The Study Of Impacts And Control Standard Of Drilling And Blasting Method On Primary Support

With the rapid development of railway engineering construction, drilling and blasting method will be widely used to excavation of railway tunneling. Therefore, it is of vital importance to study impacts and control standard of blasting vibration on primary support. This paper is supported by the drilling and blasting method of Qipanshan tunnel, combining the branch project of Ministry of Railway ("The study of impacts and control standard of drilling and blasting method on primary support"), and makes a systemic research based on the existing research results.In this paper, we introduced the blasting vibration monitoring test in Qipanshan tunnel, and used the measured blasting vibration data to do a regression analysis, concluding the attenuation law of the blasting vibration velocity in the near-field and far-field of the blasting. We compared the vibration velocities produced by the different blastholes, and found that the maximum vibration velocity was mainly caused by the blasting of the cutting hole. Two reasons are placed to explain this result:(1) The single explosive charge of the cutting hole is the maximum among all the different blastholes. (2) As the freeing surface condition of the cutting hole is poor, the freeing surface is exposed to larger press effects, which lead the blasting wave energy to spread into the internal part of the rock mass, and cause a larger blasting vibration intensity.In addition, we used the blasting vibration measured data of the whole section to analyze the relationship of the particle vibration velocities in vault, hance, and side wall.Based on the regression analysis of the attenuation law of the blasting vibration velocity, we also analyzed the characteristics of the blasting vibration of the far-field and the near-field, and stated the influence characteristics of the blasting vibration on shotcrete. Meanwhile, with the comparison of the attenuation law of the blasting vibration in the near-field and the far-field, we concluded that the attenuation law of the tunnel blasting vibration has a regional characteristic. Further, with the reference to the existing research results and the combination of the data obtained from this blast vibration monitoring test, we divided the area of the blasting vibration in Qipanshan tunnel initially.Besides, we used the stress wave theory to analyze the reflection progress and the transmission progress of the stress wave in different medium, and study the mechanism of the blasting vibration to the shotcrete. As a result, we concluded that in the progress of the impacts of the blasting vibration on the shotcrete, first, the tensile stress produced by the stress wave was larger than the tensile stress of the shotcrete; next, the tensile stress produced by the reflected tension shock wave was larger than the bond strength of the concrete and rock; at last, the compressive stress of the compression wave was larger than the compressive strength of the shotcrete. Therefore, under the effects of the blasting stress wave the tensile strength of the shotcrete controls the destructions of the shotcrete. Through calculation, we obtained the allowable maximum vibration velocity of the shotcrete. And, through analyzing the mechanism of the wire mesh concrete, we gave the advice of the maximum safe vibrating velocity under the effects of vibration loading on the wire mesh concrete.Furthermore, we summarized the present situation of the research of the blasting vibration to cement mortar bolt. Through analyzing the reflection progress and the transmission progress of the stress wave in the surrounding rock, mortar, and bolt, we studied the impacts of tunnel blasting vibration on the cement mortar bolt, and indicated that the destruction of the cement mortar bolt under the vibration loading influences was mainly controlled by the tensile strength of the cement mortar. Based on this result, we gave the advised value of the allowable maximum blasting vibration velocity of the cement mortar bolt through calculation.Based on the research result of this test, we pointed out some specific measures, which reduced the impacts of blasting vibration velocity on the primary support.