Study On The Structure Safety Of Cross Tunnel With Small Spacing During Construction And Operation

This thesis carried out a study on the structrue saftey of cross tunnel with small spacing during construction and operation by the methods of numerial analysis, in-situation test and analoy, including the structure safety in static and dynamic. The study is based on diversion tunnel adjacent project in Lanzhou City, Gansu Province, which is Bei Huan new tunnel upper pass Hong Shanding existing tunnel. The new tunnel is belong to the interurban railway, as the existing tunnel belong to Lanzhou hub of transportation.The following achievement and outcoming was listed:1.According to practical engineering,the bench blasting process of intersecting tunnel with small spacing is simulated by FLAC3d numerical simulation software. The peak values of simulative vibration velocity are compared to the actual, it’s found that the deviation is small, and both velocity curves are in good agreement, which prove the validity of FLAC3d analysis. It’s assumed that if the velocity is greater than2cm/s, the velocity have the strong influence on existing tunnel structure, If the velocity is less than2cm/s, but bigger than0.5cm/s, it have weak influence, if the velocity is less than0.5cm/s, it means that the velocity has little influence. When the blasting section is located at cross section of new tunnel, the existing tunnel was divided By this criterion, the strong influence zone is around9m from the cross section, the influence weak zone is around9-16m, the little influence zone is out16m; When blasting section is changed, the strong influence blasting zone in new tunnel is between12m after cross section and10m before it。2.To analyze the lining safety of new tunnel and existing tunnel during the benching construction. This paper defines a CF (crack factor) to judge the crack of lining, which is from the Griffith criterion within Fracture Mechanics, and presume that if CF>1, lining have cracks, if CF<1, lining without crack. According to practical project, this paper combines the safety factor of line section stipulated in tunnel design specification with the crack factor CF to analyze the lining safety through ANSYS software. The analysis found that:during the process of the benching construction at new tunnel, the ring safety factor is less than the longitudinal safety factor at cross section of new tunnel, but both meet the requirements of specifications. At the same time, the value of cracking factors within existing tunnel are less than1, which means existing tunnel without crack. And the cracking factor cloud picture of existing tunnel is symmetrical about the axis of new tunnel. The conclusions are meaningful for the construction of new tunnel and the protection of existing tunnel.3.The train load is considered as the excitation function, FLAC3D is adopted to establish the operation process of small clear distance space crossing tunnel of the whole model, to simulate the operation process of new tunnel, the lantau island by a single, double, and cross the tunnel all by train when dynamic response of three kinds of working conditions. From tunnel structure and vibration velocity, stress, surrounding rock plastic three aspects analyzes the train loads of small clear distance space cross the response characteristics of the tunnel, and determine the structure safety.4. by the characteristics of seismic wave period and cross small clear distance tunnel site characteristics, determine the design speed of seismic waves, and choose the international commonly used EI_Centro north-south wave as cross tunnel seismic waves. According to seismic wave transmission characteristics, only consider a single horizontal wave to cross the tunnel effect, namely new tunnel seismic wave direction perpendicular to the axis of cross when the dynamic response of the tunnel. To cross the FLAC3D is adopted to small clear distance tunnel seismic dynamic response is simulated, and the cross force and deformation of tunnel lining, surrounding rock plastic three aspects analysis under the earthquake action, cross small clear distance tunnel structure safety.