The Structural (Un)safety of Tunnels Explained by Analytical Approach

From soft soil tunnelling practice it has been observed that the segmental thickness of the tunnel lining has a constant ratio to the tunnel diameter. Nevertheless many engineering models are published in literature and used in practice, which describe the structural behaviour of the tunnel lining. These models are used to analyse the structural safety of the tunnels. In this paper a new analytical approach is described which clearly reveals the influence on structural behaviour of longitudinal joints and lateral interaction between adjoining rings of the lining. Furthermore it is explained that a common missing parameter in today's models is the influence of the construction of the tunnel, and especially the influence of grouting. In this paper the influence of the grouting is assessed. It turns out that the observed lining thickness can be dominated by the influence of groutingCivil Engineering and Geoscience

Design philosophy of concrete linings for tunnels in soft soils

Civil Engineering and Geoscience

Ultimate limit state design for linings of bored tunnels: Tübbingbemessung im Grenzzustand der Tragfähigkeit beim Schildvortrieb

According to modern design codes, such as the Eurocode 7, also Soil Retaining structures should be designed according to Ultimate Limit State analysis, see [1]. From an economic point of view, the design of the lining, i.e. the thickness and reinforcement of it, would be optimal if the loading during construction is less critical than the loading during service life, i.e. to the overburden loading. If necessary one could take measures to prevent that any loading during construction becomes more critical than the overburden loading. If this can be achieved, the structural design would be limited to establishing the overburden pressures, and calculating equilibrium between lining strength and overburden. For optimisation one could use Probabilistic theory and Risk Analytic techniques to establish a sufficient distance between actual loading and design parameters to get the most economic lining thickness and reinforcement. In order to evaluate our present situation with respect to lining design, some observations from engineering practice are iscussed: the first, from the construction of the 2nd Heinenoord tunnel, where the damage to the lining during construction was above average; the second from the construction of the Green Hart tunnel where measurements show, that flexibility of the tube and the influence of interaction between structure and underground can also lead to critical loading conditions for the lining. Finally the analyses and observations are generalized and some conclusions with respect to lining design are drawn.Hydraulic EngineeringCivil Engineering and Geoscience

Analysis of tunnel lining behaviour in soft soil during the construction stage, Second Heinenoord Tunnel

The paper addresses observations of the structural behaviour of the Tweede Heine-noordtunnel, a shield-driven tunnel in typical Dutch soft soils. Two rings were equipped with structural monitoring instrumentation. The measurements have shown that the assembly of the rings causes very significant initial forces and moments in the segments. Moreover, these initial forces and moments do not decrease significantly, as is often believed. Since conventional tunnel design models do not consider the effects of assembly on forces and moments, predicted maximum forces and moments in the lining appeared to be about half the measured values. Another impor-tant observation is that near the closing segment strong three dimensional effects occur as ring forces seem to migrate through small zones of the key segment

Geboorde tunnels met betonnen segmenten

Deze syllabus 'Betonnen tunnellinings' geeft een introductie in het constructief ontwerpen van betonnen wanden in boortunnels met grote diameter (> 5 meter), ook wel tunnellinings genoemd. Wereldwijd zijn verschillende typen linings toegepast in boortunnelprojecten. Echter, de functie van een aangebrachte lining is in de meeste gevallen dezelfde: in samenwerking met de omringende grond vormt de lining de tunnelconstructie, die moet zorgen voor draagkracht en stabiliteit zodat de gewenste processen ongehinderd plaats kunnen vinden in de speciaal hiervoor ontgraven ruimte. In deze syllabus concentreren we ons met name op de gesegmenteerde, betonnen tunnellining

Spalling of concrete due to fire exposure: A coupled fracture mechanics and pore pressure approach

In this paper results are presented from a by STW funded research project “spalling of concrete due to fire exposure” between Eindhoven University of Technology and Delft University of Technology and aimed at developing an integral spalling model. In this paper two coupled Finite Element based models are presented in which the first model describes the physical behaviour of concrete and is used to determine the temperature and pore pressure development and the second model describes the fracture mechanics behaviour of concrete and is used to determine the crack development

Probabilistic traffic load model for short-span city bridges

In the coming years numerous existing traffic bridges in cities are subject to re-evaluation. In this paper a new probabilistic traffic load model for short-span bridges is proposed. As an example, site-specific weigh-in-motion data from Rotterdam, the Netherlands, is included in the model. The method proposed in this paper allows for a very efficient computation and at the same time takes into account the stochastics in axle loads and distances. For a simply supported 6 m single lane bridge the probabilistic load model provides a design load effect that is slightly lower than currently prescribed EN 1991-2 and the Dutch Guidelines for existing structures NEN 8700 and NEN 8701. This indicates that there is possible potential for a small reduction of the traffic load for short-span city bridges compared to the current standards. However, given the questionable quality of recorded measurements, a more extensive measurement campaign using WIM measurements is needed to get an adequate quantification of the traffic load parameters for city traffic conditions.Steel & Composite Structure

Geboorde tunnels met betonnen segmenten

Deze syllabus 'Betonnen tunnellinings' geeft een introductie in het constructief ontwerpen van betonnen wanden in boortunnels met grote diameter (> 5 meter), ook wel tunnellinings genoemd. Wereldwijd zijn verschillende typen linings toegepast in boortunnelprojecten. Echter, de functie van een aangebrachte lining is in de meeste gevallen dezelfde: in samenwerking met de omringende grond vormt de lining de tunnelconstructie, die moet zorgen voor draagkracht en stabiliteit zodat de gewenste processen ongehinderd plaats kunnen vinden in de speciaal hiervoor ontgraven ruimte. In deze syllabus concentreren we ons met name op de gesegmenteerde, betonnen tunnellining.Civil Engineering and GeosciencesMechanica, Materialen en Constructie

Longitudinal time-dependent response of segmental tunnel linings

The longitudinal forces introduced by tunnel boring machines (TBMs) to the segmental tunnel linings influence their structural response. The analyses of the linings construction process and the ground-structure interaction mechanisms have shown the influence of the lining creep on the progressive loss of the initial longitudinal force. An analytical formulation to predict the remaining compression of the linings as a function of time is proposed, supported by means of a complete numerical model, which considers the effect of creep during the sequential construction process. An experimental program to determine the creep of plastic packers was developed, revealing its significant influence on the global lining creep factor and the evolution of the remaining compressive stresses.Peer Reviewe

Spalling of concrete due to fire exposure: A coupled fracture mechanics and pore pressure approach

In this paper results are presented from a by STW funded research project “spalling of concrete due to fire exposure” between Eindhoven University of Technology and Delft University of Technology and aimed at developing an integral spalling model. In this paper two coupled Finite Element based models are presented in which the first model describes the physical behaviour of concrete and is used to determine the temperature and pore pressure development and the second model describes the fracture mechanics behaviour of concrete and is used to determine the crack development.Structural EngineeringCivil Engineering and Geoscience