Poly-Axial (True Triaxial) Rock Testing Equipment
Testing accessories and preparation equipment
RPX-150 Poly-Axial (True Triaxial) Rock Testing Fixture

The GCTS RPX-150 Polyaxial Rock Testing Fixture can be used to study the intermediate principal stress effect on rock engineering behavior and describe the strength of the rock under a general system of polyaxial compressive stresses. This fixture enhances the capabilities of GCTS rock triaxial systems.


  • Stainless steel construction.
  • Perform poly-axial (true triaxial) tests within GCTS rock triaxial cell.
  • Independent control of σ1, σ2, σ3 (where σ1≠σ2≠σ3) or e1, e2, e3 or a combination of stress or strain control for each axis.
  • Measures strains in all three orthogonal directions.
  • Accommodates cubical or cylindrical rock specimens with maximum dimensions of 38.1 mm x 38.1 mm x 76.2 mm or 38.1 mm diameter by 76.2 mm height.
  • Stress control up to 70 MPa.
  • Available ultrasonic sensors to measure P and S wave velocities under different stress states.
  • Optional hydraulic fracturing platens available to perform wellbore stability tests.
  • Customized fixtures available to fit existing triaxial cells.
  • GCTS also offers stand-alone, large scale polyaxial (true triaxial) systems built to customer specifications.

The GCTS RPX-150 Polyaxial fixture can be used to study the intermediate principal stress effect on rock engineering behavior and describe adequately the strength of rock under a general system of Polyaxial compressive stresses. The RPX-150 is a simple and economical fixture that enhances the capabilities of standard GCTS Rock Triaxial systems that includes both, cell and pore pressure control. This fixture is designed to fit inside GCTS triaxial cells and use the load frame to (typically) apply σ1, the cell pressure to apply σ2 and the pore pressure system to apply σ3 through the fixture’s flat jacks.


GCTS also offer semi-circular platens to test cylindrical specimens together with GCTS hydraulic fracturing fixtures and approximate the effects of anisotropic stress state on borehole stability. Even though the stress state applied with these semicircular loading jacks is not uniform, it is much easier to prepare and test cylindrical specimens.


Ultrasonic sensors can also be provided to study the effects anisotropic stress conditions on compression and shear wave velocities. Velocities for all three axes can easily be measured during Polyaxial tests with this option.


Please contact GCTS for details on the RPX-150 and compatibility with your triaxial system.

Please contact GCTS for full specifications.