Effect of suction on shear strength of soils

1992 Fiscal Year Final Research Report Summary

• Project/Area Number: 03660245
• Research Category: Grant-in-Aid for General Scientific Research (C)
• Allocation Type: Single-year Grants
• Research Field: 農業土木
• Research Institution: Okayama University
• Principal Investigator: SHIMADA Kiyoshi Okayama Univ., Fac.of Agri., Associate Prof., 農学部, 助教授 (20123234)
• Co-Investigator(Kenkyū-buntansha): NISHIMURA Shin-ichi Okayama Univ., Fac.of Agri., Research Asso., 農学部, 助手 (30198501) ; FUJII Hiroaki Okayama Univ., Fac.of Agri., Prof., 農学部, 教授 (70033264)
• Project Period (FY): 1991 – 1992
• Keywords: Unsaturated soil / Masa soil / Suction / Direct shear test / Shear strength

Research Abstract

This research report discusses the effect of suction on the shear strength of unsaturated soils.
Unsaturated MASA soil produced in Okayama was used in experiments. The test specimens were statically compacted in the shear box of direct shear apparatus developed by Prof. MIKASA. Suction was applied to the specimens through the ceramic disc imbeded in the lower pressure plate of the apparatus.
Stress-controlled drainage shear test were carried out under the condition of constant suction. Normal stress was set to 1.0, 2.0, 3.0kgf/cm^2 and suction to 0, 0.1, 0.2, 0.4, 0.6, 0.8 kgf/cm^2.
The test result shows the increase of shear strength with the increase of suction. However, the increase of the shear strength is found to be negligible over the range of 0.4 kgf/cm^2 of suction. The normally compressed and over-compressed MASA soils show the same tendency of the increase of the shear strength with suction.
The bonding force produced by the pore water between two spheres causes the increase of the effective normal stress, then the increase of the shear strength. The force is calculated theoretically under the condition of random packing of the same size spheres. The theoretical relationship between suction and shear strength shows the good agreement with the experimental results.