| With the gradual improvement of transportation infrastructure projects, large deformation in soft rock tunnel has become a worldwide problem puzzled the tunnel construction engineering. A variety of classification of soft rocks and complicated geological condition are main factors resulted in large deformation. There has no unified theory and method to solve the problem. Based on the study of the expansion reconstruction project of Mudanjiang to Suifenhe segment of Binsui line, Xingyuan tunnel was taken as research object. On the basis of overview previous study fully, data collection and collation and field test were used. A combination method of theoretical research and numerical simulation was adopted to study the rheological properties of carbonaceous shale and support parameters. The numerical simulation results were compared with engineering practice results, analyzing the merits of various construction conditions, and the best supporting parameters were selected. The main results were showed as follows:(1) The soft rock stability and deformation mechanism were theoretical analyzed, including the concept and classification, study methods, deformation characteristics, supporting status of soft rock and so on.(2) The engineering properties of carbonaceous shale in Heilongjiang region were introduced, such as expansibility, strong weathering, disintegration, rheological property, structure complexity of rock mass and disturbing properties.(3) The main reasons of carbonaceous shale tunnel instability were theoretical analyzed. The carbonaceous shale strength is low, resulting higher disintegration, weathering resistance and rheological properties. In the early period of tunnel excavation, a large amount of structure faults and fractures were generated because of rock dislocation squeezed between each other. At the same time, abundant underground water infiltrated to rocks through fissures and faults, and strength is further reduced because of carbonaceous shale easily water softening. It is main reasons of Xingyuan tunnel large deformation occurs.(4) Through the monitored data analysis of construction site section, the carbonaceous shale tunnel deformation showed the laws that high strain rate at initial stage, large total amount of deformation, long settling time of deformation. After completion of tunnel secondary lining frame, partial steel arch stress of tunnel facilities has gradually grow, reflecting the highly rheological characteristics of carbonaceous shale tunnel. Influenced by bias pressure and tunnel construction methods, deformation and support force curves showed a significant asymmetry.(5) Numerical simulation method was adopted to analyze the effects of carbonaceous shale area composite supporting parameters changes to the rock stability. The length and direction of the lock pin into the anchor tube and layout, the thickness of the concrete in secondary lining and the spacing of initial support are main study elements. Comparative analysis of rock deformation and the steel arch force, the most favorable support parameters to rock deformation and steel arch force were selected.as: 8m length of lock anchor leg tube, 30 ° ramp of under lock foot anchor pipe, 89 mm diameter of lock anchor leg tube(2 threads per point), 0.5m spacing of the steel arch, 0.6m of the secondary lining thickness. |
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