American Society of Civil Engineers


Suction and its Effects on Shear Strength of Unsaturated Undisturbed Samples of a Volcanic Pumiceous Soil


by M. Shimizu, (Member of ISSMGE; Associate professor, Department of Civil Engineering, Faculty of Engineering, Tottori University, Koyama-Minami, Tottori City, Japan, 680-8552 E-mail: mshimizu@cv.tottori-u.ac.jp), D. Yamamoto, (Student, Graduate School of Engineering, Tottori University, Koyama-Minami, Tottori City, Japan, 680-8552 E-mail: yamamoto@geotec.cv.tottori-u.ac.jp), and Y. Tahara, (Student, Graduate School of Engineering, Tottori University, Koyama-Minami, Tottori City, Japan, 680-8552 E-mail: tahara@geotec.cv.tottori-u.ac.jp)
Section: Laboratory Studies of Unsaturated Soil Shear Strength, pp. 1235-1246, (doi:  http://dx.doi.org/10.1061/40802(189)101)

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Document type: Conference Proceeding Paper
Part of: Unsaturated Soils 2006
Abstract: This paper is concerned with the shear strength of undisturbed natural samples of volcanic pumiceous soil. The shear strength varies in a complicated manner with the normal stress lower than the consolidation yield stress pc. Considering the suction as a factor affecting the shear strength characteristics, direct shear box tests were conducted after the consolidation during which the suction was measured and regulated. When consolidation pressures higher than pc were applied, the suction decreased, eventually, to null with almost full degree of saturation; the shear strength with such high normal stresses obeyed the Mohr Coulomb criterion. To some specimens the suction was regulated with a normal stress lower than pc; they mobilized shear strengths exhibiting a good correlation with the suction. Conclusions emphasize that the suction should be measured for unsaturated specimens even if they have so high degree of saturation as 80 percent or more, and that the suction will be effective for interpreting the variation of the shear strength, especially determined with relatively low normal stresses, of undisturbed natural samples.


ASCE Subject Headings:
Soil suction
Shear strength
Unsaturated soils
Volcanic ash
Latin America
Asia