pavement drainage problem 1

[itlionel]

Can anyone tell me what is the main difference between these two pavement drainage systems?
Thank you!

Type 1

Type 2

 

[Ron]

These are not pavement drainage systems. It looks like the plan view of a drop inlet or similar. Not enough information to tell you anything other than the grating design is different.

 

[itlionel]

I has been told that one of them is about sewage, but I still cannot identify them.

 

[hokie66]

I think they are manhole covers. The HK reminded me that I might have seen something like these in Hong Kong, but I can't be sure. If that thought is right, one may be a sanitary sewer and the other a storm sewer.

 

[hokie66]

Yep, here it is, with a little help from Mr. Google. The top one is for sewers, and the bottom one is for storm drains.

http://www.dsd.gov.hk/EN/Technical_Manuals/Standard_Drawings/

 

[itlionel]

That should be the answer!
Thank you!

 

[Ron]

Nice, hokie66! Experience and a little forensic research.....problem solved!

 

[dicksewerrat]

Square manhole covers are dangerous.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[Huck85]

Very good, hokie66.

And thanks Richard. I've heard of this statement before.
But how are they dangerous?
Can you please explain?

 

[jgailla]

Square manhole covers, unless seated correctly, can fall in when someone steps on them or a car drives over them.

 

[DaMeRy]

i The top one is for sewers, and agree with this opinion the bottom one is for storm drains. but I still cannot identify them.

 

[hokie66]

DaMeRy,
The link I referenced above identifies them.

jgailla and dicksewerrat,
Depends on the size of the cover. If large enough so it won't go down the hole in the frame, no problem. Just a geometry issue, and the Hong Kong covers seem to have considered the safety issue, I think.

 

[dicksewerrat]

Square cover have a tendency to fall into the pipe while trying to remove or replace. Diagonal measurement of the opening is much larger than the length of one side. Round covers outside diameter is usually 1 inch larger than inside diameter of the manhole ring. Won't fit without a major fight. Also if the square cover bounces, it may fall through.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[hokie66]

As I said, it is a matter of geometry. If the cover and frame sufficiently overlap the hole, the problem goes away.

 

[brandonbw]

I have known surveyors who accidentally drop them in when dipping the inverts on a pipe.

B+W Engineering and Design
Los Angeles Civil Engineer and Structural Engineer

http://bwengr.com

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http://bwstructuralengineer.com

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http://bwcivilengineer.com

 

[Huck85]

I see

Since Diagonal=(2^0.5)*length of the side