Underreaming
Underreaming is a process used to widen the foot of a bored hole or foundation pier so as to increase its loadbearing area.
It is generally undertaken for safety and/or efficiency reasons, or because of restrictions in the ground, that prevent the use of a pier or pile that is wider along its entire length, and is most common on offshore drilling operations, exploration wells, extended reach drilling, and so on.
Underreaming may also be carried out to create tension piles, where the widened foot resists uplift forces that might otherwise cause the pile to be extracted from the ground. For more information see: Tension pile.
It can also be used in the formation of ground anchors.
Typically, the process involves a drill pipe with cutter blades that can be forced open by pumping a fluid into the pipe. The underreaming tool is kept open by the drilling weight and hydraulics from the pump pressure. The pumps are disengaged when the desired depth has been reached. The underreamer closes and is pulled out of the hole.
It may be necessary to use water flushing systems to remove the reamed spoil from the hole and grout to maintain the integrity of the underream.
There is the risk that if the underreamer is left in the hole for too long, the amount of material left in the hole increases. Also, if penetration rates are too high, this can result in a corkscrewed, under-gauged hole.
It is possible to drill a pilot hole and then underream, or to drill and underream as part of the the same drilling operation.
[edit] Find out more
[edit] Related articles on Designing Buildings Wiki
Featured articles and news
Conservation in the heritage cities of Venice and Liverpool.
Which room is the most fun to design? Find out the 'Grand Designs' presenter's unusual choice in our interview.
Full suite of speakers are announced for this year's BSRIA Briefing event.
Book your place for the Architectural Technology Awards 2018.
There are many ways of classifying types of building. Have a look at our range of building articles.
BSRIA have launched the 'major update' of the go-to design framework guide for building services.
How to get results with building life cycle assessment.
Government publishes a prospectus inviting proposals for new 'garden communities'.
The Morandi motorway bridge in Genoa collapses during rainstorm while undergoing maintenance works.
'Developed design' is a phrase coined by the RIBA for their 2013 Plan of Work. But what does it actually mean?
New green paper published aiming to rebalance the relationship between landlords and residents and tackle stigma.