A Study Of The Influence Upon The Stability Of Tunnel Surrounding Rocks And Primary Support Structure Played By Explosion

The drilling-blasting method is a major construction method in the excavation of highway tunnels. It’s sure that the explosion will cause vibration to the surrounding rocks and the primary support structure. If the vibration speed resulted from the explosion is higher than the critical vibration speed of the surrounding rock and primary support structure, the surrounding rocks and primary support structure will be damaged and resulted in engineering accidents. To study this problem, this paper has taken Luheshan Tunnel of Guangxi Qinzhou-Congzuo freeway as the research object and analyzed the influence upon the tunnel surrounding rocks and primary support structure played by the explosion based on the study of declining rule of explosion vibration speed through the measures of field supervision and value simulation. This paper has proposed the reasonable vibration speed to ensure the safety of construction; and optimized the supporting parameters of the bolt.By testing the K39+946.6loose ring of Luheshan Tunnel, the scope of the loose ring of the surrounding rock section. When re-classifying the surrounding rock in accordance with the size of the loose ring, we can conclude that the grade of the tunnel surrounding rock is Ⅲ. At this moment, the bolt has played the major role in the primary support structure, while the spraying of concrete cement only plays the role that support the surrounding rock between the bolts and preventing the surrounding rock from weathering.Through the on-the-spot explosion vibration speed testing, the vertical explosion vibration speed of the tunnel top and foot arch and the explosion vibration speed of the close tunnel which is blown up and excavated are reached. By adopting the M.A. Sadaovsk Formula regression analysis, the declining rule model of the vibration speed of the arch top, arch foot of Luheshan Tunnel and the excavated tunnel has been established.By carrying out the value simulation calculation for the explosion process of Luheshan Tunnel with the use of LS-DYNA dynamic analysis software, this study has obtained the vibration speed of each mass point during the explosion construction of IV surrounding rock; besides, this study has made a comparison between the result of theoretical analysis and testing value.By analyzing the influence upon the surrounding rock by the explosion, this study has stated the critical vibration speed of the surrounding rock during the elastic, elastic-plastic stage and plastic stage.By studying the influence upon the primary support played by the explosion based on the transmission theory of stress wave, this study argues that the damage to the spray concrete is mainly caused by the tension crack and has proposed the critical vibration speed corresponding to the different age of spray concrete; the damage to the bolt is mainly resulted from the damage to the contact surface between the mortar and the surrounding rock, and thus the suggestion value is given to the critical vibration speed of the bolt.By burying a steel bar meter in the section of the tunnel, we can test the force borne by the bolt under different construction load. In the meantime, by analyzing the optimized parameters of the bolt after the loose ring test of the surrounding rock, the reasonable parameters of the bolt are decided.