A new appraisal technique for stability of tunnel face

Abstract

There are plenty of numerical methods that enable engineers and researchers to compute st,ress and strain staks in soil medium and in t,unnel lining. Thc classical methods (FEM, BEM, etc.) possess well-known disadvantages. 'The dist,inct methods, such as PFC (particle flow code), FLAC, static version of the PFC, etc., are burdened by errors, which follow from uncertain mechanical properties of contact condit,ions. In this paper, a new concept will br introduced starting with the RChl (this method could be the hest met,hod for most of moving boundary prob lcms). The region in frolit of'the tunnel heading is split into two park tl~p stable part and the moving part, which is admissible to slip into the turrnel. Similar idea, hl~t much silnpler tlian here, is known from assessment of slope shbility. The movement of t,he moving part is controlled by variational principle, which is known as inverse variational principle. In this way, the problern is transformed into the problem of optimal shape design with constraints on the contact boundary. The inverse variat,ional principles are most,ly formulated for give11 exrernal loading. In tthis case the external load is transfened via the unmovahli~ part; the interaction of moving and stable parts have to he ensured. Bot,l~ parts arc- in carth gravity field.