The embankment soils are too steep and were not compacted, which has led to filling in the orifice.Backfill of soils under, adjacent to, and atop culverts is extremely important in realizing their full service life. Pipes should be separated enough so that the soil can be worked into a tight bond with a compactor. Where fill is loosely placed or voids occur in the backfill next to the culvert, a phenomenon called piping can occur. Piping means that water enters the space between the culvert and the backfill, saturates the soil, and slowly washes away fine particles. Over time this action creates larger voids and erodes the soil away until a failure occurs, either when a storm washes out the remaining soil and causes a blowout or when a vehicle sinks into a hole and crushes the culvert. Rule 4. Compact Clean Soil Tightly in and Around Culverts and the Cover MaterialYou can rent a “wacker” for a few dollars at most rental centers. A wacker is a gas-operated, vibratory, single-operator compactor that can be brought to the site in a pickup truck. You can build a great road and design an incredible culvert crossing, but without compaction of the backfill, you will get to do it all over again. Poor compaction and debris-laced fill are the most commonly diagnosed failures in culvert crossings.Careful placement and compaction of clean fill is needed to install a culvert properly. Installing a granular backfill of pea gravel, often called pipe bedding, in the trench to a depth of 6 in. under the pipe and on both sides up to the midway point aids in draining groundwater and seepage away from the outer walls of the pipe and reliably assists in preventing piping failures.Rule 5. Construct the Road Section Low or Allow for Overtopping to One SideThe sizing of the culvert crossing is for an average year storm. Blockage, larger storms, rapid snowmelt, and debris flows all endanger the roadway and crossing. A prudent designer purposely will depress the road grade to allow for a storm-flow section equal to twice the cross-sectional area developed in Rule 2 to pass over the roadway. The site geometry will determine whether the overtopping section should be directly over the culvert or whether placing it to one side will be adequate. If possible, the overtop section should be placed to one side to prevent the erosive forces of the overtopping mixture of water and debris from destroying the downstream embankment face directly over the culvert. Overtopping to one side often causes the water to flow on a thinner fill section or, even better, over stable native ground. If the overtopping section is strategically placed and sufficiently armored, the access road will still be in place once the floodwaters have passed. Rule 6. Use Maximum Sideslopes of 2:1 (H:V) and a Road Surface Width of at Least 12 Ft. to Calculate the Pipe LengthA common problem with culvert installations is trying to get by with a short pipe length. The design needs to take into account the sideslopes, depth of cover, and roadway width to calculate the necessary length of pipe. Sideslopes steeper than 2:1 generally are not stable and erode quickly in the first few years. Steep slopes are difficult to establish vegetation on and hard to maintain. The slope should meet the bottom of the pipe and not the top; the latter causes a very steep point over the pipe that easily is eroded. Add together the diameter of the pipe twice, the slope length (cover times slope) twice, and the roadway width to determine the pipe width. For pipes set in steeply sloped channels, more length is needed, but in general this approach works for a majority of the crossings. If possible, always install a factory-made flared end section on the pipe, which aids in outfall dispersal of the stormwater and makes road embankment sideslopes above the pipe more stable.