concrete vault for water line

[Structures33]

Hey all - I'm working on the design for an underground vault to house valves for a 42" water line. It's gotten a lot more complicated than I anticipated and I'm not sure of the best way to go about designing the critical wall. Inner dimensions are 17'-4" x 10' x 9'-11" deep.
The short wall is the critical wall as it has an enormous amt of thrust. Here's what we're looking at:
surcharge load on soil above - large - aprox 5330psf (unfactored)
active soil load on wall
thrust force (due to water hammer) where pipe enters wall - 497,677# (factored)
I've designed the long wall as a plate and that went fine. I'm not sure how to design the short wall. My initial thought is to design as a small beam section (one in each direction), taking a chunk of the thrust plus the other loads? Bottom is fixed and top would be pinned.
I'm not worried about the over all sliding- I'll address that w/ wingwalls and keys. I'm just worried about the wall surrounding the pipe entrance.
Any thoughts or suggestions appreciated!

 

[JedClampett]

I'm confused why the vault needs to carry the thrust from the water hammer. Usually the thrust forces are resolved through the continuation of the pipe, not in a structure. Maybe if the pipe terminates in the vault, but then you have a closed system and the thrust goes whence it came. The main places we have thrust issues are when push on fittings are used and there's a elbow or valve. Maybe the pipe should use restrained fittings as they're more efficient.
Some of your other forces look a bit high also. A surcharge of 5330 psf converts to an additional 42 ft. of soil.
If the thrust force is 500 kips, you're not only going to have problems designing the wall, but problems getting the force from the pipe to the wall.

 

[hokie66]

Agree with Jed. If that surcharge is correct, you should look at transferring it by structure to a level below the vault rather than imposing the large lateral load on your concrete box.

 

[Structures33]

Our water resources engineers gave me the thrust force and said that the vault would be taking it because of the configuration of the pipe. They are using restrained fittings along the line but because of the configuration they said this part would not be restraining itself. The valve is a few feet inside of the vault so when they shut it down, the water hammer will hit in there.
I haven't designed one of these before but it sounds like I may need to go through the details of the restraint and the thrust force with them???
As for the surcharge... It was created based on an assumed load of a very large backhoe servicing the vault - both the weight of the backhoe and the lid section of the vault that it will be lifting. I designed the long walls with this surcharge and they didn't seem excessive.
Thanks for the input and any additional advice is greatly appreciated.
JAH

 

[civilperson]

How does the force from the valve,(water hammer) get to the 9' x 10' wall? I would design a valve seat to take the longitudinal force of 500 kips. How does a valve close fast enough to make 500 kips of force, hydraulic or electric or what? Most valves have many,(50 plus), rotations of valve key to reach closed position. Workmen are knowledgeable and take a long time to finish this closing to minimize hammer.