Stability Analysis Of Surrounding Rock-Slope Of Large Section Tunnel With Small Clear Spacing

In the actual construction process of tunnel entrance section,due to the extremely complex construction environment of tunnel engineering,it is easy to produce inestimable dangers and losses in the construction process of highway tunnel.Based on the tunnel entrance section of No.13 tender section of Leye-Baise Expressway in Guangxi,this paper mainly studies the deformation mechanism and failure mode of surrounding rock-slope of large section and small net distance tunnel entrance section by combining theoretical analysis,field monitoring and numerical simulation.The tunnel construction safety factor calculated by strength reduction method is compared and analyzed.In the process of construction,the disturbance of surrounding rock and slope is greater and the corresponding supporting measures are taken.The main work and achievements are as follows:(1)The failure modes of surrounding rock-slope at the entrance of Naxian tunnel are studied,which are mainly local rockfall failure,overall failure of surrounding rock and tidal expansion failure,while the failure modes of slope are mainly plane sliding failure and local collapse failure.(2)Through on-site monitoring and data processing,the change law of tunnel surrounding rock-slope is analyzed from the time effect and space effect of tunnel construction.It is concluded that the time effect of large section and small net distance tunnel is similar to the space effect law,and the cumulative displacement and displacement rate of monitoring points will gradually become stable with the continuous progress of construction time or the continuous advancement of face.(3)With the help of the finite difference program FLAC3 D,the stability of the surrounding rock-slope of the existing tunnel is analyzed from two aspects: the stress and displacement effects of excavation are not considered,and the construction method and excavation procedure are considered.The numerical simulation results show that the sliding range of the slope will extend to the top and foot of the slope,and the sliding body will extend to the tunnel.The diversion of the middle intercalated rock makes the expansion deformation of the first tunnel and the compression deformation of the second;the excavation of the inner and outer upper part of the first tunnel and the arc-shaped guide pit of the core soil of the second tunnel are relatively large construction steps of surrounding rock disturbance,while the middle intercalated rock,the left arch foot of the left tunnel and the right arch waist of the right tunnel are the most dangerous parts of the surrounding rock of the small net distance tunnel.(4)Summarizing the concept of large deformation control of tunnel soft surrounding rock,on the basis of which the comprehensive control system of large deformation of tunnel soft surrounding rock is established.Finally,according to the established comprehensive control system of large deformation of tunnel soft surrounding rock,the corresponding measures are designed in detail,such as advance support,excavation method,support measures,monitoring and measurement.According to the actual situation of the tunnel project,the corresponding treatment measures are given,such as applying anti-slide piles,grouting to reinforce loose rock mass,carrying out inverted arch construction as early as possible after excavation,releasing concrete at the intersection of the wall and the vault in the left tunnel,and pre-constructing the secondary lining of the tunnel entrance.This paper has 51 figures,4 tables and 61 references.