Determination of internal friction angle of rock materials using the drilling data

Abstract

Rock cutting is a critical process occurring in several rock excavation activities such as drilling, cutting, sawing, and is common across various industries such as petroleum, geothermal, geo-technical, and underground engineering. Rock cutting or scratching test can be defined by the action of a cutting tool whose relative movement is parallel across to the surface of a material to be cut.

The current work is prepared with the objective of providing experimental evidence that the internal friction angle of rocks can be assessed using a scratch test with a blunt polycrystalline diamond compact (PDC) cutter. For this purpose, a comprehensive set of cutting experiments was carried out to determine the wear flat-rock friction coefficient in two limestones and one coarse-grained sandstone using state-of-the-art scratch-based rock cutting equipment. Additional triaxial compression (TC) experiments were conducted on specimens of these rock formations, and a Coulomb failure analysis was conducted to independently estimate the internal friction coefficient of each specimen. The experimental results indicate that the value of internal friction angle (intrinsic rock property) derived from TC experiments is related to the apparent friction angle at the wear flat-rock interface of the blunt PDC cutter when the wear flat surface is inclined at inclination angles ranging between 0◦ to 1◦. Further, new results on one rock specimen were obtained by performing novel scratch tests with blunt PDC cutters with different wear flat properties, showing that the apparent friction angle at the wear flat-rock interface of a blunt cutting tool is significantly affected by the wear flat roughness and the wear flat material properties.