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Moist/wet soils under foundation
2

Moist/wet soils under foundation

Moist/wet soils under foundation

(OP)
I am wondering if soils under foundations are typically assumed to be wet? They are in the earth, after all.

We make foundation drains, but is the point of these to keep the the supporting soils dry? Or to keep bulk water out of the foundation for other reasons?

I am still trying to understand if water migrating underneath a footer/beam foundation is a structural threat, or just inconvenient(mold, not nice to work in puddled water, etc)

Soils are sandy clay. Non-expansive as far as I know.

RE: Moist/wet soils under foundation

Foundation does not like water, because it can't swim. The water washes particles beneath the footing, weaken the soil structure, and exert additional force on the foundation. The soil can be wet, but not to the extent that it is fully saturated. A big structural threatd, if not controlled.

RE: Moist/wet soils under foundation

Wet granular soils shouldn't be a problem as long as the effective (buoyant) unit weight for that material is used to evaluate the bearing capacity. Wet cohesive soils can be a problem because excess water can soften the soil to the point where it loses strength derived from cohesion.

We often see a requirement to place a relatively thin lean concrete "mud mat" over freshly excavated cohesive foundation soils to protect the soil from ponding water.

Another detail seen is placement of geotextile on the cohesive soil (which prevents the fine-grained soil particles from migrating) with a layer of relatively free-draining granular over. The granular soil is often connected to or incorporates a drain connected to a sump pit to remove any water collecting in this layer.

RE: Moist/wet soils under foundation

(OP)
How can you tell if soil is saturated vs. wet?

What about all those millions of houses that rely on sump pumps? Aren't those soils fully saturated if they have pumps that essentially run the whole rainy season? The sump is just managing the excess water so as to not flood the house, right?

Thanks

RE: Moist/wet soils under foundation

(OP)
What would be a good solution to controlling ponding water in portions of a foundation?

these are low spots on the crawlspace floor where water migrates. If I was to fill the crawlspace with 1 inch of granular fill I would not even know the water was there.

I already have two drains in place, one at the footer that surrounds the entire building and drains to daylight.

The other I dug after the fact on the uphill side(wet)of the building. This also drains to daylight. This pipe is below the level of the footer by 6 inches. It is raining heavily now and that pipe is exiting ALOT of water, but there is still a bit creeping under the house.

The footers are on a thin layer of granular fill, but no more than an inch.

RE: Moist/wet soils under foundation

The key factors to your problem are "groundwater level/range" in the area, and the frost depth. Talk to a local geotechnical engineering company, or a contractor familiar with local conditions.

For areas with high groundwater, you will see the pump runs 24/7 in certain seasons (like mine). Also, its not rare that a house is damaged after flood with pump failed - always get a spare one is wise.

RE: Moist/wet soils under foundation

I think the builder of you house has done a decent job, by enclosing your foundation/house with granular back fill, and properly slopped the drain to daylight. But I don't quite get the description of "creeping under the house", since you have done correctly to fill the depression at the crawlspace - don't forget to slop the crawlspace to drain, otherwise, the puddle will return soon or later.

RE: Moist/wet soils under foundation

(OP)
I think this is an interesting case.

The water table is not necessarily "high" in the area as the soils are predominately sand. The day I dug for my foundation I was 100% expecting to be digging in a sandbox. Instead, to my surprise, it was fairly heavy clay with a mix of sand and glacial erratics.

The clay layer must rise closer to the surface just on my lot, so the sand drains free in the surrounding area and the water shows up at my place. Not ideal, but its what I got.

Everyone local builder I talked to in the area said it shouldn't be a problem, just proceed as usual. There are a lot of clay sites here. It is a rural area so Geotech's are few and far between. It is very rare to get a geotechnical involved with a residential build.

The good news is the soils "feel" solid, but that's pretty meaningless from an engineers perspective.



RE: Moist/wet soils under foundation

If you are somewhat concerned, dig a hole at suspect location and observe. If necessary, you may consider construct a pumping well, intercept the sand layer, to draw down the flow.

RE: Moist/wet soils under foundation

(OP)
The crawlspace was done with an "over-dig" technique.

The entire footprint of the house is dug out and then some, to prove room to from the footer and stem wall, this also leaves room to install the drain at the base of the footer.

What I mean by "creeping under the foundation" is that the crawlspace floor is at the same level as the drain or even a little lower. So any rainwater that finds its way to the base of the footer will not be caught by the drain. Instead it will leak under the footer and into the the crawl, to the low points. Again, if I would have filled the interior of the crawl with fill like some have suggested, I would not even be seeing this water and probably not writing in this forum with concern.

RE: Moist/wet soils under foundation

(OP)
"If you are somewhat concerned, dig a hole at suspect location and observe. If necessary, you may consider construct a pumping well, intercept the sand layer, to draw down the flow."


I guess that's just what I am wondering, is if I need to be concerned or not.

RE: Moist/wet soils under foundation

A saturated soil is a cohesive soil where all the available pore space is filled with water. Due tot he low permeability of cohesive soils, it generally takes a great deal of time for water to get in or out of these pore spaces. However, free water (ponded or within a granular soil) against the surface of cohesive soils is a problem. It may take a long time to manifest as a noticeable problem.

In the case of granular soils, they are described as wet if free water falls out of them when removed from the ground.

RE: Moist/wet soils under foundation

I think your assessment is quite plausible. Good luck.

RE: Moist/wet soils under foundation

all soil strength is determined in the laboratory (and by extension via correlation) under saturated conditions. Saturated soil strength is the design norm.

If wet soil turned to mud all embankment dams would fail.

I don't buy all the hand wringing! (Nor the internal erosion concern!)

f-d

ípapß gordo ainÆt no madre flaca!

RE: Moist/wet soils under foundation

Correct, cohesive soil takes long time to dry out, meanwhile, it is highly difficult to let it reach fully saturated state, unless there is persistent high ground water present, which is not likely to happen on a hill side though. I think you should concentrate on surface water runoff at this moment. And, just to make sure there is no noticeable crack(s) around the house and on the floor.

RE: Moist/wet soils under foundation

(OP)
Thank you all for your responses.

I find it interesting that there is a split in opinions. Some people seem to say any water is bad anytime and will ultimately ruin your house.

Others point out what fattdad said, "all soil strength is determined in the laboratory (and by extension via correlation) under saturated conditions. Saturated soil strength is the design norm.

If wet soil turned to mud all embankment dams would fail."


Either way, I enjoy the discussion!

RE: Moist/wet soils under foundation

The test is concerning cohesion at Θ = 0 for cohesive/clay material, if I haven't returned my learning to my professor. I still vote "no water" for/under my house, but tap water service. :)

RE: Moist/wet soils under foundation

(OP)
My vote is "no water" also. But dang that stuff is persistent.

Interesting to try to understand the forces at work.

thanks

RE: Moist/wet soils under foundation

Hotwire,

Don't be confused with joking. You can mold a clay with water, once your kid can put finger into it, it is in a state of saturation, if not fully.

RE: Moist/wet soils under foundation

The "no water" folks are dreaming. Because of climate changes, one can never expect a for sure "no water' situation. I now refer to my experience as a young person when we moved to a country house where the ground was on a side hill. Out of that hill came ground water flowing and springs emerged.
The house was built over one of those springs, for "water supply" early on, before city water came. The crawl space under the house was always wet with standing eater. Made it difficult to get under there for maintenance of things. The foundations were stone with mortar extending about a foot or so under the surface because even in a cold climate the ground never froze more than an inch or so. When water freezes it gives off heat energy and the crawl space was protected from outside cold air.. No cracks or settlement noticed in the building, even over 80 years old when we moved in. Just recognize how saturation affects bearing capacity and live with it. To prove my point some 60 years after going elsewhere, I stopped in one day when going through the area. Still no change.

RE: Moist/wet soils under foundation

(OP)
OK.

If it's malleable then its saturated. Got it.

But soils are tested assuming saturated conditions, correct? So if the foundation was designed with the strengths of saturated clay in mind, then theoretically things are OK, Correct?

thanks

RE: Moist/wet soils under foundation

(OP)
Oldestguy,

That is a reassuring anecdote, thank you. But wouldn't it matter what type of soil old cabin on the side of the hill is sitting on? If its sitting on rock then we know why it didn't settle or have issue from the water.

RE: Moist/wet soils under foundation

No. The geotechnical guy provides something called bearing capacity (actually is to limit settlement to the allowable) to the structural nuts to design the foundation. From the words, "bearing" and "settlement", you can see if a saturated clay can provide. Although sometimes we have to put something over a weak soil medium without costly, or difficult, soil modification, that something is usually deep pile foundation, or mat foundation, which are not common for residential constructions.

Pay attention to oldestguy's comment, which was caught in between our conversations. You shall explore if you have "free water supply" beneath your house. But hack, the geo guys confirmed there is no changes after 60 years, then forget about it. I don't want to start a muddy war :)

RE: Moist/wet soils under foundation

I'd want a foundation drain if I had a house with a crawl space. It's more to do with indoor air quality and comfort (i.e., not to get mold).

I'd want a foundation drain if I had a house with a basement too. No reason to design for hydrostatic forces and add all that waterproofing (all concrete cracks) if a drain will help.

I just think it's important to consider our first principals when having engineering conversations.

Otherwise, it's somebody's money and they can spend it as they wish. Just need proper advice!

f-d

ípapß gordo ainÆt no madre flaca!

RE: Moist/wet soils under foundation

(OP)
Fatdad-

The house has a foundation drain to daylight. I went to great lengths to install it properly. It's rigid PVC at the base of the footer with a separate pipe for gutters.

The problem seems to be this: The crawlspace floor was left at the same elevation as the base of the footer, which is the norm around here. When water from the exterior runs along the clay layer that the foundation sits on, it easily goes underneath this pipe and to slightly (1 inch or less)lower elevations within the floor of the crawlspace.

With a little bit of gravel on the floor and a vapor barrier, I will not know the water is present.

But the question is whether its a structural concern to the foundation?

Again, what about all the houses that run 24/7 with sumps? Isn't the ground saturated in this situation? And it is considered normal, right?

RE: Moist/wet soils under foundation

We will never know if there's a structural concern with the foundation unless we had a boring log and possibly even testing.

If the clay is relatively stiff, the loads are relatively light, and the clay is unsaturated or partially saturated, it shouldn't be a problem for a residence.

Water does not mean there is a problem and it also doesn't mean its not a problem. But we (and you) don't have enough information on the subsurface conditions and structural design.

Houses that run sumps 24/7 aren't considered normal but it does happen. It's a large electric bill that I personally would never want to pay. We also construct buildings and (expensive) homes under the groundwater and seal the basements to prevent water getting inside. Since the building can become buoyant, the structural, geotechnical, and civil engineers need to come together to prevent that from happening. If the building loads are not high enough, ground anchors are installed.

Are you on the hillside? Can you install an interceptor drain at the base of the excavation and divert the water around the residence? Maybe that could give you a piece of mind.

RE: Moist/wet soils under foundation

(OP)
I've already dug the interceptor drain, it flows steadily during rains so its working.

But somehow there is still water creeping in. To be clear this is not a heavy flow into the crawl.

I am not interested in running pumps either, but I read about people having to do it. I'm on a hill so I figure I should be able to manage the water.

Thanks for the responses

RE: Moist/wet soils under foundation

(OP)
What kind of machine is needed for a boring test? Would they test from crawlspace or from outside?

RE: Moist/wet soils under foundation

You would need a drill rig that can collect soil samples (and normally a geotechnical firm to send someone to oversee).

An interceptor drain would be installed upstream of the residence if you had shallow groudwater. It's similar to a footing drain except it runs around the property instead of next to the house. You would then let the drain daylight downhill. Care would have to be taken as to where you discharge the interceptor drain.

If the issue is that surface water is running towards your structure, then just create proper grading and swales to divert the water around the residence.

Edit: Also cap any granular foundation fill with onsite, fine-grained soil to keep water from getting in.

RE: Moist/wet soils under foundation

(OP)
see my previous post. I already have an interceptor drain on the watery side of property, its just not getting everything

RE: Moist/wet soils under foundation

This might best be cleared up as to what is best by using an experienced geotech engineer whom has access to or owns test boring equipment. You wouldn't have to go under, but usually one or two outside test borings outside will be all that is needed. In any case so far I do not see anyone cautioning about what can happen if the drainage system erodes soil or worse yet plugs up. The drain system should be filtered to keep from eroding fine grained soil along with flowing water.. An experienced geotech can advise on that for you for your case. Be wary of a contractor that will install the drains, yet is not an experienced engineer.

So tell us the detail of what you installed as to filter, etc.

RE: Moist/wet soils under foundation

(OP)
The drain is simply a trench dug with a slope to daylight. A rigid pipe with holes placed at the bottom, and gravel filled to the top. No filter.

This is already done so to re-do it for a filter is out of the question.

RE: Moist/wet soils under foundation

Just keep an eye on it. It may already have developed a filter having lost a minimum of adjacent fine material. A build up of a delta at the discharge end would tell a story.

RE: Moist/wet soils under foundation

Sounds like the interceptor drain and footing drain aren’t working properly. If designed and constructed correctly, you shouldn’t see anything. Next option that I would use is a sump and sump pump.

RE: Moist/wet soils under foundation

(OP)
The intercepter drain is working very well.

It's the footing drain that is not functioning properly. But I believe it is a function of where it sits in relation to the floor of the crawlspace. How could it be expected to work if the drain sits on the same level as the floor its supposed to drain. It would have to be slightly lower. But this is not how most of the diagrams for footing drains are drawn. Some even have the drain on the top of the footer.

How in the world could a drain function to de-water the a concrete footer if its sitting on top of it?

RE: Moist/wet soils under foundation

When groundwater is anticipated, it should always be below the footing elevation. I usually spec 1’ below BOF elevation.

RE: Moist/wet soils under foundation

One function of drains that I once check as a Master's degree project. I checked the installation of several under highways where there was a high ground water problem. I had instruments measuring water content in soil at several locations both up stream and downstream of the interceptor drains. I specifically wanted to see if a drain down gradient from a saturated zone would "draw down" the water table up there. In all cases the so called draw down of the zone up-stream of the drain was minimal. Could be due to many things,such as layering, etc. Thus, to protect any zone from high ground water the drain has to be as low as what one wants for water table down stream from the drain. For the subject house, it may be the outside "moat" of drains has to surround the house at sufficiently low elevation to accomplish that. Don't pay any attention to "standard" details that usually are not applicable to a situation such as this one. Meaning a drain located higher than the low water table you want can't expect to do any good, as you point out. Think of the "
moat" around the castle an apply that here. By the way use filtered drains especially near footings. Check out the US Corps of Engineers web sites for drainage and you will seethe gradations that serve best as drain backfill to filter the soil from eroding.

RE: Moist/wet soils under foundation



This usually fits the size for concrete fine aggregate and is a great filter.


Note: single size gravel is not shown here as a filter This is all sand for the most part.

RE: Moist/wet soils under foundation

(OP)
Thank you all for all the posts. Amazing what can be gleaned through the internet.

Although I must say, I'm still confused as to whether I have an actual problem to worry about. I suppose the best bet is to have a Geotech take a look.

RE: Moist/wet soils under foundation

While I am at it some comment on jobs done. Most of the time a perimeter drain system either inside or outside the foundation ass low as possible does a job of lowering the water table. However, in cases, maybe like this site, there is lateral seepage, maybe springs, etc. so a flow of water getting around the drain has to be collected somehow. I have seen a few cases where perimeter drains do not do much for the interior, due to seepage flow from up-hill in soil at depths below the site. The seepage gets around the up-hill drain and due to its pressure and emerges inside the foundation area. Then interior drains are needed, sometimes requiring one to cut slots in the slab for the drains. I usually would try one and see how it does. If not use more interior drains.

Edit: PEr the latest from the OP. I'd not get too excited about this, especially if you don't see any problem. Erosion under footings is darned unlikely unless the flow is open water flowing RIGHT THERE. If your UN-filtered drain is RIGHT THERE, maybe yes. Otherwise very unlikely, ,just moisture.

One more comment. Ya can't expect to always have a site where there is no ground water at shallow depths, as one commenter above would like.

I hasten to add. My preset house sits on low round not far from a swamp. It has a perimeter drain leading to a sump pump and in very wet weather that pump runs. I was not the owner when it was built 20 years ago,but assume the usual dumb construction of gravel backfill, even meeting a state spec will YA? So with water inches below my basement I do expect that maybe some day the drain will plug and a big replacement is in order. Meanwhile, no excess moisture, etc. Just normal stuff down there.

RE: Moist/wet soils under foundation

Agree with fattdad and OG. If saturated soils were such a problem, we would not be able to build in my area of practice. We often have water tables that are at or near the surface, yet we place foundations (footings, not footers!) on these soils. Yes, there are many geotechnical considerations that should be made; however, the picture is not doom and gloom.

For off grade construction with wood joists, my concern would be wood rot. So for that reason, draining the water away from the crawl space is a good idea. Structurally...not usually a big deal.

RE: Moist/wet soils under foundation

joenorm,

Your water problem is two fold - surface water and ground water. Since your house is on hillside, provides the area is predominately sandy soil, I don't think the latter is a thing to be concerned with, unless you dig a hole in the yard and see sitting/standing water in it. The water creeping through your crawl space and ponding, apparently is caused by surface water runoff. This problem will be gone, if you slope the fill, and either simply excavate a ditch, or embed a French drain, under your crawl space. Also, slop the ground, and check around the house to see whether there is any indication of movement - large cracks, stair landing is higher than your indoor floor... If nothing is find/suspicious, your foundation should be free of concern for a long time to come. Note, since you don't have basement, pump is not needed, unless you want to draw down the ground water as mentioned before.

Below is something I want to settle the misunderstanding between the geo heavy weights and the structural nuts. Please do not hesitate to correct me, as I like to advise people to keep foundation away from water, stay dry, if minimal effort and care can achieve it.

Can we put footing on saturated cohesive soil? Surely we can, Since cohesion c (Ø = 0) is the primary term in derivation of cohesive soil bearing strength, and the consideration of its use is as stated below.

Quote:

The ultimate bearing capacity of saturated cohesive soils (clay and silt) with low permeability is most critical immediately after construction, before the excess porewater pressure has had time to dissipate i.e. undrained conditions. As time proceeds, consolidation occurs, the soil becomes stiffer and has more strength.

Unfortunately, for lightly build house without significant consolidation could occur, but with persistent presence of groundwater at/above the footing, will that anticipated "excess porewater pressure has had time to dissipate", and "becomes stiffer" to happen?

A study has shown the relationship between moisture content and cohesion for a cohesive soil (Kubishi clay):

Moisture Content (%) - Cohesion (kg/cm2)
0.0 - 6.5
2.6 - 4.8
5.3 - 4.3
17.5 - 3.8
19.9 - 2.6
22.3 - 1.4
25.1 - 1.1
27.4 - 0.7
30.4 - 0.6

I don't see water is very kind. It can lift a footing, also can sink.


RE: Moist/wet soils under foundation

Comment to "stood 60 years without problem" - all I can say is we don't exactly know the soil below, water table, and system for drain. Also, it could be a mercy from the nature - as we all know 100 years event will occur sooner or later; earthquake destroys one house but not the next with the same built. We are engineers, not the god, practices/given pointed advices cautiously should always be in our mind.

RE: Moist/wet soils under foundation

I won't try to "educate" our friend. However, assuming the subject site has water, due to surface water likely is wrong. There are many reasons for soil "holding" water at certain moisture contents, among them the various internal atomic attractions can't be easily changed. Perhaps explain this one. Knowing high water content in soils of high content of certain minerals, we usually will try to dry them some so that compaction can create a good su0port situation. That weer content is considered "optimum". So a new college site of several buildings in such an area had some rather soft water laid during glacial times soil that was far above "optimum" water content. Our engineering firm sent an engineer (held a Master's in geotechnics) to test and oK soil that was then dried and compacted to optimum. The site was rather low and so soil was excavated from, what would be a future lake. It was compacted in layers at 95% of Max. to build up several building sites upon which would be footings place and then buildings. So the job was done and everything looked fine. The architect decided the roof rain water from the buildings should go to the excavation as the lake source.
Those drain lines were perforated in sand filled trenches to also collect rain water. Roof water was collected and drained to the lake in these buried pipes. Drain lines to external sanitary sewers from inside the building were buried in sand filled trenches that extended past the sand filled outside drain pipes. Low and behold that compacted under building clay in contact with water that came from the roofs decided it wanted to go back to its "natural" water content somewhat higher water content than the optimum. THEN WHAT AN UNHOLY MESS DEVELOPED. The under floor top layer of fill also had a layer of bentonite clay "for waterproofing" said the architect. HIGHLY EXPANDABLE. In addition this natural clay had high expansive mineral content. Floors were bulged up, doors would not open. Interior partitions all bent out of shape. A hill developed in each class room so the blackboards were badly out of line. Luckily footings were sufficiently deep that the "surcharge" over them minimized the swelling of soil beneath them. Fortunately a gymnasium building job was delayed until later when that compacted clay expanded to ts "natural" water content and then stayed unmoving. The common spec of 95% compaction surely did not apply to that site.
Moral: never presume anything about a site until you know ALL the details.

RE: Moist/wet soils under foundation

Quote:

However, assuming the subject site has water, due to surface water likely is wrong.

Never in my mind, nor attempted to. Maybe my poor wording caused some confusion? Below was one of my response before realized this house was on the hill.

Quote (retired13)

The key factors to your problem are "groundwater level/range" in the area, and the frost depth. Talk to a local geotechnical engineering company, or a contractor familiar with local conditions.
For areas with high groundwater, you will see the pump runs 24/7 in certain seasons (like mine). Also, its not rare that a house is damaged after flood with pump failed - always get a spare one is wise.

After more info were present, I said:

Quote:

I think the builder of you house has done a decent job, by enclosing your foundation/house with granular back fill, and properly slopped the drain to daylight. But I don't quite get the description of "creeping under the house", since you have done correctly to fill the depression at the crawlspace - don't forget to slop the crawlspace to drain, otherwise, the puddle will return soon or later.

And:

Quote:

If you are somewhat concerned, dig a hole at suspect location and observe. If necessary, you may consider construct a pumping well, intercept the sand layer, to draw down the flow.

And:

Quote:

Correct, cohesive soil takes long time to dry out, meanwhile, it is highly difficult to let it reach fully saturated state, unless there is persistent high ground water present, which is not likely to happen on a hill side though. I think you should concentrate on surface water runoff at this moment. And, just to make sure there is no noticeable crack(s) around the house and on the floor.

If I have made any "assumption" in my responses, please point out, I shall learn better.

RE: Moist/wet soils under foundation

Enuff of this back and forth. Owner seems pretty good at evaluating responses. If ever in doubt, my advice is see what Ron has to say. He is pretty good at resolving differences.

RE: Moist/wet soils under foundation

Quote (retired13)

I think your assessment is quite plausible. Good luck.

Quote (retired13)

Pay attention to oldestguy's comment, which was caught in between our conversations. You shall explore if you have "free water supply" beneath your house. But hack, the geo guys confirmed there is no changes after 60 years, then forget about it. I don't want to start a muddy war :)

Terzaghi and Peck can confirm I said goodbye (good luck) quite early on.

RE: Moist/wet soils under foundation

(OP)
I am not as concerned with rot.

My plan all along is to add drain rock to the portions of the crawl that are pooling. At that point, nobody but me will know the water is even there. After that I will neatly detail a robust vapor barrier, taping where it meets the foundation.

Very little water vapor, will make it though. If it does, the crawl is vented.

My theory about the site is as mentioned. The surrounding area drains through sand and my lot happens to be where the fly comes shallow to the surface. So that would be subsurface ground runoff, I'm not sure how you'd classify it in the business.

It's not rising from below, but is not on the surface either.

Again, the discussion is much appreciated and a nice glance into the professional world. Like all subjects in building, there seems to be differing opinions.

RE: Moist/wet soils under foundation

all the foundation drains in the world will not stop capillary rise! Never forget about soil suction!

f-d

ípapß gordo ainÆt no madre flaca!

RE: Moist/wet soils under foundation

(OP)
FattDad,

Perhaps you can expand on how soil suction and capillary rise are relevant here?

thanks

RE: Moist/wet soils under foundation

You will lower the phreatic surface by installing drains. Let's say, you lower the phreatic surface to below the pipe drain. Capillarity will allow water to rise above the phreatic surface. Such capillary rise, may increase the water content of the soil to the point where it will be reduced to mud upon disturbance.

The height of capillary rise is determined by the pore size in the soil. I have an equation in a book somewhere. Turns out it is something to be mindful about; however. . .

f-d

ípapß gordo ainÆt no madre flaca!

RE: Moist/wet soils under foundation

Quote from above, not always a true action. "Such capillary rise, may increase the water content of the soil to the point where it will be reduced to mud upon disturbancee." Depends on many factors. For instance, why does montmorilonite swell when there is no air-water interface needed for capillary rise.?

RE: Moist/wet soils under foundation

not taking the bait and remain with my statement.

f-d

ípapß gordo ainÆt no madre flaca!

RE: Moist/wet soils under foundation

(OP)
Update On this.

It's been really wet the last week and the "intercepter" drain runs like a small steam. This drain is about four feet from the footer and 6 inches deeper than the bottom of footer. Higher flow while raining, petering off after the rain but still flowing.

It has helped with the water infiltration into crawl but not solved it. I am wondering if that water is still entering from above as my excavation contractor backfilled with gravel all around the two wettest sids of house, essentially leaving the open to the elements.

The water comes and goes with heavy rain, so I don't think it is a permanently high water table. I just happen to be in an area where drainage is working against me. But I am on a hillside so it theoretically can drain away.

One concern is that there is an asphalt driveway on the uphill side of me on the adjacent property. A lot of the drained water off of here is likely ending up in my "intercept" drain, perhaps working it harder than it needs to work.

I'm truly puzzled as to a solution here, I cannot afford too much more excavation unless I know it will solve the problem.

In the meantime most of you have giving me some confidence that this will not turn into a structural issue which is my main concern for a newly built house.

Not sure how to proceed.



RE: Moist/wet soils under foundation

Make sure that gravel backfill around the house is capped with fine-grained, low permeability soil or hardscape. I typically spec a minimum of 2 feet of low perm. soil where water can be an issue. I'm sure you already did this but make sure the downspouts are discharging far enough away where they are not causing an issue with infiltration.

RE: Moist/wet soils under foundation

In line with Mountain Climber. On way you can "waterproof" an area with that fine grained soil is to do some hand labor or easier with a roto tiller. Go to a distributor of well drilling products, such as a heavy hardware outlet. There you can get what they term "driller's mud". It is a dried natural clay called bentonite or montmorillonite. Be sure it is the powder variety, not granulated. Well Drillers use it mixed with water for keeping a the hole open while drilling. It is VERY expandible. Use too much in a mix with soil can cause problems. So experiment before dong much with it. Mix in to native soil maybe 3 to 5 pounds per cubic foot of natural soil. This mix will take on water and be practically impermeable. Too high a percentage mixed in will have a constant soft sloppy condition. A little goes a long ways. It is cheap, but don't over do it. When I have done this we strip off the sod and then work it into a soil layer about 3 or 4 inches with a roto tiller. Thorough mixing is required. Replace sod.

Do your experimenting with it by carefully measuring and use something like a kitchen sieve into which you put the mix. Dampen it and test how well it holds water. I'd do the test on a thin layer of soil, maybe 1 to 2 inches thick and have some way to get a "Head' of water on it. A tin can with fine holes punched in bottom might do it. Be precise with measuring. Maybe do the mixing test on site but only one or two square feet.

RE: Moist/wet soils under foundation

(OP)
Have any of you guys in the business ever specified using plastic as the water barrier around the house?

One could theoretically slope heavy-duty plastic away from the house to the same affect as the clay that you suggest above?

thanks

RE: Moist/wet soils under foundation

My experience with plastic sheet was it deteriorate rather fast. I put down a sheet under my bed to prevent the drift from the cold basement and through the wood floor, it worked a season or two, then wrapped, and seemed loosing its elastic property. I wouldn't suggest outdoor application as yours.

RE: Moist/wet soils under foundation

(OP)
I didn't mention that I assumed it to be buried under gravel, so not sunlight exposed

RE: Moist/wet soils under foundation

There was no sunlight under my bed, I put mattress directly over it.

RE: Moist/wet soils under foundation

I remember you have mentioned encounter sand layer in a shallow depth. I think it is better to dig a trench behind your house with good slope to divert the water away. The trench should be at least a few inches deeper than the sand layer, so it wouldn't fully inundated by the runoff. If this cuts off the water flow at the crawlspace, then you are good to make further improvement.

RE: Moist/wet soils under foundation

(OP)
I have not encountered sand in this particular area. Sandy/rocky clay, and that is part of the problem. I mentioned sand because basically above and below my house area footprint is mostly sand. I seem to have built on a clay island in a sea of sand.

RE: Moist/wet soils under foundation

I would not advise putting in poly around the building. From what I've been told, it was attempted on several projects where the structure was placed on moisture sensitive soils. Apparently it trapped a lot of moisture and created issues in crawlspaces (mold and flooring issues) and in some cases made the foundations move. I'm not sure why that would happen since theoretically its very similar as capping with low perm soil but the practice of using poly around a building has been abandoned in my neck of the woods.

RE: Moist/wet soils under foundation

Then, don't bother to dig down to any layer, just a trench deep enough not letting the runoff to flow over. Or, build clay berm as suggested.

RE: Moist/wet soils under foundation

Just an idea. The berm needs not to cover up the crawl space *which could be much higher than shown), you may adjust the height to fit your need. The ditch can be filled with gravel to protect the toe of the berm.

RE: Moist/wet soils under foundation

(OP)
Thank you for the drawing. What exists currently is essentially what you've drawn, but without the berm.

So most of the water coming toward the ditch(6 inches lower than footer)gets taken away, but with heavy rain there is quite a bite still making it into the crawl.

What I do not know if this is water coming from above, or water coming from the side that is overtaking the ditch drain.

It almost seems like an underground flow.

Appreciate all the feedback

RE: Moist/wet soils under foundation

Since your house is on the hill, for an intense rain fall even in a short duration, overflow may occur. Make a small berm (6" say) to test if the overflow stops. Also, another source of water infiltration is from the wind side of crawlspace opening, depending on how height is the crawlspace. Come back and let us know if the problem persists after all these efforts.

RE: Moist/wet soils under foundation

If questions still remain (apparently) as to really what is going on, I'd like to see some side view cross sections. And as to water flowing in the ground, it is common if water flows over the surface, it also is moving under the surface,about the same direction, but slower.

RE: Moist/wet soils under foundation

(OP)
The soil around the wet area is certainly softer than the soil around the more dry portion. But I suppose that is to be expected with clay?

I am guessing the problems associated with these sorts of situations are over the long term? Years of wetting and drying cycles could shift things a bit.

RE: Moist/wet soils under foundation

(OP)
I started digging a little sump pit in the crawl space today and noticed I was carving through layers of pretty dry, dense, hard, clay.

As I dug the moister only seemed to enter from the top where there is a bit of standing water.

Tried to attach images but not sure if it worked.

RE: Moist/wet soils under foundation

As to long term changes, I'd not expect that unless some work is done to make things different. I seldom see these problems (or solutions),changing significantly overtime.

RE: Moist/wet soils under foundation

(OP)
OG-

Do you mean to say the problem will stay the same unless addressed or that things will likely not get any worse?

RE: Moist/wet soils under foundation

Likely no significant change with time. That's from this 91 year old very old guy.

RE: Moist/wet soils under foundation

joenorm,

Take the old man's advice, don't worry too much about the top soil condition, unless erosion has occurred.

Dig the trench and build the berm, water shall stop to get in the crawlspace. Then you can cover the crawlspace with vapor barrier, and add sand as weight to hold the barrier in place.

RE: Moist/wet soils under foundation

This old guy reviewed this post and, in line with a recent post, I ask what is the actual experience of these guys? My bet is darn little. Have they ever done the steps I see they expound about? Ask the question and if not directly answered, the answer is NONE.

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