| At present,China's large construction of roads and other infrastructure projects inevitably produce a large number of transport interchange projects.Here,traffic tunnel under the existing lines(railways,roads,etc)engineering problems would also be very prominent,and tunnel under the airport runway with the drilling and blasting is rare.During the progress of tunnel excavation,seismic effect by blasting will inevitably have an iMPact on the normal operations of the airport runway.Therefore,it will be an urgent problem to be solved in blasting construction to know transmission laws and dynamic characteristics of blasting vibration waves of undercrossing tunnels objectively as well as reasonable evaluation and control of adverse effects of blasting vibration.Based on the comprehensive research methods of "field test","numerical simulation" and "theoretical calculation and analysis",this article carrys out a series of research work such as study on the structural parameters of tunnel under the airport,analysis on the blasting vibration test of the airport runways,study on the dynamic characteristics of tunnel excavation blasting,the dynamic response of the airport runways by blasting and the safety criterion of the airport runways blasting.The main contents and achievements are as follows:(1)Study on the structural parameters of tunnel under the airport.According to the geotechnical survey data and the inversion study on the mechanical parameters of surrounding rocks through the combination of orthogonal test,finite difference method and BP neural network method,the equivalent parameters of the surrounding rocks and the runways in the whole area are acquired and the problems of rock parameters section which exist in the numerical simulation calculation progress are solved.(2)Analysis on the blasting vibration test of the airport runways.Depending on tunnel excavation blasting technical characteristics and the surrounding environment,the plan of blasting vibration test in the tunnel blasting excavation progress are developed and the blasting vibration test are conducted.Besides,amplitude frequency analysis on the results of blasting vibration test are performed to get frequency characteristics of tunnel excavation blasting and the prediction model of blasting vibration are built.The results suggest that the mainshock frequency distribution of blasting vibration shows a difference among the X direction,the Y and Z direction,for example,the minimum vibration frequency is 35 Hz in the X and Y direction but 43 Hz in the Z direction and this shows a great difference in inherent frequency coMPared withtunnel,the airport runways and other constructions so that the resonance phenomenon would not occur.The test results demonstrate that the maximum vibration speed is1.328 cm each second during tunnel excavation blasting and is less than 3cm each second in the stipulation of the airport,so the influence which blasting vibration makes the airport in tunnel excavation could be got valid control.(3)Analysis on the dynamic loading characteristics of tunnel excavation blasting.Depending on the blasting plan,the principle of finite element numerical simulation and the theorem on moment of resultant force in theoretical mechanics,dynamic load characteristics of the 3cm,5cm,10 cm,20cm,40 cm,50cm and other side strip kits as well as the tunnel excavation blasting of full cross section are calculated and analyzed.And the equivalent blasting loads of tunnel excavation blasting dynamic analysis by coMParing blasting stress characteristics in different conditions of blasting sources have been put on.The results indicate that the characteristics of blasting wave are almost consensus between the blast model of charge hole which side length is 10 cm and of full cross section by the contrastive analyses on the load characteristics of blasting stress wave before and after equivalent;And also,within the scope of the area near explosive sources,blasting stress wave loads show some diversities in different charge structures by the contrastive analysis on them before and after equivalent but these diversities are less with the distance increasing and the minimum value even reaches 0.037 Mp,so it contributes to studying the blasting dynamic characteristics of the area away from explosive source in this equivalent way;Besides,blasting stress wave's vector superposition of vibration velocities within the scope of the aera near explosive source exist some differences by coMParing and analyzing them before and after equivalent but the diversities are less with the distance increasing and the minimum value even reaches 0.002 cm each second,so it also contributes to studying the blasting dynamic characteristics of the area away from explosive source in the same way.(4)Analysis on the response mechanism of the airport runways by tunnel excavation blasting.Based on the equivalent model of full cross section blasting loads,the tunnel blasting excavation numerical models in different blasting rounds are built,the dynamic response of the airport runways under the tunnel cycling blasting dynamic loads are analyzed as well as adjacent tunnels and the airport runways are judged whether safe or not to analyze the optimal penetration under the condition of full cross section blasting.When the excavation progress is 1.5m under the condition of thesite blasting,the simulation results suggest that the maximal principal stress of the tunnel linings and the runways both do not reach their ultimate tensile strengths and they are in safe state.When the blasting is in different circulation excavations from one meter to three meters,effective stress,the maximal principal stress and synthetic vibration velocity of each monitoring point on the airport runways above tunnel section all present symmetric distribution along right above the blasting source.Besides,their each maximum also occurs in the area and increases with the circulation excavation lengthening;Under different circulation excavations,effective stress,the maximal principal stress and synthetic vibration velocity all present the trend which is fast followed by slow with the circulation excavation increasing.When the circulation excavation is shorter than two meters,the increasing rate varies from large to small.Due to the blasting stress waves produce reflex action in the surface of molding grotto and creat multiple stacking in the surface,the molding grotto has a relative magnifying iMPact on the surface vibration with a certain range.(5)Study on the dynamic response of the nearby tunnel subjected to blasting seismic P-waves.The blast-induced waves are simplified as cylindrical waves.The wave function expansion method and multi-polar coordinates are adopted to derive the formula for dynamic stress concentration factor of tunnel surrounding rock under cylindrical P-waves.Combined with a special case,the influence of frequency and scaled distance r* on dynamic stress concentration factor is analyzed.Results show that:the frequency of incident wave has a little effect on the distribution of dynamic stress concentration factor,but a large effect on the amplitude;when the explosive is close,large dynamic stress concentration factor will occur at both the near side and the far side,which is quite different from plane incident P-waves;with an increasing r*,the distribution of dynamic stress concentration factor changes towards to the case of plane P-waves;r*=15 defines the boundary between plane and cylindrical waves.(6)Study on the safe criterion of the airport runways blasting.Based on the theory of stress waves propagation,the reflection and refraction of explosive stress waves spreading to the airport runways are conducted a theoretical analysis and the theoretical calculation model of blasting vibration velocity are built.And combined with the criterion of ultimate tensile strength as well as the actual solution and analysis of blasting engineering of tunnel under the airport runways,the safety criterion of blasting vibration velocity on the basis of the theory of stress waves propagation arerequired.According to the findings of blasting dynamic response of the airport runways,the statistical relationship between the tensile stress peak of the airport runways and the vibration velocity peak are established,the functional equation of them are approximately determined from the perspective of statistics,and the safety criterion of blasting vibration velocity of the airport runways on the basis of numerical calculation are discussed combined with the criterion of ultimate tensile stress;Comprehensively coMParing the results solved by theoretical analysis and by numerical calculation,and also considering the safety regulations for blasting,the criterion of blasting vibration velocity of the airport runways in Xujiaping are carried out.The study results suggest the safe-vaule of blasting vibration vibration of the airport runways in Xujiaping is considered as 8.83 cm each second based on the theory of stress waves and the criterions of ultimate tensile stress but 12.83 cm each second based on the numerical calculation model and the criterion of ultimate tensile stress.Therefore,comprehensively coMParing the two calculation results and considering the safety regulations for blasting,the final safe-vaule is determined as8.0cm each second.When the length of blasthole is adopted as 1.5m or 3m in tunnel blasting excavation,each monitoring point's vibration velocity of the latter is smaller coMPared with which of the former as a result of same priming dose possessing different charging densities.But on the premise of ensuring the normal function of the airport and the safety of adjencent tunnels,the biggest single priming dose is determined as 40 kg. |
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