| With the rapid development of our country's basic undertaking,tunnel forms also tend to be diversified.A series of problems exist in the construction of tunnel cross structure in soft rock under strong earthquake,such as excessive deformation,stress concentration and accompanied by cracking and failure of lining,etc.In order to ensure the normal use of cross structure tunnel in soft rock under strong earthquake,research was carried out.This paper takes Yuelongmen railway tunnel project in Maoxian County,Sichuan Province as the background.The cross structure of the transverse passage and the main tunnel is selected as the research object.Threedimensional numerical model of nonlinear finite element is established.The damage constitutive equation of concrete is used.The vulnerability analysis method is combined.The vulnerability of the cross structure between cross tunnel and main tunnel is analyzed.The extended finite element theory is applied.Combined with the results of vulnerability analysis,the cracking mechanism of cross structures between the transverse passage and main tunnel under the most unfavorable earthquake conditions is studied.The aseismic measures for the combination of shock absorption layer and flexible connectors are put forward.The conclusions of this paper are as follows:(1)The three-dimensional finite element model of railway tunnel with transverse passage is established,the structural vulnerability method of tunnel and underground engineering is proposed,and the influence of seismic directivity on the secondary lining damage of railway tunnel with transverse passage is studied.Combine the influence of seismic waves on secondary lining damage of tunnel cross structures,the most unfavorable incident angle of secondary lining damage of the tunnel cross structure is 45o~60o,the worst angle of force is 90o,the maximum probability of complete damage is 25% higher than that of 0o incident angle.The location distribution of the maximum response of the secondary lining steel bar in the cross structure of the tunnel is relatively concentrated.The maximum response location distribution of concrete is dispersed.(2)By using the extended finite element principle,the fracture mechanics mechanism of railway tunnel with transverse passage under the action of seismic intensity of degree IX is studied.The crack propagation pattern of the structure is revealed when the incidence angle of earthquake is 45 and 90 respectively.The cracking area is mainly located at the arch top at the intersection of arch foot and cross passage.The inverted arch has not applied the initial support in the construction,the secondary lining invert to bear all the surrounding rock pressure.The equivalent plastic strain of surrounding rock is most serious in the inverted arch of tunnel and resulting in excessive deformation of surrounding rock.When the incident angle of the earthquake is 90o,the width of the split crack reaches 120 mm.Stress concentration appear at intersection of main tunnel and crossing and the most severe position is on the intersection.When the incident angle of the earthquake is 45o,the maximum width of the slip crack reaches 17 mm.When the incidence angle of earthquake is 45,the maximum crack is larger than the maximum crack when the incidence angle of earthquake is 90.(3)The aseismic model of the tunnel combined with flexible joints is presented,and the good anti-crack effect of the initial timbering,damping layer and secondary lining support is confirmed.The installation of flexible connectors prevents the extension of longitudinal cracks.Setting a circular flexible connector in the middle of the intersection can completely prevent the formation of cracks in the arch of the intersection.Installation of shock absorption layer between initial support and secondary lining give more deformation space to lining.And the secondary lining is not easily affected by the initial support deformation and cracking. |
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