Application Of Time Sequence Controlled Pre-splitting Blasting In BAIHETAN Rock Anchor Beam Excavation

With respect to conventional blasting fracture controlled blasting method,time sequence controlled pre-splitting blasting can not only reduce the blasting holes and save explosives,but also decrease the blasting damage to rock mass,with only other process except changing the detonating order and arrangement pitch of the holes.In which the main plant site BAIHETAN hydropower rock typical of columnar jointed basalt-based will affect the plant excavation of rock anchor beam forming effect,but Optimizing the time sequence controlled pre-splitting blasting scientifically,can provide an effective way to ensure excavation quality of the rock anchor beam in BAIHETAN hydropower.According to the site geological conditions and rock physical and mechanical parameters of BAIHETAN underground hydropower plant,the use of finite element analysis software ANSYS / LS-DYNA timing control blasting indoor simulation,optimization for live rock anchor beam blasting parameters,and based on simulation results,timing control fracture blasting field trials.The main findings are as follows:(1)when studying time sequence controlled pre-splitting blasting by simulating,during the explosive stress wave which from the earlier detonated holes effecting,there will be an obvious stress concentration phenomenon in the later detonated hole’s wall,and the formation of prefabricated in the blasting distributed holes side seam,which confirmed the validity and feasibility of the time sequence controlled pre-splitting blasting;(2)For the excavation in BAIHETAN hydropower station on the right bank of the main plant,when the use of small diameter(42mm)were smooth blasting,the borehole of gunpowder charge density Optional 114 g / m or so.When the distance between former detonated holes is 35 cm,the reasonable initiation time between the former holes and later holes is about 50 ~ 60us;(3)When sequential control fracture blasting is adopted to improve the smooth blasting,blasting stress wave on the damage of the rock with after blasting from distributed and weakening,numerical simulation results show that when the hole diameter is 42 mm,first distributed distance using 35 cm,the best distance between later detonated holes for 60 cm;(4)Through the field of comparative tests available,the time sequence controlled pre-splitting blasting is turn to be more conventional than smooth blasting,the blasting can effectively reduce the damage to the reserved rock,and can protect in the surrounding rock stability.The best pitch of 70 cm,slightly larger than the numerical simulation results,mainly because of the numerical simulation does not consider the impact of rock structural surface like.Time sequence controlled pre-splitting blasting can increase the pitch and reduce the amount of drilling and explosive without increasing other basis,just by changing the order of detonating the blast holes and blast hole arrangement pitch.