Mechanism Research On System Rockbolts Of Shallow-Buried Undercut Loess Subway Tunnel

The anchor technology has already became the most economical and effective methods to enhance stability of the geotechnical engineering, and it has been already applied widely in geotechnical engineering domain, like slope engineering, tunnel engineering and building foundation ditch and so on. However, there has been debate on the effete of system rockbolts for soil tunnel structure. Now the construction of subway is moving into top gear in Xi'an city, because of the city's status as an ancient city with history and culture in the world and it's special geological condition, there are some problems must be resolved during the construction of subway tunnel, such as: how are the system rockbolts working, how are the system rockbolts to play an important role and whether are they necessary in the subway loess tunnel.Based on the Second Subway Line of Xi'an, researchers have carried out large-scale field experiment, the experiment pays more attention to Contrastive research on the change regulations of pressure acting between primary support and surrounding rock, axial force of grid-steel, and axial force of rockbolts with two working condition: no system rockbolts and have system rockbolts. With the help of large numerical simulation program the researchers make a simulative analysis of the surface sedimentation after construction, plastic zone and stress distribution of surrounding soil. Compared with the field experiment and simulation analysis, the result is that in the construction of shallow-buried undercut subway tunnel, the system rockbolts can control the development of plastic zone and the sedimentation of surface and stratum effectively. Before the construction of secondary lining, combined supporting structure based on system rockbolts and grid-steel can offer higher security and better supporting effect. The sidewall rockbolts play an important role on support and restriction during the transmutation of surrounding rock. While the rockbolts at arch-parts and crown not only have no function, but increase combined supporting structure's burden. So arch-parts and crown rockbolts should be abolished and the rockbolts at arch springing, sidewall and basement should be reserved, and construction quality of rockbolts at foot anchors should be controlled strictly.