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New Construction Helical Piles - St. Benedict's Catholic Church Addition

Nebraska City, NE

November 2005 -- Built in 1861, St. Benedict's Catholic Church is the oldest brick Catholic Church in Nebraska. It is listed with the National Register of Historic Places.

In 2005, various site and structural improvements were scheduled, including the addition of a single-story entrance on the west side of the building.

The proposed addition measured approximately 18 feet by 32 feet.

Due to limited site access, shallow test borings were completed with hand equipment.

The on-site test borings and soil information gathered from visual observation of other site excavations indicated variable, undocumented fill soils to depths of about 10 to 15 feet.

Due to the risk of potential damaging differential settlements, traditional spread footings within the existing fill soils were not recommended for the new addition.

Instead, three foundation support options were considered, including the complete removal of all existing fill soils and replacement with compacted and tested fill.

A second option involved supporting the foundations on deep, cast-in-place concrete shafts drilled to bedrock or other high load-bearing strata. The third option utilized a helical pier system.

Helical piers were selected as the ideal foundation support option given the limited site access and minimal expected site disturbance throughout installation. In addition, the tight construction schedule dictated that equipment be mobilized quickly and installation be completed within days.

Ten (10) helical piers were planned to support the wall loads and the cast-in-place structural slab. Design loads ranged from 5 kips to 25 kips with a design depth of at least 15 feet for the uppermost helix.

Two (2) 12-inch diameter single-helix lead sections and eight (8) 10-inch, 12-inch, 14-inch diameter triple-helix lead sections were installed to depths ranging from 21 to 31 feet. The helical pier installation was completed in less than one day.