Abstract: Under natural conditions, the karstic bedrock and soil system are generally stable. The human activities, however, disturbs the subtle balance and changes the original geostress and groundwater flow pattern. These changes might result in the development of rock fissures and trigger the geological hazards such as groundwater and mudflow intrusion during the tunnel excavations. This paper presents an approach of establishing a model that the minimum thickness of the bedrock layer that can avoid the groundwater and mudflow intrusion during the tunnel excavation based on practical engineering applications. Various thickness of different filling material during the tunnel excavation were numerically simulated in order to evaluate the possibility of the groundwater and mudflow intrusion of excavation in karstic environment. Throughout the analysis and prediction, a safe tunnel excavation can be warranted.

Key words: groundwater flow channel, imperious rock mass, finite differential method, groundwater and mudflow intrusion