Abstract
Bentonite-sand mixtures can be used as the base material of engineered barriers in deep high-level radioactive waste geological repositories. Swelling, compression, and permeability tests were conducted out on bentonite-sand mixtures with 30%, 50%, 70% and 85% sand content. Influence of sand content and particle size on the deformation and permeability characteristics of bentonite-sand mixtures were analyzed. The sand particle size affects the deformation characteristics by influencing the vertical stress required to form a sand skeleton, and the skeleton’s stability. When the sand content is less than the critical sand content, bentonite-sand mixtures cannot form a sand skeleton, and particle size has no effect on their characteristics. When the sand content is greater than the critical sand content and the vertical stress exceeds the initial deviation stress, a sand skeleton forms. In this case, smaller the sand particle size, lesser will be the vertical stress required to form a sand skeleton, and more the swelling of bentonite-sand mixtures. Further, more uniform particle size, more stable will be its structure and lesser the compressibility of bentonite-sand mixtures. The hydraulic conductivity is related to the flow area and the seepage path length, and particle size has no obvious effect on either with the same sand content. Therefore, the sand particle size has no obvious effect on mixtures’ permeability.
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Abbreviations
- a, b :
-
Material parameters
- a v :
-
Compression coefficient between the previous level pressure and the current level pressure
- BCS :
-
Bentonite mixed with coarse-grained sand group
- BFS :
-
Bentonite mixed with fine-grained sand group
- BSS :
-
Bentonite mixed with standard sand group
- CS :
-
Coarse-grained sand group
- C u :
-
Uniformity coefficient
- C C :
-
Curvature coefficient
- D 50 :
-
Average particle size
- e 0 :
-
Initial void ratio
- e 1 :
-
Void ratio under the previous level pressure
- e i :
-
Void ratio after stabilization under all levels of loading
- e m :
-
Montmorillonite void ratio
- e max :
-
Maximum void ratio
- e min :
-
Minimum void ratio
- FS :
-
Fine-grained sand group
- G S :
-
Specific gravity
- k :
-
Hydraulic conductivity
- w 0 :
-
Initial moisture content
- ρ d0 :
-
Initial dry density
- ρ dmax :
-
Maximum dry density
- ρ dmin :
-
Minimum dry density
- ρ sb :
-
Particle density of bentonite
- ρ sm :
-
Particle density of the montmorillonite components of bentonite
- ρ sme :
-
Particle density of mixtures
- ρ snm :
-
Particle density of the non-montmorillonite components of bentonite
- ρ ss :
-
Particle density of quartz sand
- Sr 0 :
-
Initial saturation
- SS :
-
Standard sand group
- α :
-
Sand content of mixtures
- α f :
-
Critical filling sand content
- α s :
-
Critical sand content
- β :
-
Mass percentage of montmorillonite in bentonite
- δ f :
-
Free swelling rate of bentonite
- ∆e m :
-
Increase in the montmorillonite void ratio
- γ w :
-
Unit weight of wate
- σ v :
-
Vertical stress
- σ s :
-
Initial deviation stress
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Acknowledgments
The authors are grateful to the National Sciences Foundation of China (Grant No.41572284, 41977214 and 51979150) and the National Key and R&D Program of China (Grant No. 2019YFC1520500) for the financial supports.
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Lu, TH., Sun, WJ., Liu, K. et al. Effect of Sand Particle Size on Hydraulic-Mechanical Behavior of Bentonite-Sand Mixtures. KSCE J Civ Eng 26, 3287–3300 (2022). https://doi.org/10.1007/s12205-022-1271-2
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DOI: https://doi.org/10.1007/s12205-022-1271-2