Study On The Behavior Of Heave Deformation Of Tunnel Invert And Its Engineering Countermeasures

As an important part of the tunnel bottom structure,invert directly affects the overall stability of the tunnel structure.The base structure of some newly built tunnels and operating tunnels is cracked,damaged or even subsidence in the wrong platform,which jeopardizes traffic safety.In view of the phenomenon of the heave deformation of tunnel invert,the main influencing factors and deformation mechanism of the heave deformation of tunnel invert are analyzed by investigating domestic and foreign literatures.Based on the strength deterioration model,a numerical model is set up by FLAC3D to simulate the heave deformation of tunnel invert.The effect of bolt on suppressing the uplift of the inverted arch is discussed.A new type of invert structure is put forward,and its rationality is discussed through analysis and comparison.The main research results are as follows:(1)Through literature investigation,the main factors causing the heave deformation of tunnel invert are high ground stress,expansive surrounding rock and groundwater.The geological condition of heave deformation of the tunnels is mostly sedimentary rocks,and the main rocks are mudstone,sandstone and tuff.The uniaxial compressive strength and cohesion of rock gradually decrease with increasing moisture content.(2)Based on the strength degradation model,the Fuchuan tunnel numerical model is established by FLAC3D.The numerical simulation results are compared with the in-situ monitoring data,and the two are more consistent.With the increase of water content,the uniaxial compressive strength and shear strength of mudstone,argillaceous sandstone and tuff gradually decrease.The numerical simulation results show that with the decrease of cohesive force of the surrounding rock at the bottom of the tunnel,the deformation of invert increases gradually and the heave deformation speed increases,and the deformation value decreases gradually from the center of the invert to the two ends.The force behind the invert increases gradually.The force at the center of the invert is gradually changed from compression to tension.The plastic zone gradually expanded from top to bottom.(3)The restraining effect of the bolts on the heave deformation of invert is discussed.With the increase of the bolts length and the decrease of the spacing,the heave deformation of the bottom structure,the plastic zone and the back force behind the invert gradually decrease.Considering the actual situation of the project,the reasonable parameters of the bolts are selected as 8.0m and 1.5m.(4)Through analysis and comparison,the rationality of the new invert structure is discussed.The new inverted arch structure has a good inhibition effect on the uplift deformation of the invert arch and the development of the plastic zone of the bottom structure.The combination of new invert structure and bolts has a more significant effect on reducing the disease of the heave deformation of tunnel invert.