Rock drilling is quantified by a rock’s PSI. Rock density ranges from the highest hard rock PSIs (marble, granite, coral) to the lowest PSIs soft rock (cobble).
It’s important to gather as much information as possible about the soil conditions and any rock formations along the bore path before you start.
For softer rock formations (8,000 psi compressive strength and lower) milled tooth bits offer the fastest penetration rates at a lower cost.