Triaxial Strength Assessment of Geomaterials

Triaxial strength assessment evaluates the mechanical behaviour of soils, rocks and other geomaterials under controlled combinations of three principal stresses. Conventional triaxial tests impose equal lateral confinements while varying axial stress, whereas true triaxial testing independently controls the intermediate principal stress, enabling more realistic simulation of in-situ stress conditions. These tests underpin the development and calibration of strength criteria, such as the Mohr–Coulomb and Hoek–Brown formulations, and inform numerical models for stability analysis in tunnelling, slope design, deep mining and underground storage. Advances in acoustic emission monitoring, microcrack imaging and pore‐pressure coupling have elucidated the progressive damage mechanisms across brittle to ductile regimes. Non-linear strength envelopes derived from stress-dependent cohesion and friction parameters now better capture the transition from initial crack closure through stable crack growth to ultimate failure. The integration of true triaxial data into three-dimensional failure criteria accounts for the often-neglected influence of the intermediate principal stress, yielding more accurate predictions of peak strength, post-peak softening and residual behaviour. Such improvements in experimental protocols and constitutive models have global significance for risk mitigation in civil and mining engineering, geological carbon sequestration, geothermal exploitation and nuclear waste disposal.

Research from Nature Portfolio

Recent work has employed true triaxial compression tests on sandstone to resolve the influence of the intermediate principal stress on deformation and progressive damage. Volume strain and acoustic emission analyses showed that under conventional triaxial conditions, crack growth and volume change accelerate with increased confinement, whereas under true triaxial conditions the intermediate stress initially suppresses lateral expansion but eventually promotes anisotropic microcrack evolution. A three-dimensional theoretical model incorporating microcrack defects successfully reproduced these trends, revealing how stress paths govern the shift between stable and unstable crack growth stages.

Triaxial Strength Assessment of Geomaterials publication trend

The graph below shows the total number of articles in triaxial strength assessment of geomaterials across all publications each year (not limited to Nature Index journals).

Technical terms

Principal stresses (σ1, σ2, σ3): The maximum, intermediate and minimum normal stresses acting on mutually orthogonal planes.

Confining pressure: The uniform lateral stress applied during conventional triaxial tests.

True triaxial test: An experimental method that independently controls all three principal stresses to simulate realistic subsurface conditions.

Mohr–Coulomb criterion: A linear strength model defined by cohesion and friction angle that predicts failure under biaxial stress states.

Hoek–Brown criterion: A non-linear empirical strength criterion for rocks, incorporating material constants and principal stress dependencies.

References

1. Stress-dependent instantaneous cohesion and friction angle for the Mohr–Coulomb criterion. International Journal of Mechanical Sciences (2024).
2. Experimental investigation on True Triaxial Deformation and Progressive Damage Behaviour of Sandstone. Scientific Reports (2019).
3. A modified three-dimensional Hoek–Brown criterion for intact rocks and jointed rock masses. Geomechanics and Geophysics for Geo-Energy and Geo-Resources (2023).
4. A conceptual three-dimensional frictional model to predict the effect of the intermediate principal stress based on the Mohr-Coulomb and Hoek-Brown failure criteria. International Journal of Rock Mechanics and Mining Sciences (2023).