Manhole Covers Failure: Causes & Prevention Tips

May 13, 2025
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Introduction

Manhole covers are an essential but often overlooked part of modern infrastructure. Designed to provide access to sewer systems, water lines, and electrical vaults, they also ensure safety for pedestrians and vehicles.

However, manhole cover failure can lead to accidents, traffic disruptions, and costly repairs. Understanding why manhole covers fail and how to prevent it is crucial for municipalities, contractors, and infrastructure planners.

Common Causes of Manhole Cover Failure

1. Corrosion and Environmental Exposure

Corrosion is one of the most frequent causes of failure, especially in areas with high humidity, salinity, or chemical runoff. When manhole covers are not properly treated or coated, exposure to the elements can degrade their metal over time.

2. Improper Installation Practices

Even a high-quality manhole cover can fail if it’s installed incorrectly. Poor leveling, misalignment, and lack of bedding material can cause uneven load distribution, leading to cracks and early failure.

3. Overloading and Load-Bearing Limits

Every manhole cover is designed for a specific load-bearing capacity, classified under ratings like A15, B125, D400, etc. Using a low-rated cover in a high-traffic zone can cause it to collapse or crack under pressure.

4. Material Cracking and Fatigue

Over time, materials can degrade due to repeated stress, temperature fluctuations, and traffic vibrations. This leads to manhole cover cracking, a common form of fatigue failure that compromises safety.

5. Vandalism and External Forces

Intentional tampering or unintentional damage from vehicles and construction activities can displace or damage manhole covers. Loose or missing covers pose immediate dangers to vehicles and pedestrians.

Understanding Load-Bearing Capacity

Each manhole cover is rated based on its load-bearing class, typically following international standards such as EN 124. Here's a quick overview:

Class Load Capacity Recommended Use
A15 1.5 tonnes Pedestrian areas
B125 12.5 tonnes Residential driveways
C250 25 tonnes Light traffic areas
D400 40 tonnes Roads and highways
E600 60 tonnes Industrial zones, ports
F900 90 tonnes Airports, extreme load zones

Incorrect use of class ratings is a leading contributor to premature manhole failure.

Manhole Cover Maintenance Best Practices

To extend the life of manhole covers and reduce failures, regular manhole cover maintenance is essential.

1. Routine Cleaning

Clearing debris prevents water pooling and reduces corrosion. It also ensures the cover fits snugly and doesn't become a hazard.

2. Anti-Corrosion Coating

Applying protective coatings or using corrosion-resistant materials like ductile iron helps extend the product's lifespan.

3. Lubrication of Hinges and Locking Mechanisms

For hinged or locked covers, lubrication prevents seizing, ensures proper sealing, and allows safe access when needed.

Manhole Cover Inspection Checklist

A structured manhole cover inspection checklist helps identify issues before they become failures:

1. Check for visible cracks or chips
2. Ensure the cover sits flush with the frame
3. Look for corrosion, rust, or pitting
4. Inspect for signs of displacement or a loose fit
5. Confirm markings and class rating visibility
6. Test the frame and fasteners for stability

Documentation during inspections aids in maintenance scheduling and safety audits.

Recommended Inspection Frequency

How often should manhole covers be inspected? It depends on the location, traffic, and environmental exposure.

Suggested Frequencies:
High-traffic urban zones: Every 3 months
Industrial/commercial areas: Semi-annually
Low-traffic residential zones: Annually
Post-extreme weather or construction: Immediate inspection

Smart sensors and IoT monitoring are emerging as tools for real-time condition tracking.

Preventing Manhole Cover Failure

1. Select the Right Load Class

Ensure the manhole cover is correctly rated for the environment. For highways, use D400 or higher.

2. Use Ductile Iron Over Grey Iron

Ductile iron provides better strength, flexibility, and resistance to cracking under stress then Grey Iron.

3. Install Properly With Supportive Bedding

Levelling the frame, using the right mortar, and sealing the edges are key to a stable manhole cover installation.

4. Maintain a Maintenance Log

Track each inspection, cleaning, and repair to ensure accountability and early issue detection.

Conclusion

Manhole cover failure isn't just a maintenance issue - it's a public safety risk. Fortunately, most failures are preventable through routine inspection, proper installation, and material selection.

By following load-rating guidelines, adopting preventive maintenance practices, and using advanced materials like ductile iron, infrastructure managers can reduce risks, cut costs, and protect both people and property.

FAQs

1. What causes manhole covers to fail most often?

Corrosion, overloading, improper installation, and material fatigue are the leading causes.

2. How do you prevent manhole cover cracking?

Use ductile iron, install according to load specs, and inspect regularly for early signs of stress.

3. What is the best inspection frequency?

High-traffic areas need quarterly inspections, while low-traffic zones can be inspected annually.

4. Are there standards for manhole cover strength?

Yes, covers follow EN 124 and other regional standards that specify load-bearing capacity.

5. What should I look for during an inspection?

Check for cracks, displacement, rust, class label clarity, and ensure the cover is flush and stable.