This Design-Build project includes a new high-level fixed-span bridge and removal of the existing swing-span bridge along US 21 (Sea Island Parkway) over the Harbor River in Beaufort County, SC which is the only vehicular access route to Harbor and Fripp islands. The replacement bridge is 3,340’ long x 47.25’wide with two 12′ lanes, 10′ shoulders, and 90′ of horizontal and 65′ vertical clearance for river navigation. The spansover the tidal marshes include 24” square prestressed concrete pile foundation with footing, column, and cap substructures supporting2 & 3-span continuous Florida BT-78 prestressed concrete beams (167.5’ for each span) with concrete or steel intermediate diaphragms, concrete end diaphragms, and cast-in-place concrete decks. The spans over the tidal waterwayand navigable channel are founded on 96”diameter drilled shafts with column and cap substructuressupporting3-span continuous Florida BT-78 prestressed concrete beams (167.5’ long) with steel intermediate diaphragms, concrete end diaphragms, and cast-in-placeconcrete decks.The approach roadways are constructed on timber-pile supported platformswith earthquake drains and reinforced soil slopes. During construction the embankment was surcharged and monitored for settlement, and after approx. 5’ of settlementthe remainder of the roadway work was completed. Additionally, vibration of the existing bridge was monitored using instrumentation during construction.UIG utilized their fleet of sectional barges to install a 41’wide causeways with fingers from both river banksto provide uninhibited construction access regardless of tides and moratoriums.Sectional barges were also utilized for floating crane rig platforms, drill rig platform, and material storage platforms. This approach to construction access allowed three construction headings to work and proceed simultaneously with a continuous supply of material to facilitate completion within an aggressive schedule. After completion of the new bridge, UIG’s demolition company (United Demolition) will implement an aggressive demolition schedule which includes:only two 24-hour closures of the navigational channel, removal of the navigational portion of existing bridge within 45 days,recycling 85% of the demolition materials, top-down removal of spans and bents to minimize wetland impacts,and construction of an off-shore reef and several near shore reefs. To ensure all work is completed on time, UIG voluntarily doubledthe contract LDs from $10k to $20k per dayas a value-added item along with numerous other value added items to achieve one of the highest technical scores ever earned by a design-build team.
United Infrastructure Group, Inc. and design partner Infrastructure Consulting & Engineering, PLLC received award the 2022 National Award of Merit for South Carolina Department of Transportation US 21 over Harbor River Bridge Replacement. The award was received by UIG Project Manager Billy Hardwick.
