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RISS 인기검색어
- 검색키워드
- 저자 : Huayan Yao (검색결과 4 건)
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Experimental Study on the Permeability Characteristics of Sandstone in Different Chemical Solutions
Yao Huayan,Zhang Zhenhua,Li Dezhong 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.9
Groundwater seepage is one of the important factors which affect the physical and mechanical properties of soft rock. In this study, the permeability evolution of sandstone was investigated using water solution seepage tests with different pH values. The results show that the chemical nature of the solutions has a great influence on the evolution of the permeability coefficients of sandstone specimens. Over time, it was determined that the permeability coefficient under the solution with PH = 2 was significantly greater than those under the PH = 7 and PH = 12 solutions used in this study. During the infiltrations, the ions of H+ and OH- which were involved in the water-rock interaction made the pH value of the solution change with different degrees. After the seepage, the ions in the solutions changed significantly. The ion concentrations seeping from sandstone specimen in the acidic solution, such as Ca2+, Mg2+, Fe3+ (Fe2+), Al3+ and K+, were found to be much greater than in the neutral and alkaline solutions. However, the ion concentrations seeping from sandstone specimen in the neutral solution displayed little differences from those in the alkaline solution. The concentration of the Si ion in the alkaline solution was much higher than those of the acid and neutral solutions, and the concentration of the acid solution was slightly higher than that of the neutral solution. The changes in the ion concentration in the osmotic solution reflected that there had been different forms of chemical reactions between the minerals of the sandstone and the solutions. The seepage pressures also had some effects on the permeability coefficients, pH values, and concentrations of ions in the solutions. After the seepage tests, the rock microstructures were observed by the means of a Scanning Electron Microscope (SEM). The results show that some new holes have been formed in the sandstone specimen due to the seepage, especially in the sample with the acid solution. The internal structural changes of the sandstone are found to be the main reasons for the changes in the permeability coefficients.
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Improved Mechanical Behaviour and Microstructure of Cemented Soil with Nanomaterials
Jianguo Lu,Huayan Yao,Isam Shahrour,Qingyao Fang,Weilong Song,Guang Liu 대한토목학회 2024 KSCE Journal of Civil Engineering Vol.28 No.7
This paper presents an experimental study of nanomaterials' influence on improving the mechanical behaviour and microstructure of cemented soils. The strength characteristics were obtained through uniaxial compressive strength test. The influences of nanomaterials on the pore size distribution and micromorphology of cemented soil were investigated by nuclear magnetic resonance, scanning electron microscope, and X-ray diffraction. The results show that the uniaxial compressive strength of the cemented soil increases with the nano-SiO2content. When the content is 4%, the strength of the cemented soil increases by about 40%. Improvement with nano-Fe3O4 shows different trends. The strength of the cemented soil increases with the nano-Fe3O4 content, reaching a peak at 3% of the nano content, and then decreases with the increase in the content. The transverse relaxation time spectrum curve of the cemented soil is trimodal, and the main peak covers a dominant area. Adding nanomaterials improves the pore distribution, transforms large pores into small pores, and greatly reduces the pores of the cemented soil. The porosity of the cemented soil decreases exponentially with the increase of nano-SiO2 content. On the contrary, with the increase of nano-Fe3O4 content, the porosity of the cemented soil specimen first decreases and then increases, the porosity reaches the minimum at 3% content. Nano-SiO2 and nano-Fe3O4 can effectively fill the internal pores of the cemented soil and accelerate the hydration process. In addition, nano-SiO2 participates in the hydration reaction of cement and has a good promoting effect on the mechanical properties of cemented soil.
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Zhenhua Zhang,Xiaochuan Chen,Huayan Yao,Xiang Huang,Luwang Chen 대한토목학회 2021 KSCE JOURNAL OF CIVIL ENGINEERING Vol.25 No.7
Jurassic Red-Bed sandstone is one of the main types of rock composing unstable slopes on both banks of the Three Gorges Reservoir (TGR) in China. It is vulnerable to tensile strength degradation when exposed to cyclic wet-dry conditions under reservoir operation. Therefore, the law behind this needs to be clarified in order to accurately evaluate the stability of a sandstone slope located in the drawdown area of the TGR. In this paper, Jurassic Red-Bed sandstone specimens from the Majiagou landslide in the TGR area were collected for experiments with cyclic wet-dry procedures. After each wet-dry cycle, efforts were made to implement splitting tests, measure clay mineral contents and ion contents in the soak solution, and observe changes in microstructures. The tensile strength is experimentally demonstrated to be a process of damage accumulation under the integrated actions of water pressure, calcite dissolution, and clay mineral hydration, among which hydration of illite contributes the most to the damage. The loss of the cement material and the cyclic expansion and shrinkage of clay minerals weaken the cementation between grains, leading to the tensile strength degradation.
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Jian Ma,Liang Bian,Jie Zhang,Kai Zhao,Huayan Yao,Yongliang Zhang Techno-Press 2023 Advances in concrete construction Vol.16 No.2
Steel fiber reinforced self-compacting concrete (SFRSCC) has good workability such as high flowability and good cohesiveness. The workability, compressive strength, splitting tensile strength, and anti-penetration characteristics of three kinds of SFRSCC were investigated in this paper. The fraction of steel fibers of the SFRSCC is 0.5%, 1.5% and 2.0% respectively. The results of the static tests show that the splitting tensile strength increases with the increase of fraction of steel fibers, while the compressive strength of 1.5% SFRSCC is lowest. It is demonstrated that the anti-penetration ability of 1.5% SFRSCC subjected to a velocity projectile (200-500 m/s) is better than 0.5% and 2.0% SFRSCC according to the experimental results. Considering the steel fiber effects, the existing formula is revised to predict penetration depth, and it is revealed that the revised predicted depth of penetration is in good agreement with the experimental results. The conclusion of this paper is helpful to the experimental investigations and engineering application.
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