Horizontal Bore Design
Every site is unique and every horizontal bore design and installation method should be selected to address the characteristics of the site.
Drawing upon the experience of the engineer and directional driller, as well as meeting the needs of the client are essential. With this as a caveat, the following have been described by directional boring designers and constructors:
- Under good conditions, an experienced horizontal directional driller can install 200- 300 ft of pipe per day
- A setback is needed for entrance and exit points of the horizontal bore and must be included in the total 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 horizontal boring on each side of the installation for the set backs
- Accuracy of monitoring and placement of boreholes less than 30 feet below grade is measured in inches
- Mobilization and set up usually takes less than an hour for a horizontal borehole
- Cobbles are the nemesis of the directional driller, because cobbles can deflect drill strings. Difficult-to-penetrate conditions increase the time needed to complete a project and increase costs
Limitations of Horizontal Directional Drilling
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.