| Swelling mudstone is widely distributed in China,and due to its swelling and softening characteristics in contact with water,the softening and swelling of the mudstone around the tunnel in contact with water have serious impact on the safety of the lining structure during the tunnel construction and operation,which leads to the deformation of the tunnel structure and thus the tunnel disease.Therefore,in this thesis,we take the swelling mudstone section of Baotai Mountain Tunnel of China-Lanzhou Passenger Highway as the background,and use FLAC3 D numerical simulation software to calculate and analyze the deformation law of tunnel structure caused by water pressure,water softening and swelling.The specific analysis conclusions are as follows:(1)A typical section of the mudstone section of Baotai Mountain Tunnel was selected to study the tunnel stability of the deeply buried section of the tunnel at different water level heights,and the deformation and force distribution around the tunnel structure after construction were obtained at different surrounding rock levels.The results show that the vertical displacement,as well as the horizontal convergence values on both sides,increase with the increase of the water table,with obvious changes in the displacement of the arch bottom and arch top.The maximum horizontal stress of the lining structure is mainly at the top of the arch,and the maximum vertical stress is mainly at the waist of the arch;with the decrease of the surrounding rock level,the change of displacement at the bottom of the arch is significant,and the change of displacement at the foot of the arch is small.(2)According to the characteristics of softening of surrounding rocks in contact with water,the influence of overall softening of surrounding rocks caused by groundwater and local softening of surrounding rocks around the tunnel on the deformation of tunnel structure is investigated,and different softening coefficients are set to analyze and study the deformation law of tunnel structure.From the overall softening results of the surrounding rock,the settlement rate of the vault changes significantly with the increase of water level;the side walls are under greater stress at the arch waist and the outer parts of the vault.From the local surrounding rock softening results,it is seen that the softening of the surrounding rock at the bottom part of the tunnel changes significantly after the arch bottom bulge.(3)In the context of deeply buried tunnels,four different parts(tunnel bottom,both sides of the sidewalls,both sides of the tunnel bottom and sidewalls,and the whole perimeter)were studied in different expansion levels and different expansion depths on the tunnel structure.The results show that when the expansion depth is the same,the deformation value of the bottom of the tunnel increases with the increase of the expansion level of the mudstone,while the deformation of the vault is basically insignificant when the local surrounding rock expands in each part.When the expansion grade is certain,the expansion depth has the greatest influence on the deformation of the tunnel bottom.(4)Four different parts of the tunnel are used to investigate the deformation of the tunnel structure under the effect of expansion and softening of the surrounding rock in each part of the tunnel.Only the sidewall area shows a trend of gradually increasing arch deformation and decreasing bottom elevation under the effect of expansion and softening of surrounding rock;the remaining three locations show an increase in arch bottom elevation and decrease in arch settlement when the surrounding rock expands and softens.(5)According to the characteristics of mudstone in the deeply buried section of Baotai Mountain tunnel,FLAC3 D finite element software is used to enhance the stability of the tunnel by changing the thickness of the surrounding rock grout,changing the strength of the elevation arch structure and applying the elevation arch anchors,considering the combined effect of softening and swelling of the mudstone when it encounters water. |
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