Study On Optimizing Structural Scheme And Its Key Support Parameters For Exceptionally Large Scale Underground Railway Station

BADALING underground station is one of station of the intercity railway between BEIJING and ZHANGJIAKOU, and locates in the scenic spot of the Greatwall. In the initial design, this station has been designed 4 structural schemes, namely, three-arch structure scheme, three-single-cavity structure scheme, two-single-cavity structure scheme and single-arch structure scheme. This station has an exceptional cross-section and complex structure system, and its total excavation area of this station is over 1,000 m2. In this paper, based on BADALING underground station,optimization of structure schemes and key support parameters systematicly studied.Firstly, based on field investigation of rock structure, in-situ testing of virgin stress in rock mass, conducted by high water pressure inducing cracking method, hydraulic testing in borehole and laboratory testing of rock mechanical properties, characteristics and class of rock mass of this station are estimated and determined:(1)the strike of the main joint set of the main rock mass and the station axis intersect at a large angle, and this joint set with very steep dip angle is very favorable for stability of surrounding rock in the process of excavation; (2)Elastic modulus E, internal friction angleφ, cohesion c and Poisson's ratio v of rock are 53.73GPa,58.5°,12.83MPa,0.29, respectively; (3)the virgin stress in rock mass is mainly caused by tectonic movement, and the ratio of horizontal principal stress to vertical stress ranged from 1.44 to 2.16; and the direction of principal stress and the station axis intersect at a small angle; (4) the permeability coefficient of water in rock fissure and the unit water inflow are 0.014m/d and 0.0809m3/d·m, respectively; (5)class of monzogranite with respect to RMR system at roof arch and its upper height range of 10 m and below invert are III and IV, respectively, and class of syenite vein is IV.Secondly, based on rock classification and E.F.Bieniawski empirical equation, the calculation parameters of 3D-numerical analysis are estimated and determined.Thirdly, based on nonlinear finite element software ABAQUS, the stress and deformation of the surrounding rock and the supports of these 4 structures schemes in the excavating sequences are systematically and deeply analysised.Fourthly, based on the characteristics of rock structure and the numerical calculation results, the optimum key support parameters are estimated and determined, i.e. the length of rockbolt and thickness of shotcrete are 4m and 30cm, respectively.Finally, based on the mechanical behavior of the station structure system in the excavating sequences, in combination with parametric and Spearman non-parametric optimizing analysis, the optimum structure,namely three-single-cavity scheme is estimated and determined. excavation areas of two side-cavity and middle cavity are 328.744m2 and 138.567m2, respectively, and distance between the two side cavities and the middle cavity is 10.2m.