Study On Technology Of Controlled Blasting In Tunnel Construction Under Special Unfavorable Geological Conditions

With the development of traffic engineering,more and more tunnels are constructed with drilling and blasting technology,and it is necessary to encounter some special unfavorable geological conditions,which puts high requirements on the control of blasting technology during construction on site.However,at present,there is little research on controlled blasting technology under special unfavorable geological conditions at home and abroad.In this paper,the Hengshan tunnel passing through spherical weathering igneoμs rock and the Dufu tunnel passing through layered and jointed strata are the research objects,and the controlled blasting technology under two special unfavorable geological conditions has been studied,and the following results have been obtained:(1)Based on the analysis of blasting theory and rock mass strength theory,the evaluation criterion of rock mass rupture in tunnel controlled blasting is determined,and the LS-DYNA algorithm in tunnel blasting dynamic analysis is selected.(2)Through the study on the blasting of the boulders in the tunnel passing through the spherical weathering igneoμs rock,a double-hole blasting model μsing air and water as the filling medium and a model adopting the forward and reverse blasting methods have been established.The research shows that the reverse blasting at the bottom is more conducive to breaking Rock mass;further calculations show that when water is μsed as the filling medium,blasting can produce a larger fissure area and can effectively reduce the vibration caμsed by blasting,and determine the optimal blast hole spacing of 95 cm.(3)The calculation model of typical lone rock blasting at the site of Hengshan Tunnel is established.The research shows that the vibration velocity can be effectively reduced to a safe range by combining the vibration-damping groove and blasting in the 10 ms differential zone,and the differential zone blasting can reduce the vibration at close range.It has better damping efficiency than μsing damping groove.Combining with the scene,an optimized lone rock blasting scheme with 10 ms millisecond three divisions is proposed.The scheme has been verified and has a good effect.(4)Based on the study of the smooth blasting method of the tunnel passing through the layered joint stratum,the peripheral eye blasting model under different joint inclination angles is established.The calculation shows that the uncoupling coefficient is 2,the minimum resistance line distance is 60 cm,and the peripheral eye spacing is 40 cm.The peripheral eye is 20 cm away from the design contour line,and the peripheral eye layout with a density coefficient of 0.667 can effectively control the over-digging phenomenon in the presence of joints;Further research shows that the reason for over-excavation of the blasting around the layered joint stratum is due to the stress concentration during blasting and the breakage of the weak interlayer surrounding rock leading to the large area of the hard surrounding rock falling off.For the blasting around the layered joint stratum,the charge is increased.Uncoupling coefficient to reduce the blast hole spacing can effectively control the phenomenon of over-digging,and the research results have been verified by on-site construction.