How Triaxial Testing Helps Predict Soil Behaviour

Our advanced automated triaxial testing systems provide comprehensive solutions for all sample sizes—disturbed or undisturbed—while adhering to specific client requirements and failure criteria. Here’s a breakdown of our key testing methods:

AS 1289.6.4.1 | CU Triaxial 
Ideal for determining friction angle (ϕ), cohesion (c'), and pore water pressure (pwp) in saturated cohesive soils under undrained conditions.

AS 1289.6.4.1 | UU Triaxial
Focused on undrained shear strength (Su) for unsaturated soils under undrained conditions.

ASTM D7181-11 | CD Triaxial
Suitable for determining drained shear strength after sample consolidation under controlled drainage.

In geotechnical engineering, the Consolidated Undrained (CU) triaxial test is a fundamental tool for understanding soil behaviour under real-world undrained conditions, critical for projects like embankments, foundations, and retaining walls.

One of the key outcomes of the CU triaxial test is the Mohr’s circle, a graphical tool that helps us visualise the stresses within the soil sample at failure. Here’s why Mohr’s circle matters: 

Visualising Stress
Mohr’s circle plots the relationship between normal stress and shear stress, giving us a clear picture of how the soil is likely to fail. In the CU test, we use both total and effective stress circles to account for pore water pressure, a critical factor in soil strength. 

Failure Criteria
By analysing multiple Mohr’s circles from different test conditions, we can establish the failure envelope, which helps us determine the soil’s shear strength parameters—the cohesion and angle of internal friction. These values are crucial for design in geotechnical projects. 

Practical Application
Whether you’re designing foundations for a building or evaluating slope stability, understanding the relationship between stress and failure through Mohr’s circle helps engineers predict when and how soils will fail, ensuring more resilient designs.