Meet the Expert: A Conversation with Zhan Tang on Triaxial Testing

At Civiltest, advanced laboratory testing plays a vital role in helping engineers make informed design decisions. We sat down with Zhan Tang, Chartered Geotechnical Engineer and Technical Development Manager, to learn more about triaxial testing, why it matters, and what goes on behind the scenes in our geotechnical laboratory.

Can you introduce yourself and tell us about your role?

I'm Zhan Tang, a Chartered Geotechnical Engineer and Technical Development Manager at Civiltest. My role combines geotechnical consulting, field investigations, advanced laboratory testing, technical review, and the development of new testing and reporting capabilities.

How long have you been involved with triaxial testing?

I first became involved in triaxial testing more than 10 years ago during my PhD research. Since then, I've continued applying and developing the method in commercial geotechnical practice, with a particular interest in connecting laboratory behaviour to real project risks and design requirements.

For those unfamiliar with it, what is triaxial testing?

Triaxial testing is one of the most comprehensive laboratory methods available for understanding how soils behave under load.

The test places a cylindrical soil specimen under controlled confining pressure while applying an axial load, allowing us to recreate the stress conditions that occur underground. By carefully controlling drainage and loading conditions, we can measure a range of engineering properties including:

• Shear strength
• Stress-strain behaviour
• Soil stiffness
• Cohesion and friction angle
• Pore water pressure response
• Failure mechanisms

Depending on the testing program, we can also investigate consolidation, permeability, creep behaviour, resilient modulus and other advanced soil characteristics.

What types of projects typically require triaxial testing?

Triaxial testing is commonly used on projects where understanding soil behaviour is critical to the design. That includes:

• Slope stability assessments
• Embankments
• Retaining structures
• Deep excavations
• Foundation design
• Working platforms
• Major civil infrastructure
• Mining and resource developments

It's particularly valuable on technically complex or higher-risk projects where drainage conditions, construction sequencing or long-term ground performance can significantly influence the design.

Civiltest performs several different types of triaxial testing. Can you explain the differences?

We perform the three principal forms of triaxial testing, each designed to simulate different field conditions.

Unconsolidated Undrained (UU)

UU testing measures the short-term undrained strength of soil. The specimen isn't consolidated or allowed to drain before or during shearing, making it well suited to situations where rapid loading occurs or where fast turnaround is needed.

Consolidated Undrained (CU)

CU testing allows the specimen to consolidate before shearing while monitoring pore water pressures throughout the test. This provides both total stress and effective stress parameters, making it one of the most widely used methods for engineering design.

Consolidated Drained (CD)

CD testing allows the specimen to fully consolidate and drain during shearing, providing parameters that represent long-term soil behaviour. These tests take considerably longer, particularly for low-permeability clays, but they provide valuable information where long-term performance is important.

What happens behind the scenes during a triaxial testing program?

There's a lot more involved than simply placing a sample into a testing machine.

Every project begins with understanding the engineering objectives and reviewing the available site information. From there we select representative specimens, prepare and trim the samples, calibrate the equipment, saturate and consolidate the specimens, carefully monitor the testing process and then interpret the results in the context of the engineering problem we're trying to solve.

The laboratory procedure is only one part of the process, the engineering judgement behind the testing is just as important.

What's the biggest challenge when undertaking triaxial testing?

The real challenge is understanding the project requirements and designing the test to answer the right engineering questions. The better we understand the site conditions and intended use of the results, the more meaningful and valuable the outcome becomes.

How do clients benefit from triaxial testing?

The results provide engineers with reliable, project-specific design parameters rather than relying solely on published values or assumptions.

That information supports:

• Foundation design
• Retaining wall design
• Slope stability analysis
• Excavation assessments
• Embankment design
• Working platform design
• Numerical modelling

Ultimately, better quality data leads to safer, more efficient and more economical designs.

What do you enjoy most about this area of geotechnical engineering?

I enjoy the problem-solving involved in developing the full potential of triaxial testing. Reading technical papers, research and industry developments continually gives me ideas for improving our own methods and interpretation.

Combining careful specimen preparation, advanced laboratory testing and engineering judgement gives the work a real sense of craftsmanship, and it's rewarding knowing the results directly contribute to better engineering outcomes for our clients.