A Research On The Application Of Steel-Fiber Reinforced Shotcrete As The Primary Support For Tunnels And Its Econominc Effect

Steel fiber reinforced concrete (hereafter mentioned as SFRC) has been widely used in various foreign projects concerning roads, tunnels, underground, industrial and civil construction, highways and railways and has obtained successful experience. In spite of the universal approval for its excellent performance, it is still not extensively applied to domestic tunnel projects because of the different construction technology between home and abroad. Therefore, it is beneficial for the promotion of SFRC in domestic tunnel projects by exploring its fine performance and analyzing its reduction of project duration, and its economic and social effect as well.With the research of the primary tunnel support being the main object, this thesis demonstrates the feasibility of the use steel fiber as primary support from ductility, mechanics, model tests and numerical simulation respectively. Meanwhile, this thesis explains the prospect economic and social benefits by replacing mesh reinforced shotcrete with steel-fiber reinforced shotcrete from the perpective of the construction cost and the the project duration, which is expounded from the following four aspects:1. It can be seen from the four points bending tests and the concrete slab test that the steel-fiber reinforced shotcrete has fine ductiliy which enables it to continue bearing weight and absorbing energy after cracks appear. Also, it can be drawn that the steel-fiber reinforced shotcrete with the intermingled quantity of 30 kg/m3 has superior ductility than those with the intermingled quantity of 25 kg/m3 and 35 kg/m3, and at the same time, steel-fiber reinforced shotcrete can better avoid the the problem of the distribution of tensile force in tension zone than mesh reinforced shotcrete.2. Drawn from the indoor model test, there is not much difference between the load deformation of steel-fiber reinforced shotcrete lining and steel-mesh shotcrete lining before damage. But after damage, steel-fiber reinforced shotcrete has good ductility and can continue to bear loads, which shows a different fracture mode from that of mesh reinforced shotcrete lining.3. When subjected to the same bending moment, the thickness of steel-fiber reinforced shotcrete and mesh reinforced shotcrete can be calculated by simplifying the models. Through further calculation, it can be worked out that with the same intermingled quantity of 30Kg/m3 and the volume fraction of 0.4%,105mm steel-fiber reinforced shotcrete can bear the same bending moment as the 200mm single-layer mesh reinforced shotcrete ofφ6.5@25x25cm. And through numerical simulation, it can be drawn that when used as support for tunnel spray layer, steel-fiber reinforced shotcrete of 15cm may achieve the same effect as mesh reinforced shotcrete of 20cm.4. At last, with the practical case of grade-IV wall rock and grade-V wall rock of tunnels along Guang-Gan highway, this thesis tries to confirm the fact that the appication of steel-fiber reinforced shotcrete instead of mesh reinforced shotcrete as the primary support of tunnels reduces the duration of the 1000m grade-IV wall rock by 41 days and 57 days for the 1000m grade-V wall rock.Meanwhile, the use of steel-fiber reinforced shotcrete lining saves 1774659.4 yuan for the grade-IV wall rock and 1819852.5 yuan for the grade-V wall rock, thus bringing huge social and economic profits.