huangyhg

masonry cistern
i have a 9'x9'x150' cmu storm water detention tank that i have been asked to design. the bottom is at -12' below grade. it will be full only for a few hours during peak runoff. being a little hesistant at the use of masonry, i have been insisting that the end walls where the 36" & 18" dia pipes penetrate the head wall be concrete. does any one have any thoughts on the choise of materials, control joints, leakage, tunneling & sealing around the inlets.
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in metric your tank is 2.74m x 2.74m x 45.72m, so long and narrow. is this an online or offline tank?
i would question using masonry as one, it can leak (depending on type of masonry) and two, the cost of building might be quite expensive and time consuming.
have you though about precast concrete culvert sections?
ussuri made a good suggestion.
in order for the walls to be built out of masonry, they will first need to be shored. this is a cost issue and is also a problem for constructing the masonry as the shores will get in the way of the construction.
i have seen detention tanks done with cmu, but not this deep.
i do disagree with ussuri on one thing, a small amount of leaking through the masonry is not usually an issue.
csd
reinforced masonry cisterns (8" cmus) and similar structure of that depth are the norm in most countries.
concrete slab, reinforced, grouted masonry walls coated with materials similar to thoroseal. pentrations and wall/floor joints are usually sealed with hydraulic cement first. in some case, the interior is also parged (tradition).
wht not use an hdpe twinwall pipe ?
120" diameter concrete pipe of the same length will give same volume with only 1' more depth and enormously more usability for surcharge and wall strength.
thanks to all for your comments.
i did make the suggestion to use prefab conc culverts but. . . the owner is a mason
i spec'ed bentonite rope around the penetrations and had been wondering about the need to seal the interior. but i've been going rounds with the owner on the need to make the headwalls concrete. wouldn't it be difficult to get all the cmu cells filled below the two staggered pipes?
csd72
i think it depends on your definition of 'stormwater'. if stormwater is just excess rainwater then i agree leaking is not an issue, however, if stormwater is storm runoff from a combined sewer it is contaminated with raw sewage and hence leakage means ground contamination.
i was unclear what the op meant by cmu. i understand this to dense concrete block, which is quite porous. historically engineering brick has been used to build all sorts of structures associated with wastewater even primary tanks and septic tanks, albeit 100 years ago.

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