Installing manholes at drainage pipes point of intersection

[bnard]

From manuals and books its a requirement to install manholes at intersection and in change of pipes sizes. I have noticed in one of the previous project in dallas, texas that they have used a wye pipes instead of manholes. Can anyone discuss its benefits and technicality? Will appreciate very much thanks

 

[Maury]

I'm not sure how wyes would be used. We have called for tee sections in large diameter (48" dia. or larger) concrete pipe. The brench of the tee is set vertially and extended as needed to serve as a manhole. A flat slab is set at the top. Steps are included. The advantage is that precast manholes aren't available in sizes big enough for very large pipes, and tee sections ate cheaper than poured in place structures.

Maury

 

[cvg]

OSHA regulations require ventilation and means of exist for confined spaces. One way of doing this on a storm drain is to provide manholes at frequent spacing. Typically at changes in grade or alignment, a special structure is required and this provides a good location for another manhole. If the structure is cast in place, the manhole may be necessary to allow easier construction. Where there are large angles, grade changes or lateral connections, debris may get hung up in the storm drain, the manhole allows maintenance.

As indicated by Maury, tee sections work fine for manholes, except don't allow grade or angle changes or lateral pipe connections.

 

[Maury]

cvg is right about tee manholes not acomodating lateral pipes, but in my area (northern Illinois) manufacturers are able to construct them with changes in direction, changes in pipe sizes, and minor changes in grade. Where major grade changes are required, we provide a separate bend adjacent to the tee.

 

[bank]

The only benefits I can imagine that would favor a wye over a manhole are cost and confinement (i.e., water can't surcharge up to ground level if there's no structure allowing it to escape). From a maintenance standpoint they are a nightmare and should be avoided, except, maybe for roof drains and very small lines on which cleanouts can be used in lieu manholes.