Storm Inlet Box Construction

[cveg05]

I am working with a contractor who is dead set on using CMU blocks to construct his storm inlet boxes instead of casting the walls in place with concrete. He will put rebar in the CMU wall and then fill the interior of the wall with concrete and vibrate. The top and bottom of the box will be standard. I really don't like this method but I thought before I dismissed it I'd see if anybody has positive input on this method. Has anybody used this method before? Is it durable?
Thanks for the help.

 

[TerryScan]

I think it is interesting that I read this thread on the same day you post this question:

http://www.eng-tips.com/viewthread.cfm?qid=275539&page=1

 

[Ryb01]

What has been specified in the contract drawings and documents? The contractor should be following what has been specified.

I have seen these types of inlet constrtuction used in Europe and in some parts of South America. Durability I would be unsure about but could only speculate that the seams may be may be more prone to cracking overtime vs a cast in place wall. From an aethetics point of view, the CMU blocks would be less attractive.

I would be curious to see what feedback the other members in the forum has.

 

[cveg05]

The timing of that is funny and that's the exact kind of issue I'm concerned with. I can't see any reason to allow CMU walls. I mainly wanted to see if anybody had any knowledge about them that I was missing.

Thanks for the response!

 

[cveg05]

Ryb01 - The specs and details call for a standard cast in place structure. This is for a private development and the contractor and owner are trying to reduce costs. I work with the City and, since this is a private storm system, I have some influence on whether they are permitted, but not the final say. I'm just trying to inform the owner/contractor on the best options available. I would not allow this type of structure within the City ROW.

 

[JedClampett]

Ah yes, the private developer. It doesn't matter what you've specified, they just want it to last as long as it takes them to get out of town.
Maybe you can convince them to use a precast structure. It's a little cheaper, but should last for a while.

 

[GoldDredger]

I've never heard of a storm box built with CMU, but I have heard of manholes built of brick. I've always seen manholes and boxes either made from precast concrete or cast in place. I can't imagine the costs are that significant over this CMU idea. (Contractor probably has a stockpile of it from his last masonry job)

I would be inclined not to allow this if possible, or at least require them to get an engineer to sign off on the design. How deep is the box, and is it in a traffic area recieving loads? If so you could say this is a health and safety issue.

I am not sure the CMU blocks, or the grout between them, will hold up that well against water erosion. I think the CMU blocks are only constructed with fine aggregates which might make it susceptible to eroding.

Lastly, you mentioned this is a private storm system..are you sure? For example will the storm system convey any off site flows, if so it should be considered public with an easement for the other neighbor.

Also, will this system discharge into a public storm system or drainage course (of course it does eventually), then you could claim their design doesn't mesh with the standards of practice in your area.

Is there high groundwater? Make them do a vacuum test, hehe, it will never pass.

 

[cvg]

concrete block headwalls and wingwalls and junction boxes have been used extensively for drainage and irrigation projects in the southwest and last for years. They are properly waterproofed to prevent leakage and erosion. They also are generally cheaper to construct. These structures are built to agency standard details, not by developers. I have also seen concrete block construction used for a floodwall. Again, with the proper design and waterproofing, this was approved by FEMA.

 

[beej67]

I've seen a hell of a lot of brick structures in Atlanta that have lasted decades.

My biggest concern with a CMU box would be where large magnitude flows turn corners. Momentum is a nasty thing, and rarely considered in storm drain design.

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[eea]

There is a product called manhole (MH) blocks. These usually solid units and cost more than standard CMUs. Check your local DOT guidelines. Ours has details for MH bricks, MH blocks and precast all under the same payitem, contractor's choice. The "homebrew" rebar / CMU approach would be ruled out if it were my project.