Structural Features and Engineering Application of Bell-Shaped Mining Caverns in Changyu

Cavern shape and surrounding rock structure are the important factors to cavern stability. In this work, the shape, surrounding rock structure, and rock strength of the deserted bell-shaped caverns without support in Changyu, Wenlin, Zhejiang province were investigated. Then the cavern stability with different shapes, span-depth ratios, inclination angles of sidewall was calculated and analyzed utilizing FLAC. It is shown that the bell-shaped cavern is better than other shaped caverns, such as rectangular cavern, circular cavern and a type of cavern with straight wall and top arch, because the tensile stress area of surrounding rock is smallest and the surrounding rock is more stable with high compressive strength. The smaller the span-depth radio, the smaller tensile stress area of surrounding rock and the more stable the cavern chamber. When the span-depth radio is less than 1.33, there is no tensile stress area on the top of the surrounding rock, which is favorable to the surrounding rock stability. With the decreasing of the inclination angle of sidewall, the tensile stress areas first decrease and then increase. When the inclination angle of sidewall ranges between 70 and 80, the tensile stress area of surrounding rock is small, which is favorable to the surrounding rock stability. In site investigation, 75% of the caverns has the span-depth ratio less than 1.33, while 60% of sidewall angles are between 70and 80.