CON/SPAN® can be installed on top of many different foundation types. Common to all foundation types is the keyway in the top of the foundation that accepts the leg of the precast arch. The arch units are set on top of shims in the keyway, which is grouted once all of the units are in place at the correct line and grade. This connection to the foundation is structurally modeled as a pinned connection.
Strip Footing: The most common type of footing is the strip footing. Although they can be precast, they are almost always cast-in-place. The important features of a strip footing are obviously the width, which must be designed to conform to the allowable soil bearing pressure and the depth for scour and or frost protection. It is also very important to maintain a consistent keyway. The wingwall footing is generally continuous with the culvert footing and it is important to form the backside of the wingwall foundation for the anchor on the back of the precast wingwall.
Slab Bottom: The second most common type of foundation is the slab bottom. The important considerations are obviously the uniformity of the keyway and the use of a cutoff wall at each end of the structure to protect against undermining of the slab. Slab bottoms are often used when the structure is in poor soils, or as a means of scour protection or on very long structures for ease of maintenance.
Pedestal: Pedestal foundations are used when additional vertical clearance is required. The keyway is cast into the top of the pedestal wall.
Pile Foundation: Deep foundation systems such as piling or caissons can also be utilized when soil parameters dictate their use. They are only used on a small percentage of projects; however, they are used a little more frequently in coastal areas where the soils are extremely wet and weak.