Effect of freeze-thaw cycles on water permeability of sand mixtures with nanoclay
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2024-03-29 |
| Journal | ARCTIC AND SUBARCTIC NATURAL RESOURCES |
| Authors | А Л Невзоров, Yu. V. Saenko, A. M Shiranov, Sergey Churkin |
| Institutions | Northern (Arctic) Federal University |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”This study investigates the durability and performance of sand mixtures stabilized with highly dispersed saponite clay (nanoclay waste) when subjected to cyclic freezing and thawing, focusing on their application as protective liners for solid waste isolation.
- Core Value Proposition: The mixtures offer a homogeneous, low-permeability alternative to natural clayey soils for landfill liners, utilizing industrial waste (saponite from diamond ore processing).
- Permeability Degradation: Five freeze-thaw cycles caused a significant increase in hydraulic conductivity ($k_f$) for all tested mixtures, confirming the vulnerability of saturated clay barriers to frost action.
- Low Load Performance (4% Clay, 2 kPa): Under minimal load, $k_f$ increased substantially (2.0 to 4.7 times). This was correlated with high frost heave (10.0-16.4%), indicating severe structural damage from ice lens formation.
- High Load Performance (8% Clay, 12 kPa): Applying a higher external load (12 kPa, simulating 0.7 m of overburden) effectively suppressed frost heave (reduced to 3.0-4.8%) and limited the $k_f$ increase to a more acceptable range (1.2-2.0 times).
- Mitigation Strategy: To maintain barrier integrity in cold climates, the protective liner must be covered by an inert soil layer sufficient to reduce the depth of frost penetration and apply a minimum overburden pressure of 12 kPa or greater.
- Material Performance: Even after cycling, the 8% clay mixtures under 12 kPa load maintained extremely low permeability, performing 13 to 516 times better than the original sand materials.
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| Clay Type | Saponite | - | Waste from diamond ore processing |
| Clay Particle Size | < 0.001 | mm | 92-94% of solid phase |
| Clay Content Tested | 4 and 8 | % | By mass of sand solids |
| Sample Dimensions (H x D) | 100 x 70 | mm | Cylindrical specimen |
| Initial Permeability ($k_o$) Range (4% clay) | 0.022 to 0.10 | m/day | Varies by sand type |
| Initial Permeability ($k_o$) Range (8% clay) | 1.4 x 10-3 to 64 x 10-3 | m/day | Varies by sand type |
| External Load (Low) | 2 | kPa | Used for 4% clay tests |
| External Load (High) | 12 | kPa | Used for 8% clay tests (approx. 0.7 m soil equivalent) |
| Frost Heave (4% clay, 2 kPa) | 10.0-16.4 | % | Relative to 50 mm freezing depth |
| Frost Heave (8% clay, 12 kPa) | 3.0-4.8 | % | Relative to 50 mm freezing depth |
| Permeability Increase ($k_f / k_o$) (4% clay) | 2.0-4.7 | times | After 5 freeze-thaw cycles |
| Permeability Increase ($k_f / k_o$) (8% clay) | 1.2-2.0 | times | After 5 freeze-thaw cycles |
| Freezing Chamber Temperature | -5 to -6 | °C | Maintained during freezing phase |
| Water Reservoir Temperature | 1.0-1.5 | °C | Maintained during freezing phase |
| Thawing Temperature | +20 | °C | Maintained for 4 hours for complete thaw |
| Freezing Front Speed (Observed) | ~15 | mm/day | Average rate during testing |
Key Methodologies
Section titled “Key Methodologies”- Sample Preparation and Compaction: Four types of sand were mixed with saponite clay suspension (4% or 8% solids content) and compacted into 100 mm high, 70 mm diameter cylindrical specimens, achieving a compaction coefficient of 0.94-0.96.
- Custom Apparatus: Experiments utilized a patented laboratory setup consisting of four combined frost heave and permeability devices placed in a water reservoir within a freezer. Thermistors monitored temperature profiles at 0, 25, 50, and 75 mm depths.
- Initial Permeability Determination: Saturated samples were tested at 1.0-1.5 °C using upward flow (constant head gradient up to 15) to establish the initial hydraulic conductivity ($k_o$).
- Controlled Freezing: The water level in the reservoir was gradually lowered at a programmed rate (10 mm/day) while the chamber temperature was maintained at -5 °C to -6 °C. This controlled the movement of the freezing front to simulate natural conditions.
- External Load Application: Samples were tested under external loads of either 2 kPa (low load) or 12 kPa (high load) applied via a stamp, simulating overburden pressure.
- Cyclic Testing: Five complete freeze-thaw cycles were performed. Frost heave was measured continuously during freezing.
- Controlled Thawing: To ensure complete melting of ice lenses, the water level was raised, and the chamber temperature was increased to +20 °C for 4 hours during the thawing phase.
- Final Permeability Determination: After the fifth cycle, the final hydraulic conductivity ($k_f$) was measured. The permeability of the cyclically frozen upper half of the sample ($k_1$) was calculated using the two-layer filtration model.
Commercial Applications
Section titled “Commercial Applications”The research findings and methodology are highly relevant to geotechnical and environmental engineering, particularly in cold climates:
- Landfill Barrier Systems: Designing and constructing durable, low-permeability base liners and final covers for Municipal Solid Waste (MSW) and Industrial Solid Waste (ISW) landfills, especially in Arctic and Subarctic regions.
- Contaminant Isolation: Utilizing sand-nanoclay mixtures as effective hydraulic barriers for isolating contaminated soils or hazardous waste sites, leveraging the high sorption capacity often associated with saponite and montmorillonite clays.
- Resource Recovery and Waste Utilization: Implementing industrial waste streams (like saponite clay from mining operations) as a cost-effective, high-performance component in engineered geotechnical materials, promoting circular economy principles.
- Geotechnical Design in Permafrost: Providing critical data for engineers designing foundations or subsurface structures where soil stability and hydraulic properties are affected by seasonal or long-term freeze-thaw cycles.
- Protective Layer Specification: Informing the design requirements for protective soil layers (overburden) necessary to cover clay liners, specifying minimum thickness and density required to achieve the necessary confining pressure (e.g., >12 kPa) to mitigate frost heave damage.
View Original Abstract
The mixtures of sands and nanoclays are used to isolate municipal and industrial solid wastes. Compared with natural clayey soils, these mixtures are characterized by homogeneous composition, workability, and low compressibility. This study investigated the effect of freeze-thaw cycles on their permeability. The mixtures of four sands and a saponite clay suspension generated by diamond ore processing were studied. The mixtures were prepared on the basis of 4 % and 8 % clay from sand weight. The tests were performed using an apparatus consisting of four devices for measuring frost heave and permeability, which were placed in containers with water. The water level was decreased gradually to ensure sample freezing or increased to ensure sample thawing. The frost heave of the mixtures with 4 % clay was 10.0-16.4 % under an external load of 2 kPa, and the five freeze-thaw cycles resulted in an increase in the hydraulic conductivity by 2.0-4.7 times. The mixtures with 8 % clay were tested under a load of 12 kPa, because of their high frost susceptibility. The hydraulic conductivity increased by approximately the same value as in the first case, i.e., by 1.2-2.0 times. The experiments have shown that the examined mixtures are suitable for isolating wastes. However, to eliminate the above effect, a waterproof liner should be covered with inert soil, which would reduce the depth of frost penetration and apply the load on it.