When you think of a ‘collapse’, you normally think of a bridge. This is not always the case. Pipe culverts can collapse also, leading to devastating consequences. Just because there may not be a ‘structure’, does not mean there cannot be a collapse. I think when we imagine a culvert, we are thinking of a small pipe. But these pipes can be up to 10 feet in diameter, and maybe even bigger. So if a 10 foot pipe culvert would collapse, that could mean a 10 foot hole in the road! There are several factors that can lead to the failure of a culvert, with some failures happening suddenly, and some happening over time.
Some pipe culverts collapse due to material weakness. Metal culverts can become corroded from either chemicals from runoff, or from water sitting in them for extended periods. After time, the bottom may rust, then the culvert may fail. Even though these culverts are typically designed for a 50 to 75 year service life, and have some type of corrosion protection (galvanization, asphalt coating,) corrosion may take plus much sooner. This can be sudden, or may take years. Concrete culverts have a tendency to separate at the joints. One section may start to separate, maybe even causing a chain reaction. Sometimes an end section or even more than one, may fall completely off. This can lead to the road being too narrow and steep at the culvert. Groundhogs can even make the joints weak by burrowing on top of them. Plastic culverts (HDPE, etc.) may also fail from joint separation, or possible material weakness. They can be affected by different factors such as sunlight. Proper cover must be over the culverts as well, or loads can be transferred directly to the pipe without being distributed properly over the soil/road on top of the pipe.
Culverts that become obstructed can also pose a problem. If debris is blocking a culvert, the water will find the path of least resistance. The water may try to go around the culvert, or even under it. In these instances, the pipe may be intact, but the soil around the culvert may wash out, creating a hazardous situation. This could happen during a flood, at which point the soil may wash out and cause a sudden collapse of the road.
It is a good idea to set up some kind of inspection schedule and inventory when it comes to pipe culverts. If you notice a dip in the road, or cracking above a culvert, it probably needs to be inspected.