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rbergholz (Civil/Environmental) (OP)
8 Sep 03 17:30
I have a structural engineer claiming that the minimum thickness for shotcrete is 5-inches, which is 2-inches on either side of a 1-inch rebar mesh.  The liner doesn't need to carry substantial loads, other than the weight of the water.  5-inches over the entire basin will be very costly.  Has anyone heard of a thinner concrete liner approach?
tonks (Civil/Environmental)
9 Sep 03 4:53
5" isn't really all that thick.  Achieving a consistant thickness when shotcreting is difficult enough - don't forget about the mimimum cover to the steel in order to satisfy durability requirements.  Without some margin for variation, you could have little or no cover is some places.  I would tend to agree with the structural engineer on this one.

Tonks
Bbird (Civil/Environmental)
9 Sep 03 5:48
rbergholz,

Seem to me if your liner is structural and requires a steel mesh then the 5" is reasonable and tonk's comment is highly relevant.

The statement that the liner doesn't need to carry substantial load other than water can be misleading.  If you can send a guy to shotcrete a liner we are talking height of about 1.8m and the weight of water is substantial.

Thinner shotcrete is possible if it is for a purpose other than structural, for example to increase thermal insulation people have sprayed 2" shortcrete to brick liners.

If the liner does not require to contribute strength, the thickness can withstand the water velocity and the failure of the liner has no serious consequence to your system then your may be able to economise its thickness.
cskelsey (Civil/Environmental)
9 Sep 03 9:36
What sort of application is this shotcrete / concrete / liner design for? A canal? retention pond? etc.

All best,
-cK

Christopher Kelsey, editor
GFR magazine
gfr@ifai.com
www.gmanow.com

cskelsey (Civil/Environmental)
9 Sep 03 9:39
Ah! Scratch that last post. I was reading the thread before reading the thread subject line. (More coffee required?)

All best,
-cK
JedClampett (Structural)
9 Sep 03 10:52
Depending on how leak resistant you need to make the basin, a thinner liner can be used.  We used 3 1/2 inches for many shotcrete applications in the past.  I believe that irrigation canals in Phoenix use about 2 inches of shotcrete.  However, when I had to do a oxidation ditch where leakage was an issue, I used six inches.
For some reason, cover requirements are ignored for this type of shotcrete application.
rbergholz (Civil/Environmental) (OP)
9 Sep 03 12:17
Thanks for the feedback.  I'm beginning to think that the 5-inches is acceptable.  

Here's a little more info: The existing wastewater EQ basin is made of compacted earth with a visqueen liner.  The existing liner is severely weathered and torn.  The new shotcrete liner will provide longterm leak protection to the basin.  A small section will need to be thickened, structurally, to allow for a backhoe to enter the basin for cleaning.  Otherwise, the rest of the basin only needs the shotcrete to protect against infiltration.  

I'm wondering if there are any add mixtures that could be used in the shotcrete to eliminate the need for steel, or possibly a thin woven steel mesh in stead of tied rebar.
 

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