Choosing pipe for foundation drain

[watercop]

I'm having a two story ICF house built into the side of a hill near Jacksonville, FL. It will have a drive out basement. Geo engineer cored and tested soil and determined allowed bearing of 2500 pcf on a conventional shallow spread footer. Soil is mostly sandy but with some clay layers. Structural engineering is done with the requirement that positive drainage system be provided so as not to hydroststically load walls, but gives no details.

I want a dry habitable basement using a system which will last a long long time. We are planning to use Polyguard membrane on the ICF walls to waterproof and provide code-required termite barrier.

Questions:

1) We plan a perforated pipe and gravel perimeter drain system which will be able to slope to daylight on two sides I certainly won't use the cheap black corrugated stuff. What I think I'd really like is 4" sch 40 perforated PVC pipe, but I can't find it anywhere. I've come across a thin wall PVC pipe...should I settle for that or plan to drill a thousand holes in 200' of schedule 40 myself? I've seen a spec claiming 3000 LB crush strength but I can easily compress the stuff with one hand. I want the pipe to be crush resistant and able to endure being snaked out if needed...suggestions?

2) Does the pipe need to slope or can it be level? If I slope it it won't be at the bottom of the footer in some areas. Is there any standard reference I can view or buy for designing these systems? Basements are very uncommon in Florida so I feel like I'm on my own.

3) How do I ensure using the correct geotextile fabric for my soil? I see some at HomeDepot but is it right for my application?

4) I've bought loads of both 57 and 67 gravel for other uses. 57 stones seem a bit big for drainage, but 67 might be too small assuming 1/2" perforations. One alternative might be 57 around the pipe and then 67 on top of it.

5) Structural engineer spec'd only 6 mil polyeth barrier on compacted fill - no mention of any subslab gravel or waterproofing. Will that suffice to produce a dry basement and garage? It isn't a true basement - one side is completely above grade - the driveout side.

6) Should I ask the geo engineer for specific recommendations or do I need yet another engineer? I'm an engineer myself, but not trained in any of this. I don't want to go overboard but want to get it right given cost and inconvenience of later mitigation.

Thanks!

wc

 

[msucog]

1. i don't have a problem with black corrugated pipe. sch 40 will do the same thing with less likelihood of crushing. i'm not sure the corrugated stuff would crush as long as it's got aggregate around it and as long as you don't compact right on top of it. if you don't want to have to worry about it, go with the rigid stuff. i'd say anything rigid should be fine-sch 40 will without quite a lot of loads that you probably don't necesarily need from what i understand you're trying to accomplish.
2. level is fine as long as level means that the outflow is not higher. if you put a little aggregate under one end to help with the positive drainage, that should be absolutely fine. you might want to make sure you've got a water cut at the wall/footing interface. either water stop, keyway, or water proofing on the drain side to keep water from seeping at the constructiion joint between the wall and footing.
3. the fabric should be filter fabric, seperator, and/or "punched". that should be what you find at home depot. just make sure to overlap any edge by a foot or two.
4. you could the #57 stone around the pipe and the smaller aggregate outside of that. or you could buy the drain pipe sock at home depot to help keep the pipe clean. if it were mine, i'd just do my best to keep the smaller stone away from the pipe. you're not building a watch, so it's okay if it's not perfect. the key is to have the thing in and draining.
5. where is the ground water level at in relation to your slab level? if it is within 10' or so of you slab level, i would definitely consider using underslab aggregate (#57 stone is fine). and 6 mil is the minimum that i would suggest. if the ground water is close, you might want to consider other options to upgrade your moisture protection. moisture protection behind the wall is also very important.
6. your geo engineer and/or structural should be able to fill in the blanks. this stuff is important to have, but i wouldn't lose sleep if it's not exactly perfect. if you use what you describe, i'd say you're two steps ahead of most.
one more thing to consider, backfill against walls should be "well-compacted" (with small equipment-you don't want large compactors right up against the wall and overloading it) and surface water should not be allowed to stand near the wall. if you need a definition for "well-compacted", your geo should be able to assist and provide testing depending on the level of quality assurance/documentation you're looking for.
good luck.

 

[oldestguy]

Hi: Hope you understand all of the previous post.

No problem usng the black stuff, since it seems to work in all situations I have seen. However, if it has sat around in the sales place, and sun has hit it, it turns brittle. So, make sure you have new stuff. It really is recycled milk jugs you know. An easy check is step on it. If it squashes, fine. If it breaks, look elsewhere.

Next, rethink all that discussion about types of stone. Stone is not a filter for silty soil or find sand and with any water flow, your system can plug up, even if some sort of a filter fabric is used to cover the stone on top. With fabric you need to encase all of the gravel with it, sides, top and bottom. This subject has been worked over many times in many threads. Take a look at thread 171016 and make up your own mine. No point in building something that fails some day.

The word to keep in mind about this design is "filter". Gravel is not a good filter.

A final comment. If this were my job, no gravel would be allowed on the site.

If you are using rigid pipe, use 3/16" holes on the underside only. The referenced thread tells my opinion about what filter to use.

 

[watercop]

Thank you both.

My primary objection to the corrugated stuff is the high probability that any snaking or auguring to clear it would damage it.

I agree that the role of gravel is to store, slow, and conduct water, but not to filter it.

Polyguard waterproofing will extend down the wall below the footer / wall junction.

Geo recommended walk-behind vibratory roller compaction of sub slab, sub footer and backfill, with lower Proctor percentages recommended for the backfill.