Ductile support design

Abstract

Tunnelling in weak ground under high overburden normally results in very high displacements and if a stiff support concept is applied, this requires a very high load-bearing capacity. This has again and again proved to be both an uneconomical and an unsafe concept, leading to extremely high lining thickness and brittle failure behaviour. In order to avoid such problems, ductile support systems have been developed, which allow controlled deformation of the ground and plastic dissipation of excessive stresses accumulated in the lining. For the efficient design of such systems, the aspects of spatial and time-dependent development of displacement, time-dependent properties of shotcrete, and the load-displacement behaviour of the ductile elements have to be harmonized.The requirements posed on a ductile support system are presented, together with simple principles for the determination of ground behaviour boundaries when the application of a ductile support becomes imperative. Recent developments of ductile elements for use with shotcrete linings are described, and their general performance and efficiency are reviewed. A method for calculation of shotcrete stresses using absolute displacement monitoring data is presented, allowing the identification of both inefficient (lining stresses too low and strongly variable in the cross-section) or unsafe (lining stresses almost exceeding the strength) concepts and optimisation during construction.

Tunnel Squeezing Deformation Control and the Use of Yielding Elements in Shotcrete Linings: A Review

“…Hidcon element, as shown in Figure 2 a,b, is usually made of high-strength concrete matrix with porous additives [ 24 ]. Sometimes, tunnel engineers prefer to call it the “porous concrete element”.…”

“…Up to now, a good Lining stress controller consists of axially loaded steel pipes, where additional pipes are simultaneously installed at both ends of the element, aligned concentrically with the load-bearing pipes [ 24 ], as shown in Figure 2 d. The development of load-bearing pipe buckling folds either inwards or outwards is strictly restrained due to the presence of these additional guiding pipes installed concentrically. Lining stress controller can take advantage of rationally symmetrical cylinder buckling in this way, making its load-displacement behavior better match the strength development of shotcrete.…”

“…Then, ductile lining replacing the open gaps with yielding elements was proposed with the attention to address the problems of both acceptance of considerable rock deformations and transfer of shotcrete lining internal forces. Yielding elements show a stronger deformability than shotcrete, providing shotcrete lining with high possible resistance and able to accommodate the controlled rock deformations through their compressible deformations [ 24 , 25 , 26 , 27 , 28 , 29 ]. Ductile linings were first applied in the Galgenberg tunnel, Austria, in 1994, where the yielding elements consisted of groups of axially loaded steel pipes having some manufactured local weakness, and the large squeezing deformations occurring were successfully overcome by using the yielding elements in shotcrete linings [ 30 ].…”

Computational modelling of the mechanised excavation of deep tunnels in weak rock

“…Based on the approach by Farrokh et al [12], Radoncic et al [28] incorporated a formulation assessing the radial displacement from Sulem et al [36] with the advancement rate and thus obtained the Longitudinal Displacement Profile (LDP). It was thereby possible to approximately consider the time-dependent behaviour of the ground and the effect of the advancement rate on tunnel convergence when the yielding segmental lining with the Lining Stress Controller (LSC) is used for shield-driven tunnels.…”

Verformungsverhalten von Betonen mit ausgeprägtem plastischen Stauchvermögen

“…Zementgebundene Systeme mit derartigen Materialeigenschaften kommen beispielsweise im Tunnelbau in Form von komprimierbarem Ringspaltmörtel [1–5], Stauchschichten oder ‐elementen [6–9], zum Einsatz. Durch das plastische Stauchvermögen werden Gebirgsverformungen, wie sie bei druckhaftem Gebirge auftreten können, kontrolliert zugelassen und die auf den tragenden Teil des Tunnelausbaus wirkenden Belastungen reguliert.…”