Abstract: In this paper, in view of the safety problems of the roof cutting chamber above goaf during ore extraction process step by step, by using high-level, large-diameter and deep boreholes in the stope of gently inclined and extremely thick ore body in one tin mine, the safety thickness of roof cutting in stope mining was studied based on elastic mechanics theory and numerical analysis method. According to elasticity mechanics, the length and span of drilling chamber in slope were confirmed as 26 m and 12 m, and the safety thickness of roof cutting was determined as 6 m. On this basis, the roof cutting thickness was analyzed and verified by numerical analysis, and the field monitoring including the surface displacement and surrounding rock stress of roof cutting chamber was also conducted. The results show that the maximum tensile stress value obtained from numerical analysis is 0.96 MPa, which is less than the tensile strength and the safety rate is 2.98, while the maximum displacement monitoring value is 7.58 mm, which is close to the numerical analysis value of 8 mm. Thus, the roof cutting in stope with 6 m in thickness is reasonable, which can ensure operation safety during roof cutting proces in the stope. The study results have been put into mining practices, and have effectively solved the safety problems of roof cutting chamber in the slope, when mining the gently inclined and extremely thick ore body in the tin mine by using ore extraction of large-diameter and deep boreholes.

Key words: gently inclined and extremely thick orebody, roof cutting thickness, elastic mechanics, numerical analysis