In this paper we propose a new method for computing the effect of tunnel excavation on the piezometric head field by taking into account the excavation advance rate. This method makes possible the computation of the hydraulic head in only one step, with considerable saving of computational effort. The seepage flow equations, usually formulated in a fixed co-ordinate system, are here re-formulated within a frame of reference that advances together with the tunnel heading. The advance rate appears as an additional parameter in the equations. The transformed equations are solved by the finite element method. Numerical examples are employed to illustrate the usefulness of the method proposed.


Dans cet article on presente une nouvelle methode numerique tenant compte des effets de l' avancement du tunnel sur la charge hydraulique. Les equations des ecoulements transitoires en charge, generalement formulees dans un système de coordonnees fixe, se rapportent ici à un système de coordonnees qui se deplace en fonction de l' avancement du front. La vitesse d' excavation y apparaît en tant que paramètre supplementaire. Ainsi transformees, les equations sont resolues à l' aide de la methode des elements finis. Des exemples calcules montrent que la vitesse d' excavation du tunnel est très importante pour Ie cas d' un sol peu permeable ou très compressible.


Es wird eine numerische Methode zur Berechnung der Auswirkungen eines laufenden Tunnelausbruchs auf das hydraulische Potentialfeld unter Berucksichtigung der Vortriebsgeschwindigkeit vorgestellt. Die Strömungsdifferentialgleichungen werden fuer ein Koordinatensystem formuliert, dessen Nullpunkt sich auf der fortbewegenden Ortsbrust befindet. Die transformierten Gleichungen werden nach der Methode der endlichen Elemente gelöst. Wie die durchgerechneten Beispiele zeigen, hat die Vortriebsgeschwindigkeit einen erheblichen Einfluss, falls der Baugrund wenig durchlassig oder stark zusammendrueckbar ist.


During tunnel excavation, seepage flow towards the face is usually inevitable, even when an impervious lining is installed close to the tunnel heading, as the tunnel heading is usually open (Figure 1). Predictions of the effect of tunnelling on the piezometric head field are necessary for a number of reasons. For example, a drawdown of the water level may lead to a decrease in the discharge of wells, or to inadmissible subsidence due to consolidation. Besides these - in the broader sense - environmental consequences, seepage flow may impair the stability of the tunnel face as well. The loss of hydraulic head in the vicinity of the tunnel face does not take place immediately after excavation. The lower the permeability and the higher the store activity of the ground mass, the more time must elapse to achieve a steady state (Marsily, 1986). Apart from the borderline case of highly permeable ground or very slow excavation, the excavation-advance rate v must be taken into consideration as an additional parameter of the mathematical model, for the alteration of the hydraulic head field takes place simultaneously with the process of excavation. The effect of the excavation advance rate represents the subject of this paper. In Section 2, the standard boundary-value problem is formulated and, furthermore, the - also standard - numerical method is outlined. In Section 3, some alternative methods of treating the advancing tunnel face are briefly discussed. The proposed method is presented in Section 4. The paper closes with some examples concerning the hydraulic head in the vicinity of the tunnel face and the lowering of water level due to tunnelling.

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