Triaxial & Stress Path Test System

The triaxial test method determines the shear strength and stress-strain relationship (or stiffness) of cylindrical saturated cohesive (typically) soil samples. The three common triaxial tests are the consolidated undrained (CU), consolidated drained (CD) and unconsolidated undrained (UU). The CU and CD tests incorporate all phases of saturation, consolidation and shearing while allowing effective stress control and measurement. The CU test is the most popular method offering faster rate of shearing compared to the CD test due to monitoring of excess pore pressure change. The UU test is the fastest and simplest and only allows total stresses to be controlled and measured. Test type is typically chosen based on soil type and project timeline, but CU and CD are considered superior tests.

In terms of application, triaxial compression testing is often used to provide strength information at the top of a slope or embankment, while triaxial extension is considered for the toe or base of the slope or embankment. When compared to the direct shear test, triaxial is considered more versatile, allows drainage to be well controlled and the failure plane can occur anywhere (not just on a specific horizontal plane).