Effect of joint characteristics on surrounding rock stability and stress mechanism of bolt under blasting excavation

Abstract

Joint characteristics of rock mass are the key factors of tunnel surrounding rock failure. This paper relies on the two-lane mountain tunnel project and takes the IV class surrounding rock as the research object. By means of on-site investigation, numerical simulation and on-site monitoring, the effects of different joint development characteristics under blasting vibration on tunnel surrounding rock deformation, instability mode and force mechanism of rock bolts are studied. It is found that the instability mode of tunnel is obviously affected by the larger joint dip angles. When the dip angle of one group of consecutive joints is kept unchanged and the dip angle of another group of joints is changed, the vault settlement decreases first and then increases with the increase of joint dip angles. The influence of horizontal joint spacing on surrounding rock deformation and vault settlement is much greater than that of vertical joint. Under the most disadvantageous working conditions of the two sets of consecutive joints, the effective range of the axial force of rock bolts depends on joint dip angles and has little correlation with joint spacing. The axial force of rock bolts decreases with the increase of horizontal joint spacing, while the influence of vertical joint spacing on bolt is less.