Study on 3D Mechanical Characteristics of Outburst Prevention Rock-plate in Tunnel Construction

When there is a water-inburst and mud-induced structure in front of the tunnel construction and excavation, if the thickness of the water-repellent/mud-separated soil disk is less than the minimum safe rock-soil disk thickness, the water-repellent and mud-separated soil disk is unstable and damaged under the action of the groundwater/clay pressure in the disaster causing structure, and the groundwater or clay in the disaster causing structure is outburst to form the water inburst/silt disaster. In this paper, the most common sandstone and limestone in tunnels are used to make complete and prespecified fracture specimens with a certain length and width and different thickness. The failure tests under concentrated load are carried out to explore the three-dimensional mechanical characteristics of sandstone and limestone anti-outburst rock discs and the relationship between the minimum safe rock disc thickness and the head. The results show that the crack formed by the failure of sandstone rock disc is of "X" shape, and the limestone rock disc is of "branch" shape. The crack of sandstone disk is generated along the direction of large size, and the crack tip expands to the direction of large size when there is primary fracture. The cracks in the limestone rock disk produce primary cracks along the long diagonal, and secondary cracks appear in the deeper part of the cracks, and the cracks mainly expand along one end. With the increase of the length, the maximum transverse stress of the intact sandstone disc presents a "hump-shaped" curve, the maximum transverse stress of the fractured sandstone disc presents a "peak" curve, and the maximum transverse stress of the intact and fractured limestone discs presents a "unimodal" curve, with the maximum transverse stress appearing an extreme value at a certain length. With the increase of thickness, the curve finally presents a "single peak" curve. At a certain thickness, the anti-destructive force is the strongest. The relationship between the water head and the thickness of sandstone and limestone slab is power exponential.