Research On Construction Stability Of Tunnel Underpass Highway And Analysis On Monitoring Of Support Structure

With the increasing speed of high-speed railway construction and development of the underground space, the cases of new railway tunnel crossing highway have increased. How to control the settlement of highway and to guarantee the stability of the tunnel structure in the construction is an important issue. Therefore, to study the stability of railway tunnel crossing highway in the construction and to monitor the supporting structure have very important practical significance.For the engineering background of railway tunnel crossing highway under mountain Da Ding which is in weathered shale formations layered in this study, this paper used numerical simulation and field detection. The section area of tunnel excavation is 195m2. The design used the composite supporting system which is composed by advanced support of double-layer big pipe shed of 159mm with small catheter of 42mm, double primary support and secondary lining. In the basis of the supporting structure, the paper analyzed the influences of different construction methods, the radius of curvature of temporary support and advanced support in different forms to the stability of the tunnel construction. Then frame a three-dimensional numerical model to analyze the stability of tunnel construction. Finally, monitor the internal force of the test section using the fiber grating sensor.The results indicate that the CD method is feasible and reasonable in the construction under the advanced support of double-layer big pipe shed of double 159mm and weathered shale formations layered. In this layer, the priority of advanced support is double-layer big pipe shed, single-layer big pile shed and forepoling bolt. But single-layer big pile shed or forepoling bolt is also feasible. In the method of CD, the stratum displacement and internal force of supporting structure are decreased first and then increased with the increasing of the radius of curvature of temporary support; and minimum happened in the radius of 30 meter (the excavation area is the same on both sides of temporary support). When the horizontal displacement of the temporary support reaches 9.07mm, more special attention should be paid in the construction. The demolition of temporary support is a critical step in the construction, the dismantled spacing which can control the speed of sedimentation changes legitimately is from 5 meters to 10 meters in the dismantled process. Through the analysis of the stress of the measured steel arch, the maximum principal stress of the first primary lining is 2.18 MPa, it's smaller than flexural compressive strength of the first primiary lining, the initial lining structure can meet the capacity very well.