ABSTRACT
Laminated geological formations are often encountered in different environments of underground excavations. This type of rock structure located in underground openings is a key factor in controlling the safety around underground openings in competent rock such as hydropower plants and underground marble and limestone quarries. Their behavior is governed by interbedding low tensile and shear strength which leads to separation and sliding respectively. When the rock layers are internally discontinuous, their behavior significantly diverges from that of a beam succession. In this research, the behavior of multilayered discontinuous roof in underground excavations is numerically investigated and compared to the behavior of single and multiple continuous layers as well as that of single discontinuous layer. A set of numerical analyses with the discrete element method are performed and quantification of the multilayering effect is produced for the unsupported discontinuous roof. Obviously, the control of stresses and displacements by active reinforcement or passive support of the roof is of great interest. A second set of numerical analyses for the quantification of the reinforcement effects of pre-tensioned rockbolting. The cases include up to five layers with ratio of layer thickness to span equal to 0.1 and for ratios of vertical discontinuity distance to span of the opening 0.2, 0.1 and 0.05. Conclusions are drawn with respect to the degree of decrease of vertical displacements for all groups of vertical discontinuities, which interrupt the layers in correlation to the support method. For continuous layers it is observed that the reinforcement of the roof reduces the vertical displacements to a lesser extent. In conclusion, practical guidelines for the planning of an effective reinforcement scheme are produced, which, in combination to careful monitoring of the roof ensures the safety of underground works in laminated environment.
