| The shotcrete technology has become one of the most effective means of supporting in underground engineering and geotechnical engineering; it not only can be the initial period supports which insures construction security of tunnel, but also take the structure permanent supports and protections along with supports and protections component, and maintain structure long-term stability and safety handling. In recent years, in order to adapt to the different surrounding rock condition and construction method, it appears many new kinds of shotcrete, such as high strength shotcrete, fiber shotcrete, and polyester high strength shotcrete, and so on. Speaking of the engineering mechanics performance, the steel fiber reinforced shotcrete has surpasseed ordinary shotcrete in many aspects, thus it is given more and more attention by engineering area, which is applied widely in tunnels and underground engineering, but its mechanical characteristics and related issues have been always falling behind application. Combined with the key project of the National Natural Science Foundation and National Natural Sciences Foundation Innovation Community Fund, on the basis of previous research, the mechanical characteristics of steel fiber reinforced shotcrete and action mechanism of single layer tunnel lining is systemic and thoroughly researched by theory analysis, experimental test, numerical simulation and field test. The main works and achievement of thesis can be drawn as follows:(1) The reinforced mechanism of steel fiber reinforced concrete is studied. According to the leading features of stress-strain curve, the growing of damage in steel fiber reinforced concrete is subdivided into four stages with mutual connections and characteristic stage. According to flexural mechanism analysis of steel fiber reinforced shotcrete beam, relations expression between moment capacity and cracking moment is obtained. The reinforcing and toughening mechanism of steel fiber to contrete is set forth in details from the point of view of composite material mechanics and fracture mechanics.(2) The compression strength, tensile strength, initial strength, cohesional strength and impermeability properties of steel fiber reinforced shotcrete are key researched; among basic mechanical experiments, the relationship between mechanical properties and content of different steel fiber reinforced shotcrete is grasped; a reasonable content of fiber is determined, and the mechanical proper guideposts of shotcrete used for single layer lining are presented.(3) With load and deflection test of steel fiber reinforced shotcrete, its flexural toughness is calculated and analyzed, the change pattern of curving toughness index along with the fiber contents is studied, combined with test results, the relevance of toughness index of steel fiber reinforced shotcrete is discussed. Through cube slice experiment, the distribution of steel fiber in shotcrete is obtained, and experimental results and theoretical calculation is comparative analyzed, slice test of steel fiber reinforced shotcrete proves steel fiber obeys Fisher distribution of spherical surface among shotcrete.(4) Starting with analysis of support object of single layer lining, the mechanical mechanism mechanism of single layer tunnel lining is studied; it shows two different mechanical transfer mechanisms in the load course: one is rock stress transfers to the outside, and the other is the internal stress transfers. Supporting mechanism of shotcrete is divided into two categories: the part stress and the whole one. And the mechanism of anchors for single layer tunnel lining by shotcrete is analyzed too.(5) By analyzing the impact factors of stability of tunnel surrounding rock, based on cusp catastrophe theory, the stability of composite structure from top of single layer tunnel lining is studied. Adopted simplified mechanical model of straight beam, the catastrophe model of vault complex of single layer tunnel lining and surrounding rock is set up, and necessary and sufficient conditions for instability and vault deformation at system instability as well as expression which energy releases are obtained, and thesis discusses the influence between vault complex stability and changing force on structure.(6) Using finite element method, the stability of single layer tunnel lining by steel fiber reinforced shotcrete is numerical simulation analyzed; the surrounding of tunnel rock and support system structure, displacement field, stress field, plastic zone as well as internal forces changes of support characteristics are obtained; the stability of different surrounding rock grade of tunnel excavation is studied, and reasonable spray layer thickness of single layer tunnel lining by steel fiber reinforced shotcrete is obtained. Simultaneity, the supporting effect of single layer lining by steel fiber reinforced shotcrete is also analyzed and evaluated by in-situ monitoring results.(7) With a project of inclined shaft of Motianling tunnel, based on the principles and technical demands of New Austrian Tunneling Method, the application of single layer tunnel lining by steel fiber reinforced shotcrete with wet-mix method is studied systematically by construction technology, structural design, key technology, economic analysis and waterproof and drainage, and a set of quality inspection and evaluation standards of construction technology for single layer tunnel lining is initial formed.
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