Geotechnical Testing: Proof is Possible, but Sometimes It Hurts
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- Опубліковано 12 гру 2018
- Geoff Hebner of Padstone Geotechnical Engineering returns to run a simple test on the dirt before pouring concrete, and Corbett finds out he’s not as slick as he hopes.
- Наука та технологія
You are lucky to count with the knowledge of a soil consultant.
Most important part of a building is the foundation.
This quick consultation will save you money down the road in very expensive repairs.
Those consultations can be prohibitively expensive for a small, out of the way, building. My advice is always, guess it, test it, do it.
It ain't rocket surgery.
One of the things that I learned along the way is that over-engineering stuff at the beginning of a project is often cheaper than having engineering consultants come in.
Which is NOT an argument against engineering consultants. It's an argument in favor of "over-building".
For example, and this is going back BEFORE the day recorded in this video... (Also, taking into account the rock.)
I probably would have excavated down a couple of feet and about twice the planned footer width. and blended the materials with portland cement. There are a couple of ways to do it. One way is to shovel the cement right on top and blend using a rototiller, another is to actually use a cement mixer to blend it dry, then wheelbarrow it over to the footer area and dump it in before raking it out. I would likely have chosen the latter method since it allows my to layer in some Geogrid. Everything gets compacted with a jumper or vibrating plate. That portland cement trick is an old soil correction hack that I think goes back to the 19th century. Lime also works. Mainly, you want to keep organic material out. If you think you have a lot, dilute the soil with sand before adding the cement or lime.
That's quicklime, by the way. Hydrated.
Lime is better for fine grained material like clays and silts, cement for coarse grained soils with a high sand content. Either way, when I've done it I was aiming for 5% - 10% of the total material.
There are actually formulas and specific guidelines for this stuff, but I generally just went seat-of-the-pants with it. The guiding principle was the "Nuke it from orbit" school of thought. Nobody ever complains when something is TOO strong or solid.
Why didn't the engineer perform Dynamic Cone Penetration Testing (DCP) accompanied with auger borings with DCP test at -1', -2; and -3'? Need a bearing pressure of at least 2000 pounds per square foot, and the DCP is the only way of determining. When probing alone, you may encounter small rocks that get in the way, and it may actually be softer below those obtstructions.
@@eh8899 -
I'm guessing cost.
A common procedure in some areas of the country due to type of soil etc.
In some cases a wider footing is required, others might include a deeper excavation into more stable soil.
Good shout, I like the explanatory views and what is gonna be done in compacting the soil and the reason why the windows or doors are not opening. Etc.....Excellent, now I know why a property which has excess ground movement.
Preecise recomendation to set a solid bed of rocks prior to proceed with the foundation👍👍
Thanks guys. I just started a job as a field tech. Lol, I already use a 5/8ths piece of rebar to use as my rod to determine the footings.
Nice
My house, in virginia would not stop moving. Drywall cracking, door sticking, cabinets pulling away from the wall were the indications something was wrong, it's the soil. The house was built on expansive soil, having an uplift pressure of 900lbs per sq ft, one level ranch on full basement 1600sqft. The builder and building dept failed to follow the expansive soil policy. 1.5 years of battling the building dept and builder and still not done with the repairs. My geotechnical firm designed the removal of the backfill, replace with gravel/ topsoil and 19 helical piers. By the time it's over, the cost, estimated $50k. The only way to tell if the soil(clayey soil) is good; have the soil tested for expansiveness. As far as the video goes, the point is; verify the foundation soil, to do that you need a qualified geotech to examine the soil, and it shows that.
Wow, Pat, what an experience. Sorry to hear, but thank you for sharing!
Great video. I need that tool in my box. Thanks for sharing.
Thanks for watching.
I received a lot of good information from this video thanks for taking the time to share it with us.
From Elliot Lake Ontario Canada.
Happy to hear, Scott- thanks for watching
Are there some tests that can be done by yourself before to call a specialist. Like for the soil health assestment?
I worked with Geoff on a large retaining wall south of Atlanta. Great guy!
👍🏽👍🏽
Nice work. Now couple problems: 1) You have very tricky spot for house build, as part of house is siting on rock and some parts are siting on clay based soil and these soils moves differently. Clay based soils moves as water content changes. 2) Its common practice to use gravel to boost soil load bearing but you have to compact the gravel with compacter and also use something to fill voids between gravel, or these voids will fill naturally and the footing will sink a little over course of time by volume of voids. PS English is not my native language.
Your English is perfect- our geotechnical engineer recommended the same thing, we have videos about that earlier in this series.
Tnis101 an alternative (depending on soil conditions) might be to drive pylons into the ground.
Once the pylons are driven in, then a footing base is built around each pylon using rebar and concrete.
This is an even more expensive method of dealing with poor soil conditions. So gravel and compacting the gravel in is not so bad.
I’ll count myself lucky for getting off easy then!
@@HomePerformance Can you please share the link to those videos please? Thanks.
So glad you’re sharing the real world. Lots of knowledge to be gained by understanding the details.
Thx Andy
I asked my engineer who designed my footing how deep should it go, he said “talk to you builder, not me”. Is that normal?
Haha, classic- that’s why geotechnical engineers exist, I guess. If you think you need one, get one.
how much do geotechnical engineers charge for doing the foundation soil test bores which should include wet and dry density, compaction, moisture, bearing capacity and as you say "quantifiable high performance ."
Nothing worse as a consultant geotech to tell them the bearing soils are bad after they placed rebar within the formwork. Sucks but thats why they hire us
Easy way or hard way
Was that top layer of soil originally tested prior to laying the forms down?
Yes, but then it rained for 5 years
I have seen push rods with gauges for soil testing, takes the guess work out.
Love your name... "question everything".
It’s called a penetrometer.
@@Pseudify That sounds a bit kinky...
Are you pouring a alaskan slab? Is water table to high for a basement?
Don’t need the extra space, and we’d have to break a ton of rock to get down there.
Aren't these tests compulsory in the State of Georgia?
I have done many basements and see that you are there every day with the bad weather . I really do like the fact that you are out there kicking the shit with the workers and taking on the tough results from learning the proper way . Radon has been a factor in my stint as a Professional Laborer because of buried trees and ? Now with the form a drain you said it will be vented through the roof? My first thought was? Are the drains running into a crock with a sump pump? in the house or are they flowing with gravity away from the house and if it does run into a crock how does vent through the crock ? I have only vented for radon on the outside of a dwelling not inside . Still learning ! after retirement.
Thanks Lou! Here’s the drain detail:
Drain Trench Performance: Radon Mitigation and Foundation Drainage
ua-cam.com/video/AIiH2EkJOfM/v-deo.html
How does walking on the dirt "loosen" the dirt?? Also, wouldn't rain further compact the soil?
Walking on soaked dirt- check out ‘liquefaction’.
Nice work my friend
Thx WW
I would recommend D.C.P Dynamic Cone Penatromiter.
The Durham-Geo Slope Indicator static cone penetrometer probe has q gauge on it that actually gives q bearing strength reading and is more reliable than just a static probe
Nice
@@HomePerformance The price may have gone up, but they used to be about $530. They come come from Stone Mountain, GA so you could probably drive over there and get one! I actually work for a Geotechnical company and have used one for years. One of the contractors saw ours and bought two for themselves on future projects. We had to use them for Corps of Engineers projects on foundations and natural soils. I'm pretty savvy on that stuff if you ever need any free tips! Always glad to help!
The testing stick is also mentioned in this video. If that's all that Geoff did, where can I get one so I can be sure that my footings are resting on compacted soil before the inspection process? ua-cam.com/video/w3dR9Vs95nw/v-deo.html
definitely better to fix it now than later
What kind of soil is that?
Raw. And fresh. Tastes like chicken.
I've been a geotechnical engineer for 5+ years now... I would never give a baring using a probe rod too much liability. But I also only do commercial and not residential. Most baring I deal with is 3000 to 8000 PSF where a home at most is 1200 to 1500 PSF.
Our geotech has been doing res for decades
@@HomePerformance I still did not get how he founds that soil is not strong.
What do you use to test soil? Pentration test? Like What the easiest method to do to test for residential? Does dynamic cone pentration works?
We use a steel hollow rod with a 40lb weight. We'll drive it in the ground by lifting and dropping 40lb weight counting blows for each 6" going a total of 18" once done pull out of ground and inspect the soil inside hollow rod, hopefully you're on natural soil or documented fill. Based on soil and blow counts i can then give you your soil bearing capacity or undercut unsuitable materials to get down to good soil.
@@abdullahn9827 if you wanted to use a DCP you really need a data point in your area to compare your blow counts to
Depending on the extent of the soil I may have went with helical piles and pier cap
this is great.
Thanks Danny
We are about to pour a stem wall foundation (footings first, then stem walls) at the same place where the old house crawl space foundation stem wall and footings (demolished in Sep 2022) used to be. After the full demo, the trenching from the old footings was filled with what was left of the natural soil around but is still slightly lower than the overall (flat) lot elevation. The idea is to place the new footings at elevation about 2' higher than where the old footings used to be so we can have the top of the foundation stem wall be at least 1' above the final grade which in turn I want to be at my neighbours' (on each side) soil elevations. Our soil is sandy (Granby-Morocco complex), appears to drains ok and building inspector advised that soil has good PSI and no compaction is needed. In Mar 2023, I tested the soil where the original footings used to be with a 5' steel probing rod. At some spots of the old perimeter, the rod went down all the way to the handle relatively easy which concerns me. Neighbour says that our area has a high water table. Code requires footings and wall to be at least 42" below grade (we are in SW MI). After excavating (probably 2-3' deep and then bring fill to make wall under grade per code), I plan on compacting and placing stone (#57) under where the footings will sit. Footings will be 8" high X 16" wide with 2 rows of #5 rebar and 3,000 PSI concrete. Backfilling will be with stone on both sides of stem wall. I will have to bring fill (pit run) to raise the overall lot elevation before compacting and placing stone which will be under the slab. Since I want footings to sit higher than where old footings used to be, do I bring fill first, excavate to 42"+ depth, compact, place stone, pour footings last? Or, I excavate first (I guess not as deep), compact, place stone, pour footings, bring fill to cover foundation per code? Do I need to go with wider/thicker footings? More rebar? More PSI concrete? Need a cost effective piece of insurance. I am waiting for a Humboldt pocket size penetrometer to be delivered and intend to use to further test the soil. Thanks in advance.
shouldnt the footing always be on native material, cause right now youre building your footings on engineered fill
As long as it’s compacted, ESPECIALLY if the native material is not as good
Humm.... seems like a few piers would have been a good idea on a slab with rock on one side and compacted soil on the other. Which is what they put in after it shifts.
Yeah, we have 10 piers too!
12” of wet dirt deep and a shovel widths wide x 400’ as a guess.. sounds like a good work out. The soon to be house that will sit there just sighed a sigh of relief. your future wallet just said thank you and your future self just said..am I gonna build another house or get a gym membership.. peace
This stuff for sure is more interesting than treadmills and deadweights 👍🏻
The bearer of bad news was the ground itself.
Good one dad
@@HomePerformance ;-)
Yay you!
Nice Y/C hat!
Where was this filmed?
Atlanta
Home Performance tell your buddy I live in Big Sky, that’s where the YC or Yellowstone Club is. A private billionaires ski resort, mansion cabins that are unbelievable.
Beautiful place to live
Home Performance I’m going to be building a house and there’s a lot of clay in big sky soooo doing some research, nice video.
Thanks Josh! Clay can be a pain in the butt. Good luck.
Take time and do it right first time so you don’t have to fix it!
Right on
For real? Why did they not put down a gravel bed in the first place. Compacted dirt is rarely going to cut it -basically only if the home is being laid directly atop hard till (northwest) / bedrock. That's highly unlikely.
lay down cement powder, re compact with a jump jack, and also why is there no rebar in the footing ??
There is rebar (??)
Steven He - Emotional Damage!!!
Y'all need to run a hand huger and dcp with proctors and compaction tests for optimum results. Probe rods are ok but its better for measuring GAB that is placed in footings after an undercut.
Hand auger u mean
Yeah in all honesty he saved you alot of money in the long run even though its bad news and more work
Exactly
@@HomePerformance If you donr mind please. I sent a reply to one of your videos and had a question about your framing details. It was about your framing detail on your sloped roof and how the top corners meet up. If you would and have time can you please answer that question.
When I see someone using a probe rod, I lose attention to anything they have to say. HPT meter, dig down to get a 10 ft reading and if soils are bad there, helical to 25 kps and call it a day.
Is that "high tech" tool shown in the video called a soil probe? I ask because the ones I've seen are fiberglass and not steel. I know you guys are making a joke but I believe the reason its a "soil probe" is because if it was any other material like steel then it would be easier to punch a hole in the soil vs it being made out of fiberglass.
No idea, but I know from using a simple length of rebar that it’s not easy to go deeper than 1-2” if the dirt is really compacted
it's the cross sectional area ( and the profile of the "point") that matters, the material , as long as it does deform, has nothing to do with. The units (P.S.I) are the give away Pounds Per Square inch/foot of the bearing area.) ,. Ponder snowshoes vs stiletto's ;-).
Nice, thanks for the explanation
this test looks completely unreliable and might give you wrong sense of security based on pure assumption.
You might as well look at the chart of different type of soils and their typical bearing capacity. Run a plate compactor before building forms and be done with it.
Testing is the opposite of assumption. And charts are nice in the office, but you can’t tell what the soil is doing (or what it’s made of) without getting in there and testing it. Also, we used a vibrating drum compactor, much more effective than s plate.
The technical name for dirt is soil...😁
I'm in blairsville ga would love to get this. Dode
Sechelt excellence
Instead of a Geotechnical Engineer thats gonna push on a probe, You're third party should be a great lab technician that can look at the soil and tell you the expansion index values of that soil. In this case looks like saturation is not a problem. Appears to be a consolidation problem "or as geotech engineers say, compressibility". In my experience, the geotech engineer only ran a few PI's, and a few gradation/sieve analysis, and a few proctor's in college, and really don't understand proctor modified to standard. Get someone that has actually ran the gambit of lab tests and calculated that shit by hand. BTW, he is putting at least 8000psf effort on that probe to go down 12". I'm guessing foundation was deigned for 2000 - 2500psf. Expansion/shrinkage of what looks like soft clay (CL) should be your main concern. In any case, It was clearly not acceptable to put concrete on, and I find it crazy that you had to bring in a third party for this.
just had mine tested by a geo engineer says that after 1' mine is fat clay (CH) the remaining depth of the 10' tested ,his recommendation is to dig 7' down and replace dirt and can use the lean clay to compact back into foundation
Wizardry
Better leave that pos in ur truck and a better way of testing hell a troxler is better than a probe rod
No doubt, the dudes gay. Information is accurate though, i respect it.
Lol wtf 😂
I’ve never seen a comment assassinate a dude making a video so hard 😂
The sound stinks
Darren, that’s not very nice. It’s a free educational video shot outside, if you want HGTV, go watch that instead.
As a contractor, his little intersections of humor are incredibly obnoxious.
As a guy who made an educational video, I find trolls with one liners incredibly obnoxious too.