Void Ratio Calculator
Free Void ratio Calculator for soil & sediment mechanics. Enter variables to compute results with formulas and detailed steps.
Formula
Void Ratio (e) = Vv / Vs
Void ratio equals the volume of voids divided by the volume of solids. It can also be calculated from porosity: e = n / (1 - n), or from dry density: e = (Gs x gamma_w / gamma_d) - 1, where Gs is specific gravity of solids and gamma_w is the unit weight of water.
Worked Examples
Example 1: Sandy Soil Sample
Problem: A soil sample has void volume of 35 cm3 and solid volume of 65 cm3.
Solution: Void Ratio = Vv / Vs = 35 / 65 = 0.538\nPorosity = Vv / (Vv + Vs) = 35 / 100 = 35%\nDry Density = (2.65 / (1 + 0.538)) x 1000 = 1723 kg/m3\nThis is a medium-density sand.
Result: Void ratio: 0.538 | Porosity: 35% | Medium density
Example 2: Soft Clay Analysis
Problem: A clay sample has void volume of 55 cm3 and solid volume of 45 cm3. Gs = 2.70.
Solution: Void Ratio = 55 / 45 = 1.222\nPorosity = 55 / 100 = 55%\nDry Density = (2.70 / (1 + 1.222)) x 1000 = 1215 kg/m3\nHigh void ratio indicates a loose, compressible clay.
Result: Void ratio: 1.222 | Porosity: 55% | Loose/compressible
Frequently Asked Questions
What is void ratio in soil mechanics?
Void ratio (e) is the ratio of the volume of voids (air and water spaces) to the volume of solid particles in a soil sample. Unlike porosity, which relates voids to total volume, void ratio relates voids to solids only. It can exceed 1.0, meaning there is more void space than solid material. Typical values range from 0.3 for dense gravel to 1.5 for soft clay, though organic soils and marine clays can have void ratios exceeding 3.0.
How are void ratio and porosity related?
Void ratio (e) and porosity (n) are both measures of void space but use different references. They convert between each other using: e = n / (1 - n) and n = e / (1 + e). For example, a porosity of 40% (0.4) gives a void ratio of 0.667. While porosity is bounded between 0 and 1 (or 0-100%), void ratio can theoretically range from 0 to infinity. Geotechnical engineers generally prefer void ratio because it keeps the solid volume constant in the denominator during compression.
Why do geotechnical engineers prefer void ratio over porosity?
Engineers prefer void ratio because the solid volume (denominator) remains constant when soil is compressed, while the void volume (numerator) changes. This makes mathematical relationships simpler. When soil consolidates under load, the void ratio decreases linearly on a semi-log plot against stress, producing the well-known e-log(p) curve used in settlement calculations. Porosity changes are harder to work with because both the numerator and denominator change simultaneously during compression.
What void ratio values indicate good foundation soil?
For foundations, lower void ratios generally indicate stronger, less compressible soil. Dense sands with void ratios of 0.3-0.5 are excellent foundation materials with high bearing capacity and minimal settlement. Medium-density soils (e = 0.5-0.8) are acceptable for most structures. Loose soils with void ratios above 0.8 may require ground improvement. Clays with void ratios above 1.0 are highly compressible and prone to significant long-term settlement under loading.
How is void ratio measured in the laboratory?
Void ratio is typically determined from phase relationships using measured quantities. The most common method involves measuring the dry density of an undisturbed soil sample and the specific gravity of solids: e = (Gs * gamma_w / gamma_d) - 1. Alternatively, it can be found directly from volume measurements using a wax-coated sample for total volume and an oven-dried weight for solid volume. In consolidation tests, void ratio changes are tracked continuously as load is applied.
What formula does Void Ratio Calculator use?
The formula used is described in the Formula section on this page. It is based on widely accepted standards in the relevant field. If you need a specific reference or citation, the References section provides links to authoritative sources.