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土のダイレイタンシーと異方性
土のダイレイタンシーと異方性
Dilatancy characteristics and anisotropy of soils
吉田, 昭治
The author has shown in his previous paper (YOSHIDA, 1978) that a set of mean pressure and deviatoric stress (which is not identical to principal stress difference) can be adopted reasonably to describe the stress-strain relationship for soils; furthermore, the author’s new idea that dilatancy is defined as the volumetric strain induced by deviatoric stress led to the conclusion that diIatancy is a phenomenon caused by anisotropy in deformation. And two types of coefficients of deformation, D and G, are introduced for “shear” are assumed to be expressed by the parameters of mean pressure and principal stress ratios (Eq.2). Five constants n,(a, α) and (b, P) are used to define these coefficients of deformation and were determined directly from the results of conventional triaxial compression tests. The two typical results of triaxial tests on dilatancy of sands are well accounted for by the simplified, nonlinear and anisotropic stress-strain relationship for soils (Eqs. (1) and (2)) in this paper as follows: 1) The samples of a sand contract first and subsequently expand until failure is reached under constant mean pressure (TATSUOKA and ISHIHARA, 1971). This experimental evidence has been expressed by the relationship between volumetric strain and stress ratio q/σm in many investigations. The relationship is well accounted for by Eq.(3) or (4), by which the results calculated agree well with TATSUOKA’s data as shown in Fig.1. 2)For dense sands, the volumetric change due to the increase of mean pressure, σm, is generally a contraction, but volumetric change may become an expansion at higher principal stress ratio, R=σ_1/σ_8, than a certain value of R (El-SOHBY, 1969). This can be explained by Eq. (6) as follows. Under the condition a>b and α<β, one gets D<G at higher stress ratios than at a certain value of R, and, further, when the absolute of the second term (= an expansion due to dilatancy) on the right-hand side of Eq.(6) superior to the first term(= a contraction due to mean pressure σm) on the right-hand side of Eq.(6) with the increase of principal stress ratio R, an expansion occurs while mean pressure increases. Herin, the condition n<1.0 is necessary for such cases to be realized. The relationships between volumetric strain and mean pressure or axial strain are calculated by the use of the coefficients of deformation determined from TATSUOKA’s data for medium samples of Sagami River sand and are shown in Fig.2 and Fig.3.
新潟大学積雪地域災害研究センター
1980-03
jpn
departmental bulletin paper
http://hdl.handle.net/10191/38992
https://niigata-u.repo.nii.ac.jp/records/28232
AN00183327
03877892
新潟大学積雪地域災害研究センター研究年報
新潟大学積雪地域災害研究センター研究年報
2
115
122
https://niigata-u.repo.nii.ac.jp/record/28232/files/2_115-122.pdf
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2019-08-20