Study On Rock Breaking Mechanism And Parameter Optimization Of Cumulative Hydraulic Controlled Blasting In Tunnel

As a kind of energy-reservation and eco-friendly control blasting construction method which has emerged in recent years,cumulative hydraulic blasting technology has achieved preliminary application in practical engineering.While the theoretical research of this method is insufficient,and there is the great experience and uncertainty in the actual construction,which restricts the development and application of the process.In this paper,by means of numerical analysis and in situ test,the development of the shaped jet,the key parameters of the single and double hole charging structure and the application of the shaped charge hydraulic presplitting control blasting engineering are studied in depth.The main research contents and conclusions of this paper are as follows:(1)By means of numerical analysis,the kinetic analysis of the PVC shaped charge tube was carried out,the development process and law of shaped charge jet were studied,the indexes such as the velocity and effective plastic strain at different positions of the shaped charge tube and the stress at the hole wall were analyzed,the energy-collecting effect and regularity of the PVC shaped energy hood structure at the gathering point were analyzed.(2)Through the comparative study of four different apertures,the influence of the radial uncoupling coefficient on the conventional charge structures and the shaped charge structure is analyzed.It is concluded that the structure of water-coupled PVC shaped charge hood not only formed the main flaw in 0° direction,60°~90°direction distribution transfixion crack in favor of the formation of the tunnel blasting layer,which is the optimum charge structure for tunnel blasting in the charge structure with a diameter of 42mm.(3)Through the study of three different axially coupled shaped charge structures,the influence of coupling medium and the presence or absence of blockage on rock penetration is analyzed.The results show that the stress level in the direction of energy accumulation is always higher than that in the direction of non-energy accumulation.Compared with other structures,the water-coupled charge structure can effectively increase the detonation pressure and rock stress level,and the rock failure range is more uniform.The presence of mud can effectively increase the detonation pressure and rock stress of the hole wall under the mud.(4)Through the study of rock penetration law of conventional charge structure and shaped charge hood structure under four different apertures,it is concluded that the stress at the center of the hole is symmetrical with that at the right,and the detonation pressure decreases with the spacing.The optimal hole spacing of conventional charge structure was obtained to be 50cm,while that of PVC shaped charge structure can increase the optimum hole spacing to 70cm.(5)Based on the study of the penetration law of conventional charge structure and cumulative charge structure in rocks under three different perimeter blasting layer thicknesses(minimum burden),it is concluded that the greater the thickness of the blasting layer,the more concentrated the explosive energy in the inner region,the smaller the thickness of the blasting layer,and the larger the failure range on the free boundary line.The optimal thickness of conventional charge structure is 60cm,and the cumulative charge structure can be increased to 80cm.(6)Through the optimization and improvement of the blasting scheme of the Linjia’ao tunnel project,and combining with the parameter optimization results in this paper,simplified numerical analysis is carried out on the pre-crack of the shaped charge,the variation law of the existing tunnel lining stress and vibration velocity is obtained by comparing and analyzing the presence or absence of pre-crack.It is concluded the existence of the pre-crack can reduce the stress and vibration velocity of lining by more than 50% and 45% respectively;Through the blasting vibration monitoring of the conventional blasting scheme and the shaped charge pre-splitting scheme,the pre-crack equivalent analysis method,the feasibility and superiority of the cumulative hydraulic pre-splitting blasting scheme are verified.