We often specify helical piers for foundation underpinning projects to correct building settlement conditions (see our previous post, “Screw It” http://blog.etc-web.com/?p=83 ), but occasionally we need to use micro piles instead.
As the name suggests, micro piles are small diameter piles (generally 3” to 10” in diameter) that are installed by a drilling process. These piles consist of a steel casing and/or threaded bar that is made of high strength steel. We specify this process when there is shallow bedrock, boulders, or layers of soil that are very hard.
In the past, micro piling was not a highly used process because of cost considerations and a slow installment time. But lately, it has been gaining popularity. The main reason for this are requirement to comply with low noise and vibration regulations that are generally found in urban or highly populated areas. Micro piling is also a useful technique for underpinning at sites with difficult or restricted access, including low headroom interiors and facilities that require minimal disruption to normal operations