A dog house manhole is appropriate when a structure must be placed over an existing active line to allow for the addition of another line.
Precast saves time.
1. A CIP or precast slab may be placed under the existing line.
2. A precast riser section with openings (that look like an entrance for a dog house) is placed over the existing pipe and set on the CIP or precast slab. The riser may cemeted to to the base with mortar or concrete may be placed in the manhole to a point below the springline. The active pipe may then be broken out to expose the channel.
4. The new pipe will usually add to the flow and not be used for discharge.
5. Or you could construct a new manhole using brick/block and then break open the existing pipe.
More flexibility when working with brick and block - requires more time than precast doghouses.
Thanks.
When you are adding a manhole b/c of new upstream pipe (i.e., new and active pipe meet and there is a change in direction), what would be the procedure for construction?
I am not clear on how you construct without interrupting flow. You build doghouse and new upstream pipe. Then you break active pipe and have a hole that needs to be plugged while you have flow through the manhole from new upstream pipe.
I think you're a little confused. There is no need to plug the hole. The new pipe remains inactive until the top of the existing pipe is broken. The existing pipe is broken inside of the new manhole to allow the flow from the new pipe to enter it. The existing pipe isn't broken until the new manhole is completely in place and sealed.
I think I am explaining poorly. My situation is that a building is being expanded over an existing sanitary line. Obviously, we plan to lay new pipe outside of the building envelope. Where the new pipe intersects the existing pipe we will use doghouse manholes. My question relates to the order in which construction occurs.
I will construct upstream doghouse manhole with existing active line running through manhole to service upstream users. Then, I will lay new pipe down to downstream intersection and construct another doghouse mahhole. When I break active line to redirect flow through new pipe, the existing pipe entrance through the doghouse manhole will be open, allowing flow through existing pipe. How do you deal with this? Hope this makes sense.
you are right - it will be a messy job to break and plug the existing pipe. once you break the pipe, you will have water in the manhole. you could plug an upstream manhole and then pump to the next downstream manhole. this would allow work to be done in the dry.
