Culverts, the structures designed to allow water to pass below roads, railways, or embankments, play an essential role in managing surface water and preventing flooding. However, these structures are not immune to degenerative issues, and they can sometimes fail. Reviewing the most common reasons for culvert failure, explained below, will help stormwater agencies understand and mitigate the risks of culvert failure.

Which Types of Culverts Fail Most Often?

Before delving into the reasons behind culvert failure, it is essential to understand which types of culverts are most susceptible to failure. Generally, there are three main types of culverts: pipe culverts, box culverts, arch culverts, and open-bottomed or bottomless culverts.

Pipe Culverts: These are the most common type of culverts. They consist of a round, arched, or elliptical pipe placed horizontally beneath an embankment. Due to their wide usage, they also tend to have the highest number of failures. Damaged pipes can be repaired with slip-liners and other trenchless rehabilitation solutions. In extreme cases, the entire culvert must be reconstructed.

Box Culverts: These culverts are usually made of reinforced concrete or steel and come in various shapes, including square, rectangular, and top-arch. They’re often placed in narrow streams and have a higher resistance to water pressure compared to pipe culverts.

Box culvert rehabilitation with box culvert liners is a commonly used method of repairing culverts to restore their structural integrity.

Open-Bottomed or Bottomless Culverts: These culverts are typically used in areas with significant flow and have no bottom, or only a partial bottom, allowing water to pass through freely. They are prone to clogging and sediment buildup, which can lead to failure.

Of these four types, pipe culverts and box culverts are the most frequently used and have a higher likelihood of failure. Common reasons for culvert failure include:

Poor Design or Construction

If a culvert is not designed correctly, it may result in inadequate size or hydraulic capacity, enhancing the likelihood of failure. Similarly, flawed construction can compromise a culvert’s structural integrity and lead to failure in the future.

In order to prevent these types of failure, it is crucial for stormwater management agencies and counties that oversee infrastructure improvements to hire experienced engineers and contractors who have a thorough understanding of culvert design and construction.

Inadequate Maintenance or Neglect

Culverts that are not properly maintained can become clogged with debris, vegetation, or sediment, reducing their capacity to convey water and increasing the risk of failure.

Regular inspections and routine maintenance, such as clearing debris and sediment buildup, can help prevent this type of failure.

Additionally, proper vegetation management around culverts can prevent erosion and reduce incursion by grasses and weeds, helping to maintain a culvert’s functionality as well as reduce the rate of soil erosion around culvert openings. Neglecting these maintenance tasks can result in costly repairs and potentially cause road or railway closures.

Abrasion, Especially of the Invert

Abrasion is another significant cause of culvert failure, particularly in metal or concrete culverts. Over time, exposure to water and the flow of soil, sand, and other abrasive materials can lead to scour of the culvert’s invert (the bottom portion), which can then lead to failure. An invert with exposure to the soil below will allow water to undermine the structure, eventually compromising the culvert’s structural integrity. This type of failure is more common in areas with high levels of acidity or salinity in the soil.

To prevent failing inverts, it is essential to use materials that are thick and inherently resistant to abrasion and to regularly inspect culverts for any signs of deterioration. If damage is detected early on, repairs can be implemented to prevent failure.

Inadequate Capacity

Overloading is another common reason for culvert failure. Culverts designed and built to carry a specific amount of water can fail in the face of excess flow that can put stress on the structure, leading to failure. This can happen due to changes in land use or development, such as increased urbanization or deforestation, which results in more water runoff.

It is crucial to consider potential changes in water flow and factor them into the design of a culvert during the planning phases of infrastructure improvement projects. Additionally, regular inspections can help identify any potential overloading issues and allow for necessary maintenance or upgrades.

Extreme Weather Events

Heavy rainfall, floods, hurricanes, and other natural disasters can put significant stress on culverts, causing them to fail. These events may have been unpredictable at the time of a culvert’s construction, but given the increasing frequency of extreme weather events, factoring in the need for higher capacity and greater structural integrity should be a part of any new culvert construction or rehabilitation project.

Woody Debris and Other Obstructions

Culverts can also fail due to blockages resulting from woody debris, vegetation, or other obstructions. These obstructions can decrease the culvert’s capacity to convey water, increasing the risk of failure during heavy rainfall.

Conduct regular inspections and clear any debris or vegetation buildup that may obstruct the culvert’s flow. Incorporate appropriate debris and sediment management strategies into culvert design to help prevent blockages.

Erosion of the Supporting Soil and Fill

The supporting soil and fill around a culvert can also erode over time, especially if there is corrosion or damage to the invert or the soil around the perimeter of the pipe, whether concrete or metal. Failure due to erosion is more common in areas with high water flow or significant changes in elevation.

Consider potential erosion risks during the design phase and implement appropriate measures such as armored slopes or riprap protection. Regular inspections can also help identify any erosion issues and allow for necessary repairs or reinforcements.

Increased Traffic or Road Expansion

Road and bridge expansion or reconstruction can result in greater weight and traffic, which can put increased stress on the culverts below, potentially causing them to fail.

Accounting for potential increases in weight and traffic during planning and construction or repair can help prevent this type of failure. Regular inspections can identify any potential issues and allow for necessary maintenance or upgrades to support increased traffic.

Proper design, construction, regular inspections, and maintenance are crucial in preventing culvert failure. It is essential to keep an eye on any signs of deterioration or potential issues that may lead to culvert failure and take appropriate action to prevent it. With proper care and attention, culverts can continue to serve their purpose effectively for many years to come.

The Most Common Reasons for Culvert Failure, Explained