Void Ratio Calculator

What is Void Ratio?

Void Ratio is a fundamental concept in geotechnical engineering, defined as the ratio of the volume of voids (spaces occupied by air or water) to the volume of solids in a soil sample. It is denoted by the symbol e and is expressed as:

e = V_v / V_s

where:

  • V_v = Volume of voids
  • V_s = Volume of solids

It indicates how much void space exists relative to the solid particles and is used to assess soil properties like porosity, compressibility, and permeability.

How to Calculate Void Ratio?

To calculate the Void Ratio, follow these steps:

  1. Determine the volume of voids (V_v): This can be found by subtracting the volume of solids (V_s) from the total volume of the soil sample (V_t). Alternatively, if the sample is saturated, the volume of voids equals the volume of water (V_w).
    • V_v = V_t – V_s
  2. Determine the volume of solids (V_s): This can be calculated using the dry weight of the soil (W_d) and the specific gravity of the soil solids (G_s) with the density of water (ρ_w, typically 1 g/cm³):
    • V_s = W_d / (G_s * ρ_w)
  3. Calculate Void Ratio (e):
    • e = V_v / V_s

Alternatively, if porosity (n) is known, Void Ratio can be calculated as:

  • e = n / (1 – n), where n = V_v / V_t.

Sample Calculation of How to Find Void Ratio?

Problem: A soil sample has a total volume of 100 cm³, a dry weight of 150 g, and a specific gravity of solids (G_s) of 2.65. The density of water is 1 g/cm³. Calculate the Void Ratio.

Solution:

  1. Find the volume of solids (V_s):
    • V_s = W_d / (G_s * ρ_w)
    • V_s = 150 / (2.65 * 1) = 56.60 cm³
  2. Find the volume of voids (V_v):
    • V_v = V_t – V_s = 100 – 56.60 = 43.40 cm³
  3. Calculate Void Ratio (e):
    • e = V_v / V_s = 43.40 / 56.60 ≈ 0.767

Answer: The Void Ratio of the soil sample is approximately 0.767.

FAQs about Void Ratio

Q1: What is a typical range for Void Ratio in soils?

  • A: Void Ratios vary depending on soil type. Loose sands may have Void Ratios around 0.6–1.0, while dense sands are closer to 0.3–0.6. Clays can have higher Void Ratios, often 0.8–2.0 or more, depending on their water content and compaction.

Q2: How does Void Ratio affect soil behavior?

  • A: A higher Void Ratio indicates more void space, leading to higher compressibility and permeability but lower shear strength. Conversely, a lower Void Ratio suggests denser, stronger soil with lower permeability.

Q3: Can Void Ratio be greater than 1?

  • A: Yes, Void Ratio can exceed 1, especially in loose or highly porous soils like clays, where the volume of voids is greater than the volume of solids.

Q4: How is Void Ratio related to porosity?

  • A: Void Ratio (e) and porosity (n) are related by the formulas:
    • e = n / (1 – n)
    • n = e / (1 + e) Porosity is the ratio of void volume to total volume, while Void Ratio compares void volume to solid volume.

Q5: Why is Void Ratio important in construction?

  • A: Void Ratio helps engineers assess soil stability, settlement potential, and drainage characteristics, which are critical for designing foundations, embankments, and other structures.