Grading – Particle Size Distribution

At Atlas Engineering and Technology Group, we provide comprehensive particle size distribution (PSD) testing, also known as grading analysis, for a wide range of soil and aggregate materials. Understanding the grading of materials is crucial for assessing their engineering properties and suitability for various construction and geotechnical applications across Sydney.

The Importance of Particle Size Distribution

Particle size distribution significantly influences the' physical and mechanical behaviour of soils and aggregates. Accurate PSD analysis helps determine:

  • Soil classification (e.g., according to AS 1726).
  • Permeability and drainage characteristics.
  • Shear strength and compressibility.
  • Workability and compaction properties.
  • Suitability as fill, base course, concrete aggregates, or filter materials.
  • Susceptibility to frost heave, erosion, or liquefaction.

Our Particle Size Distribution Testing Methods

Atlas Engineering and Technology Group conducts PSD testing in accordance with relevant Australian Standards, ensuring reliable and accurate results. Our primary methods include:

Sieve Analysis (AS 1289.3.6.1)

This method is used to determine the grain size distribution of coarse-grained soils (e.g., gravels and sands) and aggregates. The material is passed through a series of standard test sieves with progressively smaller mesh openings. The weight of material retained on each sieve is measured to calculate the percentage passing.

Hydrometer Analysis (AS 1289.3.6.3)

Hydrometer analysis is employed for fine-grained soils (e.g., silts and clays), where sieving is not practical for the finest particles. This method is based on the sedimentation principle, where particles settle in a liquid medium at different rates depending on their size, shape, and density.

Combined Sieve and Hydrometer Analysis

A combined analysis is performed for soils containing a mix of coarse and fine particles to provide a complete grading curve across the entire particle size range.

Understanding Your Grading Results

Particle size distribution testing results are typically presented as a grading curve on a semi-logarithmic chart. This visual representation helps in:

  • Classifying the soil or aggregate.
  • Comparing the material against project specifications or standard requirements.
  • Deriving key parameters such as:
    • D10 (adequate size): Particle diameter at which 10% of the material is finer.
    • D30: Particle diameter at which 30% of the material is finer.
    • D60: Particle diameter at which 60% of the material is finer.
    • Coefficient of Uniformity (Cu): ($C_u = \frac{D_{60}}{D_{10}}$)
    • Coefficient of Curvature (Cc): ($C_c = \frac{(D_{30})^2}{D_{10} \times D_{60}}$)

These parameters are essential for assessing material quality, predicting engineering behaviour, and designing various geotechnical structures like filters, drains, and pavement layers.

Applications of Particle Size Distribution Analysis

  • Soil Classification: Essential for classifying soils according to standards like AS 1726 – Geotechnical site investigations.
  • Pavement Design: Assessing the suitability of materials for road bases, sub-bases, and asphalt or concrete aggregates.
  • Earthworks and Foundations: Determining compaction characteristics and suitability of fill materials.
  • Concrete Technology: Ensuring aggregates meet concrete's strength, durability, and workability specifications.
  • Filter Design: Designing effective granular filters for drainage and earth retaining structures.
  • Environmental Assessments: Characterising soil for contaminant transport studies.