How Soil Destroys Buildings


When most people think property damage, they
think about natural disasters. But what if I told you, there’s a slow-moving
geologic phenomenon that causes more damage in the United States than earthquakes, floods,
hurricanes, and tornadoes combined? Hey I’m Grady and this is Practical Engineering. Today we’re talking about expansive soils. If you’ve ever been to a place where the
ground looks like this, or if you’ve been in a building that looks like this or this,
there’s a good chance you were in a place that had expansive soils. Just like these dinosaur toys, certain types
of clay soils change their volume depending on moisture content. They swell when they get wet, and shrink as
they dry. This is a microscopic mechanism where the
shape and arrangement of the molecules actually change according to the amount of water mixed
in. And, large portions of the U.S. gulf coast
and great plains have these kinds of soils. If you’re starting a foundation repair or
road paving business, this is an important map for one very good reason: expansive
soils break stuff. Movement on its own, and especially very slow
movement, is usually not a problem for structures. This is why we can lift buildings and even
move them to new locations. What causes damage is differential movement. This is where certain parts of a structure
move relative to each other. Differential movement leads to sticking doors
and windows, cracked walls, and just general out-of-plumbness. And this is why expansive soils are so insidious,
because they don’t expand and contract evenly. For example, if your house sits on a concrete
slab and you haven’t had any rain, the soils around the edges of the slab that are more
exposed will dry out and shrink while the interior remains moist. Now you’ve got a foundation with no support
around the edges. This breaks one of the fundamental laws of
civil engineering, which says, and I quote, “You gotta have dirt underneath your concrete.” Expansive clay isn’t just an issue for buildings. All kinds of infrastructure are at risk of
damage from a shifting foundation. Leaking pipes can cause swelling of the soil,
pulling apart joints and eventually leading to issues like sinkholes. Rain water infiltrating through the cracks
in roadways causes localized areas of swelling, making the road bumpy and uneven. Not even sidewalks, and by proxy rollerbladers,
are spared. When designing to account for expansive clays,
engineers not only have to know how much the soil can change in volume, but also how hard
it can push on anything sitting above, also known as swell pressure. So I’ve rigged up a little test so that
we can see not only how soil swells, but also how much pressure it can exert. This apparatus called an oedometer. It’s similar to a hydraulic cylinder, except
I’m using dirt instead of oil, and I’ll use a dial indicator to measure how far the
sample is able to move the piston. If you work in a soil laboratory, I’ll just
apologize now for the rest of this video. For my first test, I’ve got some soil straight
from my own backyard. After all, there’s no place like a geologic
unit containing abundant clay with high swelling potential. I put this in the oven to dry it out first,
don’t tell my wife. Just kidding she knows who she married. Now let’s put it in the apparatus and watch
what happens. As it saturates, the soil expands over time,
eventually reaching a 10% increase in volume over its dry state. Trust me, that’s enough to put a crack in
the drywall. But, it’s really not that dramatic on video. So, to help illustrate these concepts a little
better, I’ve got a bag of instant viral video. That’s right I’m talking about Superabsorbent
Polymer Beads, also known as Orbeez. These beads behave very similar to expansive
soils, except they’re way cooler than dirt in almost every way, even for a civil engineer. First I tested these with no confining pressure,
and went a bit overboard. You can imagine if you built a house on this,
you might get motion sickness every time it rains. It would wreak havoc on your structure. I tried it again with fewer orbeez, but it
was still too much. This is an exaggerated view of what happens
as water penetrates the subsurface and saturates an expansive soil. It’s hard to imagine anything that could
avoid damage in this environment. So, let’s add some weight – and fewer orbeez
this time so I don’t max out the range of my dial indicator. You can see that these fishing weights hardly
make a difference. And that makes sense, right? A house probably puts more pressure on the
ground below it than a few fishing weights. What about ten times that weight? It takes them a lot longer, but the orbeez
are still able to swell to their full dimensions under this 20lb barbell, which is about the
most my little acrylic oedometer can handle. This is not just the case for orbeez by the
way. Some clay soils have swell pressures on the
order of megapascals (that’s hundreds of pounds per square inch). So you can see how big of a challenge these
expansive soils can pose. There are lots of ways that engineers try
to mitigate damage from these kinds of soils. You can simply remove all the expansive clay
and bring in better soils for your project. You can grade the site so that water drains
away from your structure, keeping moisture fluctuations down. You mix chemicals into the soil that limit
its ability to absorb water. Finally, you can simply to build heavy enough
to counteract the swell pressure and keep the soil from expanding. But as we saw in the demonstration, even a
small amount of soil or in this case a colorful soil surrogate, can lift a lot of weight. I’m leaving out the simplest solution, which
is simply to avoid expansive soils, because it’s generally not feasible. It may be true in the parable that the wise
man built his house on rock, but some civil engineer had to build a road to that guy’s
house, and the engineer didn’t get to choose what kind of soil was on the way. Expansive soils are not a particularly newsworthy
or exciting hazard (unless you’re the type of person who makes videos about dirt in your
garage), but they still cause a tremendous amount of damage to buildings and the public
infrastructure we rely on every day. They are one of the many factors taken into
account when designing civil structures and the subject of ongoing research to find cost-effective
and sustainable practices for mitigating the damage they cause. Thank you for watching, and let me know what you think!

100 thoughts on “How Soil Destroys Buildings

  1. 5:58 I agre with de the first three solutions, but disagree with the last one. Because we must consider that not only an expansion is being generated, but also a force. And if we want to know about the origin of this force, we should talk about molecular levels and the forces at molecular levels will always be bigger.
    Pd: You have amazing channel congratulations. Excellent content!

  2. couldnt you build a moisture spreader?

    a moisture spreader would be the moisture equiv to a head spreader.

    a heat spreader is usually a heat pipe witch is a piece of pipe with a heat transfer liquit and the pipe usually runs the length of the heatsink and helps prevent hot spots in the cooling device.

    so a moisture pipe would be a bit of plumbing that would allow airflow or better drainage so the ground can dry out more evenly

  3. Would love to see videos about some of the various site prep and foundation techniques to deal with this. I grew up in central Texas where temperature and ground moisture swings dramatically and can destroy things in this same way all the time.

  4. You could also drive down Steel pipes as a pile, down in The Mountain under The ground, with a drill, and Then drive down an anker through each pile also with a drill, that Will make The building more stable.

    I am at a Counstruction site right know where we are doing just that, normal piles around The building edges, and Then The drilled piles in The center of the building (mostly because of the dry period, than you need normal piles at The edge to keep The building up)

    English is my second language so I do not know The terms for these things in english, so I am. Sorry for that!

    But love your videos, most of it have made me learn more about my job, since I am not an engineer, I am just a normal Female counstructionworker 😂 I know what to do in my field and a General idea of why we do it, but your videos bring more Light into The "why we do it" part, that makes me appriciate my job even more!

  5. You could also drive down Steel pipes as a pile, down in The Mountain under The ground, with a drill, and Then drive down an anker through each pile also with a drill, that Will make The building more stable.

    I am at a Counstruction site right know where we are doing just that, normal piles around The building edges, and Then The drilled piles in The center of the building (mostly because of the dry period, than you need normal piles at The edge to keep The building up)

    English is my second language so I do not know The terms for these things in english, so I am. Sorry for that!

    But love your videos, most of it have made me learn more about my job, since I am not an engineer, I am just a normal Female counstructionworker 😂 I know what to do in my field and a General idea of why we do it, but your videos bring more Light into The "why we do it" part, that makes me appriciate my job even more!

  6. Grady, I just love your videos. They are not only informative, but you deliver them in such a concise and thorough approach that the most lay person could grasp! I, much like yourself, live in the great state of Texas(approx 60 miles from SA) and I am all to familiar with the devastating affects of our expansive soil base. It wreaks havoc on my homes! Every season I see the same crack in the mortar joints of my brick veneer expand and contract at least 1/2”!
    Thank you for your well thought out and well articulated series’.

  7. Video bout dirt=nah

    Video bout dirt + Practical engineering = me watching a 9 minute video bout dirt

    Dirt video + Practical Engineering + 1: 00 AM = this meta comment 👍

  8. I hope engineers appreciated that Rick and Morty scene where Rick built a surface so level that Morty didn't want to leave it as much as I did.

  9. Hello there, I am not an engineer, but I have just found out about your channel and I must say I love it. The way you explain makes it easy for non specialists like me. Congratulations for your work and thank you for sharing your know-how in a fun and clear way. This is why the internet is the best invention ever. Cheers, from Central Brazil.

  10. Excellent… It's not easy to make such videos with high quality precision on its content… Keep up your good work…

  11. 5:34 solutions to the problems. Grady, could you suggest solutions for a home already built on expansive soils? What do you think about reinforcing the foundation with carbon fiber fabric and epoxy? They are repairing bridges with this technology all over the nation.

  12. As always, very good, Grady.
    Road engineers use lots of lime to reduce swelling under their roads.
    Mollisol for soil nerds: https://en.wikipedia.org/wiki/Mollisol

  13. In the UK we always dig through the clay onto rock and then pour a concrete foundation at least 10” thick to sit your outer house (sometimes inner too) walls on. Many of the Victorian houses throughout Britain have subsidence issues as the house foundations only went down about a foot or two foot, at most.

  14. In the Dallas/Ft. Worth area a program called moisture conditioning was implemented several years ago. There are chiefly two methods of achieving this process one being water and or chemical injection the other being mechanical where the sub-soil is excavated and replaced with moisture levels at 3 to 7 percent above optimum levels. The purpose of course is to expand the soil to its optimum and yet still be able to accomplish compaction to support the building and foundation system. There is a layer of non-expansive material immediately below the foundation to both support and seal in the moisture. There are other parameters that will help in this process also performed. I believe that the shrinkage is controlled very successfully as the two most powerful drying forces of wind and sun are removed and the weakest source, gravity is the only remaining energy to have a drastic effect. Moisture will " wick" away but this is more of a minimal effect with the percentage of moisture above optimal. Keep in mind that this process is under the entire structure creating pretty balanced movements providing grading and other sources of water intrusions are performed correctly. However, vertical rise can occur in those instances where these items are not addressed along with in some instances migrating waters affecting deeper expansive soils can occur.

  15. I propose a ship hull like, or bowl like structure as foundation against this type of soil. Therefore I hope the soil pressure is channeled to side, also increase surface area pressurized by the soil, therefore weakening the pressure. The empty space on top can be filled by gravel sand/soil mix, and covered by flat concrete.

    I am not civil engineer, btw.

  16. I took a course at the University Maryland that included this topic. Your demonstration should’ve been in the course as it was much more informative. Thanks

  17. Poor soil that can expand is only on the top layer of the ground, if you dig deep enough you will found bedrock, the strong layer of ground made of sediment stone that will not expand. In my country Indonesia we use "chicken foot" foundation to solve expanding poor soil problem. We dig holes on the ground until we found the bed rock level. We put some reinforced concrete "foot" for the building's bottom fondation on that holes. So, it's pretty solved the problem. You have poor soil that always expands but under your poor soil there are your building's "foot" that stood on the strongest layer of ground you can have.

  18. Great video! Learned something new today. I have a civil engineering related question. When a developer wants to put houses on a property, what types of materials are considered acceptable?
    A link will do since I know there probably isnt a quick answer.

  19. It's not dirt, its soil! Yes, I know I'm picky, but I was on my FFA Soil Judging team for three years and work in the California agricultural industry.

  20. What if a truss undergoes a differential settlement ? Will there be any fracture in the structure or simple rigid body movement ?
    I think there'll be no fracture.

  21. What about pylons driven down to bedrock as the underpinning the concrete footer sits on, and replacing expansive soil under the foundation/ concrete pad with ABC gravel?

  22. Build on pilons? Use a plastic mesh and a synthetic fiber just below the foundation . And put a drainage system below.

  23. Hi bro, I am a non-engineer, and I love the way you simplify it for laymen to get you point in all you videos I have seen so far. Thanks for such simplicity, and practical visual everyday examples, instead of complex math equations.

  24. Interesting to see the South mostly covered by the expansive soil section of the map. How much does this impact the economy of Mississippi, Georgia, and Alabama compared to North and South Carolinas?

  25. So the message of the video is that the course of human history has been shaped from the shadows by a secret society of colorful dinosaurs.

    Got it! 😉

  26. I see this all the time! Seems 6 inch steel studs buckle 8 inches!! Looks like a car ran into the wall but the soil was just D compacting

  27. are there any practical applications in use in the world where this extreme power of expansive materials is turned to productive work? like for example if you wanted to break open a safe you could fill it up with expansive material through a small hole and then apply water till it splits the door off its hinges

  28. You can't keep expansive clay dry all the time but you can keep it wet all the time. Bury a weepy pipe a couple feet down all the way around the foundation and put a moisture sensor down there. Keep the soil moisture constant and you won't have the differential movement.

  29. What about a new building material like a honeycomb shaped polymer used in a modular system? Honeycombs can handle weight and are flexible….

    (ie; “suspension system for a structure”)

  30. Simply LOVE this video.
    Been contracting 30 plus years. And customers always ask about this due to damage I find.
    I have sent several customers to this video for a better understanding.

  31. fuck off man!!!!! the reason soil move rapidly because of all your noobness! cutting trees, not doing tests on soil before building. you guys have to learn a lotabout soil!!! GT

  32. On new homes, people want to buy fancy things that look nice. Before they build I tell them they are going to have soil, water or sewer or water problems. They tell me that those things are not in their budget. After they move in and have the problems it is a different story.

  33. Very nice video. So what can a home owner do about this? are foundation repair companies a real solution? Do sprinkler systems make a difference? How do you know when the grown is moist enough to avoid movement? Can you monitor movement inside your house? how much can a house tolerate before cracks show up? I"m in DFW and the soild here sucks!

  34. How this is countered in the Netherlands which consists of almost all clay is to drill long concrete poles into the ground through the clay layer and onto the sand layer below it and the foundation is then build on these poles.
    This way the clay can shrink and expand without moving the houses on top of it.

  35. Hey man! Just so you know, your channel is watched in Brazil. You're fantastic, thanks for taking ur time to teach and remind us of some concepts.

  36. Are foundations ever poured with a curved under-side to help avoid differential settling? Like an upside-down arch?

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