Study On Influence Of Shallow Buried Bias On Construction Of Large Span And Small Span Tunnels

The rapid development of modern society is inseparable from the high efficiency of transport facilities,the choice of highway tunnels can effectively shorten the distance between time and space,with the development of the western region and the "one way all the way" strategy implementation,tunnel construction carried out in full swing.Due to the large number of tunneling through the soft and loose surrounding rock and often located in the shallow buried bias section,the tunnel deformation caused by adverse effects.Large-span small-pitch tunnels can improve traffic efficiency and reduce construction and maintenance costs compared to ordinary highway tunnels.However,the large span of small-distance tunnel excavation section is large,the construction process is complex,by the shallow buried bias weak loose surrounding rock obvious impact,can easily lead to engineering accidents,resulting in casualties and huge losses.Therefore,it is very important to study the interaction mechanism between surrounding rock and large span and small span tunnels under shallow burial conditions.This paper relies on a practical project in Nanning to carry out shallow buried bias on the construction of large span small pitch tunnel.The numerical simulation model was established by Midas GTS software.Firstly,the influence of different construction methods on the surrounding rock and supporting structure of single tunnel was studied.It was concluded that the adverse effects of the double-side wall guide method on the tunnel were the least.Further,The influence of different slope and depth on the stress and deformation of the surrounding rock of the tunnel is studied.Then,the influence of different construction methods on the surrounding rock and supporting structure of the double tunnel is simulated.The main research results and conclusions are as follows:(1)The construction of large-span single tunnel in shallow-buried biased rock is constructed by double-wall guide pit method.The maximum compressive stress is 48.5%and 15.8%higher than that of step method and CD method respectively.In the case of displacement of the surrounding rock,the double-side wall guide pit method is used,the maximum settlement of the ground,the settlement of the arch and the arch uplift are-16.5mm,-24.75mm,28.32mm respectively,about 85%lower than the step method,60%?75%,especially for the rock displacement control requirements of the project;double sidewall guide pit excavation section is smaller,relatively small degree of disturbance of the soil,and the formation of closed support in time,caused by The axial force of the bolt is 51.1 kN,which is 72.7%?71%smaller than that of the step method and CD method.The axial force distribution is uniformly distributed.For the bending moment distribution,Deformation,reducing the secondary lining to deal with the pressure of deformation of the surrounding rock,causing the maximum bending moment 6975.6 kN · m around the arch,left and right arch bending moment values in the range of 1000?3500 kN · m,compared with the other two Planting method is small,can give full play to the two lining structure bearing capacity.On the whole,the double wall method has the least effect on the tunnel and the CD method.(2)Based on the research of double-side wall guide method,the influence of bias and shallow burial on tunnel excavation is studied.By combining the buried depth and slope condition,12 kinds of working conditions are obtained,and the main influence range of tunnel bias is 0?30m.When the slope is more than 1:1.5,the shallow and biased conditions have a significant effect on the deformation and stress distribution of the surrounding rock.With the increase of the buried depth and the slope,the influence of the shallow buried bias becomes smaller.(3)The construction of parallel tunnel with large span and small spacing is carried out.The compressive stress is about 31%?43%smaller than that of the step method,which is about 8%,The stress distribution of the surrounding rock is more reasonable than the other two methods.The double-side wall guide method can effectively reduce the excavation section and complete the closed support system as soon as possible.The vertical displacement is 50%-69.8%Which is 45%?65%smaller than the CD method.The double-side wall guide method causes the axial force of the bolt to be 13.8%?22.6%smaller than that of the step method,5%?12%less than the CD method,effectively control the displacement of the surrounding rock;The maximum diameter of the left and right holes in the initial support force of the wall guide pit is 4000.8kN and 5352.5kN respectively.The arch of the left and right arch and the left and right arch are different.Support the axial force distribution is reasonable;double sidewall guide pit method of secondary lining bending moment,left and right hole vault bending moment is smaller,followed by arches,arch waist maximum,the maximum value of?3698.6 kN · m,bending moment distribution Which can effectively exert the ability of secondary lining to resist the deformation of surrounding rock.The double-side wall guide method can reduce the ability of the tunnel after tunneling.The impact of construction to protect the construction safety.On the whole,the adverse effects of the double-side wall guide method and the CD method on the parallel tunnel with large span and small spacing are the least.(4)Based on the study of the double-side wall guide method,the construction process of the shallow-buried biased small-distance tunnel is carried out.The excavation of the deep-buried tunnel is carried out.The excavation tunnel is located near the middle pillar side of the middle rock pillar.The tunnel can be used to control the influence of the construction bias on the tunnel,and it can control the displacement of the surrounding rock well and further reduce the The adverse effects of parallel tunneling.