Abstract:

Shallowcovered large crosssection and largespan doublearch tunnels have such characteristics as large span, shallow cover and frequent conversion of construction procedures. The multiblast causes disturbance to the surrounding rock mass. Therefore, extensive monitoring of the tunnel is necessary. The contents, technique and method of the monitoring of the construction deformation of shallowcovered large crosssection and largespan doublearch tunnels are descried in detail. The deformation characteristics during the overall construction process and during different excavation stages are analyzed in detail. The following conclusions are drawn: 1) The excavation of the top heading of the left tube and the right tube changes the deformation of the preceding tube greatly. Especially the excavation of the top heading of the proceeding left tube causes larger deformation than the other procedures. Therefore, that procedure is the main point for ensuring the tunnel stability. 2) The construction of the proceeding tube has some influence on the deformation of the preceding tube. Therefore, the disturbance effect of the proceeding tube should be paid attention to. 3) The longitudinal incidence to the right tube deformation of the top heading excavation of the right tube is about 1/4 of the tunnel span and that of the bench excavation of the right tube and the top heading excavation of the left tube is about 1/3 of the tunnel span. As to the longitudinal incidence to the left tube deformation, the top heading excavation of the left tube is also about 1/3 of the tunnel span. 4) The secondary lining must be timely installed to control the tunnel deformation. The experience and conclusions presented can be referred to in the design, construction and monitoring of similar works in the future.

Key words: shallowcovered large crosssection and largespan doublearch tunnel, tunnel deformation, monitoring