Design Method And Application Of Prestressed Anchorage System Based On Displacement Difference In Soft Rock Tunnel With Large Deformation

At present,due to the complex geological environment,tunnel construction problems emerge in an endless stream in the construction of tunnels in the western region.There is a problem of large compression deformation induced by high ground stress in the soft surrounding rock,which often leads to the cracking and spalling of the initial support,the distortion and breaking of the steel arch frame,and even the intrusion of the support,so it is necessary to remove and replace the arch frame and the support form,It seriously affects the safety and progress of tunnel construction.In order to solve this kind of problem,we should change the traditional strong passive support form,and adopt the concept of "active support" to design the support form for the weak surrounding rock,so as to use the prestressed anchor support system to improve the tunnel support environment from the inside of the surrounding rock.This paper studies the timely active prestressed anchorage system of Muzhailing highway tunnel in Gansu Province by means of data investigation,theoretical analysis,numerical simulation and field test The main results are as follows:(1)It is analyzed that the evolution of three commonly used supporting systems in soft rock tunnel lies in the change of anchorage system,so the accurate design of anchorage system parameters is very important.The design of prestressed anchorage system can be based on displacement field,according to displacement difference,combined with the double control rules of material elongation and axial force,and studied by numerical simulation,This is the design method of prestressed anchorage system based on displacement difference.(2)Based on the design method of prestressed anchorage system in(1),this section studies the large deformation application scope of strong passive support and active prestressed anchorage support currently used in this project,and modifies the parameters of surrounding rock weakening under confining pressure and strengthening under prestressed anchorage twice in numerical simulation,The most conservative parameters of the active prestressed anchorage support for Muzhailing highway tunnel are proposed.The calculation results show that the applicable range of the strong passive support is not supported displacement ≤ 50 cm,and the applicable range of the active prestressed anchorage support is not supported displacement 51 ～ 110 cm.(3)According to the application scope of large deformation of timely active prestressed anchor support obtained in(2),combined with the actual situation of Muzhailing highway tunnel,this section puts forward the form and composition of prestressed anchor system with permanent support function,and uses numerical simulation method to optimize the parameters of active prestressed anchor support,such as prestress size,anchor cable length,anchor cable spacing,etc,The appropriate support parameters corresponding to different large deformation range are obtained.(4)According to the parameters of the prestressed anchorage system designed in(3),the research on the test section is carried out in the field.According to the predicted large deformation of the test section,the corresponding prestressed anchorage support parameters are adopted.The field monitoring and measurement data show that the stability of surrounding rock is good and the normal construction can be maintained,which verifies the suitability and rationality of the designed active prestressed support parameters,It provides a reference for the subsequent design and construction.