The standard size ranges vary between manufacturers but typically range from 6′ Span X 3′ Rise to 16′ Span X 14′ Rise, but they are also available in 20′ spans from select manufacturers. Standard lay lengths are 6′, and the sections are connected with tongue and groove joints packed with gasket material. Precast box culverts are designed and manufactured to meet the ASHTO, ASTM, or AREMA* load-bearing requirements for the specific construction site. With Precast Box Culverts, the load-bearing capabilities are typically predetermined. However, hydraulic analysis needs to be performed to ensure the correct sizing of the structure.
*American Association of State of Highway Transportation Officials, American Society for Testing and Materials, American Railway Engineering and Maintenance-of-Way Association
Cast-In-Place Concrete Box Culverts
Box culverts that are made of reinforced concrete and fabricated in the field are considered cast-in-place. These structures are built with concrete and rebar at the project site. Forms are constructed to outline and create the dimensions and shape of the box culvert, and concrete is poured into them.
Building the box culvert in the field requires engineering and planning that make this method a longer installation process than working with Precast structures. However, since these culverts are explicitly designed for the project site, project owners have more size ranges and specialty options to meet their needs. The design of these structures often requires that the project design engineers perform structural and hydraulic analysis to ensure that the Box Culvert meets the project requirements.
Corrugated Steel Box Culvert Designs
Corrugated steel box culverts are galvanized to help prevent corrosion. When the steel plate is corrugated, it is made stronger, allowing lightweight steel to meet required load-bearing requirements. They can also be reinforced with ribs to reach spans up to 53′, and they are most commonly designed for culverts or storm sewers with a natural streambed bottom.
Corrugated steel box culverts are designed and manufactured to meet the load-bearing requirements of the project owner. Over time abrasion, caused by the flow of water with gravel and sand over the galvanized invert, removes the galvanizing and causes corrosion and structural failure.
Corrugated Aluminum Box Culverts
Box culverts are also manufactured with corrugated aluminum. They are very similar to corrugated steel box culverts, and they can be designed to reach spans of 35′. The lightweight design is easy to install and is best suited for applications with low rise and wide span requirements. Although aluminum is not as strong as steel, it will not rust and require any coating. Aluminum box culverts are designed to meet ASHTO, ASTM, and AREMA load-bearing requirements for highway and railway use.
Other Types And Uses Of Box Culverts
Workers may pour a trough on the bottom of a box culvert to accommodate low flow applications. Also, box culverts constructed without a base may be set on footings and used to maintain a natural stream bed bottom inside of the structure.
Besides their use in stormwater management, box culverts are often used for pedestrian crossings, cattle/wildlife crossings, utility tunnels, and utility vaults. They can even be used for underground storage, tornado shelters, and wine cellars. When properly installed, box culverts can have a design life of 100 years.
Box Culvert Failure
Box culvert failure commonly occurs when the joints separate or cracks develop in the concrete structure. Joint failure may occur if the joints were not installed correctly by not pulling them together, not installing the joint packing correctly, and/or not waterproofing the joints. Joint failure allows water and soil to penetrate the culvert, which can cause sinkholes to develop above the culvert. Cracks may develop and expand in concrete structures due to external stress on the structure’s top, bottom, or sides.
Box Culvert Rehabilitation Methods
Failing inverts, voids, and cracks: If a box culvert is failing along the bottom of the structure, it is typically caused by abrasion and scour. The invert of the failing culvert may be poured with concrete or a new bottom may be built with reinforced concrete. Geopolymer mortar may be used to fill voids and cracks in existing reinforced concrete culverts. Geopolymer mortar and other spray-on linings are applied to the ID (interior diameter) of the box culvert, and offer structural enhancement to the existing structure, contributing to extended service life.
Culvert slip lining: Failing box culverts may also be slip lined with a variety of common culvert products.
When considering slip lining, the size of the hydraulic opening of the liner is an important consideration. Although slip lining a box culvert with round polyethylene pipe might be commonly done, the cross-sectional area of round pipe is significantly less than the original box culvert.