Study on the Mechanical Properties and Design Scheme of Horseshoe Prefabricated Primary Support

In order to solve the problems of poor construction environment, difficult construction quality control, serious waste of concrete rebound and slow strength improvement in the traditional shotcrete initial support tunnel, a new type of prefabricated initial support structure is proposed. Combined with the full-scale test of horseshoe prefabricated initial support, the mechanical properties and deformation law of prefabricated initial support are studied. According to the test results and theoretical calculation, the research on the design scheme of the new initial support from the aspects of assembly mode, block scheme, connection mode, bolt design and deformation capacity can provide reference for the popularization and application of the new initial support. The main conclusions are as follows: (1) The ultimate bearing capacity of prefabricated initial support is 2.8 times of the design load, and the maximum deformation is 115.6 mm. It has good deformation capacity and can give full play to the self-supporting capacity of surrounding rock while meeting the construction safety; (2) The initial support of horseshoe prefabrication adopts odd and even rings to realize staggered joint assembly. The curvature of the arch foot is large and the assembly is difficult. The concave convex tenon will lead to the damage of the segment during assembly, which requires high control accuracy, so the segment should not be set with concave convex tenon; (3) The arch foot of precast initial support is the most unfavorable position, and the arch foot needs to be strengthened; (4) The scheme of "pipe before anchor" should be adopted for the initial support of prefabrication; (5) After the assembly of the prefabricated initial support is completed, the design strength is used to participate in the stress of the surrounding rock, which avoids the situation that the shotcrete bears the pressure of the surrounding rock in the strength improvement stage, greatly improves the stress of the structure, reduces the development of cracks, and has better mechanical properties.