How long does it take to drill a 9-meter extension rod on a rock drilling rig

However, to understand why the range is so wide, let's break down the key factors:

1. Rock Hardness and Abrasiveness (The Biggest Factor)

This is the primary determinant of drilling speed.

Soft Rock (e.g., shale, limestone, sandstone): A top-hammer rig can achieve penetration rates of 1.5 to 2.5+ meters per minute. Drilling a 9m rod could take as little as 4 to 6 minutes of pure drilling time.

Medium Hard Rock (e.g., granite, hard limestone): Penetration rates slow to 0.7 to 1.5 meters per minute. Drilling time per rod: 6 to 13 minutes.

Very Hard / Abrasive Rock (e.g., quartzite, highly abrasive granite): Penetration rates can drop dramatically to 0.3 to 0.7 meters per minute. Drilling a single rod could take 13 to 30 minutes or even longer.

2. Type of Drilling Rig and Hammer

Top-Hammer Rigs: Common for blast hole drilling up to ~30m depths. They are generally faster for shorter holes but lose efficiency with depth due to energy loss up the drill string.

Down-The-Hole (DTH) Rigs: The hammer is located at the bottom of the hole. Much more efficient for deeper drilling (e.g., 30m+), especially in hard rock, as there is no energy loss in the rods. They can maintain a consistent, often faster, penetration rate in hard rock compared to top-hammers.

3. Drilling Diameter

Larger Diameter Holes (e.g., 115mm - 127mm) require more energy to break the rock and evacuate the cuttings, resulting in a slower penetration rate.

Smaller Diameter Holes (e.g., 64mm - 89mm) drill significantly faster.

4. "Chip-to-Chip" or "Rod-to-Rod" Time

This is a critical concept. The total time to complete a rod isn't just the drilling time. It includes the entire cycle:

Drilling the 9-meter length.

Stopping the hammer and rotation.

Retracting the drill head to add a new rod (or in this case, the next extension).

Connecting the new rod to the string and to the rig.

Resuming drilling.

This "add-on" time can add 2 to 5 minutes per rod to the operation.

Realistic Time Calculation Example

Let's assume you are using a top-hammer rig to drill a 102mm (4-inch) blast hole in hard granite.

Penetration Rate: Estimated at 0.8 meters per minute.

Pure Drilling Time for 9m: 9 meters / 0.8 m/min = 11.25 minutes.

Rod Change Time: Allow ~3 minutes for stopping, adding the rod, and restarting.

Total Estimated Time per 9m Rod: ~14.25 minutes.

For a softer rock like sandstone, the calculation might look like this:

Penetration Rate: 2.0 meters per minute.

Pure Drilling Time: 9 / 2.0 = 4.5 minutes.

Rod Change Time: ~3 minutes.

Total Estimated Time: ~7.5 minutes.

Summary Table