Renovation of vaulted basin

[EntryLevelEIT]

I am currently surveying an underground clear water storage basin for cracking and potential cave in areas. Access is through manholes only. The basin is constructed of concrete vaults supported by columns all unreinforced. Worst case senario is that construction will need to be done with the basin in service, yet to be determined. Assuming worst case I was wondering if their is some way to safely section off/drain certain parts of this basin that may need to have portions of the roof replaced. This type of construction is so old my concrete design book really doesn't mention it at all. If anyone has seen or dealt with anything like this before I would appreciate your input. Thanks in advance.

 

[JedClampett]

You can bulkhead off sections or even use some kind of temporary bladders.
How many gallons is the clearwell and how deep is the water in it? I have some suggestions, but unless you really love that clearwell, the solution might be a rebuild.

 

[EntryLevelEIT]

Water is 10' deep with a total of about 30 Million Gallons.

 

[csd72]

beware of the thrust lines in multiple arches.

If you remove or prop a single arch then this can disturb the equilibrium.

 

[JedClampett]

As far as blocking off portions, you can build temporary bulkheads, line them with an impervious membrane, like HDPE, and proceed. You have to watch for load imbalances, like csd72 said. Usually the bulkheads are made of steel frames, with plywood faces and of course, a liner, battened to the floor. There are companies who make such creatures. There are also water filled bladders, that act like sandbagging.

http://www.waterstructures.com/

 

[msquared48]

Is this for storm water, fire, or stored water to be treated later for drinking, or ?????

Can the cistern be bypassed temporarily during construction?

How much overburden, if any?

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[csd72]

The support formwork for an arch is called centring and even if this is properly used it can still created load imbalances so you may need to introduce additional horizontal props/ties.

http://en.wikipedia.org/wiki/Centring

http://www.unhabitat.org/pmss/getElectronicVersion.aspx?nr=1774...1

 

[EntryLevelEIT]

msquared:
This is stored domestic water (already treated). So, as you would imagine sediment/debris and even storm water falling into the supply is also a concern.
Whether the entire basin can be bypassed during temporary construction is still being determined. This structure was built to last 100 years, unfortunately that time has come and gone.

csd:
I wasn't able to open the second link. I'll continue to get as much information as possible regarding thrust lines and centring. If a portion of this roof needs to be removed every component needs to be in equilibrium.

 

[csd72]

yes I thought it may not work, just google brick vaulted roof and it is the third or fourth link. A good PDF with a few force diagrams.

I know yours is concrete but the principles still apply.