ABSTRACT
Leaving aside the factors like shape and dimension of the tunnel, depth, characteristics of rock mass (deformational, strength, structural) and hydro-geological conditions of the rock environment in which the tunnel is being realized, among the basic factors, which determine the face stability and loading of the support, belong the technological factor of tunnelling and supporting of the tunnel, particularly the system of division of the face of the excavation and the length of the unsupported part behind the face. From this point of view, it is necessary to evaluate the time factor of supporting of the tunnel from two viewpoints, one is with regard to the influence on face stability and the other is with regard to its influence on loading of the support. Increased time lag between the stoppage of excavation and it’s supporting may indicate increase in stability problems in transverse as well as in longitudinal direction. On the contrary, however, from the view point of loading of the support, the optimum time lag in supporting may contribute to the reduction of loading of rock mass on the support. Effective utilisation of co-acting of system “rock-support”, for attaining minimum loading of the support while maintaining the stability and allowable deformation of rock mass (in transverse as well as in longitudinal direction), assumes, among others, objective determination of manifestation of deformation in the rock mass, not
only in the part behind the face but also ahead of it, with the objective to determine that part of the total deformation which is not brought on the support. Stress-deformational manifestations of the rock mass are, however, influenced as well by the stabilisation measures at the face. For the purpose of stabilisation, it is possible to use different types of anchors and bolts, whose purpose is not only to anchor the potential unstable area around the face, but also to increase parameters of deformational and strength properties in the anchored part ahead of the face.
