Abstract: An open-pit limestone mine is developed with a flat tunnel，and the coarse crushing cham⁃ ber is at the bottom of the stope，which is a high-wall and large-span chamber，and a top-to-bottom lay⁃ ered construction plan is formulated. The first floor is excavated with the full section of the construction sup⁃ port. After the excavation is completed，the vault is lined with concrete，and the lining and the rock wall are rigidly bonded with anchor rods，and the arch feet are supported in the form of "rock anchor beams". The second，third and fourth floors adopt the method of pulling the groove in the middle first，and then blasting the two sides with smooth surface. After the excavation is completed，the chamber is lined. Com⁃ pared with the excavation of the trackless spiral ramp，this solution saves construction time，and after the completion of the first floor construction，the subsequent construction is carried out under the protection of the reinforced concrete dome，which greatly improves the construction safety.

Key words: large section chamber excavation, layered excavation, rock anchor beam, dome