Study On Fine Blasting Excavation Of Deep Underground Cavern Based On Timing Sequence Control Fracture And Borehole Notching

In southwest and northwest region of our country,a great amount number of large scale hydropower projects were located in high mountains.Those projects are all related to explosion excavation of large-span underground caverns in high situ-stress situation.And some key parts may be used as the hydropower operation structure,such as rock anchor beam.Not only the previous geological exploration is needed to choose the proper location with fine rock properties,but also to strictly control the damage effect on retained rock mass during blasting excavation to improve the overall rock stability.This article focuses on the thesis of fine controlled blasting excavation of key parts of underground caverns,comprehensively use the technical measures like theoretical analysis,laboratory tests,field tests,and numerical analysis,revealed the mechanism of timing sequence control fracture blasting method.The excavation effect of different blasting excavation methods in deep jointed rock mass was studied and proposed a new method of fine blasting excavation based on timing sequence control fracture and borehole notching.Mainly completed the following aspects of the work:(1)Based on the damage and destruction of the surrounding rock due to the dynamic disturbance of deep underground rock mass blasting excavation,two kinds of fine blasting methods,timing sequence control fracture blasting and notched blasting,are proposed.According to the characteristics of low tensile strength of rock mass,the conditions for the initiation and propagation of initial crack on the borehole wall in two kinds of blasting methods are discussed.The above research provides the basis for the determination of the initial crack propagation direction of target borehole and the expansion and crack arrest of notched blasting.(2)The stress and displacement of rock mass under single hole blasting are theoretically deduced according to the wave equation of cylindrical wave in the ideal elastic body,the stress concentration effect of the bull hole in infinite plate subjected to uniaxial tension is analyzed.Based on this,a similar model specimen with two round holes was designed and fabricated,one of them was used as a borehole charge for blasting and the other as a bull hole,study on the dynamic stress concentration effect on the target borehole before itself detonated.Then a numerical model for related experiments was established.Its validity was proved by comparing hoop strain peaks of the same place.Analyze the time effectiveness of the stress concentration effect around the void hole.(3)Through in-situ test of timing sequence control fracture presplitting blasting,study on the excavation effect in different spacing of adjacent target borehole.The superimposed form of the longitudinal and transverse waves stimulated by the primary borehole on the target borehole was analyzed.Based on the propagation velocity and form of the longitudinal waves and shear waves in the rock mass,combined with the detonation test of the adjacent blasting holes in the chamber,the method for determining the delay time between primary boreholes and target boreholes is summarized.Based on the in-situ test,a theoretical model of 1 ms difference between detonating holes was established,which verified the rationality of the theoretical calculation time delay.(4)Based on the guiding role that the notched borehole plays in the expansion of the crack initiation,a V-shaped notching process was applied to the smooth blasting holes in the rock anchor beam of the underground powerhouse of Baihetan Hydropower Station.Three sets of tests have been carried out with line charge densities of 65g/m,70g/m and 85g/m respectively.Conventional blasting excavations with the same charge were carried out after each notched blasting excavation was completed.Monitored the dynamic response of the surrounding rock in the process of blasting excavation through the velocity meter and acoustic meter.Combined with the flatness of excavation profile surface,comparative analysis the blasting excavation results of the notched hole and round hole.Carried out comparison validation in numerical model and in-situ test,and gain the effect of different in-situ stress on the blasting excavation result.(5)Put forward a new method of timing sequence control fracture blasting for the primary boreholes cutting notch,studying the the crack formation figures of under different shape primary borehole.Then study on the relationship between the in-site stress and the explosive payload in the condition of primary boreholes cutting notch.Finally,keep the in-situ stress unchanged,numerically studied the 7 kinds of joint direction of 4 kinds of filling joint materials theoretical model for blasting excavation,and analyzed the influence of obvious stress concentration and non-stress obvious concentrated target boreholes on the crack propagation rules between adjacent filling joints.