Sometimes you're just not lucky as a structural engineer.
I was engaged to design two residential projects…
But both had the same surprise:
A massive stormwater main and a sewer line running right through the property.
Building near or over underground services like sewer mains and stormwater pipes means you’ve got to follow strict rules.
Why?
To make sure your footings don’t collapse into a trench one day and so council can access the pipes for maintenance.
Here’s what I had to follow on these jobs:
1. Minimum Clearances
• 1.5m from stormwater drains
• 1.2m from sewer mains (measured horizontally from the pipe’s centerline)
2. Manhole Access (Open to Sky)
• A 1.5m clear zone is required in all directions around the maintenance cover
• No structures allowed over this area not even lightweight sheds or awnings
3. Excavation Rules
• No excavation within 600mm of the pipe
• If you need to dig close, use a backhoe in layers or a vac truck for safety
4. Footing Design
Depending on the layout, I’d use:
• Cantilever strip footings to span over the pipe near building edges
• Reinforced concrete ground beams supported on piers to bridge the service
5. Retaining Walls
• I prefer concrete sleeper walls (soldier piles) in these areas
• Or even block walls with strip footings + piers. Same concept, adapted to the wall type
And yes, if you’re in Queensland, all this must follow the QDC MP 1.4.
PS: We don’t use bored piers less than 1200mm away from the pipe because they might drill through pipes and damage them.
Backhoe excavates in layers, and a vac truck uses suction to safely remove soil and debris without damaging underground utilities.
Hope that helps next time you hit pipes on site!
PPS: We're opening BengLab's May cohort shortly with exclusive bonuses for those in the email list.
BEng The Brazilian Engineer in Australia
Sometimes you're just not lucky as a structural engineer.
I was engaged to design two residential projects…
But both had the same surprise:
A massive stormwater main and a sewer line running right through the property.
Building near or over underground services like sewer mains and stormwater pipes
means you’ve got to follow strict rules.
Why?
To make sure your footings don’t collapse into a trench one day and so council can access the pipes for maintenance.
Here’s what I had to follow on these jobs:
1. Minimum Clearances
• 1.5m from stormwater drains
• 1.2m from sewer mains (measured horizontally from the pipe’s centerline)
2. Manhole Access (Open to Sky)
• A 1.5m clear zone is required in all directions around the maintenance cover
• No structures allowed over this area not even lightweight sheds or awnings
3. Excavation Rules
• No excavation within 600mm of the pipe
• If you need to dig close, use a backhoe in layers or a vac truck for safety
4. Footing Design
Depending on the layout, I’d use:
• Cantilever strip footings to span over the pipe near building edges
• Reinforced concrete ground beams supported on piers to bridge the service
5. Retaining Walls
• I prefer concrete sleeper walls (soldier piles) in these areas
• Or even block walls with strip footings + piers. Same concept, adapted to the wall type
And yes, if you’re in Queensland, all this must follow the QDC MP 1.4.
PS: We don’t use bored piers less than 1200mm away from the pipe because they might drill through pipes and damage them.
Backhoe excavates in layers, and a vac truck uses suction to safely remove soil and debris without damaging underground utilities.
Hope that helps next time you hit pipes on site!
PPS: We're opening BengLab's May cohort shortly with exclusive bonuses for those in the email list.
Cheers,
Gabe
5 months ago | [YT] | 29