| The geological conditions of Gonghe tunnel are very complex. It meets the special geological disease which is between the soft rock large deforming and the hard rock bursting, when the tunnel was constructing. To get the mechanism of the special geological disease and design the reasonable initial support, this paper has done research in the following areas:①The engineering geological problems and the disease forms of Gonghe tunnel are analyzed.②Test on the mechanical properties of the rock tunnel, and the uniaxial compaction test, the triaxial test, the water-saturated soften rock test and creep test of the surrounding rock are completed.③The constructing process of the Gonghe tunnel's cracked segment is studied by DEM. The evolution process of the stress in the surrounding rock, the possible broken mode of the surrounding rock, the impact of the joint's parameters on the tunnel distortion and the force situation of the supporting structure in tunnel are analyzed.④The initial support crack mechanism of Gonghe tunnel is analyzed by field -measurement and field -test.⑤The secondary lining structure dynamic reliability is studied, and the secondary lining structure dynamic reliability in the large deformation zone of Gonghe tunnel impacted by the detonation at the heading is computed.The results are as follow:①The basic mechanics parameters of the surrounding rock are got, the rigidity and strength are a little low, and the rigidity is 27380 MPa, the uniaxial compressive strength is 47.35MPa.②The change rule of shale Dynamic elastic modulus and uniaxia compressive strength whit water-saturated time is got. The rock soften equations are got.③The creep rules of Shale under the 15MPa, 20 MPa, 25 MPa and 30 MPa pressure are got. And corresponding creep constitutive equations and parameters are got.④In the tunnel region the crustal stress is a little high, and the maximum stress is 17MPa. After the tunnel is caved, the maximum stress reduces to 12MPa, there is a big stress unloading zone and the stress on right upper tunnel is bigger than left upper tunnel.⑤The minimum thickness of the broken stratification is 0.35 ~ 0.45mm, the broken location is the right spandrel of tunnel, and the displacement is between 10.8cm and 14.4cm.⑥The parameters of joint have a little impact on the distortion of surrounding rock.⑦The suitable length of anchor is 6.5m, the maximum stress of the anchor is at the spandrel of tunnel, and the stress on right upper tunnel is bigger than left upper tunnel.⑧The DEM can simulate the non-continuum mechanics very well, and the numerical simulation results agree with the field maturation data.⑨The surrounding rock distorts slowly but sustains for a long time after the initial support is completed. Although the convergence rate of the surrounding rock has decreased trend, in the end all the test sections are not convergent and there is vertical crack, the maximum level convergence is 79.64mm, and the maximum crown settlement is 67.45mm.⑩The loose rock area in the test section is much larger than in the normal section (generally less than 3m in the normal section). The anchor length in the test section is 3.5m, which is less than the scope of loose rock, so the anchor can't play the role of suspension.11 The disease of Gonghe tunnel are caused by the gravitational stress, bed-parallel bias, micro-fracture in rock, rock creep and water-saturated rock soften, which is a special tunnel geological disease, and it's reasonable support isⅢ(H1).12 Based on the failure criterion of single confines exceeded at first, the analytic model for structure dynamic reliability is established. The detonation at the tunnel heading has little impact on the secondary lining structure dynamic reliability in the large deformation zone.13 When design the structure dynamic reliability, it's more insurance to use the Rayleigh distribution function.
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