Application Of Ductility Of Steel Fiber Reinforced Concrete In The Design Of Tunnel Structure

As a new kind of compound material, Steel Fiber Reinforced Concrete (SFRC) is now widely used in civil engineering for its superior ductility and impulsion resistance. Different from normal concrete, SFRC shows great capacity of dissipating energy in its cracking stage because of the pull out effect of steel fibers. It is of great importance for the design of SFRC structures to study intensively on this energy dissipating property of the material.The use of shotcrete as early linings of tunnel is a prevalent technique in underground engineering today. In cases with reliable rock situation, shotcrete linings can even be used as permanent prop for tunnel. The SFRC can act as a substitute for normal concrete and yields good results in such situation. The paper deals mainly about the application of SFRC in permanent shotcrete linings in tunnel construction. The study lies in following aspects:1) A great number of experiments on SFRC are carried out to obtain the basic data of SFRC energy properties, which are the fundamental parts of further study.2) A probability analysis based on statistical theory is done to all the experiment data. In the end, energy criterion for SFRC associated with security criterion are calculated and listed for future use.3) With rational supposition, the energy dissipating mechanics in SFRC cracks is studied intensively. And the relation between the amount of energy dissipated in cracking and the form of cracks is proposed so that the energy data obtained in the standard tests could be used in design of linings.4) A 3-demensional finite element model is constructed to simulate the excavation of the tunnel. The change of energy in wall rock is tracked in the whole process and the amount of energy transferred to linings is also evaluated.5) Based on the principal of energy invariance and the energy properties of SFRC, a practical design equation that related the thickness of projecting SFRC to the energy related properties of tunnel is given in the end. This equation is then used to design a single-track railway tunnel in III grade rock condition.