The Construction Monitoring And The Limit Displacement Analysis Of Shallow-buried Highway Tunnel In Landslide Section

With the development of transportation construction, more and more problems in construction process will be meet. Especially in the tunnel project, more and more projects will be constructed in special geological conditions. This article based on the background of Sun Jia’ai tunnel of Fengjie to Wuxi highway in Chongqing, and combine with the ubiety of the Sun Jia’ai tunnel and Daping landslide,monitorring the deformation of the surrounding rock、the mechanics of supporting structure and the deformation of Daping landslide in the process of construction.Using the numerical simulation method to simulate the process of actual construction,get the deformation of the surrounding rock and the deformation of Daping landslide in the ideal state,compared with the data in actual to assess the stability of the surrounding rock and the landslide.The content and methods of the research:(1) Choosed representative sections and monitored the deformation of the surrounding rock, construct the left line tunnel which influenced the landslide more.use the nonlinear fitting function of Matlab software to analysis the monitored database to forecast the total displacement of the surrounding rock and get the relationship between the deformation of the surrounding rock of Sun jia’ai tunnel and its construction progress.(2) Pressure boxes, strain gauges and concrete strain gauge were fitted in the same monitored sections, so as to monitor the stress of primary support.By analyzing the relationship between the changes of the stress of the primary support and the construction of the tunnel, this paper deduced the extent that the tunnel construction influenced supporting structure and grasped the stress of the support structure in time.(3) Fixing monitored positions and tilt tapping holes in the area of landslide which was upper of the tunnel and severely affected by the tunnel construction, this paper used total station instrument and clinometer to measure absolutely coordinates of the monitored points of the landslide surface and the displacement of the deep soil, in order to analyse the relationship among the slide displacement of the landslide surface,the displacement of the deep soil and the construction of the tunnel.(4) Using finite element software Midas-GTS to simulate the actual tunnel construction steps and detail the stress release rate of the tunnel surrounding rock to find mutational points of strain of the surrounding rock in the tunnel construction process.this paper deduced mutational points of the displacement of surrounding rock and got the limit displacement of the surrounding rock and the landslide.By compareing with the actual monitored data to evaluate the stability of surrounding rock and landslide.The main research results: (1) By analyzing the displacement of surrounding rock, the surface of the landslide and the deep soil of the landslide and combining with the progress of tunnel construction, this paper got the relationship among the deformation of the surrounding rock, the displacement of the landslide and the tunnel construction progress.(2) The frequently change of the displacement of surrounding rock、stress of primary support and the force of primary support come from surrounding rock mainly caused by the tunnel construction and the displacement of surrounding rock、stress of primary support and the force of primary support of surrounding rock appear obvious asymmetric,especially near the slippery presplit face.(3) Using finite element software Midas—GTS to simulate the actual tunnel construction steps and get the displacement of the tunnel and the distribution along the tunnel surrounding, it was same with the distribution regularity of the data in actual. According to the deformation of the surrounding rock was big and much more than pre-deformation,the surrounding rock was under unstable state.The actual data of the landslide approach the results of numerical analysis,so the landslide was relative stable state.(4) By comparing the monitored data with the actual data, this paper established the deformation control benchmark of shallow-buried tunnel in landslide section according to displacement of the tunnel and slide deformation of sliding plane.(5) Monitored data shows that, the displacement of the observation point started obvious sign of convergence after the inverted arch and the secondary lining of the tunnel constructions. So the initial support should be closed and the secondary lining should be contractored as early as possible in order to effectively inhibit the deformation of surrounding rock and slide deformation.(6) When the tunnel started to construction, anti-slide pile was still in construction and the bearing capacity of the anti-slide pile was not fully achieved the design strength and abandon soil of the anti-slide pile which added the load of the landslides surface had not clear in time. Those caused the displacement of the landslides and the deformation of surrounding rock slide too much.