Installed with an air rotary drill rig this premium approach to foundation support requires level ground, clear access and minimally 12′ clearance. With a level site no excavation preparation work is necessary. 10" diameter boreholes are advanced to bedrock, or to a depth sufficient to provide adequate frictional support for 6" diameter steel casing. Mini piles enable removing thick zones of contaminated soil from beneath multi floored residential and commercial structures. Note, this is the same approach used to provide earthquake protection to buildings. A 3" diameter steel post is centered into the casing and then the casing is filled with grout. This provides a firm base onto which the foundation bracket can be mounted. The bracket is snugged up to pre mounted 8" angle iron, which span from pile to pile and are anchored to the existing footing. Note if the structure has no footing, then a 12" high x 18" wide reinforced concrete footing needs to be constructed beneath the existing wall prior to the mini pile installation. This provides a clean edge to which the angle iron is attached and add significantly to the project cost.
Piles spans are typically 6-9′ and allow enough width to adequately pass conveyors or excavators. This method enables deep excavating beneath buildings where the structural load is carried by perimeter foundations. There remains significant reconstruction work following contaminated soil dig out as the undermined foundation must be replaced. This will add two to five days of work at the end of the contamination dig out project. This approach is understandably the most costly, with individual mini piles priced at about $2,500 each plus excavation crew support of about $6,000 to $8,000.
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