Situation: The Mt. Carmel Health, Wellness, and Community Center development included
a number of exciting engineering and construction challenges. The project
entailed constructing a basement link addition between the Mt. Carmel
Church and the adjacent Music Hall, and a new walkout basement beneath
the historic church.
The historic Mt. Carmel Church was built in 1907 by Jesuit Fathers with
an unreinforced sandstone block foundation. Innovative design and construction
methods were required to successfully complete construction underneath
the existing structure. Straight Line Construction, together with Printz
Engineering Services, LLC, a shoring and underpinning engineering firm,
developed a thoughtful, creative, and practical solution to address the
unique challenges this project presented.
PHASE 1-Soil Nail Construction
The first phase of the project involved constructing a temporary soil
nail wall along the existing alley to allow excavation of the basement
link addition. The soil nail wall was 16 to 22 feet high with soil nail
lengths of 15 and 20 feet. Between 3 and 5 rows of soil nails were installed,
depending on the wall height. The soil nails were drilled with a 3 inch
diameter sacrificial drill bit, reinforced with 32mm hollow reinforcing
bars, and the annular area around the bars was grouted solid. The face
of the excavation was reinforced with welded wire fabric and horizontal
waler steel and a 4-inch thick shotcrete facing was applied to prevent
raveling and sloughing of the retained soils.
The soils nail wall not only had to retain the soils during excavation,
it also had to withstand traffic loads from the adjacent alley. Once the
soil nail wall was completed, the foundation for the basement link addition
was constructed and underpinning of the church began.
PHASE 2-Foundation Stabilization
The initial phase of the foundation stabilization consisted of reinforcing
the historic sandstone block foundation by drilling through the foundation
and bolting channel steel on both sides. Welded wire fabric was then installed
and both sides of the newly reinforced foundation were sprayed with shotcrete
to allow the foundation to span between the underpinning elements.
PHASE 3-Underpinning and Excavation
Underpinning of the church foundation consisted of installing cased micropiles
adjacent to the foundation wall. The micropiles were installed at a spacing
of 6 feet, alternating between the interior and exterior of the foundation
to reduce eccentricity on the piles. The micropiles consisted of 4-½ inch diameter elements reinforced with
38mm hollow reinforcing bars and 3-½ inch diameter J-65 steel casing.
The hollow bar and continuous grouting method was chosen to help keep
the piles as close to the face of the wall as possible, again to reduce
eccentric loads. Pilasters were supported by groups of micropiles with
underpinning brackets. After the micropiles were installed, the general
contractor excavated under the existing foundation in approximately 6-feet
long sections and installed new footings and Basement foundation walls.
Conclusion: Between the time excavation occurred and new foundations were constructed,
the foundation below the excavated areas was supported completely by the
The project received a prestigious American Council of Engineering Companies
of Colorado (ACEC/CO) Engineering Excellence Award in 2011. By virtue
of winning the Engineering Excellence Award, the project advanced to national
competition in Washington D.C. in the spring of 2012.
This unique and challenging project highlights the capabilities and innovation
provided by Straight Line Construction and Printz Engineering Services,
LLC. We stand behind (and under) our designs and construction. Let us
help make your next challenging project as successful as the Mount Carmel
Health, Wellness, and Community Center.
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