continuum and discontinuum modelling in tunnel engineering

Rud.-geol.-naft. zb., Vol. 12, Zagreb, 2000.56 Barla, G., Barla M.: Continuum and discontinuum modelling%I(a) iFigure 24. YeIded blocks undsheardi.splacements along the join& aroundthe tunnel; (a) determmisfic model, (b) DFN modelplaced on the adoption of discontinuum models whichgive a far more realistic and representative picture ofrock mass behaviour than equivalent continuum models.Modelling of rock mass around a 4.75 m diametertunnel excavated by an open TBM configuration throughquartzitic michaschists has been described, with attentionpaid to the instability conditions that developedwhen crossing through a fault zone. The calculationswere performed by using the finite element method andthe distinct element method, according to a two dimensionalmodelling format, three-dimensional representationbeing too limited and not justifiable in respectof the uncertainties of the input data.With the finite element method an equivalent continuumapproach was applied, including the influence oftwo major discontinuities on the right wall. With thedistinct element method a fully dicontinuum approachwas used by either a deterministic or discrete featurenetwork model. The discontinuum representation of therock mass captures in a remarkable manner the instabilityconditions that developed at the TBM head duringexcavation. In comparison, the continuum representationgives a more idealised illustration of the instability.It is concluded that for stability analysis peculiargeologic conditions such as fault zones around the tunnelrequire specific models, which reflect the given conditionsin the most realistic way possible.Received: 2000-05-24Accepted: 2000-09-21Figure 25. Block movemertls around the funnel, (a) deterministic model,(6) DFN d lREFERENCESBarla, G., M. Barla, L. Repetto (1999): Continuug anddiscontinuum modelling for design analysis of tunnels. 9 . Int.Coner. on Rock Mech. Paris. France.Band is ,"s . (1993): ~n~ineerine properties and characterization ofrock discontinuities. Com~rehenslve Rock Eneinee~e. Volume1. Fundamentals ~udsoi J.A, editor). pp. 153-183. PergamonPre~s, Oxford (U Ii ).Barton , N ., R . ' ~ e.n i , J . L u n d e (1974): Engineering classificationof jointed rock maqses for the design of tunnel supportRock Mechanics. Vol. 6, pp.189-236.Bart on, N. (1997): Pont Ventoux Hydropower Project. TunnelF2-Poet Ventoux. Assessment of geological condilwns andsuppofifor ch 2350-dWO Report to Nocon. 25 October;%gdBarton, N. (1998): Quantitative description of rock mawes for thedesign of NMT reinforcement Spec~al Lecture 1). Int. Conf. onHydro Power Development In h imalayas. Shimla, IndiaBart on, N. 61999): General report concerning some 2Dth centurylessons an 21S'century challenges in ap lied rock mechanics. 9thInternational Congress on Rock ~ecianics. August 25 -28.1999, Paris.Brown, E.T., J.W. Bray, B. Ladanyi, E. Hoek 1983):Characteristic line calculations fur rock tunnels. J. Geotec I, . Eng.Div. Am. Soc. Civ. Enp. 109. pp.15-39.Cundall, P. A., R. D. Hart (1993): Numerical modelling ofdiscontinua. Comprehensive Rock Engineering. Volume 2.Analysis and Design Methods (Hudson J.A., editor). pp. 231-261. Pergamon Press, Oxford (UK).Curran, J. H. and Corkun, B. T. (1997): phase2. 2D finiteelcment program for calculating stresses and estimating su portaround underground excavations. Reference Manual and futorialManual. Rock Engineering Group. University of Toronto.Dershowitz, W., G. Lcc, J. Geier, P. La Pointc,(1995):FracMan Interactivc Discrcte Feature Data Analysis,