| With the increasing volume of traffic,the construction of highways,railway tunnels in the mountains can be seen everywhere.Under the influence of the excavation conditions,a large number of bias tunnel is formed,but in the tunnel portal area,construction is more difficult with the poor geological condition and surface water collection,slightly improper construction can cause accidents,such as serious rock mass deformation,destruction of the supporting structure,cave-collapse and slope-slippage after tunnel excavation.Therefore,it is necessary to carry out a detailed study on the construction scheme of tunnel portal section.The present situations of shallow buried and unsymmetrical pressure tunnel at home and abroad was summarized in this paper,the important and difficult points in design and construction of shallow buried bias tunnel of soft surrounding rock were studied,and the research method was determined.Based on Huang Zhushan tunnel in Beijing-Taiwan highway,this paper introduced the general situation of Huang Zhushan tunnel briefly,three-dimensional model of the shallowly-buried and unsymmetrical pressure of Huang Zhushan tunnel was established by finite element analysis software MIDAS GTS,The relationship of the displacement of surrounding rock,internal force of support structure and the equivalent strain zone were compared and analyzed in CD method and bench cut method;analyzed the effect of remove median septum or not on primary support in the process of excavating with CD method;and the law of the supporting structure's stress were compared and analyzed in CD method after the removal of median septum and bench cut method,and given a reasonable tunnel excavation method at last.In order to provide a reference for similar projects in the later period,combined with the specific conditions,the construction control measures of shallow buried and unsymmetrical pressure are given. |
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