The Determination Of Parameters Of Millisecond Blasting In Near-Surface Tunnel

In recent years, along with the a large of construction of urban rail transit, tunnelexcavation blasting caused many scholars researching, especially the excavationblasting seismic effect caused by blasting is becoming more and more attention by thepeople. In many measures to reduce the blasting vibration effect, the millisecondblasting is the most commonly used and practical measures, not only can effectivelyreduce the blasting seismic effect also can improve the effect of rock crushing.This paper are introduced on the influencing factors of millisecond blasting seismiceffect, and the two main factors, namely the millisecond blasting intervals and themaximum explosive payload are in-depth researched.First of all, summarizes and analyzes the basic principle of rock breaking anddamage to the building of the blasting seismic wave mode, simply elaborated the brokenrock blasting theory model and the destruction mechanism of blasting seismic energy.Second, the elastic dynamics theory is used to analyze the millisecond blastingintervals, introduce "spherical cavity" principle, the particle’s displacement to evaluate,and to analyze the vibration of the particle，and come to a conclusion that the particleattenuation vibration very quickly, soon after a reciprocating movement, vibrationintensity becomes0.012of the original, which later became very weak.So in fact only areciprocating motion, and vibration can be seen as the elastic vibration after thereciprocating motion. Vibration from the beginning to the end of the reciprocatingvibration for the first time, this paragraph of time is a period. Then come to a conclusionthat the period T becomes direct ratio with R₀, as the dynamite quantity increases, so theblasting explosive quantity, the greater the time is the radius of the spherical cavity is,the greater the vibration period T. And the period T can be considered a main shock ofthe blasting seismic wave period time. Simultaneous contrast analyzed using thismethod and semiempiricalmethod andthe advantages of millisecond blasting interval tobe determined.Third, research and analyze for the maximum explosive payload, thendeterminedby the velocity control of point on the ground, and transform Sa Dao Fu,experiential formula to calculate the results.Finally, using the finite element software ANSYS/ls-dyna numerical simulation of millisecond blasting vibration effect is calculated.The numerical model select theappropriate material model and boundary conditions. Based on the measured vibrationvelocity and vibration velocity time history curve and numerical simulation analysis,shows the results of numerical simulation and engineering coincided basically with theactual situation. Practice proves the principle of elastic dynamics is used to determinethe millisecond blasting intervals is feasible, and through the large charge and holeparameters of the design, specification of the project design of blasting scheme isreasonable.The results of this paper to choose a reasonable millisecond blasting parameters, toreduce the blasting seismic effect and ensure the safety of excavation blasting ofsurrounding buildings play an important reference role.