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A modified shear strength reduction finite element method for soil slope under wetting-drying cycles
Tu, Yiliang,Zhong, Zuliang,Luo, Weikun,Liu, Xinrong,Wang, Sui Techno-Press 2016 Geomechanics & engineering Vol.11 No.6
The shear strength reduction finite element method (SSRFEM) is a powerful tool for slope stability analysis. The factor of safety (FOS) of the slope can be easily calculated only through reducing effective cohesion (c′) and tangent of effective friction angle ($tan{\varphi}^{\prime}$) in equal proportion. However, this method may not be applicable to soil slope under wetting-drying cycles (WDCs), because the influence of WDCs on c′ and $tan{\varphi}^{\prime}$ may be different. To research the method of estimating FOS of soil slopes under WDCs, this paper presents an experimental study firstly to investigate the effects of WDCs on the parameters of shear strength and stiffness. Twelve silty clay samples were subjected to different number of WDCs and then tested with triaxial test equipment. The test results show that WDCs have a degradation effect on shear strength (${\sigma}_1-{\sigma}_3)_f$, secant modulus of elasticity ($E_s$) and c′ while little influence on ${\varphi}^{\prime}$. Hence, conventional SSRFEM which reduces c′ and $tan{\varphi}^{\prime}$ in equal proportion cannot be adopted to compute the FOS of slope under conditions of WDCs. The SSRFEM should be modified. In detail, c′ is merely reduced among shear strength parameters, and elasticity modulus is reduced correspondingly. Besides, a new approach based on sudden substantial changes in the displacement of marked nodes is proposed to identify the slope failure in SSRFEM. Finally, the modified SSRFEM is applied to compute the FOS of a slope example.
Influences of Principal Stress Rotation on the Deformation of Saturated Loess under Traffic Loading
Sui Wang,Zuliang Zhong,Xinrong Liu,Yiliang Tu 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.5
This study focuses on the undrained behavior of saturated remolded loess under long-term traffic loading in Lishi, China. In this work, a series of stress-controlled monotonic and cyclic hollow cylinder tests were conducted. In the monotonic tests, the samples were sheared under different inclinations of the major principal stress. According to the results, the saturated remolded loess clearly shows strength anisotropy and shear dilation features. In the cyclic tests, the experimental results show that the evolutions of the pore pressure and generalized shear strain are highly dependent on the principal stress rotation (PSR). The evolution of the strain can be categorized into stable and destructive types. For the stable type, the change in pore pressure increases with the number of loading cycles and then becomes stable. The change in the difference in pore pressure is approximately the same under the same vertical stress ratio. The development of pore pressure shows the hysteresis property, the PSR decreases the degree of the pore pressure hysteresis.
Study on the Fracture Toughness of Polypropylene-Basalt Fiber-Reinforced Concrete
Ninghui Liang,Lianxi Ren,Shuo Tian,Xinrong Liu,Zuliang Zhong,Zhiyun Deng,Ru Yan 한국콘크리트학회 2021 International Journal of Concrete Structures and M Vol.15 No.5
To study the hybrid effects of polypropylene fiber and basalt fiber on the fracture toughness of concrete, 13 groups of notched concrete beam specimens with different fiber contents and mass ratios were prepared for the three-point bending test. Based on acoustic emission monitoring data, the initiation cracking load and instability load of each group of specimens were obtained, and the fracture toughness parameters were calculated according to the double- K fracture criterion. The test results show that the basalt fiber-reinforced concrete has a greater increase in initial fracture toughness, and the toughness of coarse polypropylene fiber-reinforced concrete is more unstable. Moreover, after the coarse polypropylene fiber content reaches 6 kg/m³ and the basalt fiber content reaches 3 kg/m³, increasing the content will not significantly improve the fracture toughness of the concrete. The polypropylene-basalt fiber will produce positive and negative effects when mixed, and the mass ratio of 2:1 was optimal. Finally, the fitting analysis revealed that the fracture process of polypropylene-basalt fiber-reinforced concrete (PBFRC) can be objectively described by the bilinear softening constitutive curve improved by Xu and Reinhardt.