The combined from two small section cavern excavation method to expand a large section of the cavern

The present invention to solve the technical problem area railway turnout bored tunnel caverns from the merger of two small sections cavern excavation method to expand a large section cavern; first were excavated from the adjacent already formed two small sections cavern, the upper large section of the front side of the excavation in the same step side heading; secondly two end small section cavern, stepped from the side of the large section cavern to the other side heading Chamber side of the large section of the side heading step, the step section cavern excavation of large transverse hole wall; transverse wall from the pit and then to pick up the top section and dig Tai Chamber vault; then followed by excavation of stairs under the stairs left and right demi demi large section cavern large section cavern, the last large section cavern excavation invert, from a small section of two caverns and dig into one large section cavern. It simple construction method, the conversion process time is short, simple excavation and support measures, small construction safety risks, which will help cavern surrounding rock and initial support and stability.