Recent Developments in Tunnel Engineering

Schubert W. & Riedmueller G.

 Institute of Rock Mechanics and Tunnelling and Institute of Engineering Geology and Applied Mineralogy Geotechnical Group Graz, Graz University of Technology  

ICCEMCE-03, International Conference on Earthquake Engineering, Computational Mechanics, Geotechnical and Transportation Engineering

 Addis Ababa, Ethiopia - January 9-10, 2003.

Design and construction of tunnels traditionally to a good part is based on experience. A huge number of rock mass classification systems and suggestions for the selection of supports empirically derived from those classifications demonstrate this. There are several shortcomings of those systems. One of the most important issues in this context is, that by using those systems the engineers may believe to have solved the problem. An analytical approach to the problem at hand thus is not promoted.

Over the last decades numerical methods have developed to a stage, that would allow relatively realistic modelling. But as the classification methods, also these tools are frequently misused.

The Geotechnical Group Graz recently has outlined a procedure, which allows a coherent step by step approach to the problem of tunnel engineering, from investigation throughout construction. The procedure is incorporated in a guideline recently published. Experience from the use of this guideline is reported.

The incorporation of probabilistic methods into this analytical procedure allows a realistic risk assessment. Comparisons of different construction methods can be made on an objective basis.

The ongoing design on site requires a continuous update of the geotechnical model, and short term prediction. The traditional face mapping techniques do not allow an up to date modelling, besides being inaccurate and biased. A system, using digital imaging is presented, which is hoped to upgrade the on-site investigation.

Measuring absolute displacements of tunnels with electronic total stations contributes to a better understanding of the rock mass behaviour. Recently developed evaluation methods allow a reasonably accurate prediction of rock mass structure ahead of the tunnel face, as well as a prediction of the displacement development. A software for comprehensive measurement data evaluation has been developed. With case histories, the capabilities of this tool will be demonstrated.

Tunnelling in poor and heterogeneous rock mass requires special considerations with respect to excavation and support. The high and usually strongly varying displacements cause high stresses or stress concentrations in linings. A ductile lining system has been developed to cope with those adverse conditions. The principle and applications will be shown.

Case histories from tunnels constructed in difficult geotechnical conditions are presented.

Authors: Prof. Dr. Wulf Schubert, Institute of Rock Mechanics and Tunnelling,
Prof. Dr. Gunter Riedmueller, Institute of Engineering Geology and Applied Mineralogy Geotechnical Group Graz, Graz University of Technology

A-8010 Graz, Austria

Rechbauerstrasse 12

e-mail: tunnel@fmt.tu-graz.ac.at