Every site is unique and every installation method should be selected to draw on the experience of the engineer and contractor as well as meet the needs of the client and address the characteristics of the site. With this as a caveat, the following Rules of Thumb have been described by directional boring designers and constructors:
- Under good conditions a driller can install 200- 300 ft of pipe per day
- A setback is needed for entrance and exit points and must be included in the length of the borehole. Setbacks range from 3 to 5 feet for each foot below grade of the installation. For example, for a placement 5 feet below grade, include 15 to 25 feet of boring on each side of the installation for the set backs.
- Accuracy of monitoring and placement of bore holes less than 30 feet below grade is measured in inches.
- Mobilization and set up usually takes less than an hour
- Cobbles are the nemesis of directional drillers and can deflect drill strings. Difficult-to-penetrate conditions will increase the time needed to complete a project and increase the cost.
Directional Drilling – Limitations
The price of the project is determined by several factors, such as the length and size of the installed product, the expected ground conditions, and the ongoing operation. If the expected ground conditions are bedrock, or other hard to drill conditions, horizontal directional drilling may be cost prohibitive.