Stability Analysis Of Portal Construction Methods And Yang Slope Support Of Mountain Highway Tunnel

Since the surrounding rock of tunnel entrance transition shallow depth,weathered,broken and loose,once the excavation is unreasonable,can easily lead to occur geological disasters,such as tunnel portal collapse and landslip of tunnel yang slope.For construction method of entrance transition section of Shallow Tunnel in V₂-Grade Rock,tunnel design rules（JTG/T D70-2010）does not concretely explain which kind of excavation is optimal,and what field conditions the Yang slope under should adopt the appropriate method to prevent landslides and other geological disasters.Therefore,excavation of the transition section of the entrance tunnel using the more reasonable method and which slope angle of slope is unstable and elevation method can by used to reinforce the Yang slope are main content in this thesis,which should provide a theoretical basis for the construction of the transition tunnel portal section.In this paper,author uses the numerical simulation method of FLAC^3D to analysis the end wall and cut bamboo formula Portal of transition section of Shallow tunnel in V₂-Grade Rock,respectively establishes four excavation methods models:"model one a single-side Drift Law,""model two core reserved earth Law,""model three pairs of side Drift Law,""model four step method".Besides,the establishment of Yang slope angle of slope 20°,30°,40°,45°,50°,etc.5 model and using surface slope anchor grouting to reinforce the Yang slope are used to studied by analyzing the displacement and stress of tunnel surrounding rock,displacement and stress of lining structure,displacement and stress of portal,the axial force of bolt,the plastic zone,etc.Get the following main conclusion:1、The entrance tunnel transition section using double side Drift excavation method,the value of the vertical displacement of surrounding rock and Yang slope is the minimum,which is smaller than the other three models and will decrease about 10%to 20%;Early lining can maximumly reduce the stress amplitude between surrounding rock and two lining,reaching 0.6MPa.It can give full play to the support resistance of the early lining;Bolt anchor mortar can play an efficient role in the distribution of the axial force of bolt;Hence,the double side tunnel entrance hole method is regarded as the most reasonable construction method of the transition tunnel portal section.2、The values of vertical deformation of the concrete of the cutting bamboo tunnel portal is smaller than the end wall Portal.The concrete of the cut bamboo tunnel portal is mainly under the pressure,which is mainly beneficial to working performance of the concrete;The bamboo cutting formula of the portal is adopted to ease the effects of the displacement of the Yang slope acting on the tunnel portal and reduce the destruction of the mountain vegetation,which has a good driving safety and comfort.3、When the slope angle of the tunnel elevation slope is greater than 40°,the maximum vertical settlement with the maximum longitudinal displacement of Yang slope are simultaneously occurred in tunnel entrance at the foot of the slope（Y=6m section）,which has a wide range of plastic deformation;The paper argues that,without effects on the vertical displacement and plastic zone volume of surrounding rock in tunnel excavation,the anchor grouting in surface of Yang slope enables to reduce the maximum value of the vertical displacement by 14.4%,reduce the maximum value of the longitudinal displacement by 33.26%,and enable the vertical displacement of the portal concrete decreasing 6.94%in the case of Yang slope angle of 50 degrees.