Micromechanical-Based Shear Strength Equation Considering the Stress-State Effect for Unsaturated Soils
Publication: International Journal of Geomechanics
Volume 22, Issue 9
Abstract
Unsaturated soil shear strength is a crucial and useful parameter for predicting geostructure stability, soil erosion, seasonal variation, and land management. Unsaturated shear strength measurement, however, is frequently costly, complex, and time-consuming. The main objective of this paper is to present a new generalized equation for the shear strength estimation of unsaturated soils. The proposed equation is derived from a micromechanical equilibrium condition considering the interaction of air, water, and solid phases. The particle contact area effect is taken into account in the proposed model, even though it is thought to be negligible in existing equations. In comparison with existing equations, the proposed one has the benefit of being able to capture the nonlinear influence of saturation degree and matric suction on unsaturated shear strength. The proposed equation is compared with several other existing equations as well as experimental data for four different soil types to verify its validity. The findings indicate that the proposed equation has a potential application in estimating unsaturated soil shear strength and that it outperforms existing equations. The stress state also has a substantial impact on the shear strength properties of unsaturated soils, which was extended to include in the proposed equation. The results reveal that the proposed equation is capable of accurately predicting the variation of the soil–water characteristic curve and unsaturated soil shear strength as a function of the stress state.
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Acknowledgments
The author would like to acknowledge the financial support from Heriot-Watt University, UK. The author is grateful to the reviewers for giving constructive and insightful suggestions, which have helped greatly improve the quality of this paper.
Notation
The following symbols are used in this paper:
- u
- pore pressure (Pa);
- ua
- pore-air pressure (Pa);
- (ua – uw)
- matric suction (Pa);
- uw
- pore-water pressure (Pa);
- V
- total soil volume (m3);
- Vv
- void volume (m3);
- Vw
- volume occupied by the water phase (m3);
- δ
- calibrated parameter considering the real shape and orientation of particles (dimensionless);
- θ
- volumetric water content (dimensionless);
- θe
- effective volumetric water content (dimensionless);
- θr
- volumetric water content at residual suction (dimensionless);
- θs
- saturated volumetric water content (dimensionless);
- σ
- total stress (Pa);
- σ′
- effective stress (Pa);
- (σ – ua)
- net normal stress (Pa);
- τ
- shear strength (Pa); and
- ϕ′
- angle of internal friction (degree).
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Published In
International Journal of Geomechanics
Volume 22 • Issue 9 • September 2022
Copyright
© 2022 American Society of Civil Engineers.
History
Received: Jul 26, 2021
Accepted: Mar 30, 2022
Published online: Jun 30, 2022
Published in print: Sep 1, 2022
Discussion open until: Nov 30, 2022
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