The paper presents discontinuities effect on tunnel stability conditions analyzed with MSB numerical simulation method. Based on statistical description of discontinuities network the MSB method and code creates representation of a blocky structure around a tunnel and analyzes it within a general statistical simulation scheme. Comprehensive description of geology in the vicinity of underground tunnel in Manhattan, New York was a basis for building a statistical model of discontinuities network followed by numerical simulation of stability conditions. Results for two different tunnel directions and for unsupported and rock bolted tunnel were compared. Information on observed geometry, location and size of real unstable blocks around the excavated tunnel allowed comparing computation results with observations.
