Abstract
Glacial tills are widely distributed in Tibet, China, and are highly susceptible to landslides under intense rainfalls. Failures of the slope during rainfall are closely related to the shear behavior of glacial tills at different moisture conditions. This study investigates the shear behavior and critical state of saturated and unsaturated glacial tills through a series of drained direct shear tests. The tests were conducted on two types of compacted glacial tills with different water contents and total normal stresses. A strain softening mode of failure is observed for all water content conditions accompanied by noticeable dilation. Dilatancy is found to decrease with increasing water content. Unsaturated samples showed increased rates of dilation as water content is decreased for all applied normal stresses a behavior which cannot be predicted well by classical stress-dilatancy models. Furthermore, it was found that the Critical State Line (CSL), plotted on the (e-lnσn) plane, can be used to define the shear behavior of unsaturated glacial tills at different water contents. The CSL of saturated glacial tills run parallel to this line. The experimental results in this study are aimed to provide a basic understanding to the underlying failure mechanisms of glacial tills.
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Abbreviations
- c′:
-
True cohesion of saturated soil
- C c :
-
Coefficient of curvature
- C u :
-
Uniformity coefficient
- c p :
-
Apparent peak cohesion
- d 10 :
-
Effective diameter
- d 30 :
-
Continuous diameter
- d 50 :
-
Average diameter
- d 60 :
-
Constrained diameter
- σ n :
-
Total normal stress
- σ′n :
-
Effective normal stress
- e :
-
Initial void ratio
- e c :
-
Consolidation void ratio
- e s :
-
Shear void ratio
- ρ s :
-
Particle density
- I p :
-
Plastic index
- p′:
-
Effective mean stress
- s :
-
Matric Suction
- S r :
-
Degree of saturation
- S e r :
-
Effective degree of saturation
- u a :
-
Pore-air pressure
- u w :
-
Pore-water pressure
- V w :
-
Volumetric water content
- w :
-
Water content
- W L :
-
Liquid limit
- W p :
-
Plastic limit
- ρ d :
-
Dry density
- τ :
-
Shear strength
- τ p :
-
Peak strength
- τ c :
-
Critical strength
- φ′:
-
Effective angle of shearing resistance
- φ p :
-
Peak angle of friction
- φ c :
-
Critical angle of friction
- φ′c :
-
Effective critical state friction angle
- φ b :
-
Angle of shearing resistance with respect to the matric suction
- Ψ :
-
Dilation angle
- Ψmax :
-
Maximum angle of dilation
- x :
-
Horizontal displacement
- χ :
-
Effective stress parameter
- y :
-
Vertical displacement
- h :
-
Height of sample
- ε :
-
Vertical strain
- θ :
-
Soil volumetric water content
- θ s :
-
Saturated volumetric water content
- θ r :
-
Residual state volumetric water content
- δx :
-
Increment of horizontal displacement
- δy :
-
Increment of vertical displacement
- λ u :
-
Slope of unsaturated critical state line
- λ s :
-
Slope of saturated critical state line
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Acknowledgements
The authors acknowledge the financial support from the Key Research Program of Frontier Sciences, Chinese Academy of Sciences (CAS) (grant no. QYZDB-SSW-DQC010) and the Youth Innovation Promotion Association, Chinese Academy of Sciences (CAS).
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Zhou, G.G.D., Chen, Ll., Mu, Qy. et al. Effects of water content on the shear behavior and critical state of glacial till in Tianmo Gully of Tibet, China. J. Mt. Sci. 16, 1743–1759 (2019). https://doi.org/10.1007/s11629-019-5440-9
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DOI: https://doi.org/10.1007/s11629-019-5440-9