lithologies were compiled from the SAPHYR rock physical property database. The tested models were evaluated both in terms of misfit between observed and synthetic gravity data, and also in terms of correlation between misfit trend and topography of the target profile. The results indicate that the locally sampled densities provide a better fit to the data for the considered lithologies, rather than density data averaged over a wider set of Alpine rock samples for the same lithology. Furthermore, using one homogeneous and constant density value for all the topographic corrections does not provide an optimal fit to the data, which instead confirms density variations along the profile. Structurally, a satisfactory fit could be found without modifying the 2D geological model, which thus can be considered gravimetry-proof. From a more general perspective, the gravity data processing routines and the density-dependent corrections developed in this case study represent a remarkable potential for further high-resolution gravity investigations of geological structures.

Bad guy or good guy? The framing of an imam

In this paper, we investigate framing in the case of an imam in Switzerland. We conducted a qualitative content analysis of 175 articles from Swiss newspapers and public broadcasting websites in German and French to examine how Bekim Alimi, an imam in Wil, Switzerland, was portrayed in the news media from 2015–2019. Powerful and / or prominent actors who made an effort, journalists, as well as the object of the debate, Bekim Alimi, contribute to frame building. We identify two key events (the inauguration of the Gotthard Base Tunnel and Alimi’s naturalization process) as highly crucial for the framing of the debate because they stimulate some frame sponsors to become active. When they speak out, the debates become more intense and broader. In this way, key events hold the possibility to discuss a situation in depth, to create orientation, to offer solutions (prognostic framing), or to motivate people (motivational framing) to become active.

Main long-term policy impacts of the Gotthard base tunnel construction on cross-border land consumption and transformation

The Gotthard transalpine base tunnel is located in Switzerland, it is considered the longest in the world. The purpose of this research is to detect the main effects of long-term policies on the occupation and transformation of cross-border land, in productive, industrial and commercial uses, due to the construction of the Saint Gotthard base tunnel, and the complementary works that enhance it. There are three levels of study proposed, three temporary scenarios (before, during and after the construction) and a comparative analysis with the future Lyon-Turin base tunnel. Maps are made with geodata from Switzerland, Italy and France and interviews with experts by class groups, this was essential to obtain a broader vision of the situation to be analyzed, it is concluded that the use of mixed methods proved to be useful for the stated objectives. A greater displacement of the impact at cross-border levels between Switzerland and Italy is demonstrated, with 43,776.6 ha of productive, industrial and commercial use, in relation to the cross-border areas between Italy and France of 15,593.6 ha related to the Lyon-Turin tunnel. Two types of compensation and empowerment works of the Gotthard System are identified and advantages in formulating long-term articulated policies and well-structured financing processes with participatory mechanisms. This research contributes to the current literature, aimed at researchers and policymakers on intermodal transport as a response to sustainable logistics.

Deep hydrochemical section through the Central Alps: evolution of deep water in the continental upper crust and solute acquisition during water\u2013rock-interaction along the Sedrun section of the Gotthard Base Tunnel

Drilling of the Gotthard Rail Base Tunnel through the Central Alps from 2005 to 2010 opened up fractured basement units and frequent water inflows provided access to the major fluid-rock interactions processes in orogenic crystalline upper crust. Construction of the 57 km long tunnel was divided into five different sections. Here we report data and observations from the 10 km long central Sedrun section 211 water samples were collected at inflow points 900 to 2350 m below the surface. The exceptional samples and data provide a comprehension of the hydrochemical evolution and solute acquisition of deep groundwater in basement units. The investigated tunnel section drilled through steeply dipping rock units and vertical fracture systems at high angle. It cuts across granite, gneiss and schist of the pre-Alpine basement and across two narrow zones of meta-sediments. Rock temperature along the Sedrun section varies from 30 to 45 °C depending on the thickness of the overburden. The fracture water is of meteoric origin and acquires its composition exclusively by chemical interaction with the surrounding rocks along the flow path. Water from inflow points in the basement of the Gotthard Massif has typically a high pH of about 10 and total dissolved solids in the range of 100 to 300 mg L−1. Sodium is the prime cation of most waters. Although plentiful in the rocks, calcium, potassium and magnesium are low to very low in water. The anions associated with Na are carbonate/bicarbonate, sulfate, fluoride and chloride in widely varying proportions. High fluoride concentrations of up to 15.4 mg L−1 are characteristic for most waters. As a result of the high pH dissolved silica (SiO2) reached concentrations of up to 58 mg L−1 and represents 25—30 wt% of the solutes. The meteoric recharge provides dissolved O2 and CO2 to the fluid-rock interaction processes. The solutes derive from the dissolution of feldspar (Na+, SiO2aq), oxidation of sulfides to sulfate (SO42−), alteration of biotite (F−), and fluid inclusions opened by brittle deformation (Cl−). The solids formed during fluid-rock interaction, mainly zeolites, chlorite (and other clay minerals) and secondary Fe-minerals, remove Mg, Fe, and K almost quantitatively from the water. The high pH results from hydrolysis of silicates. The data distinctly show that within the depth interval of 1.0–2.5 km below surface deep water in continental basement evolves to a low TDS, high pH, sodium carbonate and silica solution by interaction of gneiss and granite with infiltrating pristine meteoric water, snow and rain.

Concrete admixtures - sustainable concrete

Durability of concrete, an important part of the sustainability theme, was, is, and will be one of the main topics for large infrastructure projects like the Gotthard base tunnel. For such important structures a service life of more than 80 years is expected. The prevailing underground conditions like water ingress, aggressive waters etc. will influence the choice of the concrete system and mix design. Therefore, a focus is on the potential damage mechanisms on the concrete like chloride ingress or sulfate attack. A well-designed concrete will be durable concrete which can withstand various external attacks and achieves or even extends the designed service life of the concrete structure. Based on the knowledge that the main damaging mechanisms for concrete are based on water penetration into the concrete, various measures can be taken to achieve concrete structures with significantly reduced permeability. These measure ranges from reduction of the water/binder-ratio, increasing the density of the concrete using silica fume, to the use of special admixtures in order to increase the durability of concrete. In an extensive research program, the influence of mix design components e.g. different admixture types, water/binder-ratio on hardened concrete properties like chloride resistance (chloride migration coefficient), sulfate resistance and water conductivity have been tested and analyzed.

Gotthard Base Tunnel : World's Longest Railway Mountain Tunnel

Switzerland was suffering from serious traffic problem and so it proposed a gigantic project. Over 35 miles long tunnel would cut through the heart of the Swiss Alps. Redirecting the rush and traffic of Europe not over the Alps but under the Alps. To do this, miners had to punch their way through the hardest rock on this planet. For this a TBM was required, each 3 stories high and larger than 4 football fields, working continuously for 6 years. This project was very dangerous and outrageously expensive at a price tag of $10 billion.

Fault reactivation induced by tunneling activity in clay material: Hints from numerical modeling

Seismic events with magnitude 3 and above have been associated with the removal of rock mass in mining environment since long-time. On the contrary, little is known about the possible seismic events induced by tunneling, although it presents similarities with mining. One great example is the case of the 57 km long Gotthard Base Tunnel excavation, which has been associated more than hundred seismic events, with the largest one having magnitude of ML 2.4, damaging the tunnel infrastructures (e.g. gallery floor or portal area).Different underground structures will be built probably up to 1000 m below ground for the construction of future deep geological for the storage of nuclear waste. While seismic risk will probably not constitute a liability for the storage site construction, it is important to understand the potential for reactivation of seismogenic features located nearby the future location of emplacement tunnels.Here we present numerical simulations aimed at understanding the potential for fault reactivation during tunnel construction in clay material, a potential host rock for nuclear waste repository. We evaluate the evolution of the stress changes during the simulation of the excavation with FLAC3D numerical solver. A strain-softening friction model is used to simulate the occurrence of a sudden slip on a fault zone when critical conditions for reactivation are satisfied. This constitutes a worst-case scenario, given the low seismogenic potential of clay rocks. We also present a sensitivity analysis on several critical parameters including fault frictional properties, stress conditions, as well as different tunnel sizes at varying distance from a nearby failure plane, with the final purpose of evaluating safety of a potential nuclear repository site on the short- and long-term.

Застосування трубчастого стрічкового конвеєра, працюючого зі змінною довжиною транспортування для проведення тунелів

The work is devoted to research associated with the construction of the tunnels. The article presents the characteristics of the largest foreign railway tunnels. Indicates that the speed of tunnel construction are significantly affected by the transport unit for muck removal from the face. To illustrate, the transport system that was used for the longest in the world the Gotthard base tunnel. Based on the analysis of this transport installation established that the speed of the tunnel could be increased if you apply to a tubular belt conveyor with variable-length transportation for muck removal from the face. The paper presents the results of performed engineering studies on the new transport installation operating with varying length of transportation. Dependences which can determine the technological effectiveness of application, when conducting tunnels, tubular belt conveyor with changeable length of transportation.

Risk, Contract Management, and Financing of the Gotthard Base Tunnel in Switzerland

Risk, Contract Management, and Financing of the Gotthard Base Tunnel in Switzerland

LOOKING FOR PROJECT SUCCESS IN INFRASTRUCTURE PROJECTS: HOW CAN WE ACHIEVE IT?

Even though the main aim of project management (PM) is to assure successful projects, the PM literature still lacks a clear definition of project success (PS), since it highly depends on the stakeholders' expectations and the point in time in which the project was evaluated. In this context and due to their specialties e.g. long duration or a large number of stakeholders, the infrastructure projects are subjected to time delays and cost overruns and therefore, criticized in the society and described as failed or unsuccessful projects. This paper hypothesizes the need to adapt our PM approach to follow more systemic methods and presents the main principles of systematic project management (SPM) as a success factor (SF) for infrastructure projects. In addition, a case study about the Gotthard Base Tunnel is presented to verify the literature findings.

IMU-based orientation transfer at Semmering base tunnel

Back in 2005, first experiments at the Sedrun attack of Gotthard base tunnel showed the applicability of autocollimation and IMU units to contribute as an independent measurement technique for orientation transfer down to deep shafts. Since then, evaluation strategies have been refined and in 2017 another project at the Semmering base tunnel was started to confirm the method. The paper at hand explains the base setup of the sensors, the compensation strategies and evaluation steps and gives the results of the project measurements compared to the gyroscope measurements performed at the same time. It is shown that the overall orientation is within the expected accuracy range and its quality is comparable to the gyroscope results, so the IMU orientation transfer method has proved reliable again.

Comparison of pneumatic impact and magnetostrictive vibrator sources for near surface seismic imaging in geotechnical environments

The choice of an appropriate seismic source for a specific application is crucial for the success of seismic surveys. In this study, the utilization of two novel seismic sources is discussed for geoengineering applications in the bandwidth of 80–3000 Hz. These are a pneumatic impact and a magnetostrictive vibrator source mainly designed for seismic transmission and reflection applications. Seismic test surveys were carried out on Paleozoic sediment deposits to study a near surface fault zone at the southern rim of the Taunus mountain range in Germany and in crystalline rocks to investigate fracture zones along the Piora Adit of the Gotthard Base Tunnel in Switzerland, respectively. Both sources are evaluated with respect to their seismic wave energy, the sum of the squared amplitudes of first P- and S-arrivals and frequency content, signal to random noise ratio, as well as their suitability with regard to the specific site conditions and applications. Common Midpoint-stacked data of the Taunus survey and pre-stack depth migrated data of the Piora survey were analysed to assess the ability of the seismic sources to image geological structures and to give support for geotechnical aspects.For both test sites, the vibrator source proved to be more suitable to generate body waves than the impact source, which generates strong ground roll noise signals due to its non-controlled signal amplitude spectrum. In fact the control system of the vibrator source enabled improved adaption to varying ground conditions due to a controlled adjustment of the signal amplitude spectrum to optimize resolution and penetration for a given exploration depth.

Fault induced rock bursts and micro-tremors – Experiences from the Gotthard Base Tunnel

During the construction of the Faido Multifunction Station of the Gotthard Base Tunnel, a previously unknown and unanticipated major tectonical fault has been encountered. Upon completion of the advance through the fault, systematic and major rock burst events occurred in the competent Gneiss rock mass adjacent to the fault.The Swiss Earthquake Service (Schweizer Erdbebendienst – SED) observed an increase of microtremors in the vicinity of the tunnelling site, in a region where usually very low seismic activity is present. As a consequence, the seismic monitoring grid has been enhanced in the project area, allowing reliable pin-pointing of the microtremor hypocenters and examination on the interaction with the tunnel advance and the observed rock burst events.Due to the vast amount of scientific work with regard to rock burst causes, classification, prediction and mitigation, this publication deliberately abstains from trying to add yet another set of relationships and/or classification schemes. Instead, a case study is presented, with the peculiarity that excellent seismic monitoring and very well documented rock mass conditions are seamlessly available, allowing direct correlation and insight into the interaction between seismicity and strike-slip rock bursts. In addition, the results of a dynamic analysis performed in UDEC, with excitation wave data and rock mass parameters calibrated on the field measurements, are presented. They allow greater understanding of the events caused by seismicity-induced rock burst phenomena.The experiences with prediction and mitigation of rock burst are shown, leading to conclusions with regard to efficient and safe tunnelling in rock-burst prone rock masses.

Elastic deformation modulus for estimating convergence when tunnelling through squeezing ground

Squeezing in tunnelling is commonly assessed using the linearly elastic–perfectly plastic Mohr–Coulomb (MC) model. Weak rocks and fault materials, however, exhibit confining stress-dependent and strain-hardening behaviour prior to failure; in other words, the higher the confining stress and the lower the shear strain the stiffer the rock behaviour. As the MC model assumes a strain- and stress-independent Young's modulus, the selection of an appropriate ‘operational’ value, EMC, remains a major problem in tunnel studies using this model. Although EMC has a significant effect on the deformation predictions (they are inversely proportional to this value under small strain theory), there is no widely accepted or well-validated approach to its selection. This paper shows, using the results of triaxial compression tests on weak rocks and fault materials from the Gotthard base tunnel and five other projects, and performing a theoretical analysis of the ground response to tunnel excavation, that EMC can be taken as equal to the secant modulus E50 (rather than equal to the unloading–reloading modulus) extrapolated from standard triaxial compression test results to the in situ stress level. This is particularly useful for practical purposes as it allows standard computational methods to be used with sufficient accuracy, rendering more refined models unnecessary, at least at the preliminary design stage.

Unloading-induced instability of a simulated granular fault and implications for excavation-induced seismicity

Deep excavation in rock masses has the potential to break the frictional equilibrium of nearby faults, resulting in induced seismicity. We conducted the experimental and numerical studies on a simulated granular fault to uncover the mechanism of excavation-induced seismicity. A series of laboratory experiments were used to investigate the effects of initial shear stress, initial normal stress and its unloading rate on the frictional instability of the fault, and a numerical simulation was carried out to interpret stress variation and particle evolution during the unloading process. Our results show that both normal and shear stresses sharply drop when the fault is approaching a critical stress state. The stress reduction is due to interparticle force decrease and particle contact breakage. The evolution of fault state depends on the initial stress condition and excavation process. A greater initial normal stress and a lower initial shear stress provide a favorable environment to accumulate higher strain energy in adjacent rock, leading to larger slip displacement. A larger normal stress unloading rate can also cause higher strain energy and larger slip displacement. Understanding unloading-induced instability of a simulated fault allows us to interpret the seismic events occurred during the excavation of the Gotthard Base Tunnel in Switzerland. The reduction of normal and shear stresses associated with the excavation work decreases the differential stress applied to a natural fault zone, and subsequently results in the occurrence of induced earthquakes.

E. Switzerland

In contrast to all of its neighbours, the Swiss Confederation (Switzerland) is not a member of the European Union (EU) or the European Economic Area (EEA). The country is, however, connected with the EU by a densely knit network of bilateral treaties. As to Switzerland’s state of the environment, the Organisation for Economic Co-operation and Development (OECD) published its Environmental Performance Review on Switzerland on 27 November 2017 (OECD Publishing 2017 <http://dx.doi.org/10.1787/9789264279674-en>). The OECD, of which Switzerland is a founding member, conducted similar assessments in 1998 and 2007. In its Review of 2017, said international organization pointed out that Switzerland ranks amongst the least carbon-intensive countries within the OECD, emitting 88 kilograms of carbon dioxide in order to generate US $1,000 of gross domestic product (GDP) (the average of all OECD-countries being 256 kilograms of carbon dioxide per US $1,000 of GDP generated). This conforms to roughly 6.4 tonnes per capita emitted in Switzerland per year. It is an economy dominated by not only services but also high shares of renewables and nuclear energy contributes, according to the Review, to this performance. Fossil fuels, accordingly, account for only approximately one-half of the total primary energy supply, considerably below the OECD average of 84 percent. Coal provides for as little as 1 percent of Switzerland’s primary energy supply, the lowest level amongst the OECD’s thirty-five member countries, as the Review notes. The Review furthermore approvingly acknowledges a modal shift of freight from road to rail enhanced by a ‘performance-based charge on heavy goods vehicles’ introduced in 2001, reducing the number of trucks crossing the Swiss Alps by 30 percent between 2000 and 2014. The opening of the Gotthard Base Tunnel—at fifty-seven kilometres, the longest railway tunnel worldwide—in December 2016 is projected to accelerate this shift. In regard to heavy traffic, the OECD further highlighted that Switzerland is one of the few countries taxing diesel fuel at a higher rate than petrol on the grounds of higher carbon and air pollutant emissions per unit, while taking note of Switzerland’s comparatively low and decreasing environmental tax rate currently accounting for less than 2 percent of GDP (or a mere €77 per tonne of carbon dioxide, while allowing for a wide range of exemptions).