Novel method for ductile lining pre‐design / Neues Verfahren zur Vorbemessung eines duktilen Ausbaus

Abstract

The design of a ductile lining has to incorporate a number of influences. Both the influences of the ground conditions and the construction have to be considered in order to develop a safe and economical solution. Special focus has to be set on a plausible prediction of the time-and excavation-dependent displacement development and its interaction with the transient shotcrete properties, load-displacement behaviour of the yielding elements and the entire excavation sequence. The rather underdeveloped state of the state-of-the-art methods for ductile support pre-design is somewhat contrasting the frequent practical usage of this support concept. Especially the development of semi-empirical or analytical methods, allowing a quick initial assessment of the system behaviour and incorporating the influences mentioned above, has been neglected in favour of the numerical analysis methods.A novel calculation method, analogous to the convergence confinement method, applicable to non-circular excavation geometries and unsymmetrical displacement fields is presented in the course of this paper. Castigliano's second law and the associated balance of the outer work enable determining the equilibrium point between the ground and the installed support measures and the determination of the support capacity. Additional semi-empirical relationships, derived from a series of systematic 3D numerical simulations, allow prediction of the pre-relaxation and of the longitudinal displacement profiles for a top heading advance. The combination of these relationships with the proposed energy-based equilibrium criterion allows the establishment of a coherent calculation method, addressing and incorporating all relevant geomechanical and constructional influences. A practical application example and the verification of the method are shown and discussed, with the calculation results compared to the measurement data from the exploratory tunnel Paierdorf (Lavanttal fault system).The same ideas regarding the balance of outer work between the support measures and the rock mass can be used for finding clear boundaries of ground conditions where a flexible support becomes imperative.

Yielding elements – requirements, overview and comparison / Stauchelemente – Anforderungen, Überblick und Vergleich

“…Maintaining the already determined rock mass parameters, the resulting displacements and displacement characteristics were determined (Fig. 19) [17] [18].…”