huangyhg

corrugated metal pipe under a building
my philosophy is not to place a building over an existing active corrugated metal pipe carrying storm water unless i encase the pipe in reinforced concrete. is this being too conservative? my thinking is that the lifespan of the pipe is shorter than the building, so it must be encased to prevent deterioration and subsequent potential settling problems, even if the c.m.p. is strong enough or deep enough to prevent crushing. is this typical practice for you other guys out there?

storm drain pipes, encased or otherwise are rarely placed under buildings. if you must do it, don't use cmp - use something with watertight joints such as rubber gasketed reinforced concrete pipe, ductile iron etc. or put it in a casing pipe.
yes, it's never a good idea if there is any way to avoid it. but i am asking about existing drains - not new. my first choice then is to rerout the drain so that it is not under the building - but what if the pipe cannot be re-routed. that's when i think the encasement is the best option. would still like to have some other opinions, standard practices, etc.
exhaust your other options first including putting the building somewhere else. encasement is probably not the best option, what happens when the cmp rusts through? are you going to rely on the encasement to convey the storm water? better to install a casing and then the drain pipe can be maintained in the future without disturbing the building.
the encasement would work like a concrete culvert if the cmp rusts through. how would you install a casing, and what kind of casing? i'm not sure this is as practical as just exposing the cmp and pouring concrete with reinforcing around it.
by practical, do you mean cheap and easy? casing is definitely not cheap, but probably better protection than encasement. unless you add quite a bit of steel reinforcement, your concrete encasement will become an unreinforced concrete pipe once the cmp rusts out. without sufficient reinforcement it will also not be watertight.
remove the culvert, install the casing, backfill, place the drainage pipe in the casing and then build your building
quoting the op
" encase the pipe in reinforced concrete"
it should work if designed adequately and i don't think it is too conservative.
thanks for your advice and opinions. nothing wrong with cheap and easy as long as it works! i have thought about inserting another pipe in the existing cmp (the geotech's suggestion), but i'm not sure how to specify this. uncovering the pipe in sections and using reinforced concrete while keeping the pipe in service makes sense to me.
in water treatment plants, we often run pipes under buildings using pipe encasements. common practice is to design the pipe encasement as secondary containment, including waterstops. the encasement is designed to take the full building load, neglecting any contribution from the pipe.
i normally encase all pipes larger than 3 or 4 inches when they're under a building. i've encased pipes as large as 72 inches under buildings.
cmp has a life of 25-30 years. how old is it? if more than 12-15 years, relay with a quality pipe around the bldg. it can be done even if you go to a larger pipe. who owns the pipe? what does it drain? what is going in the bldg? all these things have to be investigated. what happens if the pipe fails?
richard a. cornelius, p.e.

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