The stability of a tunnel face with a free span and a non‐uniform support

Abstract

We investigate the effects of the support pressure distribution and of the free unsupported span on the stability of the tunnel face by means of limit equilibrium computations, which are based upon the so‐called method of slices. Design equations and diagrams are introduced for the estimation of the necessary support pressure taking into account these effects assuming a linear pressure distribution. Furthermore, the errors introduced by the common assumption of support pressure uniformity are discussed for the typical distributions of face support pressure in tunnelling by slurry shields, EPB shields and compressed air shields. The error is less than 10% in the case of closed‐shield tunnelling but may be significant in the case of face reinforcement.Der Einfluss der Stützdruckverteilung und der freien Spannweite auf die Stabilität der Tunnelortsbrust. Im vorliegenden Beitrag wird untersucht, in welchem Maß sich der erforderliche Stützdruck im Vorhandensein einer freien Spannweite zwischen Ausbruchsicherung und Ortsbrust erhöht. Ferner wird der Effekt der Verteilung des Stützdrucks unter der Annahme eines linearen Verlaufs quantifiziert. Das zugrunde liegende Berechnungsmodell untersucht das Grenzgleichgewicht eines Bruchmechanismus nach der sogenannten Lamellenmethode. Die Berechnungsergebnisse werden in Form von Bemessungsformeln und Diagrammen dargestellt. Ferner wird der Fehler der gängigen vereinfachenden Annahme eines gleichmäßig verteilten Stützdrucks für typische Problemstellungen diskutiert. Der Fehler beträgt weniger als 10% im Fall von geschlossenen Schildvortrieben (Erddruck‐, Flüssigkeits‐ oder Druckluftstützung), kann aber im Fall einer Ortsbrustbewehrung sehr groß und auf der unsicheren Seite sein.

Analysis method and design charts for bolt reinforcement of the tunnel face in cohesive-frictional soils

“…Anagnostou and Perazzelli (2013) already solved the problem of linear support distribution in the context of closed shield tunnelling. Following the same method, one can generalize Eq.…”

Face Stability Analysis of Shield Tunnel Using Slip Line Method

“…Figure 5, F is a point on the upper edge OB of the tunnel and q is uniform load applied to the ground. e effect of the cover layer can be considered as a distribution force [39][40][41].…”

Face Stability Analysis of Shield Tunnels in Homogeneous Soil Overlaid by Multilayered Cohesive-Frictional Soils

“…The new failure mechanism considers the effect of the cover layers as a distributed force according to the Terzaghi earth theory. The same treatments were adopted in the works of Broere [18]; Kirsch and Kolymbas [19]; Anagnostou [20]; and Anagnostou and Perazzelli [21], which are based on the limit equilibrium method.…”

“…For cohesive-frictional soils, the results obtained from experimental tests and numerical simulations show that the failure of soil in front of tunnel face demonstrates two main features, that is, shear failure band in the lower part and pressure arch effect in the upper part. The existing researches [18][19][20][21] considered the effect of the cover layers as a distributed force and achieved satisfactory results, which is calculated using the Terzaghi earth pressure theory. In this paper, the distributed force acting on the two truncated cones is also calculated by Terzaghi earth pressure theory as shown in Figure 2.…”

“…The stability of tunnel face in cohesive-frictional soils has been analyzed by using experimental tests (laboratory centrifuge tests [1][2][3] or 1 g model tests [4][5][6]) and the numerical simulations (the Finite Element Method [7][8][9], the Finite Difference Method [6,10,11], and the Discrete Element Method [12][13][14]). Both the limit equilibrium methods [15][16][17][18][19][20][21][22][23] and the limit analysis methods [9][10][11][24][25][26][27][28][29][30][31] were used by other researchers to investigate the stability of tunnel face in cohesive-frictional soils. Actually, from the analytical approaches mentioned above, it can be concluded that either limit equilibrium methods or limit analysis methods have advantages and disadvantages.…”