Application of suction stress for estimating unsaturated shear strength of soils using direct shear testing under low confining pressure

Byeongsu Kim, Satoru Shibuya, Seong Wan Park, Shoji Kato

Research output: Contribution to journalArticle

29 Citations (Scopus)


The primary objective of this study is to evaluate effects of suction on shear strength of unsaturated soils under low confining pressure and to examine the relationships between suction, shear strength behavior, and volumetric deformation using newly developed direct shear testing equipment for compacted weathered granite soils. The soil-water retention curves (SWRCs) of unsaturated soils were obtained under various overburden pressures. To analyze test results from the direct shear test under unsaturated conditions, a new method, suction stress-SWRC method (SSM), is proposed to determine the suction value for each overburden pressure and the suction stresses. As a result, it has been found that the stress states at the peak shear strength point are on the same failure line for the saturated state when the suction stress is treated as a component of confining pressure. The relationship between stress ratio and dilatancy for the saturated state can be extended to the unsaturated state. It is also noted that the estimated unsaturated shear strengths using the SSM agree well with the measured values from laboratory testing.

Original languageEnglish
Pages (from-to)955-970
Number of pages16
JournalCanadian Geotechnical Journal
Issue number9
Publication statusPublished - 2010
Externally publishedYes



  • Direct shear test
  • Soil-water retention curve (SWRC)
  • Suction stress
  • Suction stress-SWRC method (SSM)
  • Unsaturated soils

ASJC Scopus subject areas

  • Geotechnical Engineering and Engineering Geology

Cite this