The excavation-induced convergences in the Sedrun section of the Gotthard Base Tunnel

Mezger, Florence; Anagnostou, Georg; Ziegler, H

doi:10.1016/j.tust.2013.07.016

Cited by 36 publications

(7 citation statements)

References 2 publications

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“…Over 95% of the rocks in the CZ may be designated as cataclasites or cataclastic fault rocks. However, the degree of late brittle deformation varies considerably (Guntli et al, 2016;Leu & Wyss, 1992;Mezger et al, 2013). The rocks of the CZ are probably of Permo-Carboniferous age (Guntli et al, 2016).…”

Section: Geological Outline Of the Sedrun Sectionmentioning

confidence: 99%

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

Stober

Giovanoli²,

Wiebe

et al. 2022

Swiss J Geosci

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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.

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Section: Geological Outline Of the Sedrun Sectionmentioning

confidence: 99%

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

Stober

Giovanoli²,

Wiebe

et al. 2022

Swiss J Geosci

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“…Chapter 1 was published in Mezger et al (2013a) and presented in Mezger et al (2013b), whereby the contribution of Dr. Hans-Jakob Ziegler concerned geological aspects. Chapter 2 was presented in Mezger and Anagnostou (2015).…”

Section: Publicationsmentioning

confidence: 99%

On the variability of squeezing behaviour in tunnelling

Mezger¹

2020

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The magnitude of squeezing deformations in tunnelling often varies over short distances, even if there is no obvious change in the construction method, in the depth of cover, in the lithology or rock structure. As long as the reasons for the variability are not known, the tunnelling-induced convergences cannot be predicted with sufficient reliability. Reliable predictions, however, are important for determining the temporary support or the excavation diameter. Otherwise, large-scale tunnel repairs may be necessary, which can cause delay and additional costs due to remedial actions as well as due to the enforced interruption of other operations in progress at the same time. The analysis of different case studies concerning the AlpTransit project shows that the squeezing variability can be traced back to the heterogeneities in the rock mass at different scales as well as the variation of the orientation of the planes of anisotropy (bedding or schistosity) to the tunnel axis. In order to improve safety and economy of tunnel construction in squeezing ground, the influence of these factors on the convergences was determined quantitatively (by means of analytical solutions or numerical modelling), so that they can be used as indicators during construction for the timely identification and prediction of the squeezing behaviour. Particular attention was paid on factors, whose variation, even if small, may affect the convergences sensitively . Based on these quantitative investigations, design aids were developed, which should help the project engineer to estimate and better understand the variability of the squeezing intensity. The squeezing variability also concerns TBM tunnelling: In contrast to conventional tunnelling, shielded TBMs are particularly vulnerable to squeezing due to the very limited space available. Therefore, in order to better deal with the squeezing variability in TBM tunnelling, different (stiff as well as deformable) lining options were discussed.

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“…Even major engineering disasters such as tunnel collapse occur. During the construction phase, such damage frequently occurs, such as the Jiazhuqing Tunnel of the Nankun Line in my country [ 3 ], the Muzhailing Tunnel in Gansu [ 4 ], the Tauern Tunnel in Austria [ 5 ], the Enasan Tunnel in Japan [ 6 ], the Gotthard Railway Tunnel [ 7 ], etc., severe extrusion and large deformation disasters occurred, resulting in slow construction progress [ 8 ].…”

Section: Introductionmentioning

confidence: 99%

Pressure-relief joints of initial support structural system used in tunnels with high-stress surrounding rock

Xu,

Bai

2024

PLoS ONE

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To address the problem of large deformations in weak surrounding rock tunnels under high ground stress, which cause damage to initial support structures, this study proposes a novel type of circumferential pressure-relief joint based on the concept of relieving deformation pressure of the surrounding rock. Key parameters of the pressure-relief joint, such as initial bearing capacity peak, constant bearing capacity, and allowable pressure-relief displacement, were obtained through numerical simulations and laboratory experiments. A comparison was made between the mechanical characteristics of rigid joints and the new type of pressure-relief joint. The applicability of the pressure-relief joint was verified through field tests, monitoring the surrounding rock pressure, internal forces in the steel frames, and the convergence displacement of the support structure. The results show that: (1) In the elastic stage, the stiffness of the new pressure-relief joint is similar to that of rigid joints. In the plastic stage, rigid joints fail directly, whereas the pressure-relief joint can control deformation and effectively release the deformation pressure of the surrounding rock while providing a constant bearing capacity. (2) The right arch foot in the experiment had poor rock quality, leading to high stress in the steel frame and significant horizontal displacement. After the deformation of the pressure-relief joint, the stress in the surrounding rock and steel frame significantly reduced, and the rate of horizontal deformation of the support structure slowed down. (3) The vertical and horizontal final displacements of the pressure-relief joint in the experiment were 61mm and 15mm, respectively, which did not exceed the allowable deformation values. The components of the support structure remained intact, ensuring safety. However, this study has limitations: the design of the new pressure-relief joint only allows for a vertical deformation of 150mm and a horizontal deformation of 50mm, limiting the range of pressure-relief deformation.

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The excavation-induced convergences in the Sedrun section of the Gotthard Base Tunnel

Cited by 36 publications

References 2 publications

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

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

On the variability of squeezing behaviour in tunnelling

Pressure-relief joints of initial support structural system used in tunnels with high-stress surrounding rock

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