| With the rapid development of social economy,the construction of tunnel projects in China shows a continuous growth trend in scale and quantity.The drilling and blasting method has the characteristics of fast excavation effect and high circulation footage.It is widely used in tunnel engineering and is the main method of tunnel excavation.However,with the gradual improvement of national environmental awareness,the traditional drilling and blasting method has been gradually eliminated due to its high dust concentration and low utilization rate of explosion energy.Scholars have begun to tend to an economical,green and efficient blasting technology,that is,hydraulic blasting technology.Hydraulic blasting plays an active role in improving the blasting effect of tunnel excavation and improving the environment of construction operation.Therefore,the study of hydraulic blasting technology has certain theoretical significance and engineering value.Through theoretical analysis and numerical simulation,the mechanism of water pressure blasting and the parameters of smooth blasting hole network were studied.Based on the background of highway tunnel project in plateau mountainous area,this paper studies the theoretical research,numerical simulation and field test in view of the shortcomings of poor smooth blasting effect and low cycle footage in Mengsheng tunnel.Furthermore,in view of the fact that the tunnel surrounding rock is often disturbed by the explosion cycle,the damage evolution of the tunnel surrounding rock under cyclic load is studied by using LS-DYNA restart technology.Finally,combined with the field test,the conventional blasting and hydraulic blasting are compared and analyzed in terms of blasting effect and economic index.The main research results of the paper are as follows :(1)Based on the propagation and attenuation law of the explosion stress wave,combined with the Starfield superposition method,the Von-Mises failure criterion was used to calculate the stress and damage range of the borehole wall under different radial and axial decoupling coefficients.The influence of two different media(water and air)charge blasting on the hole wall is analyzed,which can provide theoretical guidance for the design of similar tunnel blasting hole network parameters.(2)Based on indoor static and dynamic tests,the RHT constitutive parameters of dolomite limestone were calibrated.ANSYS / LS-DYNA finite analysis software was used to establish three-dimensional numerical models of three different linear charge densities(200 g / m,250 g /m,300 g / m),four hole spacings(60 cm,70 cm,80 cm,90 cm)and three kinds of photoexplosion layer thicknesses(60 cm,70 cm,80 cm).By comparing and analyzing the evolution process of damage with different linear charge density,different hole spacing and different smooth blasting layer thickness model blasting,the optimal hydraulic smooth blasting parameters are obtained,that is,the optimal linear charge density is 300 g / m,the optimal hole spacing is 70 ～90 cm,and the optimal smooth blasting layer thickness is 60 ～ 80 cm.(3)Aiming at the influence of cyclic blasting load on the large section surrounding rock of Mengsheng Tunnel,a three-dimensional numerical model of the tunnel was established by using LS-DYNA finite analysis software.Based on the DYNA restart program,the RHT constitutive model is used to calculate the cumulative damage of surrounding rock by conventional blasting and hydraulic blasting under cyclic load.The cumulative characteristics of rock mass damage under cyclic blasting are studied,which can provide some guidance for blasting excavation of similar plateau mountain tunnel projects.(4)Through the field test of smooth blasting in Mengsheng Expressway Tunnel,the conventional smooth blasting scheme and the hydraulic smooth blasting scheme are compared and analyzed.It is found that the optimized hydraulic smooth blasting is superior to the conventional smooth blasting in economic indicators.In addition,hydraulic smooth blasting can significantly reduce overbreak and underbreak,improve half hole rate and tunneling effect.The optimized water pressure smooth blasting brings good economic results to the tunnel project,which can provide a reference scheme for tunnel excavation in plateau mountainous areas. |
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