Part C - Culvert inspection

Section analysis 2.1 – Scope

Types of inspections include but are not limited to:

• visual
• detailed
• scour
• hydraulic
• underwater
• special

A culvert with undetected or unreported damage or deterioration can present a severe risk to safe railway operations. Evaluating a culvert requires the application of engineering principles by a professional engineer, who is usually not present during the inspection. For this reason, an inspection report should show any conditions on the culvert that might lead to a reduction in capacity, initiation of repair work, or a more detailed inspection of the condition.

Section analysis 2.3.4 – Submerged culvert inspection

The condition of underwater culvert components is usually not evident from above. Determining their condition might be as simple as using a measuring rod or might need periodic or special diving inspections. Advanced technology might also be able to determine underwater conditions.

Not all culverts need an underwater inspection. Not every part of a culvert underwater needs an underwater inspection. If a railway engineer determines a culvert to be susceptible to conditions that will need underwater inspections, then appropriate provisions and procedures are put in place.

Underwater inspection equipment can be ineffective due to murky water conditions. In this case, a railway engineer may consider a diving inspection for a larger diameter culvert to determine its condition. For smaller diameter culverts, the railway company could monitor the track and embankment on an ongoing basis and look for any signs of culvert failure as soon as it occurs. This monitoring should also include a documented inspection at the companies’ required frequency.

Section analysis 2.8 – Culvert risk identification  

Safety issues and concerns associated with culverts include, but are not limited to:

1. Waterway adequacy

Evaluate the stream channel and drainage area for:

• changes in stream channel alignment, which may reduce hydraulic capacity or cause scour
  • a change in the direction of flow or its velocity can contribute to culvert failures
  • wing walls and barrels can break off due to settlement caused by scour
• changes in upstream land use may change the peak flow rates and stream stability
  • these include clearing, deforestation, significant construction and new development, channel improvements, and removal of dams
  • obstructions downstream that back water up to the culvert may also affect the performance of the culvert or cause saturation of the roadbed
• excessive bank erosion, stream channel aggradation/degradation that may indicate a change in water flow
• high water marks which indicate that a culvert may be inadequately sized
  • this increases the potential for flooding damage or track flooding
  • check culverts during or immediately after peak flows to determine if water has ponded, adjoining properties are flooded, or the track is flooded
• water should flow in and out of a culvert smoothly and without interference or obstruction
  • channel obstructions such as deposits of debris, ballast, driftwood, mudslides, beaver dams, and organic growth affect the hydraulic capacity of a culvert

If any of the above conditions exist, the railway company should consider an analysis to determine if a culvert is adequately sized.

2. Beaver activity

Beaver dams located upstream and downstream from the track represent a potential hazard to the track structure. The primary hazard caused by beaver activity is washouts. It also causes gullying or seepage erosion of the railway grade. Railway companies should regularly inspect for beaver dams and take appropriate actions if conditions are hazardous. An aerial survey of beaver dams may be required in the spring and fall of each year to support ground inspections.

3. Debris and sediment blocking culverts

The culvert must be able to handle the design flow. If the culvert is blocked with deposits of debris, driftwood, organic growth (including beaver dams) or sediment, the culvert may be unable to handle design flows. This may cause excessive ponding, flooding of nearby properties, and washouts of track and embankment. Accumulations of debris and sediment in the stream may cause scour of the stream banks and embankments or changes in the channel alignment. Thus, it is imperative that railway companies remove deposits of debris and sediment if they threaten safe railway operations and property.

4. Snow and ice conditions blocking culverts

Snow and ice can prevent proper drainage by blocking a culvert and impeding flow. Railway companies should take appropriate actions to protect safe railway operations in these conditions.

5. High water condition

Some areas frequently or historically experience high or rapidly moving water conditions, such as flash floods. These areas may be protected with detection devices to sense the rise or velocity of water in or near culverts, which may be unable to carry the total storm runoff. The track bed may be washed away or flooded, which can cause significant damage. When such conditions are imminent, washout protection devices will provide sufficient warning to stop all nearby trains.

Similar to washout protection, a high water detection device detects the rate-of-rise and absolute level of water around vulnerable locations such as culverts. These locations could be inundated by rapid storm runoff conditions. Conventional rain gages could also provide early warning of high water conditions.

6. Severe weather conditions

Railway companies should watch for events, including but not limited to heavy precipitation, spring runoff, high river levels, and/or higher than normal flow conditions. When such conditions exist, inspections should be performed, and appropriate measures taken before and after the event to protect safe railway operations. Re-evaluate culverts to confirm both structural integrity and the ability to accommodate water flow under the track adequately.

In locations where railway companies and road authorities share a drainage basin, it is essential that they have communication protocols for sharing information relating to the protection of the infrastructure, especially during severe weather events.

Railway companies should monitor weather conditions and weather warnings. They should follow-up with special patrols for culvert inspections, including drainage assessments for the specific warning areas. Weather monitoring is an effective way to plan for adverse situations.

When identifying hazards related to culverts, railway companies should consider:

• identification of culverts which are susceptible to scour or lateral stream migration
• identification of areas subject to flooding or high flows
• identification of culverts that have been damaged by a previous event
• identification of critical culverts to determine whether, when, and where projected flooding or high flows might be consequential
• awareness of snowpack conditions and impact on spring runoff
• awareness of the effects of ice flow dams and other debris accumulation on the substructure
• developing and implementing methods to protect culverts before, during, and after a flood or high flow event
• developing and implementing monitoring technologies that could provide advance warning of pending failures due to the effects of an event
• use sonar, sensors, and other smart technologies to monitor scour-critical culverts
• defining qualification and training requirements for inspectors to monitor culverts during an event
• developing processes to monitor severe weather events
• defining the frequency and scope of inspections during a flood or high flow event

7. Highly corrosive and abrasive environments

Water and soil-related corrosion and abrasion are the 2 main ways culvert materials deteriorate. Certain soil and water conditions have a strong link to accelerated culvert deterioration. Metal culverts corrode in certain aggressive environments. The pH and electrical resistivity of soil and water indicate the likelihood of corrosion. Railway companies should create pH and resistivity guidelines based on local conditions and performance.

Abrasion may remove any protective coating on the metal. This exposes the core material to chemical and further abrasive attack. Corrosion may weaken the structural capacity of the pipe by creating perforations from either the water or soil side. Material and water moving through these holes may create voids around the culvert pipe. This undermines the supporting backfill material and further weakens its structural integrity.

The effects of water-side abrasion and corrosion are visible and easy to assess. However, soil side corrosion is not as visible; corroded fasteners or rust emanating from the seams may indicate soil side corrosion. Corrosion and abrasion of corrugated metal culverts can be a serious problem with adverse effects on structural performance.

Railway companies should be aware of aggressive environments. They should have a plan in place to monitor, address, and implement special inspection methods in those environments.

8. Buried culverts (culverts “not found” but which exist on the railway company’s inventory)

Culvert inspectors should report any inventoried culverts they are unable to locate to the railway engineer. A railway engineer is responsible for determining the effect this may have on drainage in the area and safe railway operations.

Buried culverts may cause inadequate drainage or culvert failure, which could impact safe railway operations. Railway companies should make every effort to locate such culverts and update their inventory.

9. Deferred work

A railway engineer should perform an evaluation and risk analysis before deferring any culvert work.

10. Inadequate culvert length

Culvert extension may be required because of proposed bank widening, stream deepening, track lift, or other work.