University of Connecticut Health Center—Permanent Soil Nail Wall

Cost-effective geotechnical engineering expertise proved crucial in constructing Connecticut’s highest permanent soil nail wall on schedule.

The wall was completed as design-built commission by a team lead by Fusco/Clark who chose GEODesign to be on their team. The 54-foot high structure makes parking feasible at the University of Connecticut Health Center’s outpatient center, which opens this year in Farmington, just outside Hartford, the state capital.

Construction of a new six-story pre-cast concrete parking garage at UConn Health into a steep slope required permanently lowering site grades up to 75 feet. The garage was planned to provide needed parking spaces for the new $203M, 300K square foot, privately financed, Ambulatory Care Center (ACC) for outpatient services on the Health Center campus. The State of Connecticut opted for design-built procurement for design and construction of the project to meet the desired accelerated schedule.

Based in Farmington, Connecticut—a popular suburb of the state’s capitol of Hartford—UConn Health is home to the School of Medicine, School of Dental Medicine, John Dempsey Hospital, UConn Medical Group, UConn Health Partners, University Dentists and a thriving research enterprise, which now includes the new ACC, and Cell and Genome Sciences Buildings. The new ACC building, which was opened on February 3rd this year, houses existing services and supports the work of new faculty that will be joining UConn Health as part of its expansion.

In the bridging documents issued to solicit design-build team proposals, the large cut associated with the proposed grade change was to be retained by a conventional, massive, gravity concrete retaining wall. As planned, this wall was to have a maximum height of about fifty feet, needed to be built adjacent to a thirty foot high main access roadway embankment slope, and would have been about 550 feet long.

During the proposal period, working with the Fusco/Clark Joint venture, GEODesign reviewed available project information including local geology and subsurface data and, based on its specialized geotechnical knowledge and experience, determined that a permanent soil nail wall and a steepened armored slope would be more efficient than constructing a massive gravity wall as previously envisioned. Advantages of a permanent soil wall included: accelerated construction, reduced excavation volumes, elimination of temporary excavation support, and construction economies, while meeting owner criteria for a permanent concrete-faced wall.

Thanks, in large part, to the substitution of a permanent soil nail wall, the garage construction could be started sooner and the project’s overall construction schedule was shortened.

The wall was designed with a batter of 1 horizontal to 6 vertical. The design relies on double corrosion protected 1-1/8 and 1-1/4 inch diameter, Grade 75, threaded reinforcing bars, set on a typical grid pattern of 5-ft. horizontal by 6-ft. vertical, ranging in lengths from 25 to 55 feet, and installed at a dip of 15 degrees below horizontal. Over six hundred permanent soils nails were installed during wall construction. The temporary and final reinforced shotcrete wall facings were five and eight inches thick, respectively. At a maximum height of 54 feet, the wall structure is the highest permanent soil nail wall constructed in Connecticut to date. This compares with the highest permanent soil nail wall along Connecticut highways of less than thirty feet (as of mid-2015).

The highest portion of the wall was also used to resist lateral loading imparted by the abutment of a single span vehicular bridge which connects the upper parking garage level to the Main Access Road above the wall and slope, and improves traffic flow on the Health Center campus.

Although soil nailing is an accepted technology, and its theoretical aspects are well understood, experience-based insight into design and construction considerations are critical to the long-term performance of permanent soil nail walls. For this reason, GEODesign provided construction phase quality assurance services during wall construction to document adherence with strict technical specifications for durable performance of the permanent wall, including permanent wall drainage, shotcrete durability, and consistent double corrosion protection.

Lynn Fusco, one of the two leaders of the Fusco/Clark JV praised GEODesign’s creativity in the design and cost savings which were successfully brought to the project.

The design also resulted in an accelerated construction schedule, with wall construction begun in February and completed in May 2013, and the adjacent garage opened in November 2013.

GEODesign is committed to providing our clients with cost-effective geotechnical engineering solutions.

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