Why are Manholes Round?  

Manhole covers (also called pit lids, maintenance covers or access covers) have been around since at least the Romans. They are commonly used to control access to underground pits, trenches or chambers. 

Pit Covers must be strong enough for pedestrians or vehicles to pass over, big enough for a person to enter but heavy enough to prevent accidental dislodgement.  

Manholes are typically round for several practical reasons: 

  • Stability and Safety: Unlike other shapes, a round shape is inherently stable. If you were to place a round cover over a round opening, it wouldn’t fall through, regardless of its orientation.  
  • Ease of Construction and Installation: Manufacturing and installing round covers and frames are simpler and often more cost-effective than square or rectangular ones. Round shapes are also easier to transport and handle. 
  • Uniformity and Standardisation: The use of round manhole covers allows for more standardised designs, making it easier to mass-produce them and ensuring that covers from different manufacturers are interchangeable.  
  • Pressure Distribution: When vehicles pass over a manhole cover, the pressure is distributed more evenly across the circular surface. This makes round covers less prone to cracking or breaking compared to covers with corners. 

I have a broken Manhole cover in front of my house who should I contact? 

If you notice that a manhole cover has been damaged, you can report it to the local authorities. They will assess it and take remedial action to fix any damage. 

How heavy are Terra Firma composite pit lids? 

Heavy concrete or metal pit lids are a real manual handling hazard. A 1200 x 900 concrete lid weighs approximately 200kg. The equivalent Terra Firma lid weighs 33kg.   

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