Failure Characteristics of Tunnel in Different Thickness Ratio of Soft and Hard Interbedded Mass

The stress of soft and hard interbedded mass is complex. Therefore, pre-fabricated specimens of interbedded surrounding rock tunnel in different thickness ratio of soft and hard interbedded mass were prefabricated to study the deformation and failure characteristics around the interbedded rock tunnel through experiments. The stress and strain distribution around the interbedded rock tunnel were analyzed and compared by numerical simulation. The results show that: When the relatively soft layer is thick, the damage of the tunnel is more affected by the compression of the relatively soft layer, and the axial compression deformation of the tunnel is larger. When the relatively hard layer is thick, the damage of the tunnel is more affected by the fracture of the relatively hard layer. When the interlayer thickness is thin, the thinner rock layer makes the deformation and failure of rock mass around the tunnel more continuous. (1) The overall failure mode of the test specimen under the condition of 10 mm relatively hard layer and 10 mm relatively soft layer is strong hole failure mode, in which the tensile failure is more serious at the vault and arch bottom, and pressure-shear composite crack is easily occurs at the arch shoulder and arch foot. (2) The overall failure mode of the test specimen under the condition of 10 mm relatively hard layer and 20 mm relatively soft layer is strong compression failure mode, in which the compression-shear failure is obvious at the arch waist, and the compression-shear composite crack is easily occurs at the arch shoulder and arch foot. (3) The overall failure mode of the test specimen under the condition of 20 mm relatively hard layer and 10mm relatively soft layer is fracture failure mode, in which the vault obviously sinks, and the stress level near the arch waist is high, but the failure degree of the arch waist is small.