× SPECIAL FORCES      |     LOCKSPORT      |     SCI FI      |     INSECTS      |     RECIPE      |     RED DEAD REDEMPTION      |     WOODWORKING      |     FISHING      |     SCI FY      |     CRIME STORIES      |     BIRDS      |     STYLE      |     TV      |     INTERESTING      |     ENVIRONMENT      |     STAR WARS      |     OLYMPICS      |     EASTER      |     GOD OF WAR      |     FOOD & DRINK      |     PHOTOGRAPHY      |     WEDDING      |     COLD WAR      |     WAR      |     CHRISTMAS      |     ARCHITECTURE      |     FITNESS      |     ART      |     TOYS      |     SKATEBOARDING      |     YOUR HOME      |     PSYCHOLOGY      |     RELIGION      |     HEALTH & WELLNESS      |     PETS      |     GUNS      |     MATH      |     BIOLOGY      |     WW1      |     BUSINESS      |     WORLD WAR 2      |     AUTOMOTIVE      |     STEM      |     GUITAR      |     AQUARIUM      |     HOMEBREW      |     KITCHEN      |     SPEECHES      |     KIDS      |     ECONOMICS      |     PROGRAMMING      |     REMOTE CONTROL      |     MINECRAFT      |     MOTORBIKES      |     VALENTINE'S DAY      |     MULTIPLICATION      |     LAWNCARE      |     GARDENING      |     PI DAY      |     LEGO      |     BLOCKCHAIN      |     COMPUTER SECURITY      |     SPORTS      |     CATS      |     MUSIC      |     FORTNITE BATTLE ROYALE      |     FARMING      |     ARTIFICIAL INTELLIGENCE      |     ROCKCLIMBING      |     RELAXING      |     CSGO      |     BABY      |     AVIATION      |     MENS STYLE      |     ANIMALS      |     SCIENCE      |     DOGS      |     SHOOTING SPORTS      |     MOVIES      |     OUTDOORS      |     BIKING      |     HISTORY      |     FASHION      |     FAR CRY 5      |     HALLOWEEN      |     STPATRICKS      |     CRYPTOCURRENCY      |     ENGINEERING      |     GEOPOLITICS      |     POLITICS      |     TECHNOLOGY      |     FUNNY      |     TRAVEL      |     MARTIAL ARTS      |     GAMBLING      |     GAMING      |     KNITTING      |     BEAUTY      |     PHILOSOPHY      |     ANCIENT WORLD      |     POTTERY      |     ARCHERY      |     THANKSGIVING      |     HOME REPAIR      |     CRAFTS      |     ORGANIZATION      |     BIG THOUGHTS

  • 00:00
    One of the most important considerations whenyou build anything is the material.
  • 00:05
    It impacts everything from the look and feelto the more fundamental characteristics like
  • 00:09
    weight and strength.
  • 00:11
    But maybe the most significant aspect of aconstruction material is its cost.
  • 00:16
    Infrastructure is not made to be glamorous and it’s often paid for by you and me through
  • 00:20
    taxes, so we like to keep the costs down.
  • 00:22
    And there’s one construction material that’s cheaper than just about anything else out there:
  • 00:26
  • 00:28
    Hey I’m Grady.
  • 00:30
    Today on Practical Engineering, we’re talking about reinforced earth.
  • 00:42
    You’ve probably don’t think much about the strength of the soil beneath your feet,
  • 00:45
    but some of us have dirtier minds than others.
  • 00:48
    Just about every structure out there sits on the ground.
  • 00:51
    And anyone who’s ever built a sand castle knows that soil is not all that strong.
  • 00:56
    So if we want our buildings and bridges and pipelines and roads and anything else that
  • 00:60
    sits on the ground to keep standing, and especially if we want to use earth itself as a construction
  • 01:05
    material, we’re going to need some geotechnical engineering.
  • 01:10
    Soils are frictional materials.
  • 01:13
    Rather than being held together by molecular bonding like steel or by a binder like the
  • 01:17
    cement in concrete, their strength almost completely depends on internal friction between
  • 01:22
    the soil particles themselves.
  • 01:25
    If we want to avoid sliding, the frictional force can be considered the shear strength.
  • 01:29
    The more friction, the more strength against shearing.
  • 01:33
    Just like the simple block on the plane, theshear strength of soil depends on the internal
  • 01:37
    forces too.
  • 01:38
    But unlike that example, soils have an infinite number of potential sliding planes all at once.
  • 01:44
    Let’s look at a sample of soil and applya vertical force.
  • 01:49
    If you analyze a horizontal failure plane,our force is completely perpendicular, or
  • 01:53
    normal, so it is increasing the shear strengthof the soil.
  • 01:57
    But if we look at an angled plane, thingschange.
  • 02:00
    On this plane, the force is partly actingnormal, increasing the strength, but it’s
  • 02:04
    also partly acting in parallel to the planeincreasing the shear stress.
  • 02:09
    The steeper the angle of the failure plane,the more the vertical force contributes to
  • 02:13
    shear stress and the less it adds to the shear strength.
  • 02:16
    If the shear stress exceeds the strength, sliding occurs and we say that the material
  • 02:21
    has failed.
  • 02:22
    This is why granular materials generally can’tst and vertically.
  • 02:26
    The weight of the material itself is enough to cause a shear failure along an angled plane.
  • 02:32
    Pour out some sand on a table, and you’ll notice that the pile forms a slope.
  • 02:36
    The angle of this slope is called the angleof repose which is the steepest angle at which
  • 02:40
    a soil can naturally rest.
  • 02:43
    In other words, this is the slope at which the shear stresses within the soil due to
  • 02:47
    its own weight are exactly equal to the shear strength caused by internal friction.
  • 02:53
    Any steeper and the soil will slide.
  • 02:55
    Let’s look back at our sample of soil.
  • 02:57
    If we put the sample back in the ground, now it’s surrounded by additional soil that
  • 03:02
    can apply horizontal pressure.
  • 03:05
    This is called the confining pressure, andit helps to balance out vertical forces like
  • 03:09
    the weight of the soil itself.
  • 03:11
    This confining pressure is the reason that a granular material can be stable at a slope,
  • 03:16
    but usually won’t be stable vertically.
  • 03:20
    This can be a problem if you’re trying to build an earthen structure for two reasons.
  • 03:24
    First, it takes about twice as much material than if you’re using something that can
  • 03:28
    stand vertically.
  • 03:29
    And second, is space.
  • 03:31
    In crowded cities, space is at a premium.
  • 03:34
    If you’re building an earthen structure, every foot that you go up in height, you have
  • 03:38
    to go out that far as well, or even further.
  • 03:42
    So what’s a geotechnical engineer to do?
  • 03:45
    What if there was a way to add confining pressure to the soil, without having to build on a
  • 03:49
    Reinforced earth demonstration experiment.
  • 03:49
  • 03:50
    Behold, reinforced earth.
  • 03:53
    Just like rebar in concrete, you can create an incredibly strong composite material with
  • 03:57
    soil just by adding reinforcing elements.
  • 04:01
    A wall created in this way is called mechanically stabilized earth, or MSE.
  • 04:05
    And if you look closely, MSE walls are everywhere.
  • 04:09
    Here’s a quick demonstration of how this works.
  • 04:12
    I cut up some circles of paper towel and layer them into the sand in this cup.
  • 04:18
    Without any reinforcement, the wet sand can stand up vertically, but as soon as you apply
  • 04:23
    a load, you get failure.
  • 04:25
    Even just a few discs of paper towel to reinforce the soil allow the sand to hold up this 15
  • 04:31
    pound weight.
  • 04:32
    So what’s happening here?
  • 04:33
    Mechanically stabalized earth diagram showing how it works.
  • 04:34
    The tension in the reinforcement is generating confining pressure in the soil.
  • 04:39
    This pressure acts perpendicularly to the failure planes, increasing the shear strength
  • 04:44
    of the sand.
  • 04:46
    Building an MSE wall in real life works exactly the same way, and they are primarily used
  • 04:50
    in highway projects, especially on the approaches to elevated roadways.
  • 04:55
    Compacted soil is added in layers with reinforcing elements in between each layer.
  • 05:01
    Most MSE walls have a facing of interlocked concrete panels usually with some kind of
  • 05:05
    decorative pattern, and these facing systems are what make them so recognizable.
  • 05:10
    Any time you see a vertical wall of tessellated concrete panels, you can almost be sure that
  • 05:15
    there’s reinforced earth behind it.
  • 05:17
    By the way, the only purpose of these panels is to look nice, and keep the soil on the
  • 05:21
    edges of the wall from raveling.
  • 05:23
    The wall would be completely stable without the concrete facing, just not as pretty.
  • 05:28
    So how strong is an MSE wall?
  • 05:31
    The simple answer is stronger than you would think.
  • 05:34
    Let’s try one more demo.
  • 05:35
    8 inch cube experiment using different techniques of creating mechanically stabalized earth is.
  • 05:35
    I built an 8” cube out of plywood.
  • 05:39
    Just like the cup, I layered in sand and squares of reinforcement.
  • 05:44
    For this first test, I used scraps cut from an old t-shirt.
  • 05:48
    This part is not to demonstrate the strength of MSE, but rather to show that the soil really
  • 05:53
    is transferring load into the reinforcement.
  • 05:56
    The t-shirt material is stretchy, so when the vertical load is transferred into the
  • 06:00
    reinforcement, it spreads out and deforms.
  • 06:03
    I wanted to demonstrate this because it may not be obvious in the next example.
  • 06:08
    For the next test, I used pieces of fiberglass window screen as reinforcement.
  • 06:13
    This is a much stiffer material that does not deform under load.
  • 06:17
    Under about 70 pounds it didn’t budge.
  • 06:22
    Under my weight, even bouncing up and down, it didn’t budge.
  • 06:27
    Let’s try something heavier.
  • 06:30
    For the sake of science, we should probably have a control test with no reinforcement.
  • 06:34
    But this is an engineering channel, not a science channel, and we all know what would
  • 06:38
    happen to a block of dry sand under a car wheel.
  • 06:41
    This is probably on the order of 600 pounds and you can barely even see movement as the
  • 06:45
    weight of the car is transferred to the cube.
  • 06:48
    Unfortunately, I don’t have a hydraulic press, so my Mazda grocery hauler is about
  • 06:53
    the heaviest thing I could think of to test the homemade MSE cube, so I moved on to dynamic loading.
  • 06:59
    I dropped this 25 pound barbell from about 6 feet up to simulate what would happen
  • 07:04
    if you drop a 25 lb weight on the cube from 6 feet up.
  • 07:08
    Almost no damage.
  • 07:09
    In fact if I had a facing system to keep the edges intact, you probably wouldn’t have
  • 07:13
    known the difference.
  • 07:16
    Dirt was probably your first construction material.
  • 07:18
    We are born geotechnical engineers, trying to build taller and stronger earthen structures
  • 07:24
    from probably even before we could talk.
  • 07:26
    With a little bit of reinforcement, we’ve transformed this dirty propensity into a simple,
  • 07:32
    inexpensive, construction material that you probably drive over every day.
  • 07:36
    Thanks for watching, and let me know what you think.

Sand Castle Holds Up A Car! - Mechanically Stabilized Earth

Dirt is probably the cheapest and simplest construction material out there, but it's not very strong compared to other choices. Luckily geotechnical engineers have developed a way to strengthen earthen materials with almost no additional effort - Mechanically Stabilized Earth (aka MSE or Reinforced Soil). If you look closely, you'll see MSE walls are everywhere. Thanks for watching, and let me know what you think!

Community tags: engineering stem     HOME     SIGN UP     CONTACT US