Large Cross Section Of The Clay Strata Tunnel Stairs Seven-step Excavation Of Adaptive Research

Based on construction practices of portal section of Yunyangshan Tunnel in the mild-clay stratum, the applicability of the seven-steps benching method used in the Yunyangshan Tunnel constructed in mild-clay stratum was studied by the field test and analysis of reason about the large deformation and collapse at the early phase. The results will provide the technical support for improving and extending the related construction method, and provide a demonstration project and engineering experiences for similar projects. The contents of main research work include:1. Seven steps benching method was firstly applied in the portal section of Yunyangshan Tunnel constructed in the mild-clay stratum. Base on the general analysis of stratum conditions, construction technics and parameters early adopted, the reason about the large deformation and collapse at the early construction phase, and the improved seven steps method and related technical parameters are brought forward.2. The typical tunnel section was selected and field test related with the seven steps benching method was carried out. The deformation and mechnical characteristcs of the surrounding rockmass and supporting strcture system was studied, and the safety of supporting structure was evaluated. The results indicate that the seven-steps benching method is applicable for the tunnel construction in the mild-clay stratum.3. The applicable conditions of improved seven steps benching method was summarized, and the corresponding construction technical parameters, including excavating manner, dimention of the core soil, bench length, close time of invented arch, strengthened auxiliary construction measures etc, were put forward.4. The study about the equipment matching selection related the seven-step excavation method was carried out, and the optimized equipment matching selection program related seven-step excavation method were proposed. The labor organization of construction, quality control, and control measures of construction safety and evaluation of benefit were presented according to the characteristics of seven-step excavation method.