Research on surrounding rock stability in local collapse section of highway tunnels

Combined with a mountain tunnel project in Hunan province and based on the practical geological analysis and monitoring data, the basic failure mode of surrounding rock is established firstly by key block theory and the discontinuous deformation analysis(DDA) according to the real joint occurrence in the jointed and serious collapse section of the tunnel; and then based on the collapse mode by DDA, the surrounding rock stability is analyzed; and an evaluation for designed reinforcement scheme is made by continuous medium analysis program FLAC; it indicated that the main failure mode of surrounding rock is limited to local block instability controlled by joints and with no possibility of large deformation, which is in accordance with the practice very well so as to provide the assurance for the safety construction. The proposed method of combining discontinuous deformation analysis and continuous medium method for the collapse problem analysis, has acquired satisfying results so as to provide a good reference for other similar projects.