Abstract: Assessment on stability of partial rock-block mass is essential during tunnel’s design and construction. On the basis of geological sketching explosion views, combined with projective geometry and the block theory, simple geology-geometry analytical procedure simplifies geometrical analysis of critical rock-block mass so as to define its space location, geometrical forms, different type of collapse or slippage, stability factor of single sided or double sided slippage, thus directly instructing purposive reinforcement of tunnel surrounding rock mass promptly. Finally, on the basis of geological sketching explosion views, this new simple analytical procedure is firstly applied to assess the stability of partial critical rock-block mass of tunnel Manxie 3; and a conclusion that plump collapse is the main destructive manner of critical rock-block mass is drawn. It not only assures the safety and continuity in the course of tunnel’s construction, but also has been testified having anticipated good effect in actual geology engineering application.

Key words: tunnel, critical rock-block mass, assessment on stability, geology-geometry, simple analytical procedure