Trenchless technologies, method 3: Horizontal auger boring
May 23, 2017
May 23, 2017
Understanding when and how to use horizontal auger boring (Part 4 in a series)
This is the fourth blog in a series about Trenchless Technology, a rapidly growing sector of the construction and civil engineering that requires few trenches or no continuous trenches at all. If you have not been following the last few blogs, you can give yourself some background by following links below before going through this blog. In this blog, we’ll look at horizontal auger boring or (HAB).
Horizontal auger boring (HAB), also known as horizontal earth boring or jack and bore, may be the best trenchless option for mining lengths up to 500 feet and diameters up to 60 inches in variety of soil conditions. HAB can be used to install pipes in changeable ground conditions and, in many cases, has lower overall costs compared to other trenchless methods.
HAB uses a revolving cutting head that is located at the leading end of an auger assembly to excavate the soil. Common practice is to jack the steel casing through the excavated hole as it is being bored. The spoil is then transported back to the shaft area by the rotation of the helical auger flights within the steel pipe casing.
Auger boring machines come in different sizes and capacities. Ground conditions usually dictate how powerful of a machine is needed. If the ground is sandy or heavy clay, more force is required.
The anticipated application also determines if HAB is a suitable trenchless method. Bores of less than 6 inches, usually fiber-optic or electric lines and small water pipes, are more suitable for horizontal directional drill (HDD), which require higher budgets for equipment and operation relative to the diameter and length of the bore. But for some water and gravity sewer lines that begin and end on grade, an auger bore rig could be used to potentially save costs.
There are several challenges associated with HAB. An auger boring machine usually cannot be steered. As a result, properly designed and constructed launch shafts are critical to the success of any HAB project. Slight misalignment at the start could lead to a major deviation from the original design path as the boring advances farther.
It’s also critical to have a skilled operator because the actual excavation of the soil and the soil-removal process are not visible to the operator. Changing ground conditions that are not detected can cause settlement on the surface due to over-excavation (excavation beyond specified or directed excavation).
While HAB is an established and cost-effective method for straight and level connections, one of its limitations has been accuracy constraints. However, new technology has made a major impact on auger boring, allowing for more precise bores to expand its abilities.
In the next blog, I’ll introduce pipe ramming, a trenchless technology that involves installing steel casing (pipe) from a launch shaft to a reception shaft using the force of a percussion hammer attached to the end of the pipe.