NMR-Based Measurement of AWRC and Prediction of Shear Strength of Unsaturated Soils
This article has been corrected.
VIEW CORRECTIONPublication: International Journal of Geomechanics
Volume 22, Issue 9
Abstract
In recent years, accurate determination of the effective stress factor has been found to be instrumental for classifying the types of pore water and defining the form of their contribution to the unsaturated soil strength. In this study, a series of laboratory experiments based on volumetric flask, indoor evaporation and low-field nuclear magnetic resonance (NMR) methods were conducted on Wuhan clay to determine the relationship between adsorbed water content and matrix suction, and hence the adsorbed water retention curve (AWRC). The capillary water retention curve (CWRC) is the curve derived by subtracting the AWRC from the soil water characteristic curve (SWCC). This CWRC is then utilized to obtain correlation between the degree of saturation of capillary pores (Scap) and the matrix suction. The effective stress factor was replaced with Scap for determining the shear strength of Wuhan clay with three different dry densities. It was observed that the predicted values of shear strength obtained by NMR-based methods are more accurate than two other methods available in the literature. Furthermore, the accuracy of the method is not impacted by changes in dry density or confining pressure.
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Acknowledgments
The research was supported by the Nation Natural Science Foundation of China (Grant No. 51978249) and the Innovation Group Project of Hubei Science and Technology Department (Grant No. 2020CFA046), and the International Collaborative Research Fund for Young Scholars in the Innovation Demonstration Base of Ecological Environment Geotechnical and Ecological Restoration of Rivers and Lakes.
Notation
The following symbols are used in this paper:
- cs
- pore shape factor;
- c′
- effective cohesion;
- D
- diffusion coefficient of water in pores;
- d
- pore diameter;
- ms
- weight of dry soil;
- N
- number of measured points;
- S
- degree of saturation;
- S/V
- specific surface area of pores;
- Se
- effective saturation;
- TE
- echo time;
- Ts
- surface tension of water;
- T2
- relaxation time;
- T2b
- bound pool T2 relaxation time;
- ua
- pore air pressure;
- uw
- pore water pressure;
- VA
- volume of sample;
- Vw
- total amount of pore water;
- wa
- adsorbed water content;
- xi
- measured value of ith saturation;
- predicted value of ith saturation;
- α
- soil–water contact angle;
- γ
- proton gyromagnetic ratio;
- ΔV
- volume change in volumetric flask;
- ΔVw
- water content increment;
- θ
- volumetric water content of soil in unsaturated state;
- θr
- residual water content;
- θs
- volumetric water content of soil in saturated state;
- ρwe
- density of adsorbed water;
- ρwt
- density of capillary and free water;
- ρ2
- transverse relaxation rate;
- ΣS
- cumulative signal amount;
- σ
- total stress;
- τ
- effective shear stress;
- φ′
- effective internal friction angle;
- χ
- effective stress factor; and
- ψ
- soil suction.
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International Journal of Geomechanics
Volume 22 • Issue 9 • September 2022
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© 2022 American Society of Civil Engineers.
History
Received: Oct 26, 2021
Accepted: Apr 24, 2022
Published online: Jul 7, 2022
Published in print: Sep 1, 2022
Discussion open until: Dec 7, 2022
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