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Water retaining structure joining existing building

Water retaining structure joining existing building

Water retaining structure joining existing building

(OP)
Hi there,

I have a flood defence wall (concrete) which is butting up to my existing building (reinforced hollow core block wall, rendered with waterproof render). I need to form a joint between the new concrete wall and the existing building and I'm looking for the best way to do this. The only time the joint will have water pressure is when the river floods and this will be a weak point. Any suggestions? I thought at first maybe just a 12mm expanding board sealed with polyurethane sealant but I think this could pop out under pressure? the retained height of water from the base of the wall is 1.3m. Any help would be greatly appreciated. Thanks

RE: Water retaining structure joining existing building

is there a reason the concrete wall won't be able to independently resist the water pressure and debris impact loads from a flood (100 yr storm?)? i see you are using metric so i'm guessing you probably aren't dry floodproofing to the USA NFIP design references that FEMA puts out. at the risk of threadjacking..... your question does make me wonder what differences there are with floodproofing across the world.... i'm also wondering if other countries are taking measures to anticipate climate change effects to the frequency of these flooding events and water elevations....

RE: Water retaining structure joining existing building

Is your flood defense wall parallel to, or perpendicular to your hollow core building wall?

Mike McCann, PE, SE (WA)


RE: Water retaining structure joining existing building

(OP)
hi, thanks for your response. The concrete wall does independently resist the flood water, it connects to the building which has also been made water tight (floor doors, waterproof render etc.). The idea is to make my clients site completely water tight in the event of a flood by utilising their existing structures, waterproofing them and building independent retaining structures between them. What I need to do is a detail between the new wall and the existing building to make sure the seal around the site is complete. Hope I am making sense. I'm in UK, so no we aren't dry floodproofing. thanks

RE: Water retaining structure joining existing building

Could you glue sheets of expanded polystyrene to the existing wall and use that EPS board as a form for your new wall on that one side?

The EPS sheets could be perhaps 1 to 2 inches thick (25 to 50mm).

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RE: Water retaining structure joining existing building

(OP)
The new flood defence wall is on a slight angle to the existing building (approx. 10 degrees)

RE: Water retaining structure joining existing building

Can you draw a plan and section and post them?

That would help visualize the situation.

Mike McCann, PE, SE (WA)


RE: Water retaining structure joining existing building

Cookm23:
Cut some sort of a expanding rubber water stop into the existing conc. blk. wall and then cast the new conc. wall around the other half of the water stop. Then fill and caulk the rest of the joint btwn. the two walls as your detail shows.

RE: Water retaining structure joining existing building

I would also stub some horizontal bars from the new wall to the grouted portion of the existing CMU wall.

Mike McCann, PE, SE (WA)


RE: Water retaining structure joining existing building

I vote for your first idea. Those Sika polyurethane sealants are tough.

RE: Water retaining structure joining existing building

(OP)
Hi All, thank you for your replies. msquared48 I did think about putting horizontal bars between the new wall and the existing building and putting a sleeve on one side but I was just worried that if one moved it would have an effect on the other. The flood wall is over 300m long although is does change direction a lot.

dhengr I thought about a water bar but didn't know if we would be able to cut a channel in the existing blocks and get a tight seal with a water bar? I know if it was new concrete on both sides that would be easy to do and just cast the concrete around it?

hokie66 do you think the joint would hold under pressure of water after a year of wear and tear say?

thanks everyone

RE: Water retaining structure joining existing building

Cookm23,
Yes, it will last much longer than that. Of course, the joint must be properly made as to preparation, priming, geometry etc.

RE: Water retaining structure joining existing building

(OP)
thanks everyone, gone for belt and braces and we've used the detail I attached earlier with the filler board and sealant but we've provided a water bar too as a back up.

thanks for all your help and suggestions

RE: Water retaining structure joining existing building

Just one thing about your detail. The geometry of sealant joints is critical, and normally needs to be about half as deep as it is wide. More depth promotes splitting.

RE: Water retaining structure joining existing building

Is there any provision for the new wall to move longitudinally back and forth with temperature changes, such that it may affect that joint with new wall?

RE: Water retaining structure joining existing building

(OP)
Hi Hokie66, thanks for that, we haven't specified a depth but I'll get a message out to the resident engineer to ensure that they do that, thanks.

Hi Oldestguy, there are no movement joints as such along the concrete wall as the wall changes direction a lot along the length, the person who designed the wall said the steel reinforcement has been designed to take care of thermal movement. The joint I've provided is meant to keep the 2 structures separate whilst providing a water tight joint. Hopefully I've achieved this!

RE: Water retaining structure joining existing building

I would be hesitant to rigidly connect the 2 structures. Need some gap for thermal growth and flexing due to hydrostatic and settlement.
What if you pour a short stub wall of concrete connected to the masonry wall, then put in a flexible bulbed waterstop between the stub and the rest of the wall? Could leave the required gap to accommodate movement.

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