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A “deep” foundation is used when a building load needs to be transferred to deeper soil layers for adequate support. Micropiles are relatively small (less than 12 inches in diameter) steel and grout (concrete) elements used to provide foundation support. While most often placed for permanent use, they can be used for temporary benefit. Micropiles may be used when:

  • Access to a structure’s foundation is restricted. For example, underpinning structures affected by settlement.
  • Soil conditions beneath shallow foundations are prone to excessive settlement and do not provide sufficient load capacity.

Steele Foundation has extensive experience installing micropiles as part of an underpinning or sheeting job. When ground conditions are unsuitable, we use micropiles to help ensure a safe construction environment and a stable structure built for longevity.

micropiles Spotlight

Howard Theatre

The historic Howard Theatre, located in northwest Washington, DC, was originally constructed in 1910 and closed its doors in 1970. After a brief revival of the theatre in the 1970s, the large masonry structure was closed again and sat abandoned for 30 years. In 2010, a revitalization project kicked off to include a basement addition 15 to 25 feet below the existing stage, on-grade stadium seating area and elevated balcony.

Wet, loose, silty sands at the new subgrade introduced unique design and construction challenges for supporting walls along the perimeter and within the interior of the structure. Steele Foundation teamed with the designer to develop designs and construction methods to combine traditional, pit-type underpinning, hollow bar micropiles and structural steel shoring to provide temporary and permanent support of the existing 40- to 60-foot-tall structure.

The hollow bar micropiles, used as temporary and permanent elements, provided an economical and stiff foundation system for dealing with the poor soil conditions at and below the new subgrade. The operations were successfully completed in early 2011.

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