Deltek Horizontal Directional Drilling — Rock Drilling

The video above shows the Deltek crew carrying out horizontal directional drilling in rock. Rock drilling is the most demanding HDD application: the steering done with a duckbill head in soft ground does not work in hard formations. Instead, a mud motor driven by the pressure of the drilling fluid and the tricone bit at its tip are used; the bit turns while the rods do not, and direction is given by the angled motor body (bend sub).

What matters in rock drilling?

• Fluid flow and pressure: A mud motor needs at least 500 litres of drilling fluid per minute; the mud pump and recycling unit are sized accordingly.
• Bit and reamer selection: Carbide or diamond-tipped bits according to the compressive strength of the rock, and a cone-cutter rock reamer for enlargement. The number of reaming stages is higher than in soft ground.
• Locating: Signal transmission is weaker in rock formations; on deep and long crossings a wireline magnetic guidance system is preferred.
• Time and cost: The rate of advance in rock is lower than in soft ground and bit and reamer wear is higher. The right choice of rig and equipment keeps the project on schedule and on budget.
• Torque and rig class: In rock the decisive figure is torque capacity, not pull force; rig selection is based on the compressive strength in the geotechnical survey.
• Mud recipe: Rock cuttings are heavy; the viscosity of the drilling fluid is raised with polymer additives so that it can carry them out.

Which projects require rock drilling?

In Türkiye, the limestone formations along the Aegean and Mediterranean coasts, the volcanic rocks of Central Anatolia and the weathered rock of the Marmara region in particular require rock drilling on HDD projects. Bedrock beneath river beds and the hard layers beneath motorway and railway embankments fall into the same category.

Deltek keeps mud motors, rock reamers and high-capacity fluid systems for rock drilling in its Istanbul and Izmir fleet, and has completed river and motorway crossings in limestone, andesite and weathered rock formations. If you have an HDD project in rock, contact us with your geotechnical survey and let us determine the method and equipment together.