The specific weight of sand varies depending primarily on its moisture content. Based on typical values, including those referenced from sources like Quora, the specific weight of sand is approximately 15.1 to 15.7 kN/m³ when dry and 17.3 to 19.6 kN/m³ when wet.
Understanding Specific Weight and Density
It's important to distinguish between specific weight and density, although the terms are sometimes used interchangeably in practical contexts.
- Density (ρ) is the mass per unit volume, typically measured in kilograms per cubic meter (kg/m³) or pounds-mass per cubic foot (lb/ft³).
- Specific Weight (γ) is the weight per unit volume, which is the density multiplied by the acceleration due to gravity ($ \gamma = \rho \times g $). It is typically measured in Newtons per cubic meter (N/m³) or pounds-force per cubic foot (lb/ft³).
The referenced information provides values for "unit weight" in kg/m³, which are technically units of density. To find the specific weight in kN/m³, we multiply the density by the standard acceleration due to gravity ($ g \approx 9.81 \, m/s^2 $) and convert from N to kN (1 kN = 1000 N).
Specific Weight of Sand Based on Reference Data
The provided reference states the following values, described as "unit weight" but given in density units (kg/m³):
- Sand dry: 1540 to 1600 kg/m³
- Sand wet: 1760 to 2000 kg/m³
Using the standard acceleration due to gravity ($ g \approx 9.81 \, m/s^2 $), we can calculate the specific weight:
- Dry Sand Specific Weight:
- Minimum: $ 1540 \, kg/m³ \times 9.81 \, m/s² = 15107.4 \, N/m³ \approx 15.1 \, kN/m³ $
- Maximum: $ 1600 \, kg/m³ \times 9.81 \, m/s² = 15696 \, N/m³ \approx 15.7 \, kN/m³ $
- Wet Sand Specific Weight:
- Minimum: $ 1760 \, kg/m³ \times 9.81 \, m/s² = 17265.6 \, N/m³ \approx 17.3 \, kN/m³ $
- Maximum: $ 2000 \, kg/m³ \times 9.81 \, m/s² = 19620 \, N/m³ \approx 19.6 \, kN/m³ $
Here's a summary table of these values:
| Condition | Density (from reference) (kg/m³) | Calculated Specific Weight (kN/m³) |
|---|---|---|
| Dry Sand | 1540 to 1600 | 15.1 to 15.7 |
| Wet Sand | 1760 to 2000 | 17.3 to 19.6 |
(Note: Values are rounded to one decimal place for simplicity).
Factors Influencing Sand Specific Weight
Beyond moisture content, other factors can affect the specific weight of sand:
- Grain Size Distribution: The mix of particle sizes can affect how densely the sand can pack.
- Particle Shape: Angular sand grains may not pack as tightly as rounded grains.
- Compaction: How much the sand is compacted directly impacts its density and thus its specific weight. A well-compacted sand will have a higher specific weight than loose sand of the same type and moisture content.
- Mineral Composition: While the difference is usually small compared to moisture content, the specific gravity of the mineral grains themselves can slightly vary.
In summary, the specific weight of sand is not a single fixed number but rather a range, primarily dependent on whether it is dry or saturated with water, and influenced by other characteristics like compaction and grain properties. Wet sand is significantly heavier per unit volume than dry sand due to the added mass of water filling the pore spaces.
