We frequently encounter inquiries regarding the distinction between crown and invert culverts, as well as whether one can be substituted for the other. It is important to understand the differences between these two types of culverts and their respective applications.
To begin with, what distinguishes them? Crown-style culverts are characterized by an 'inverted' U shape, with the legs oriented downward. In contrast, invert culverts are provided in a U shape with the legs facing upward. Additionally, invert culverts have the capability to incorporate a lid, which will be discussed further below.
In smaller drainage systems, both types of culverts can be employed; however, certain situations may dictate the preference for one type over the other.
For large, multicell structures, it is common to construct a structural in-situ base or slab. Crown units can be directly installed onto this base slab, with the crown forming the uppermost part of the structure.
In large structures, link slabs are often used to reduce costs on intermediate cells by eliminating the need for every second culvert. These link slabs require a crown unit on either side for proper placement.
Invert culverts are most commonly used in scenarios where the lid needs to be removed for maintenance or for the installation of additional components such as pipes or cables. These culverts may come with a load-rated precast lid or lightweight removable lids made from materials like steel or FRP.
From manufacturing standpoint, the key distinction between crown and invert culverts is the location of the lifting anchors. Crown-style culverts are designed with lifting points situated in the 'roof' or crown area, while invert culverts are rotated during production, featuring lifting points on either the interior or exterior walls. This specific arrangement of lifters means that a crown unit cannot typically be inverted to serve as an invert culvert.
The installation process for both types of culverts is quite similar. For crown units, the crowns are placed onto a grout bed contained within a shallow rebate in the base slab. In the case of invert culverts, the unit is placed directly onto the prepared subbase, and a lid is then positioned on top to complete the installation.
Project specifications and drawings typically indicate the configuration of the culvert, and the design intent should be evident from the use cases described. However, particularly for small drainage lines, the rationale for choosing one type over the other may not always be apparent. In such cases, consulting the designer to understand their preference may be necessary.
The expert team at Modcast can assist in assessing the suitability of each type of box culvert for your next project. Reach out to learn more today.