| With the rapid development of China’s economy,the demand for underground space is increasing greatly.Blasting is widely used in the excavation of underground space due to its economic efficiency and convenience,but it inevitably produces negative effects mainly including vibration,flying rock,and noise.The energy in explosives spread along the wave propagation path with stress waves,causing the vibration of rock masses and structures,which may affect and threaten both engineering safety and human body comfort.With the development and utilization of underground urban space,the geography and geomaterials become more complex,so the prediction of blasting vibration is increasingly important.The traditional blasting vibration prediction formula only considers the single explosive charge Q,geological conditions K and β,and distance from blasting center R,but does not take blast source parameters into consideration,which cannot meet the needs of blasting vibration prediction.Therefore,it is of great significance to study the effects of blasting parameters on predicting blasting vibration and controlling blasting vibration damage.In this paper,we conducted field tests and numerical simulations on the effects of three blasting methods on rock vibration,including blasting area,blasting charge,and hole distribution,based on the tunneling project of Guangzhou Railway Line 22.The dynamic response of the whole section of the double cavern under the action of up-step blasting and down-step blasting were revealed.Then,the effects of different blasting methods on the dynamic response of the cavern chamber were obtained.In the end,the dynamic response equations of the cavern chamber considering the blast source parameters were obtained.Firstly,the site monitoring program was developed according to the research content and the parameters of the geomaterials model were calibrated:the basic information such as blasting construction and geological structure information of the project site were summarized,and the vibration velocities of different monitoring points of the blast tunnel and the adjacent tunnel surrounding rock were monitored,and the rock parameters that best fit the site could be obtained by comparing the calculation results of the numerical model measurement points and the monitoring results.Secondly,LS-DYNA was applied to simulate the step blasting of the above project to study the dynamic response induced by lower bench blast and upper bench blast respectively,and the influences of different blasting areas on the dynamic response of the cavity were studied.In order to improve the computational efficiency,the above simulation is divided into two steps:firstly,the blast of a single blasthole was simulated by ALE method according to the field charging structure,and the blast load time curve was obtained;the above load could be used to simulate the blast process by input on the wall of the blasthole of the overall model.Secondly,the dynamic response of the two tunnels of the lower-stage blasting model is compared and analyzed,and a unique blast vibration attenuation law is found:(1)the diffraction wave attenuates along the cavity wall,resulting in a decreasing dynamic response of the left cavity wall along the lines of the two tunnel walls from the right sidewall to the left sidewall;(2)the reflection wave is reflected from the left tunnel to the left sidewall of the right tunnel,resulting in a slightly higher PPV of the left sidewall of the right cavity than the PPV of the right symmetric measurement point.Combined with the analysis of the upper-stage blasting model,it can be concluded that:(1)the cavity produced by the upper bench blast seriously hinders the propagation of blast waves.The vibration induced by upper step blast is much larger than the blasting vibration induced by lower bench blast with the same amount of explosives.(2)In the same blasting site,different blasting areas can seriously affect the values of K and β in Sadov’s formula.Thirdly,the simulation and comparison of blast-induced vibration with different amounts of explosive showed that(1)the amounts of explosive can seriously increase the vibration in the near field,and the amounts of explosive are positively correlated with the coefficient K and the attenuation coefficient β.(2)the prediction formulae of the dynamic response of rock mass under different amounts of explosive(blasting footage)were obtained.Fourthly,simulations and comparisons were conducted for lower bench blasting with various blasthole distributions,and the results showed that:(1)the blasthole distribution affects blasting vibration at the near-field to a greater extent,while it has almost no effect on the vibration of the mass at a scaled distance of 15 kg/m1/3:the smaller the blasthole spacing,the greater the near-field blasting vibration;the smaller the number of blasthole,the greater the near-field blasting vibration;(2)the corresponding site coefficients K and attenuation coefficients β for the blasting methods with different blasthole spacing and different number of blasthole were obtained,after fitting,the prediction equations for the dynamic response of rock masses were obtained considering different blasthole spacing and number of blasthole respectively,and the influences pattern of blasthole distribution on rock mass blasting vibration was quantified.Finally,the main findings of this thesis are summarized,and the outlook for subsequent research is provided. |
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