Is there a real preferential detection of negative stimuli? A comment on Dijksterhuis and Aarts (2003)

In a recent article, Dijksterhuis and Aarts (2003) investigated the preferential detection of negative stimuli. According to them, their data clearly indicate that it requires less stimulus input or less stimulus exposure to detect a negative stimulus than to detect a positive stimulus. However, we believe their research suffers from a number of limitations and methodological flaws that cast doubt on their conclusions. Using signal detection analyses, we demonstrate that none of their three studies provides sufficiently informative data with respect to their hypotheses. Moreover, we show that their experimental designs seem to be inadequate to test their hypotheses

Analysis of the evolution of road tunnels equilibrium conditions with a convergence-confinement approach

Since both lining structure and rock mass exhibit delayed behaviour, tunnel equilibrium conditions evolve with time. After discussing existing work done on different aspects of long-term tunnel behaviour, the aim of this paper is to "understand” the influence of rock mass and lining degradations on the long-term stability conditions of the tunnel by means of the convergence-confinement method. In order to represent the effects of degradation on tunnel long-term conditions, specific degradation models are selected according to the disorders identified during principal inspections of road tunnels in Switzerland. By simulating the reduction of the mechanical properties of both the rock mass and the lining or by using creep models, it is possible to assess the influence of the main degradation processes on tunnel stability. The results are interpreted in terms of tunnel safety factor. The presented approach for the determination of the long-term behaviour of tunnels, although valid for simple tunnel geometry and field stress conditions, allows to roughly estimate the influence of significant degradation processes that affect the rock mass and the supporting structure. Though this approach results in some simplification, it may be generalised and adopted with more refined numerical analyses for improving the assessment of tunnel long-term condition

Empirical and analytical analyses of laboratory granular flows to investigate rock avalanche propagation

Laboratory experiments which consist of releasing dry rigid non-cohesive grains or small bricks on an unconfined chute have been designed to investigate rock avalanche propagation mechanisms and to identify parameters influencing their deposit characteristics. Factors such as volume, fall height, basal friction angle, material used, structure of the material before release, i.e. bricks randomly poured into the reservoir before failure or piled orderly one on top of the other, and type of slope break, i.e. curved or sharp angular, are considered and their influence on apparent friction angle, travel angle of the centre of mass, deposit length and runout is analysed. Results highlight the influence of the structure of the material before release and of the type of transition at the toe of the slope on the mobility of granular avalanches. The more angular and sharp is the slope break, the more shearing (friction) and collisions will develop within the sliding mass as it changes its flow direction, the larger will be the energy dissipation and the shorter will be the travel distance. Shorter runout is also observed when bricks are randomly poured into the reservoir before release compared to when they are piled one on top of the other. In the first case, more energy is dissipated all along the flow through friction and collisions within the mass. Back analysis with a sled block model of experiments with a curved slope break underlines the importance of accounting centripetal acceleration in the modelling of the distance travelled by the centre of mass of a granular mass. This type of model though is not able to assess the spreading of the mass and its total runout because it does not take into account the internal deformation and the transfer of momentum within the mass which, as highlighted by the experimental results, play an important role in the mobility of rock avalanche

Prise en compte de l’eau souterraine dans les normes

La première version des normes SIA est entrée en vigueur en 2003. La pratique a montré que l’eau souterraine n’était pas toujours considérée de façon adéquate lors de l’étude et la réalisation de projets, avec parfois comme conséquence des instabilités hydrauliques. Bien que les normes ne puissent à elles seules résoudre le problème d’une mauvaise compréhension et modélisation des instabilités d’origine hydraulique, il était du devoir de la commission Géotechnique CN 267 de la SIA d’adapter un certain nombre d’articles rela-tifs à l’eau dans les sols dans le cadre de la révision des normes SIA 267 et SIA 261. S’agissant d’une révision partielle, les modifications/ajouts ont essentiellement porté sur les articles qui pouvaient poser des pro-blèmes pour le dimensionnement des ouvrages. Les principales modifications apportées se trouvent dans la section 4.4 de la SIA 261:2014 consacrée à la pression hydraulique ainsi que dans le chapitre 13 de la SIA 267:2013 dédié à la poussée d’Archimède et au renard hydraulique. Une nouvelle section (Chiffre 3.4) intitulée « Eau dans le terrain de fondation » a été ajoutée dans la partie de la SIA 267 consacrée aux reconnaissances. Le tableau 3 de la SIA 261:2014 et les figures 9 et 10 de la SIA 267:2013 ont également été retravaillés. Ce document tente de présenter de façon synthétique les principales modifications apportées dans le cadre de la révision partielle des normes SIA 261:2003 [2] et 267:2003 [3] pour résoudre les plus importants pro-blèmes de prise en compte de l’eau souterraine constatés dans la pratique. Le contenu n’est pas exhaustif et le lecteur se réfèrera aux documents normatifs pour prendre connaissance de l’ensemble des révisions apportées

Brittle Rock Failure in the Steg Lateral Adit of the Lötschberg Base Tunnel

Summary: During the crossing of brittle rock formations at the Lötschberg base tunnel, failure phenomena have been observed both at the tunnel face and at the walls. A detailed analysis has been undertaken to explain these behaviours, based on the recent developments of Canadian research on brittle failure mechanisms. At the tunnel walls, a very good agreement is found between the calculated and observed damage and between two prediction methods, i.e. a semi-empirical failure criterion and elastic calculations with the "brittle Hoek-Brown parameters.” Near the face, due to the 3D nature of the stress conditions, some limitations of these approaches have been highlighted, and the growth of wall failure has been analysed. This research allowed a better understanding of the brittle rock mass behaviour at the Lötschberg base tunnel and showed that brittle failure processes dominate the behaviour of deep, highly stressed excavations in massive to moderately jointed rock. It also illustrates where improvements to the adopted approaches are require

New Cadanav methodology for quantitative rock fall hazard assessment and zoning at the local scale

Rock fall hazard zoning is a challenging yet necessary task to be accomplished for planning an appropriate land use in mountainous areas. Methodologies currently adopted for elaborating zoning maps do not provide satisfactory results though, due to uncertainties and related assumptions characterising hazard assessment. The new Cadanav methodology, presented in this paper, aims at improving quantitative hazard assessment and zoning at the local scale, by reducing uncertainties mainly related to the technique for combining rock fall intensity and frequency of occurrence. Starting from available information on rock fall failure frequency and trajectory simulation results, the procedure merges in a strict way temporal frequency, probability of reach and energy data and evaluates the hazard degree by means of "hazard curves”. These curves are described at each point of the slope by a series of energy-return period couples representing the hazardous conditions which may possibly affect that location. The new Cadanav methodology is here detailed and compared to its original version. Hazard zoning results are illustrated along two different 2D slope profiles, for linear homogeneous cliff configurations, and according to the Swiss intensity-frequency diagram for rock fall hazard zoning. However, the procedure can be easily used with any other intensity-frequency diagram prescribed in national guidelines and, additionally, extended to problems involving 3D topographies

Analysis of the evolution of road tunnels equilibrium conditions with a convergence–confinement approach

Since both lining structure and rock mass exhibit delayed behaviour, tunnel equilibrium conditions evolve with time. After discussing existing work done on different aspects of long-term tunnel behaviour, the aim of this paper is to “understand” the influence of rock mass and lining degradations on the long-term stability conditions of the tunnel by means of the convergence–confinement method. In order to represent the effects of degradation on tunnel long-term conditions, specific degradation models are selected according to the disorders identified during principal inspections of road tunnels in Switzerland. By simulating the reduction of the mechanical properties of both the rock mass and the lining or by using creep models, it is possible to assess the influence of the main degradation processes on tunnel stability. The results are interpreted in terms of tunnel safety factor. The presented approach for the determination of the long-term behaviour of tunnels, although valid for simple tunnel geometry and field stress conditions, allows to roughly estimate the influence of significant degradation processes that affect the rock mass and the supporting structure. Though this approach results in some simplification, it may be generalised and adopted with more refined numerical analyses for improving the assessment of tunnel long-term conditions

Laboratory and In Situ Simulation Tests of the Excavation Damaged Zone Around Galleries in Opalinus Clay

In the context of nuclear waste disposal in clay formations, laboratory and in situ simulation experiments were performed to study at reduced scale the excavation damaged zone (EDZ) around tunnels in the indurated Opalinus Clay at Mont Terri, Switzerland. In the laboratory, thick-walled hollow cylindrical specimens were subjected to a mechanical unloading mimicking a gallery excavation. In samples cored parallel to bedding, cracks sub-parallel to the bedding planes open and lead to a buckling failure in two regions that extend from the borehole in the direction normal to bedding. The behaviour is clearly anisotropic. On the other hand, in experiments performed on specimens cored perpendicular to bedding, there is no indication of failure around the hole and the response of the hollow cylinder sample is mainly isotropic. The in situ experiment at Mont Terri which consisted in the overcoring of a resin-injected borehole that follows the bedding strike of the Opalinus Clay showed a striking similarity between the induced damaged zone and the fracture pattern observed in the hollow cylinder tests on samples cored parallel to bedding and such a bedding controlled "Excavation” Damaged Zone is as well consistent with the distinct fracture patterns observed at Mont Terri depending on the orientation of holes/galleries with respect to the bedding planes. Interestingly, the damaged zone observed in the hollow cylinder tests on samples cored parallel to bedding and in situ around URL galleries is found to develop in reverse directions in Boom Clay (Mol) and in Opalinus Clay (Mont Terri). This most probably results from different failure mechanisms, i.e. shear failure along conjugated planes in the plastic Boom Clay, but bedding plane splitting and buckling in the indurated Opalinus Clay