Location: Canonsburg, PA
Project Team
Owner: Pennsylvania Turnpike Commission
Contractor: Walsh Construction
Designer: MS Consultants
Construction Manager: CDR Maquire
Concrete Supplier: Stone & Company
Slag Cement: Skyway Slag Cement
Case Study
The Southern Beltway is an all-new limited access toll road under construction in Pittsburgh’s southern and western suburbs, linking the Pittsburgh International Airport at its western terminus to its future eastern terminus with the Mon Fayette Expressway. The project includes 6.6 million CY of excavation; 360,000 SY of concrete paving; 214,000 SY of temporary asphalt, 475,000 SY of subbase; and 50,000 LF of drainage. Two overhead bridges (over I-79) are to be removed, while six new bridges, three retaining walls and one box culvert are to be constructed. Skyway Slag Cement is proud of this project because their slag cement was used to achieve the concrete performance specification with a 40% replacement in the pavement mix. The 7-day spec was 3,000 psi and the 28-day spec was 3,750 psi. Average strengths for 7 days were 4,100 psi and 28 days 6,700 psi. Slag cement mixes typically well exceed the concrete strength requirements and improved the concrete durability.
The most challenging and complex of the 16 sections was section 55C2-1, which completes the final interchange with I-79. Section 55C2-1 is a $180 million project that consists of a full Interchange between I-79 and Toll Road 576 (Southern Beltway), including a half Interchange with Morganza Road. In addition to two miles of new eastbound and westbound mainline highway, the construction includes nine new ramps totaling 7.5 miles in length, and a bi-directional third lane widening of 3.5 miles of Interstate 79 within the existing median. The existing Interstate 79 carries 88,000 vehicles per day in a north south direction, consisting of both city and airport commuters and multi-state north-south interstate traffic. The design of this new east-west beltway introduces a unique twist for a new highway intersecting with an existing highway, going under, rather than over, the interstate. To achieve this, interstate traffic was temporarily shifted to the existing northbound lanes in order to construct a new southbound bridge. The completion of the I-79 work required 11 traffic stages to continuously maintain all four lanes of interstate traffic with no permissible long term lane closures.
A 13,000 SF soil nail wall was constructed top down to allow construction of the new two-span steel plate girder bridge. This bridge serves as the key element in the project, as its completion allows traffic to be temporarily shifted to the new southbound lanes, allowing not only the northbound twin structure to be completed, but also the final 2,000,000 CY of earthwork to be hauled from the east side of Interstate 79 to the west side.
