Unconfined Compressive Strength (UCS) & Indirect Tensile Strength (ITS) Testing

Atlas Engineering and Technology Group provides comprehensive geotechnical testing services across Sydney, Australia, including precise Unconfined Compressive Strength (UCS) and Indirect Tensile Strength (ITS) testing for soil and rock materials. These tests are fundamental in understanding a site's mechanical properties and form a critical component of geotechnical investigations and engineering design. Our experienced team utilises state-of-the-art equipment to deliver accurate and reliable data, ensuring your project is built on a solid foundation.

Unconfined Compressive Strength (UCS) Testing

What is UCS Testing?

Unconfined Compressive Strength (UCS) testing is a laboratory method used to determine the maximum axial compressive stress that a cylindrical specimen of soil or rock can sustain under unconfined conditions. It is a key indicator of the material's strength and is represented by the symbol $q_u$.

Why is UCS Testing Important?

Understanding the UCS of soil and rock is crucial for:

• Foundation Design: Assessing the bearing capacity of soils and rock for shallow and deep foundations.
• Slope Stability Analysis: Evaluating the stability of natural slopes, embankments, and cuttings.
• Earthwork Construction: Guiding the selection and compaction control of fill materials.
• Material Classification: Assisting in the classification of cohesive soils and intact rock strength.
• Preliminary Design: Providing essential parameters for the initial design of retaining walls, tunnels, and other geotechnical structures.

Materials Tested

UCS testing is typically performed on:

• Cohesive soils (e.g., clay, silt)
• Intact rock core samples

Testing Workflow

1. Receive & log in samples
2. Trim, end-cap and measure geometry & mass
3. Saturate/condition as specified
4. Axial or diametral loading to failure (0.5–2 MPa/s)
5. Plot stress–strain curves
6. Quality review & certification

Indirect Tensile Strength (ITS) Testing

What is ITS Testing?

Indirect Tensile Strength (ITS) testing is a laboratory method used to determine the tensile strength of brittle materials. Instead of applying direct tension (which is difficult for rock and soil), a compressive line load is applied along the diameter of a cylindrical specimen. This induces a tensile stress perpendicular to the loading direction, causing the specimen to fail in tension. The ITS is represented by the symbol $\\sigma_t$.

Why is ITS Testing Important?

ITS testing provides vital information for:

• Rock Mechanics: Assessing the tensile strength of rock, critical for designing tunnels, rock slopes, and understanding rock mass behaviour under tensile stress conditions (e.g., hydraulic fracturing).
• Pavement Design: Evaluating the tensile strength of stabilised soils, asphalt, and concrete, which influences their cracking resistance and durability.
• Brittle Material Characterisation: Understanding the failure mechanisms of materials that are strong in compression but weak in tension.

Materials Tested

ITS testing is commonly performed on:

• Rock core specimens
• Stabilised soil specimens
• Concrete cylinders or cores
• Asphalt cores

The ITS Testing Process (Simplified)

1. A cylindrical disc-shaped specimen is prepared.
2. The specimen is placed on its side between the platens of a compression testing machine.
3. A compressive load is applied diametrically at a constant rate until the specimen splits or fractures due to tensile stresses.
4. The maximum load applied at failure is recorded.
5. The indirect tensile strength is calculated using a formula that relates the failure load, specimen diameter, and thickness. For a cylindrical specimen, the formula is $\\sigma_t = \\frac{2P}{\\pi DL}$, where $P$ is the load at failure, $D$ is the specimen diameter, and $L$ is the specimen thickness.

Key Information from UCS and ITS Testing

A summary of the key parameters and applications: