Precast Box Culverts: Size and Design Offer Numerous Advantages
December 17, 2021
By Margarita Takou, Ph.D., P.E., ACPA Technical Resource Manager
At the ACPA, we talk a lot about the benefits of precast reinforced concrete pipe (RCP), but did you know the association’s membership also produces precast reinforced concrete box culverts? Like RCP, box culverts offer the benefits of precast concrete construction such as superior durability strength, and resilience. Precast box culverts can be found in standard sizes or customized to the project’s requirements. These structures are ideal in situations where minimum cover, width, and clearance problems are encountered.
Developed in the early 1970s, these precast rectangular sections are manufactured with wet or dry cast, or self-consolidated concrete (SCC). Precast box culvert design offers numerous advantages over cast-in-place structures, including:
• High quality assurance and quality control standards with the plant’s manufacturing and control system
• Box culverts are fully cured in a controlled environment before delivery
• Quick installation time, reducing time delays during construction.
• Backfill can begin immediately
• Accelerated project completion
• Decreased traffic risk due to construction speed
• Improved work-zone safety
• Minimal environmental disturbance
Benefits for Bridges
When it comes to bridge construction and rehabilitation projects, reinforced precast box culverts provide an ideal solution. With a box culvert, a bridge can become “out of sight, out of mind,” which delivers peace of mind for municipalities and city officials.
In rural areas, farmers have become advocates of box culvert construction for bridges. Because culverts extend the clear zone, farmers don’t have to contend with guardrails when they move equipment from field to field. With a precast concrete culvert, farm equipment can’t damage guardrails, snow drifting is reduced, the structure’s maintenance is minimized, and the safety of the crossing is enhanced.
Easy As ABC
Box culverts are a perfect match for Accelerated Bridge Construction (ABC). According to the Federal Highway Administration, ABC is a paradigm shift in the project planning and procurement approach for bridge construction or rehabilitation to minimize onsite construction time. The result is a safer project with fewer traffic disruptions and impacts to the public. ABC offers many other advantages over conventional bridge construction including reduced environmental impacts and life-cycle costs and improved material quality and product durability.
Consider these examples where box culvert design excelled for ABC:
Highway 248 Near Kadoka, South Dakota
In 2020, the South Dakota Department of Transportation let a project on SD 248 to replace two deficient three-span bridges with two box culverts. Concrete box culverts are the SDDOT’s preferred choice for smaller bridge type structures to eliminate the safety hazard of guardrails and the future maintenance of bridge decks.
The original plans allowed the typical options of field-cast or precast box culvert. The field-cast option was risky for washout due to the need to tie steel and set forms in the bottom of a drainage way and the time required to complete the work, in addition to the need for skilled labor that was hard to find and keep. The initial precast option required overly large pieces and mobilizing an overly large crane, among other constraints. The contractor submitted a value-engineering change proposal for a hybrid using the best of the precast with the best of the field-cast design, consistent with the SDDOT’s design requirement that the structure act as a monolithic unit.
To control stormwater and extend surface parking, 142 feet of twin cell box culvert measuring 11 feet, 5 inches by 5 feet, 6 inches were installed in 12 days. When a mixed-use development needed a solution to control stormwater runoff, a system of reinforced precast concrete box culverts provided the answer. Located south of Ann Arbor in Pittsfield Township, Michigan, the development included multiple buildings on a site containing regulated wetlands.
The site’s relatively small footprint wouldn’t allow for a retention pond. As such, the stormwater retention system was placed under a parking lot. Two underground stormwater retention systems were designed using precast concrete boxes to control discharge into the wetlands and accommodate 482 commercial and residential parking spaces. The systems capture water from impervious surfaces during large rain events and detain the stormwater until it can be slowly released into the soils and wetlands.
The retention systems were designed to support loads according to LRFD HL-93.
Resort Municipality Whistler, Canada
In Whistler, Canada, 48 sections of 12-foot by 10-foot box sections were installed in 12 hours for a pedestrian crossing spanning two vital Canadian National (CN) rail lines at mile 77.41, known as Mons Crossing. The underpass was needed to provide safe and suitable year-round pedestrian and bicycle passage to home and business owners located north of the rail line to Whistler Village.
Although a bridge overpass was initially considered, an underpass constructed with reinforced concrete box culverts provided the quickest, most cost-efficient, and reliable solution. The underpass design spanned the two active rail lines and specified 48 sections of 12- by 10-foot precast boxes, weighing approximately 33,000 pounds each. The total length measured 400 feet.
A very limited 15-hour construction window was required, due to the two active rail lines. Other unique challenges included poor soils, a seasonally high water table, pedestrian traffic, and a broad range of weather conditions seen in this mountain resort.
Applications for Box Culvert Design
What’s the best application for box culvert designs? Many!
Some of the most popular uses for box culvert designs:
• Short-span bridges (over highways, waterways, railways, etc.)
• Conveyance of stormwater, sewage, or industrial wastes
• Control of surface or subsurface water to maintain dry conditions
• Tunnels (Animal/wildlife crossing, Pedestrian/bike crossing)
• Detention Systems
• Aquatic habitats
• Tornado shelters
• Below-grade utility chambers
• Rail tunnels
Precast reinforced box culverts provide a resilient and sustainable structure with numerous advantages including ease of installation and minimal traffic disturbance. To learn more about reinforced box culvert design, visit the ACPA’s box culvert resource page. For information about box culvert sizes and requirements, contact your local ACPA member.
For more information on concrete pipe performance, contact us at info@concretepipe.org.