| With the gradually accelerated development of infrastructure in China,the application of blasting is becoming increasingly extensive.There have been heated discussions about the control of damage caused by blasting,such as poisonous gas,vibration and noise.The most popular theory predicting and controlling blasting vibration is Sadovsky formula.With long-term geological movement,most natural rock mass shows some faults,like bedding,cracks and so on,which weaken their strength,wave impedance,elastic modulus,Poisson's ratio and some other physical parameters,thus cause discontinuity and anisotropy on rock mass.When excavating the rock mass,the structural plane of the rock mass reflect,transmit and absorbed the stress wave,which seriously hinders the propagation of the stress wave and therefore accelerates the attenuation of it.Compared with the complete rock mass,it's harder to accurately predict the peak vibration velocity peak of that with structural plane with Sadovsky formula.It follows that it is necessary to optimize the formula so that it is more applicable for the geological environment with structural plane.With single-hole blasting model built with large-scale finite element analysis software such as ANSYS/LS-DYNA aiming at bedding rock mass,the author analyzes the regularity of influence of elements such as bedding dip,bedding thickness,bedding number and stratified packing on transmit of blasting stress wave and influence on changes of the peak value of vibration velocity of rock particle,thus offers modification on Sadovsky formula.Based on the excavation and blasting of the entrance tunnel of Chongqing Railway Transit Tushan Station,the author analyzes the practicability of the modified formula with numerical analysis and on-site monitoring.The main contents and result of the study are as follows:(1)The transmittance of the stress wave at the structural plane decreases as the bedding dip increases.When the inclination of the stress wave decreases with the increase of the inclination angle,the reflectivity increases with the increase of the inclination angle.Compared with the surrounding rock,the "softe" the filler material in the bedding is,the smaller the transmittance rate of the stress wave is,while the bigger the reflectivity rate is.The number of layers and the thickness of the bedding are proportional to the attenuation of the stress wave.The more is layers,the thicker the bedding,the more attenuation the stress wave has.When muti-layered bedding is as thick as the single-layered one,the latter has less attenuation of the stress wave than that of the former.(2)Based on the influence of bedding dip,bedding thickness,bedding layer and bedding filling dielectric on stress wave,the influential elements of bedding on vibration velocity because of attenuation rate of the peak value of vibration velocity of rock particle in each working condition and modified coefficient in interaction of influential elements,the author concludes the result of the modified Sadowski formula:V=??K(Q1/3/R)?(3)Based on the blasting project of the entrance and exit of Tushan station,the author compares and analyzes the peak value of vibration velocity,the simulated result of numerical value,the blasting vibration monitoring value from both the former formula and the modified formula,and it turns out that result from the modified formula is the closest.Comparing the kinetic energy ratio of bedding rock and complete rock,and the kinetic energy ratio is 0.71.With modified formula,it is about 0.77,which is relatively close.(4)Establishing a three-dimensional model to analyze the difference of the distribution of stress wave between the surrounding rock and the side wall of the tunnel during excavating blasting of the tunnel with ANSYS/LS-DYNA,the author found that when distances from explosion source are equal,the vibration speed of the side wall of the tunnel was faster than that of the vignette velocity,indicating that the stress wave generated from the blasting transmit to the wall more than to the vault.Therefore,it is important to monitor the vibration velocity of the surface particles above the tunnel,but it is more crucial to monitor that of the surrounding slope of the tunnel during monitoring excavation of the tunnel. |
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