Farm House Crawl Space

Once more from the old guy. Concrete sand turns out to be a perfect filter for all soils. We usually look at the gradations and the percentages passing the sieves at 85 and 15 percent for drainage. There are rules that we use in establishing the filter material grain sizes for such things as the material in an earth dam to prevent migration of solids, etc. Those rules also apply to under-drains. It turns out that the open pore spaces in concrete sand are small enough to hold back the 85 percent size of material in the coarse clay range and larger silt size. However, the grain size of fine clay would pass in these pores is such but that there are electrical attraction effects in that fine clay that give it high cohesion, so it does not migrate.

As to using gravel as backfill, without COMPETE envelope around it with suitable filter fabric (not just on top), it is unfortunate that seeing the large pores that builders, architects, etc. specify gravel backfill to drains. I have had numerous contacts with state building code folks, sometimes who use plumbers on their committees for codes to remove the gravel spec and use concrete sand. Problem is the gravel may work for a time and the plumber that put it in is not called back to replace a failed system of perimeter drains around the house. The plumbers on those committees apparently don't get called back to their jobs.

Now and then I have been called to see why a new house has water in the basement, yet they had a perimeter drain system at footings with gravel backfill. In checking after only one or two years I show the owner the mud filling the voids in that gravel. The builder and plumber are long gone.

Using just a slotted pipe with a sock also can fail when no filtering of the backfill is done. The buildup of mud on the sock over the spaced slots seals off any water entry. The house I bought 5 years back has such a drain with a sock and no special backfill. The soil here is all clean sand. Seldom do we find such a building site. Water table here is only a foot or two below the basement. In real wet weather, the drains may have to do their job. Soon after purchase a complete waterproofing of the ground surface around the house over the earth backfill (12 feet out) has cut this use of the sump pump way down. Former owner had the sump pump run a great deal of the time. I may get the pump running for a rare event once a year or not at all. A lot of water can come off the roofs and dumping it near the house is asking for trouble.

cerlawson said:

Once more from the old guy.

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cerlawson -

Just an "idle curiosity" question - are you the user "oldestguy" on the engineering forum eng-tips.com? I was researching ASTM C-33 for a drain I'm planning to put in, and ran across a post that said much the same as you did about the benefits of using sand rather than washed stone or gravel.

Thank you for your participation on this Kubota forum - you saved me from making a major mistake with my planned drain! I need to run about 50' of slotted PVC drainpipe along my barn, to fix an area that doesn't drain as well as I'd like. Although I'm 65 and might be gone by the time gravel would clog up, I don't want to leave a mess for my son to fix.

I would check with contractors in your area as to what they use for pipe and back fill for your area. The advice given by Cerlawsom is not the gospel truth for everywhere. Around here, almost nobody would use 3" rolled perforated slotted pipe for foundation drains and sand is not used to directly cover pipe. Most people use SDR-35 perforated rigged PVC pipe 4". This pipe is smooth walled inside and is less likely to clog up with fines than the corrugated flexible pipe. Also it maintains a grade better with no sags. The pipe is usually laid on a bed of crushed rock level with the wall footings, then covered with more crushed rock. The rock is covered with filter fabric. Then the foundation is back filled with sand and topped with crushed stone. The sand allows water to work its way down to the pipe and does not expand as much as dirt when frozen so it doesn't push as hard on the foundation walls. So what works in one part of the country does not always work in other parts. You need to choose what is appropriate for your location, not what is listed on a forum from a completely different part of the country.

Mr. BAP

Your contribution is fine. However, just because it is local practice does not make it right. I have been up against "local practice" for a long time. Plumbers install per the code, but it is then up to the owner and a landscaper to replace failed systems. Sure the plumbers swear by it, but they are not there when if fails. Cover the crushed rock on top to protect it from silting from above is fine, but it does nothing from seepage coming up from below or sideways. Where very little water has to be handled, the likelihood of failure us less than where plenty has to be carried.

Another poster early on mentioned his practice of covering the top of the rock with fabric. Again, fine, but does not completely surround the open graded stone. The reason is it is darn costly and difficult to install. Sure it works, but partially.

This reminds me of what my father told me about draining sugar beet fields in Gotland Sweden when he was a kid about 1900. they pulled a "mole' of sorts by teams of horses, making a hole below the ground to act as a drainage way for the saturated ground. Fields were so muddy the horses were fitted with wooden snow shoes about one foot square. Those "mole holes" lasted for the planting, but had to be done again every year.

And to Mr. Fuzzy Dog, Yes my handle on Eng-tips is Oldest Guy, because some other engineer got Old guy first. So far I have not found any one older, Ha.

By the way, none of the installations I have been involved with have ever failed. This includes many an instillation at Wisconsin DOT when I was the chief soil engineer.

Mr. BAP again:

In you area, I'll bet some cheating can be done that is cheaper and better. Yes, use sand for the backfill, but forget about any rock or fabric, just fill everything with sand after placing the pipe, but use a sock on the pipe.

More from the old guy. I think the reason my preaching of the need to consider filtering from all possible trench entry places is that this subject is not dwelled on much if at all by the civil engineering profession and certainly never by any plumber school. You would not expect an contractor to know either. Matter of fact the house I am in was deigned and built by the developer of the north end of this town, after his father passed on. He is a graduate civil engineer of Univ. of Wisconsin with a PE license and he had no training that brought up the subject. In my undergrad days at Cornell no such subject ever was brought up. I didn't run into it until I did the research of the effectiveness or lack thereof for under drains under highways. The general ideal of gravel with its large void spaces being looked upon as a convenient pathway for collected water has been around for a long time. Unfortunately that collected water bringing along soil particles doesn't seem to be in the minds of most users.

Go sit on a beach and watch the way the waves disappear into the sand. The more sand surface area, the faster it drains.i hope im getting a grasp on this. The more i read it,the more it makes sense.

Another story. In my consulting business a builder of clinic buildings asked me to look at a settled building just outside a small town. The area was outwash sand and gravel, mostly sand. They knew that the area usually had a high water table, but it was much lower at time of construction. Thus, the basement area was underlain with a layer of washed stone, leading to a sump. After the water table came up, the sump pump started running. In a matter of about two years the basement floor was settled and cracked and interior footings had settled. There were big voids under the slab. Out at the roadside ditch at the outlet to the discharge for pumped water there was a large delta. Enuff said.

Flyinglow: The only answer I can give is that the principles of proper filtering seem to take a long time to be known. For instance I looked at one of my early texts for Soil Mechanics and there it is. However, in that course that subject never came up. The practice you mention does work, possibly for a while and possibly for a long time, but under the situation of taking on a lot of water,erosion of nearby soil into the drain is more likely. Take that building problem, it took a few years to finally show it's action.

I even was sucker to the idea of big voids being good. When I was second year in college, supposedly learning everything. My dad bought a house situated against a hill, water seeped from that hill and the crawl space under the house was constantly flooded. We hand dug a trench along the base of the hill to collect that water and lower the ground water table at the house. We filled the lower part of the trench with big rocks, supposedly due to their large void spaces for water to run in. We backfilled with the excavated soil above the rocks. You guessed it. No change in water at the house took, place, because those voids quickly filled with mud.
Even graduating after 5 years, that filtering subject was never looked at.

Looks like quite a project and not easy to fix. On thing that would help is at lest a few elevation shots to know possible ways to best drain the area. As to crushed rock, it may or may not be suitable without protection around it to keep mud out. For insistence in Wisconsin the DOT specification for DENSE highway base course made from crushed dolomite (limestone) that it is very water tight. If the void spaces are open enough to let the larger soil and any drainage material, you need to have a filter between the soil and that crushed rock. The filter can be filter fabric or a sand similar to concrete sand. One test that some highway builders have used to rough valuate a sand or sand and gravel source that has to pass water and must not have much of any silt or clay in it is this. Unzip your fly, empty the bladder. If that puddle is gone just when the pants are zipped up, it passes. Of course open graded rock or washed stone will pass the test, but this is for sand only. The main part of the gradation of the filter sand is the smaller particles. Too much silt or clay and it does not work. That's with 5 percent or more of #200 sieve size and smaller. Such a sieve has 200 openings per inch, barely visible to the eye.. Your coffee maker sieve is about that.

Running two different pipes together in a trench is no problem as long as the one with no openings does not eventually feed water back in, as at the outlet.

Seeing your complicated situation, I'd lean to using a perforated drain pipe with a filter sock on it and only use concrete sand or similar backfill. It is almost impossible to do it wrong. Trench with can be anything to get the pipe and backfill there.

More preaching.. Here is a video showing some problems with non filtering of water going to drains. Problem is this guy, even though he found the problem partly, his fix is useless. I did a Google search of the word COREX. With this video, note the dirt in the pipe AND IN THE GRAVEL BACKFILL. Yes he showed the path for the dirt to follow to get to the pipe, but failed to say how you stop the dirt from getting in the gravel backfill to begin with. One way would be to surround the gravel and the pipe with filter fabric, THE HARD WAY.. The easy way is, drop in the pipe and then the concrete sand.

https://www.youtube.com/watch?v=zX9koyVHPXE

I think we found the drainage Oracle. Some great info here.