Study On Waterproof Test And Anti-Crack Technique Of Fiber Concrete Structure In Subway Station

The crack and leakage existed in concrete structure of subway station is dangerous for subway regular running and subway facility safely working. Level of impermeability and waterproof for concrete structure of subway station, which directly affects construction quality, becomes an important index to evaluate subway station engineering. Therefore, how to prevent concrete structure of subway station cracking and leaking is important to theory and practice. Adding different types of fibers to concrete is a primary technique to prevent concrete leaking. Fibers volume content is often determined by test results or engineering experience, which is neither economic nor reliable. To solve such problems discussed above, the following studies have been carried out.A standard 32 meters long segment between induced joints in shanghai metro line 2 is studied using finite element method. Based on FEM analysis, temperature drop load is considered to be the main load to generate crack and crack in subway station concrete to be I type crack. So there is contraction in subway station concrete structure when temperature drop load is applied to it. I type crack appears when the first principle stress exceeds tensile strength, and there is leakage in the place where crack open displacement exceeds the limited value.With Moelands-Reinhardt constitutive model, Monte-Carlo stochastic FEM is used to study crack process in plain concrete and fiber concrete under temperature drop load. Based on statistic result of stochastic FEM,it is proved that polypropylene fibers can enhance fracture energy which defers crack process and reduces crack probability by relaxing the shrink of surrounding concrete body. With comparison of crack processes in fiber concrete under different constraint conditions, condition of shrinkage is considered more significant than its aspect ratio.To get proper test method to evaluate waterproof performance of fiber concrete, waterproof grade method test and penetrating height method test is performed respectively. With the test results, it is considered that neither waterproof grade nor penetrating height can rationally evaluate the behavior, that fibers can improve waterproof ability of concrete structure in service.Conventional waterproof test is considered to be suitable to evaluate permeability of compact concrete, but not to permeability of damage concrete with load-bearing history. So splitting hold-load permeating test, which is suitable to evaluate permeability of damage fiber concrete, is presented in this thesis. In order to finish the test, a set of hold-load device and a set of hold-load permeation apparatus are invented. With splitting test, it is found that polypropylene fibers can't distinctly improve concrete tensile strength while steel fibers can distinctly improve it, and both polypropylene fiber concrete and steel fiber concrete can distinctly improve concrete fracture energy. Waterproof grade of different splitting specimens is given with hold-load permeation test.With strain equivalent hypothesis, fiber concrete damage evolution equation in tensile strain space is deduced from Moelands-Reinhardt constitutive relationship. Based on global splitting test of fiber concrete, a modified damage evolution equation containing tensile strength and fracture energy is presented in this thesis. With the modified damage evolution equation, the ultimate damage value of concrete specimen, with different type and different volume content fibers, is calculated under different waterproof grade. Ultimate temperature drop load calculation method, under different waterproof grade, is presented. According to ultimate temperature drop value under different waterproof grade, different constraint condition and different length-width ration, ultimate temperature drop equation for different waterproof grade of concrete slab of subway station is given. With ultimate temperature drop equation, volume content of polypropylene fibers or steel fibers, more economic but safe, is proposed to the soleplate of one Shanghai subway station in the end of the thesis.