Study On The Stability Of The Tunnel Group Entrance Section Based On Monitoring Measurements

With the increasing development of China’s road and railroad network,more and more roads have to cross mountains through tunnels.When it comes to a multilane road engineering,designers are more likely to choose tunnel group,in the consideration of the largest limitation of the tunnel section.A mountain area often means complex terrain,and the entrance sections are usually shallow buried and built in the weathering area.The multiply drilling of tunnel groups often becomes one of the most difficult parts of the construction.It’s necessary to conduct the research of deforming law of tunnel groups.This project which this paper based on is a two-way ten-lane tunnel crossing mountain by four tunnels in Sichuan Provence.The study analyzes the engineering geological conditions such as topography,geological structure,formation lithology,meteorological and hydrological conditions,by means of field survey,material obtaining and literature reading.To reveal the law of deforming between groups,the study appraised the adjacent construction between tunnels,on the basis of engineering geological classification of rock mass.This paper chooses a finite element simulation software called FLAC^3D,with whom a2D model was built with two tunnel section in the same surface.The two-stairs drilling method was simulated step by step in this software,and the difference of displacement and stress in each tunnel was compared.Based on monitoring and measurement operation of the NO.1 tunnel,dynamic data was collected on the spot,and the vault subsidence,the ground surface subsidence and horizontal convergence of each tunnel could be clearly described.A proper surface has been chosen by considering the arrangement of monitoring points（at the standard milage K20+305）.Influents of the second tunnel drilling acting on the first tunnel section was revealed by regression analysis,then compared and verified with the simulation result.A further research was carried out to explore the varying pattern of displacement and stress when tunnel group drilling in slope,and to find the optimal drilling scheme,the model was developed to 3D with four tunnels.By changing the depth of drilling,it shows that the displacement of the tunnel entrances could be indicators of the overall stability,and there is an optimal drilling scheme.The results suggest that when the second tunnel drilling in the surface,the increasement of displacement in the first tunnel section will pause or even spring back in a very short time.After the second tunnel passed the surface,the vertical displacement of the first tunnel will rollback,but the horizontal displacement will ultimately be smaller than before.