East Branch Dam Rehabilitation

East Branch Dam is a 184-ft high earthen flood control structure owned and operated by the Pittsburgh District of the U.S. Army Corps of Engineers. The dam had a history of seepage-related problems, and was classified by the Corps as a Dam Safety Action Class II structure.

As part of the Corps’ long-term risk reduction plan, a concrete cutoff wall needed to be constructed within the existing embankment and foundation. Schnabel provided engineering support to the contractor during this $130M construction project. We led development of the contractor’s environmental submittals.

As Lead Project Geotechnical Engineer, Schnabel was responsible for monitoring construction of the temporary work platform located on the upstream slope. We also designed several temporary features for the contractor, including haul roads and ramps, slurry pits, the work platform slab and cutoff wall guidewalls. Schnabel also served as the Lead Grouting Engineer and provided drilling inspectors during instrumentation installation and grouting operations.

Lake Peachtree Dam

Peachtree City is one of the first planned communities in Georgia. Lake Peachtree is the centerpiece of the community, providing water supply and recreation for residents. Although the state’s Safe Dams Program classified the dam as low hazard, the city proactively elected to upgrade it and the spillway to meet criteria for a high hazard structure. The effort involved over three years of planning, negotiation, design, and construction.

Increasing spillway capacity was the goal, but site conditions and economic considerations limited acceptable alternatives. The new spillway had to accommodate the existing peak inflows for storms up to and including the 100-year event. The ideal structure would safely discharge the state-required design storm without increasing flooding in the reservoir or the downstream floodplain.

Alternatives considered were raising the dam to provide additional storage, widening the spillway, or replacing it with either a labyrinth weir or piano key weir (PKW). The selected alternative was a three-stage PKW, which met all project objectives related to function, aesthetics, maintenance, construction cost, operating cost, and construction schedule. Completed in June 2018, it is the first PKW put into service in the United States and the first known multi-staged PKW in the world.

The structural design relies on extreme environmental loading conditions with the reinforced concrete proportioned to provide decades of reliable service. 3-D computational fluid dynamic modeling and structural finite element modeling was used to visualize spillway performance while still in design, which led to reduction of constructability issues before they emerged in the field.

2019 ACEC Georgia, Engineering Excellence Award, Water Resources Category
2019 ACEC Grand Award, Engineering Excellence Awards

Frostburg State University Gira Center for Communications and Information Technology

As the first new academic building at Frostburg State University in 11 years, the Catherine R. Gira Center for Communications and Information Technology successfully combines the disciplines of computer science and information technologies, graphic design, mass communication and mathematics under one roof. The three-story, 127,000 square foot facility sits at the heart of the campus and is arranged around an outdoor courtyard, with pathways to the adjacent Performing Arts Center, Compton Science Center and Lane Center.

The site was mined for coal during a period from the late 1800s to the 1950s using room and pillar construction methods. Because abandoned mines can pose an elevated risk of subsidence for any new construction, Schnabel—which had worked on numerous other campus buildings under similar conditions—was hired to conduct a mine assessment study and a geotechnical engineering study. The mine assessment study required review of historic subsurface mining information; test borings; downhole camera surveys; and a stability assessment report and recommendations. The site was stabilized by filling the mines with 3,265 cubic yards of grout and concrete.

The data collected during the geotechnical study informed the recommendations we made for design and construction of the building and related site improvements. Other tasks included development of foundation and earthwork-related specifications, geothermal testing and construction observation.

Designed by Ayers Saint Gross, the $45 million LEED Gold certified Gira Center opened in September 2014.

International Spy Museum

The International Spy Museum (SPY) is the only public museum in the United States solely dedicated to the tradecraft, history and contemporary role of espionage and intelligence. Open since July 2002, it features the largest collection of international artifacts ever placed on public display.

In 2018 the museum will relocate eight blocks south to L’Enfant Plaza, inhabiting a new $50 million building which will transform SPY, the neighborhood, and the Southwest Ecodistrict. The Malrite Company and The JBG Companies collaborated on plans for the 140,000 square foot facility, which is sited directly in front of the glass atrium on the Plaza. London-based Rogers Stirk Harbour + Partners is the architect.

Proposed construction increased the column loads on the Plaza by up to 2,800 kip (one kip equals 1,000 pounds-force), which necessitated retrofitting the existing foundation. Schnabel was hired by JBG to work with the structural engineer, SK&A, on the retrofit. To increase vertical load capacity, we recommended installing a group of micropiles through the existing footings. The solution was then fine-tuned by comparing 7-inch and 9.625-inch outside diameter micropiles. Each had advantages: better constructability with the smaller one and increased capacity with the larger one. Based on our findings and team discussions, we specified a hollow-core bar system consisting of a 7.87-inch diameter cross bit, T76S DYWIDAG hollow bar with 8.625-inch steel casing for the final design. A total of 70 micropiles with a design load of 200 kip compression and 140 kip tension were constructed in nine column locations.

Construction observation services were provided by Schnabel Engineering DC, a wholly-owned subsidiary of Schnabel Engineering.

Renderings courtesy of Rogers Stirk Harbour + Partners

Dominion Boulevard Improvements

Dominion Boulevard is a portion of U.S. Route 17 which runs north/south through Chesapeake, connecting North Carolina with Virginia Interstates 64/464. Improvements to the four-mile stretch were driven by the desire to alleviate traffic congestion and improve safety.

The roadway was widened from two to four lanes, including three new interchanges at major access points. To create this new $400 million corridor, a total of nine bridges and overpasses were constructed, including the two parallel, one-mile long bridges providing 95 feet of clearance over the Elizabeth River. WSP USA was responsible for preliminary and final design services on the project.

As part of WSP’s team, Schnabel provided geotechnical engineering services for preliminary and final design. The subsurface exploration included CPT and DMT soundings, and more than 500 test borings, some of which were performed in difficult river and tidal wetland locations. Geotechnical recommendations addressed mechanically stabilized earth walls, driven pile foundations for the bridges, and the use of pre-fabricated vertical drains, surcharges and pile-supported embankments to accommodate embankment settlements and project schedule constraints.  We also provided geostructural design for the soil nail walls supporting excavation adjacent to bridge abutments where lanes were added.

Our services continued through construction by providing engineering support and review of RFIs and submittals. The planned 48-month construction phase concluded four months ahead of schedule and $20 million under budget.

Dominion Boulevard was awarded the APWA Mid-Atlantic Chapter 2017 Project of the Year for excellence in the transportation category for projects exceeding $75 million.

Photos courtesy of WSP USA