Abstract: This paper presents the numerical analysis as well as theoretical analysis results of stability of a tunnel in the rock mass with weak rock interlayer. The coupled elasticplastic model of marble considering confining pressure effect and the perfect elastoplastic model of the chlorite schist based on MohrCoulomb criterion are adopted in the analysis. The major results are: 1) when the excavation reaches the rock mass containing weak zones, the weak rock will be intruded in a progressive failure mode and a large plastic zone is formed immediately behind the excavation face, whereas, the stability of the rock mass in front of the excavated face is not significantly affected; 2) the thickness of the weak zone has a large influence on the plastic zone of the weak zone but it has limited impact on the stability of the rock mass behind as well as in front of the excavation; 3) If multiple weak rock zones are encountered in the tunnel excavation, the time required to reach the plastic zones in the weak rock zones will be the same as the time needed in a single weak zone is encountered. The plastic zone can also be found in surrounding rock mass with better engineering properties.

Key words: Deeply Buried, Tunnel in Soft Rock Mass, Interlayer, Stability Analysis