Study On The Construction Technology Of Lianghekou Karst Multi-arch Tunnel

With the rapid development of China's transport infrastructure construction,the number of mountainous highway construction is increasing,and the proportion of tunnels is increasing.Due to the large mountainous area in China,the geological conditions of various terrain are very complicated.Tunnel construction is facing more and more difficult such in safety,quality,cost and environmental protection.Due to the unique advantages of multi-arch tunnel structure in line layout and environmental protection,it is paid more and more attention by the engineering and technical personnel in expressway tunnel construction.But the characteristics of the multi-arch tunnel structure and the complex force system conversion in the construction process,all make the construction of multi-arch tunnel have many problems to be solved urgently.Based on the comprehensive investigation and summary of the construction technology of the multi-arch tunnel under different geological conditions at home and abroad,according to the structural characteristics and the karst geological characteristics of the Lianghekou tunnel,the excavation construction scheme and supporting technology of the multi-arch tunnel are carried out.By FLAC3 D the dynamic analysis of the multi-arch tunnel were carried out.By site monitoring,the rationality and reliability of the excavation scheme,numerical analysis results,karst cavities and cavity collapse treatment were verified.The main work done is as follows:(1)Based on extensive investigation of multi-arch tunnel research status at home and abroad,through the Lianghekou tunnel geological investigation,and analysis the advantages and disadvantages of the three guide hole method,the middle guide hole method and the no guide hole method,the rationality of the tunnel construction method adopted with the upper and lower steps method of main tunnel after the middle guide hole has been complicated were demonstrated.(2)The FLAC3D numerical analysis software is used to simulate and analyze the Lianghekou multi-arch tunnel.The variation law of stress field and displacement field of surrounding rock and supporting structure under different construction schemes is studied.The influence of the middle guide hole on the stress field and the displacement field of the surrounding rock of the cavern is concentrated in the small part of the surrounding chamber.After the completion of the construction of the middle guide hole,the stress field was symmetrically arranged.When the first hole is excavated,the compressive stress of the surrounding rock in contact with the dyke wall increases rapidly and cause the tendency of the dyke fall to the second hole.In the process of construction of the first hole,the dyke is in the obvious bias state,and the displacement field is also asymmetrical.After the secondary lining of the first hole,the compressive stress of the surrounding rock and tensile stress at the bottom are decreasing.But the range of tensile stress area is expanding,it is necessary to set up the arch so that the structure of the force is more reasonable.The stress field of the surrounding rock of the excavation is greatly changed,and the stress field of the surrounding rock of first hole is also affected.The load at the top and bottom of the dyke wall is obviously increasing after the completion of the initial support.After the completion of the construction of the second hole structure,the force situation of the dyke was improved.There are a greater tensile stress at the bottom and the top of the dyke wall.It gradually close to the tensile limit of concrete.In the different stages of the construction of multi-arch tunnels,the structural force exhibits a complex transition state.(3)Through the combination of geological survey,geological sketch and geological radar,the geological prediction of the Lianghekou karst multi-arch tunnel is completed.Taking the geological prediction of K71 + 918-YK71 + 932 karst lacustrine in Lianghekou tunnel as an example,the reliability of the geological prediction of karst tunnels combined with the three methods mentioned above is verified.Aiming at the karst geologic characteristics of Karst cavity development and local cavity collapse in YK71 + 912-YK71 + 930 section,based on the stability of surrounding rock,some measures have been taken for the karst development section by invariated the initial support parameters,the reinforcement of the cavity section and the concrete backfill cavity and pre-laid drain pipe to strengthen drainage.(4)Through monitoring and measuring in the field,monitoring and measurement of Lianghekou karst multi-arch tunnel have been completed.The deformation of the surrounding rock,the deformation of karst cavity collapse after treatment and surrounding rock stress,steel arch stress,the stress and deformation of dyke are all showing increases rapidly in early,then gradually reduced,and tends to stable changes in a certain period.The difference of the geological conditions and construction technology of different surrounding rock will lead to some differences between the force and deformation,but the deformation value,deformation rate and stress value of the surrounding rock are all are smaller and have not reached the warning value.On the one hand,it shows that the karst geological conditions and excavation disturbance are smaller.On the other hand,it also verifies the reliability of the numerical analysis model and the rationality of the construction process.At the same time,monitoring and measurement also verified the rationality of treatment measures for karst cavity and cavity collapse.