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Chunyu Zhang,Mengjun Chen,Rentai Liu,Xiuhao Li,Jia Yan,Zhijing Zhu,Fengshuai Fan 대한토목학회 2022 KSCE Journal of Civil Engineering Vol.26 No.12
Operating tunnels are often located in complex geological conditions and are prone to various types of damage. Even after structural repair, the repaired material may be vulnerable to secondary damage. It is difficult to effectively repair operating tunnel damage. Hence, developing high-performance repair materials for tunnel structures is critical. This study aimed to develop repair materials by studying the synergistic effects of fiber and polymers. The effectof polyvinyl alcohol (PVA) fiber and PTB (COMPAKTUNA.PRO) emulsion on the compressive strength (40 × 40 × 40 mm, GB/T 17671-2020), flexural strength (40 × 40 × 160 mm, GB/T 17671-2020), uniaxial tensile properties (330 × 60 × 13 mm, JC/T 2461-2018), bond strength (40 × 40 × 160 mm, JC/T 2537-2019), rapid chloride migration coefficient (ϕ100 × 50 mm, GB/T 50082-2009), porosity (40 × 40 × 40 mm, SY/T 6490-2014), and scanning electron microscopy (less than 1 cm3, GB/T 27788-2020) was analysed. The test was completed in the laboratory of our school, and the average value of three specimens per mix ratio was taken. The results indicate that both PVA fiber and PTB emulsion addition reduce the compressive strength but significantly increase the flexural strength, tensile strength, and ultimate tensile strain of cementitious composite. The compressive-to-flexural strength ratio decreases, and the uniaxial compression toughness index increases. The cementitious composites exhibit good integrity after damage. The influence of the PVA fiber is more potent than that of the PTB emulsion. The PTB emulsion increases the impermeability and bonding strength of the cementitious composite and can improve the disadvantages caused by adding the PVA fibers. The bridging effect of the PVA fiber and the membrane-forming effect of the PTB emulsion together influence the performance and cause a synergistic effect to achieve superposition and complementation of advantages. The optimal content of the PVA fiber and PTB emulsion under the synergistic effect can be obtained. The findings can provide a theoretical basis for the optimal design and practical application of restoration materials.
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An Extension Theoretical Model for Grouting Effect Evaluation in Sand Stratum of Metro Construction
Jiwen Bai,Shucai Li,Yujing Jiang,Rentai Liu,Zhaofeng Li,Wei Li 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.5
Water-rich sand stratum is a common geological disaster source for the metro construction in coastal cities, and grouting is the most widely-used and efficient method to improve the characteristics of tunnel-surrounding rock. The grouting effect evaluation plays a key role in guaranteeing the subsequent construction safety. However, the grouting effect evaluation is a complex problem since it involves influence factors of uncertainty and variability. In order to comprehensively and quantitatively evaluate the grouting quality and guarantee the safety of metro construction, an extension theoretical model for grouting effect evaluation in water-rich sand stratum is established. Firstly, according to the geological and engineering influence factors, rock mass strength, permeability of surrounding rock, attitude of stratum, moisture content, grouting material, and grouting technology are selected as the grouting effect evaluation indexes, which make up the evaluation index system. The dimensionless method is used to avoid the influence of the unit and order of magnitude of each index, and index weight of each factor is ascertained by entropy-information theory. Also, through the grouting information of typical waterrich sand stratum and expert experience, the grouting effect evaluation grade classification is achieved. Combining with the extension theory and measured data, the correlation degree of each evaluation grade is obtained. Finally, according to the correlation degree identification criteria, the grouting effect evaluation categories can be judged. In the engineering application, the water-rich sand stratum grouting effect in Qingdao metro is evaluated based on the proposed model. The results show that the evaluation grade agrees well with the excavation situation. The extension theoretical model provides an effective method for grouting effect evaluation in water-rich sand stratum.
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