Comparative analysis of blasting disturbance under different hole arrangements in presplitting excavation of gentle slope of dam foundation

In the presplitting blasting excavation of gentle slope of dam foundation, to solve the problem of low drilling efficiency when the production blast-holes or buffering blast-holes are traditionally arranged along the slope (traditional blast-hole arrangement), the engineers try to adopt the way of reverse slope drilling (reverse blast-hole arrangement). However, the dynamic responses of rock mass under different ways of blast-hole arrangements are different. So, it is necessary to compare the disturbance of the reserved rock mass in dam foundation under the two blast-hole arrangements. Based on the excavation of gentle slope of the dam foundation of Baihetan Hydropower Station, the onsite blasting experiments are carried out under the two ways of blast-hole arrangements. At the same time, the blast-induced damage evolution characteristics and vibration distribution laws are analyzed by using the 3D dynamic finite element numerical simulation software (LS-DYNA). Moreover, the inherent mechanical mechanisms under different ways of blast-hole arrangements are revealed. Finally, the choice of the excavation scheme for the gentle slope of dam foundation is discussed considering the forming effects and construction efficiencies. The results indicate that the disturbance of the reserved rock mass induced by presplitting blast-holes is basically the same under different ways of blast-hole arrangements. Nevertheless, the cumulative damage effects and blast vibration caused by production blast-holes and buffering blast-holes are different. The inherent cause lies in the change of the intersection angle between the blast-hole and the reserved rock mass surface. Compared with the traditional blast-hole arrangement, the reverse blast-hole arrangement increases the intersection angle between the production blast-holes or buffering blast-holes with the contour surface, and the explosion energy transmitted to the reserved rock mass is reduced. Thus, the latter method is beneficial to reducing the disturbance to the reserved rock mass, which can reduce the damage depth by 11.6%~13.9% and the vibration velocity by 6.4%~53.7%.