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Lowick S.E.,University of Bern | Buechi M.W.,University of Bern | Gaar D.,University of Bern | Graf H.R.,Dr. von Moos AG | Preusser F.,Albert Ludwigs University of Freiburg
Boreas | Year: 2015

Optically stimulated luminescence (OSL) dating was applied to proglacial deposits from the Klettgau Valley in northern Switzerland, which is understood to record several phases of glaciation prior to the Last Interglacial. The aim was to provide an independent chronology for the different sedimentary units to understand better the complex depositional history of the region. This time range requires care when assessing the reliability of the luminescence protocols applied. Equivalent doses for fine- and coarse-grain quartz remained below 300 Gy, while dose response curves for both fractions continued to display growth above 500 Gy. Dose recovery tests confirmed the ability of the single aliquot regenerative (SAR) protocol to recover laboratory doses of a similar size to burial doses, and isothermal decay measurements confirmed the stability of the quartz signal. Having passed rigorous testing criteria, quartz OSL ages of up to ∼200ka were considered reliable but significantly underestimated expected ages and prompt a reconsideration of earlier interpretations of the stratigraphy for this site. Rather than representing three separate glaciations, quartz luminescence ages instead suggest that these deposits record up to four independent ice advances during Marine Isotope Stage 6. For both single grain and single aliquot feldspar dating, it was not possible to separate the conflicting influences of anomalous fading and partial bleaching. However, uncorrected feldspar central age model ages were found to be in reasonable agreement with quartz age estimates, and suggest that feldspar ages may still offer useful additional information in this region. © 2015 Collegium Boreas.

Loew S.,ETH Zurich | Lutzenkirchen V.,Dr. von Moos AG | Hansmann J.,ETH Zurich | Ryf A.,AlpTransit Gotthard AG | Guntli P.,Sieber CassinaHandke AG
International Journal of Rock Mechanics and Mining Sciences | Year: 2015

The Gotthard Base Tunnel (GBT) is a 57. km long and up to 2500 m deep railway tunnel constructed between 2000 and 2011 in the Central Alps of Switzerland. As drainage of fractured rocks by deep tunnels accompanied by significant decrease in groundwater pressure causes large-scale deformations even in hard crystalline rocks, a comprehensive surface deformation and tunnel inflow monitoring system has been established and operated for more than ten years. This paper presents the results from this monitoring system and explains the observed hydro-mechanically coupled and transient rock mass behavior based on detailed assessments of geological, geomechanical and hydrogeological conditions and conceptual continuum models. The collected data show that significant tunnel-drainage induced surface deformations also develop in rock masses with moderate hydraulic conductivity (2E-9 m/s) and small cumulative tunnel inflows (a few liters per second per kilometer). In this case deformations are caused by pore pressure reductions and rock mass deformations around the draining tunnel at depth, and not by groundwater table elevation changes. The pattern of surface settlements observed along the tunnel axis is very irregular (up to 11. cm in 2013) and strongly influenced by hectometer scale hydro-mechanical heterogeneities of steeply dipping geological units striking at large angle to the tunnel axes. At the depth of the studied tunnel section (1500-2500 m) about 50% of the surface settlements can be recorded. The surface settlements are connected to horizontal displacements and strains directed towards the tunnel axes or advancing tunnel face. The resulting horizontal displacement at the Nalps dam has reached about 65 mm in 2013. Compressive strains in the order of 20-50 microstrain are typically observed within a corridor of about 1 to 1.5 km width. Outside the reversal point of the settlement trough, extensile strains of similar magnitude develop. © 2015 Elsevier Ltd.

Graf H.R.,Dr. von Moos AG | Burkhalter R.,Bundesamt fur Landestopografie Swisstopo
Swiss Journal of Geosciences | Year: 2016

A. Penck’s and E. Brückner’s “classical” subdivision of Quaternary deposits, developed in the Alpine foreland of southern Germany, was used for a long time as a basis for the classification of Quaternary deposits on Swiss geological maps. Due to fundamental differences between southern Germany and northern Switzerland regarding the morphogenetic control of the drainage system—especially regarding the morphostratigraphic position of various lithostratigraphic units—this subdivision should no longer be applied in Switzerland. With this in view, a new concept for a stratigraphic classification and nomenclature is presented here. It is based on the national guidelines for stratigraphic nomenclature compiled by the Swiss Committee on Stratigraphy SCS. In addition, a corresponding system for map legends is proposed. This concept has already been applied in a number of sheets of the Geological Atlas of Switzerland 1:25,000 and will be implemented in future maps. © 2016 Swiss Geological Society

John M.,John Tunnel Consult ZTG | Matousek F.,Dr. von Moos AG | Dallapiazza W.,ILF Beratende Ingenieure AG
Geomechanik und Tunnelbau | Year: 2016

For deep tunnels with restricted possibilities for site investigation, deviations from the forecast are usually to be expected. Deviations of geological and hydrogeological conditions have different effects on tunnelling. At the Gotthard Base Tunnel it was found that some areas considered as critical actually behaved most favourably, whereas other areas, such as fault zones and zones of high rock pressure, deviated unfavourably from the forecast with considerable effects on costs and the time schedule. Unfavourable deviations could not be compensated by favourable areas. It should be also noted that these deviations had not been included in risk analyses, because they were unknown, however the original cost prognosis of 1999 provided sufficient financial reserves. These deviations were mastered by intensive probing ahead of excavation and adaptation of design, construction programme and additional measures defined during construction. On the basis of the comparison of forecast and actual conditions, the positive and negative effects of the conditions encountered on tunnelling are described. Bei einem tiefliegenden Tunnel mit beschränkten Möglichkeiten der Erkundung treten bei der Ausführung naturgemäß Abweichungen von der Prognose auf. Diese haben ihre Ursachen in den geologischen und hydrogeologischen Verhältnissen, die sich unterschiedlich auf den Vortrieb auswirken. Beim Gotthard-Basistunnel hat sich gezeigt, dass sich in einzelnen als kritisch eingestuften Bereichen das Gebirge günstiger verhalten hat als prognostiziert. Von der Prognose abweichende ungünstigere Bereiche, insbesondere Störzonen und druckhaftes Gebirge, hatten erhebliche Auswirkungen auf Kosten und Termine, die durch die günstigeren Bereiche nicht aufgewogen werden konnten. Diese Abweichungen waren in den Risikoanalysen nicht enthalten, da diese nicht bekannt waren. Allerdings waren in der ursprünglichen Kostenprognose von 1999 entsprechende finanzielle Reserven vorgesehen. Die geänderten Verhältnisse wurden mit einer intensiven Vorauserkundung erfasst; mit einer Anpassung der Planung, des Bauablaufs und dem Einsatz zusätzlicher Maßnahmen wurde ihnen Rechnung getragen und damit konnten diese zielführend bewältigt werden. Auf Basis einer Gegenüberstellung von Prognose und Befund wird aus Sicht des SIOP-Teams auf die positiven und negativen Auswirkungen der angetroffenen Verhältnisse auf den Vortrieb eingegangen. © 2016 Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH & Co. KG, Berlin

Tunneling in urban regions in the Swiss midlands with thick quarternary unconsolidated rocks makes high demands on geological and hydrogeolocial investigations. Geotechnical and hydrological properties of geological formations are often altered by former man-made constructions (buildings and their basement, existing tunnels, underground lifelines and so on), which requires especially precise definitions of the spatial distribution of the even naturally complex geological bodies. Interactions between existing buildings, geological and groundwater conditions and the underground works planned have therefore to be seen as a whole. This requires also a good understanding of technical possibilties and risks by the geologist in charge. We wish to emphasize that the engineering geologist should be involved in all stages of the project development to achieve an optimized tunnel construction (costs, risk, time). Two examples of complex tunneling in Schaffhausen (suburban national highway N4) and Zurich (new national railway line below the main city, under construction), which were accompanied by the author, shall illustrate these special conditions.

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