Study On Construction Optimization And Deformation Control Of Shallow Buried Large Span Small Spacing Tunnel In Loess Area

The paper took Yan nan four road station ~ Datang Furongyuan station storage track tunnel of metro line four in Xi'an as the engineering background,and the numerical simulation and field monitoring method were used to study the mechanical properties and deformation regularity by considering the construction processes of shallow-buried twin tunnels with small spacing in loess area.Then the formula of ground surface settlement induced by tunnel construction of shallow-buried twin tunnels with small spacing in loess area has been derived based on the principle of displacement superposition.The main work and achievements of this paper were as follows:(1)The construction sequence optimization of small clear spacing tunnel in loess shallow buried asymmetrical sectio was made.For two excavation method large cross section tunnel excavation ahead and small cross section tunnel leading excavation,the mechanical behavior and deformation of surrounding soils and support structure were studied by numerical simulaiton method.Based on the above results,the construction scheme of large section tunnel excavation was determined.(2)According to the shallow asymmetric section of loess tunnel construction,the deformation and stress characteristics caused by different large section tunnel excavation were researched.Under different excavation ways of large section tunnel and spacing between asymmetric section,all the mechanical index such as behavior of tunnel soil,middle rock pillars,supporting structure,surface subsidence and plastic zone of surrounding rock were affected.Based on the numerical analysis,the reasonable and feasible construction excavation scheme of the large section tunnel was determined.(3)For the double side excavation scheme suggested by loess shallow buried unsymmetrical section tunnel construction,a refining numerical analysis model was establised,the changes of surrounding rock,supporting structure and surface settlement was studied in detail,which were caused by different excavation parameters.The economic,reasonable and feasible setting distance was determined,the construction parameters of the double side excavation scheme suitable to loess shallow buried unsymmetrical section tunnel construction were optimized,this method can be used to guide the construction and achieve good results.The economy,rationality and feasibility of this proposed scheme was proved by the on-site monitoring analysis.(4)Based on the superposition principle,the modified settlement formula of double parallel tunnel construction was obtained.According to the characteristics of Xi'an loess shallow buried tunnel,the correction factor of loess shallow buried tunnel with small spacing was given,which can be applied to the condition of different buried depth and tunnel space.And the surface settlement prediction caused by the construction of the Xi'an Metro Line 4 Yannan Four Road Station to Datang Furongyuan Station was made.