Experimental and numerical study of Kuru granite under confined compression and indentation

• Experimental and numerical studies of a granite under confining pressure and static indentation
• An elasto-plastic material model with piecewise yield functions
• The dilatancy angle of the rock linearly decreases with pressure
• The peak force of indentation increases 11% with a confining pressure of 150 MPa.
• The equivalent stress field immediately under the indenter is affected by the confining pressure

The paper presents an experimental and numerical investigation on the response of Kuru granite rock under confining compression and static indentation. Triaxial compression tests were executed at different levels of confining pressure. Indirect tensile tests were carried out with Brazilian disks, and quasi-static indentation tests with a spherical indenter were conducted. An elasto-plastic material model with piecewise yield function, plastic hardening/softening, coupled damage and non-associated plastic flow is presented and calibrated using the experimental test results. Finite element simulations of the triaxial compression tests and static indentation are performed. The influence of the material model features (e.g., the yield function and non-associativity) is discussed, and the effect of confining pressure during indentation is evaluated. It was found that, within the investigated pressure range, the dilatancy angle of the rock linearly decreased with pressure. With a saturating yield function, the simulated force-penetration curve is in good agreement with the experimental curve for the loading phase, but the simulated stiffness during unloading and the subsequent residual penetration are overestimated. The numerical simulation showed that the peak force of indentation increased approximately 11% with a confining pressure of 150 MPa compared to the unconfined case. The shape of the equivalent stress field near the free surface of the rock is affected by the confining pressure as well.