Resilient modulus of unsaturated subgrade soil: Experimental and theoretical investigations

Charles Wang Wai Ng, C. Zhou, Q. Yuan, J. Xu

Research output: Journal article publicationJournal articleAcademic researchpeer-review

137 Citations (Scopus)


The resilient modulus,MR, of subgrade soil is an important stiffness parameter for analysing fatigue cracking in either the asphalt or concrete layer of a pavement. Although subgrade soil is often unsaturated and subject to seasonal variations of moisture content and hence suction in the field, effects of soil suction on the resilient modulus are generally not accounted for in existing testing methods. In this study, MR values of a subgrade soil under various stress and suction conditions were investigated using a suction-controlled cyclic triaxial apparatus. To enhance the accuracy of measurements, Hall-effect transducers were employed to monitor the local axial and radial deformation of each specimen. It was found that MR increases with number of load applications when a soil contracts, but decreases slightly when a soil dilates. When suction increases, the soil response tends to change from contractive to dilative due to suction-induced dilatancy. Moreover, the measured MR is highly dependent on the stress state. It decreases with cyclic stress due to the nonlinearity of the soil stress-strain behaviour, but increases significantly with suction due to the presence of water tension. At the same stress and suction conditions,MR measured along the wetting path is generally larger than that measured along the drying path. A new semi-empirical equation representing the stress-dependency of MR is proposed and was verified using experimental results of four different soils.

Original languageEnglish
Pages (from-to)223-232
Number of pages10
JournalCanadian Geotechnical Journal
Issue number2
Publication statusPublished - 1 Jan 2013
Externally publishedYes


  • Cyclic loading-unloading
  • Matric suction
  • Net stress
  • Resilient modulus
  • Unsaturated subgrade soil
  • Wetting and drying

ASJC Scopus subject areas

  • Civil and Structural Engineering
  • Geotechnical Engineering and Engineering Geology


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