Abstract:

To investigate the mechanical response behavior of excavation of shallowburied superlargespan tunnel, a case study is conducted on a fourtrack highspeed railway tunnel with a excavation span of 26.3 m and soil covering of 6~35 m using numerical simulation method under various construction methods. The results show that the stability of surrounding rock and the safety of supporting structure using composite doubleside drift method(CDDM) and doubleside drift method(DSDM) are better than those using other construction methods. The field monitoring results reveal the following: (1) During DSDM excavation, the surrounding rock deformation of superlargespan tunnel mainly occurs at the initial stage of top heading excavation of guide tunnel, and the removal of temporary support has little influence on surrounding rock deformation; the force of the primary support of the lower bench is small, while the primary support of the top heading is the main bearing structure. (2) The safety factor surplus of the primary support is large, and the supporting parameters obtained based on empirical analogy are conservative, so the thickness of shotcrete can be reduced and optimized. (3) The excavation of the lower bench in the middle guide tunnel will lead to the decline of the temporary support function, and the measures using DSDM to cancel the lower temporary support and optimize the excavation section are put forward, and the feasibility of the bench method is discussed.

Key words: shallowburied superlargespan tunnel, construction method; excavation mechanical response, primary support security, field monitoring