| As the main assembly component and permanent lining of shield construction,the quality of reinforced concrete segments is directly related to the overall quality and safety of the tunnel,and affects the waterproof performance and durability of the tunnel.However,in the process of production and construction,precast reinforced concrete segments inevitably have quality defects such as segment cracks,lack of edges,few angles and steel leakage,which not only brings difficulties to the subway construction process,but also has a certain impact on the service life of the subway.In view of the above shortcomings of reinforced concrete segments,this study relies on the subway shield construction projects of Wuhan Metro Line 8 and Line 11 to carry out experimental research on the performance of steel fiber reinforced concrete,aiming at improving the compressive,tensile and flexural strength of concrete,and combining with the subway segments,numerical simulation is carried out by MIDAS finite element software to explore the steel fiber reinforced concrete segments in the subway shield.The feasibility of the application of structural tunnels,the main work accomplished and the main conclusions drawn are as follows:(1)The mix proportion design of steel fiber reinforced concrete is carried out by using three methods: secondary synthesis method,equal volume replacement of coarse aggregate method and composition mixing method.The experimental study on compressive strength and splitting tensile strength of concrete specimens is carried out.It is concluded that under the premise of choosing reasonable steel fiber varieties and volume addition,two design methods,equal volume replacement of coarse aggregate method and secondary synthesis method,are adopted.The compressive strength of steel fiber reinforced concrete prepared by this method has increased by one strength grade on the basis of C50 matrix concrete,which reaches the strength index of CF60.Under the same mix ratio,the amount of raw materials is compared,and the cementitious material can be saved by 21% by using equal volume instead of coarse aggregate method.For segment production enterprises,equal volume replacement of coarse aggregate method is more suitable for the design and calculation of mix ratio of steel fiber reinforced concrete production.(2)Compared with the matrix concrete,the end-hook steel fibers increase the compressive and tensile strength more obviously when concrete is mixed with steel fibers of different shapes,but the friction between the end-hook steel fibers is larger and easy to winding,which is not conducive to the forming of test blocks;while the surface of wave-shaped and dumbbell-shaped steel fibers increases the bonding with concrete by indentation treatment,and the shading of test blocks is formed.It has less noise and is more suitable for the production of segment.(3)When the compressive strength,splitting tensile strength and flexural strength of steel fiber reinforced concrete meet the strength index of CF60,the thickness of steel fiber reinforced concrete segments is reduced from 350 mm to 300 mm.The finite element software MIDAS is used to simulate and analyze the steel fiber reinforced concrete segments,and the maximum internal force combination is used to design the steel fiber reinforced concrete segments.By calculating the main reinforcement of steel fiber reinforced concrete segment,the steel fiber reinforced concrete segment is selected as 12Ф18+12Ф20.Under the same pressure load,the deformation resistance of steel fiber reinforced concrete segment is 75% higher than that of reinforced concrete segment,and the crack resistance is 74% higher.At the same time,the reinforcement is about 10.4% in each link and the concrete is saved by 12.8%. |
