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RISS 인기검색어
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- 저자 : Fujun Niu (검색결과 4 건)
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Xuyang Wu,Fujun Niu,Qingguo Liang,Guoyu Li 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.6
Tensile strength is an important but seldom noticed parameter that reveals the constitutive relations of soil. For the loess, the tensile strength can be used to explain earthwork-induced damages such as tension cracks in cut slopes and corresponding slope failures, or natural disasters such as ground fissures. The present study chose an indirect method, particularly the unconfined penetration (UP) test, to measure the tensile strength of remolded loess and undisturbed Q2 and Q3 loess obtained from different districts in China. The results indicated that the tensile strength of the undisturbed loess was primary determined by the void ratio. In addition, multiple correlations were observed between the void ratio and the degree of saturation. The tensile linear stiffness exhibited an exponential increase following an increase in the tensile strength. The mechanism of the tensile-shear coupling strength criterion was proposed. Linear relations between the mechanical parameters were deduced under the tensile-shear coupling condition and were verified by the remolded and undisturbed loess, respectively. Both the unconfined compressive strength and cohesion decreased under the tensile-shear coupling condition. Comparisons with other strength models validated the suitability of the tensile-shear coupling strength criterion for the loess. This study aims to present a more comprehensive understanding on the tensile strength of loess and offer parameter guidance for stability calculations in practical engineering.
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Hailin Wang,Hong Sun,Xiurun Ge,Fujun Niu 대한토목학회 2023 KSCE Journal of Civil Engineering Vol.27 No.10
The mechanical behaviors of granular materials are dominated by internal structure, which are related to fabric evolution during loading. This study investigated the fabric evolution of granular materials with different densities and stress paths under true triaxial conditions. A series of discrete element numerical simulations with different intermediate principal stress coefficient b were carried out along the constant mean stress p and the constant minor principal stress σ3 stress paths for both loose and dense specimens. The results indicated that the constant-p stress path produced a faster increase in stress ratio than the constant-σ3 stress path at the same b. The effects of specimen density on the peak friction angle are greater than that of stress path. The microscopic analyses revealed that the constant-p stress path facilitates a much more preferential distribution of normal contact force network along the major principal direction. The discrepancies in the peak stress ratio under two stress paths were thus interpreted. The dense specimen will rapidly form a higher anisotropic distribution of the normal contact force network upon shearing, and its anisotropic intensity was almost twice that of the loose specimen at the peak stress state. In addition, a unique relationship between the strong deviatoric fabric ratio and stress ratio was presented. The ratio of the two was approximately 1.0 regardless of stress path, density and b value. Finally, an underlying relationship between the stress components and the whole fabric components at the critical state was confirmed by introducing a new stress tensor. The three principal components (F1, F2 and F3) of the whole fabric tensor can be quantitatively represented with the imposed three principal stress components (σ1, σ2 and σ3) by employing a relationship of F1:F2:F3 = σ10.27:σ20.27:σ30.27. It provides a more comprehensive perspective to analyze the macro-micro performances of granular materials at the critical state.
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An Anisotropic Failure Criterion for Cross-anisotropic Soils
Hailin Wang,Hong Sun,Xiurun Ge,Fujun Niu 대한토목학회 2023 KSCE Journal of Civil Engineering Vol.27 No.9
Strength anisotropy is an important feature closely related to soil microstructure characteristics. A new anisotropic failure criterion, extended from the Ogawa failure criterion, was developed to describe the strength anisotropy of cross-anisotropic soils. Nonlinearization of the failure curves of the Ogawa failure criterion was introduced to account for the nonlinear failure of cross-anisotropic soils in the meridian plane. Meanwhile, an anisotropic strength function based on fabric tensor was theoretically proposed to modify the failure strength under different loading directions and depositional angles. The evolution of the new anisotropic failure criterion in the deviatoric plane was investigated through a series of parametric studies. All of the undetermined parameters in the new criterion can be readily determined in laboratory tests. Compared with experimental results on several types of soils, the new anisotropic failure criterion showed good performance in strength prediction in the deviatoric plane, as well as predicting the peak friction angle. Finally, a linear theoretical relationship on construction of the anisotropic strength function was also elucidated and discussed. The new anisotropic failure criterion proposed in this paper can effectively predict the strength anisotropy of cross-anisotropic soils under different loading directions and depositional angles.
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