Study On The Infiuence Of Periphery Hole Blasting Parameters On Surrounding Rock Damage And Overbreak And Underbreak Of Tunnel

Drilling and blasting method is still the main excavation method of mountain tunnels in China at present because of its strong geological adaptability,low excavation cost and flexible construction.However,in the construction process,due to the strong blasting load,the tunnel surrounding rock will inevitably produce different degrees of damage,overbreak and underbreak.Because of the direct contact between the periphery hole and the surrounding rock of the tunnel,the blasting parameters of periphery hole play a decisive role in the tunnel surrounding rock damage,overbreak and underbreak.This paper is based on the engineering background of the tunnel of Jiangshuiquan,theoretical analysis and numerical simulation were all used to study the influence of periphery hole blasting parameters on tunnel surrounding rock damage,overbreak and underbreak.First of all,according to the blasting effect of conventional blasting scheme and smooth blasting scheme of Jiangshuiquan Tunnel,the importance of smooth blasting in controlling the damage of tunnel surrounding rock,overbreak and underbreak is compared and analyzed.Compared with conventional blasting schemes,the proportion of over-shotcrete in smooth blasting schemes is reduced from 150% to 91%,and the average linear overbreak and underbreak is reduced from 0.347 m to 0.110 m,which almost eliminates underbreak.According to the acoustic testing results,the damage range of surrounding rock of conventional blasting scheme is 65-75 cm,while that of smooth blasting is only 25-35 cm.Compared with conventional blasting scheme,the damage range of surrounding rock is reduced by about 50%.Then,with the help of large-scale finite element software ANSYS/LS-DYNA,the blasting damage of periphery hole is simulated numerically.In the case of No.2 rock emulsion explosive,by changing the radial uncoupling coefficient,it is found that when the radial uncoupling coefficient increases from 1.25 to 2.5,the damage range of surrounding rock decreases from 28 cm to 9 cm,and the damage range of surrounding rock decreases gradually with the increase of the radial uncoupling coefficient,and the decreasing trend is first fast and then slow.When the uncoupling coefficient is between 1.25 and 2,with the increase of the radial uncoupling coefficient,the range of damage zone and crushing zone decreases rapidly,and the range of fracture zone stabilizes at about 12 cm.When the uncoupling coefficient is greater than 2,the crushing zone almost disappears,and the range of fracture zone and damage zone gradually decreases with the increase of the radial uncoupling coefficient.When using low explosive speed smooth blasting cartridge with explosive speed of 1400-2600 m/s,it is found that the damage range of surrounding rock is less than 10 cm by changing the explosive speed.The lower the explosive speed,the lower the damage range and degree of surrounding rock.When the explosive speed is 1400m/s,the damage range is only 2cm and the damage degree is less than 0.3.It is suggested that in smooth blasting of tunnels,special smooth explosive cartridge with small diameter and low explosive speed should be used to reduce the damage of blasting load to surrounding rock.Finally,based on the above engineering application and numerical simulation research,the concrete control methods of surrounding rock damage,overbreak and underbreak in tunnel construction by drilling and blasting method are put forward.