We talk about a lot of big structures on this channel. But, it takes a lot of big tools to build
the roads, dams, sewage lift stations, and every other part of the constructed environment. To me,
there’s almost nothing more fun than watching something get built, and that’s made all the
better when you know what all those machines do. So, in this episode, we’re going to try
something a little bit different. I’m Grady, and this is Practical Engineering. Let’s get started!
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A big part of construction is just shifting around soil and rock. If you’ve ever had to dig a hole,
you know how limited human effort is in moving earth. Almost no major job site is
complete without at least one excavator because they’re just so versatile. Depending on size,
the heavy steel bucket of an excavator can match an entire day’s digging of one
guy or girl with a single scoop. But excavators get used for more
than just digging. They are a lifter, pusher, crane, and hammer all in one.
A skid steer is second only to an excavator when it comes to versatility. These little
machines are often equipped with a bucket, but you can attach almost any type of tool as well.
While there are often purpose built machines that can do the same job,
none of them can convert from loader to mower to forklift to drill rig quite so quickly,
and in tight confined spaces, a skid steer is the perfect tool.
A loader is one in many machines meant to carry soil and rock across
a distance. They’re often articulated in the center for tighter turns and use a
large bucket on the front for lifting and dumping.
They’re meant to carry materials over short distances, like the length of a construction site.
Longer hauls use a dump truck. These trucks feature a large open-topped tub meant to withstand
repeated loading with various heavy materials. A typical dump truck features a hydraulic cylinder
that can lift the bed, tilting it at a steep angle and allowing material to dump out of the
back.. Since dump trucks carry heavy loads, lots of them have auxiliary axles that can be lowered
to distribute the weight over more tires and keep the truck in compliance with roadway and bridge
weight limits. Articulated haulers are dump trucks used in off-road and difficult terrain.
If you want to move a lot of soil around a large construction site,
another option is a scraper. Rather than loading from the ground into a dump truck,
these machines do it all in one. A huge blade scrapes directly from the ground into
a hopper. It’s carried directly to where it’s needed and unloaded with a hydraulic ejector,
and these are often used on large embankments like for highways and dams.
Another Swiss army knife of the construction yard
is the backhoe that is kind of a combination excavator and loader.
Great for small sites where it doesn’t make sense to have two pieces of equipment.
And don’t forget the bulldozer that specializes in moving material at ground level. They can’t move
material over large distances, but they can spread out literal tons with their tank-like tracks.
The last stop on the digging train is the trencher. There are a huge variety of styles
and sizes, but ultimately they all specialize in digging long holes for pipes and utilities.
Many use a tooth chain like a giant chainsaw for the Earth!
By the way, there are about a hundred different colloquial names for almost
every piece of large equipment. Different sites, suppliers, regions,
and countries use different words for the same machine; it’s part of the fun. One easy tip to
sound like a pro is just to add the drive style to the front of the name. It’s not
a loader, it’s a wheel loader, or a tracked excavator and so on. Now let’s hit the road.
Roadwork is something we’ve all seen, and while it can be a bit frustrating if you’re
stuck in a traffic jam from it, roads might be the largest engineered structures on earth. Our
modern lives depend on them, and it takes some pretty cool tools to get them built.
A grader is technically an earthwork tool,
but it’s used mostly on roadways. The extra long wheelbase makes it well suited for
precisely leveling surfaces and evening out bumps, leaving a nice even grade.
Once all that soil is in the right place, it needs to be solidified so it doesn’t
settle over time. A roller compactor is the main tool for this job. There
are a few varieties of these depending on the material being compacted. Smooth drums are used
for most soils and asphalt. Sheep’s foot and padded drums have protrusions that work best
on clay and silt. Pneumatic tire rollers are best to knead and seal the surface. And a lot
of roller compactors have a vibration feature to shake the soil into place.
An asphalt paver is the machine where the road meets the road. Hot asphalt
is loaded into the machine, which spreads it into an even layer onto
the subgrade using a screed. Many paving machines have a wand that
follows a stringline as a reference to the exact elevation required for the roadway.
If we’re talking about making a road out of concrete, then the tool for the job is
a slip former. It’s usually more efficient and produces better quality of work when paving,
curbs, and highway barriers are installed continuously rather than building forms and
casting them in batches. Careful control of the mix makes it possible for a slip
form machine to create long concrete structures without any formwork at all.
If we just added another layer of pavement to the road every time it started to wear out,
pretty soon, we’d have walls! Roads are designed to be extraordinarily tough,
so removing the top layer isn’t easy. That’s a job for an asphalt mill or planer. These
specialized tools grind and remove the surface with a large rotating drum. The
material is routed up a conveyor system and can be loaded into a following dump truck.
It’s actually fairly common to see multiple vehicles following one another in roadwork
like this. An interesting example is the so-called paving train. On one end,
we have a dump truck full of asphalt fresh from the plant. This is loaded into the asphalt paver,
which continuously lays a layer of asphalt that is then compacted by one or more rollers. Workers
on the ground also continuously monitor the process to ensure a nice even road surface.
Not everything at a construction site is a machine with wheels or tracks.
A lot of equipment gets hauled in on a trailer, or is a trailer itself. A light tower lets you
work outside of daylight hours, illuminating the site so you can work at night or underground.
An air compressor enables the use of lots of tools on a job site, like jackhammers,
sandblasters, and painting rigs. If you need electric power instead of compressed air,
diesel generators offer access to power when grid service isn’t available.
So far, the actual material we’ve seen is in bulk like earth or asphalt. Often in construction,
the materials we need to lift or move are objects like girders or concrete
pipes. For that you need a crane or similar material-handling equipment.
This is a pipe layer. The name is a bit confusing since the workers that operate them are also
often called pipe layers. And it's no surprise what kind of jobs they do. They specialize in
handling large sections of pipe and precisely lowering them and placing them into trenches.
A telescopic handler, or a telehandler or teleporter is like an all-terrain
forklift. The boom can have attachments like a bucket, pallet forks, or a winch,
and it telescopes to make it easy to deliver materials and equipment exactly where you need it.
If you happen to be the load that needs elevating, then you’ll need a boom lift
or its cousin, the scissor lift. The operator of these controls the platform while standing
on it, allowing for very positioning of people that’s much more precise,
and usually safer, than a ladder. Another relative of the boom lift is a bucket truck
which has a boom lift in the back, used a lot of electric and utility work on poles.
Stepping up in size, we have road-rated all-terrain cranes.
If you’ve passed a giant crane driving down the highway, it was one of these,
since most other types of cranes have to be hauled to a site in pieces and assembled.
As the name implies, all-terrain cranes don’t require perfectly level,
paved surfaces to get to work. However, if your job site is particularly rough,
you need a rough-terrain crane. The giant rubber tires on these mean you’ll need to
have them transported, but once rolling, they can go where highway-rated vehicles might struggle.
If the crane you’re looking at is mounted on tracks, you’ve got a crawler crane. These
heavy-duty cranes, while slower and bulkier than all-terrain cranes and also requiring modular
transport to job sites, can carry immense loads and extend to even greater heights than any of the
cranes we’ve seen so far. Most crawler cranes can be configured according to the job with different
lengths of booms, amounts of counterweight, and extensions called jibs. A particularly fun
configuration is for demolition where a crawler crane might be fitted with a wrecking ball.
Most can move from place to place, but not all. Tower cranes use large counterbalanced
horizontal booms with an integrated operator cab on top of a large, well… tower. Like most of the
cranes we’ve seen so far, these come in a wide range of sizes but can be absolutely enormous,
almost a construction project themselves requiring other cranes for assembly.
One way to build bridges uses a specialized crane called a launching gantry. You may
have heard the term gantry before for a bridgelike overhead crane. These are in
all kinds of industries. A launching gantry uses the existing structure
of the bridge as a base and often lifts whole pre-built sections of the bridge.
Turning from the sky and looking underground,
let’s talk about a few foundation-specific machines.
The biggest and heaviest structures are supported on bedrock or some deeper geological layer. Even
if the usable soil is just clay for hundreds of feet, sinking deep subterranean columns
or piles below a heavy structure can keep it from settling too much over time. One way to
install a pile is to dig a very deep hole, place a reinforcing steel cage in the hole, then fill
the whole thing with concrete. This is the exact job that a pile drill rig is designed to do. These
large-scale drills are pretty closely related to the machines used for oil and gas exploration.
Another way to install piles is to drive them into the earth,
the job of a pile driver. Just like the name implies, they repeatedly strike wooden, steel,
or concrete piles to sink them to the required depth.
Speaking of concrete, there’s a whole subset of construction machines that are
specifically designed to handle, transport, and place this important material. You’ve
probably seen a mixer truck before, and I’ll forgive you for calling them cement trucks,
even though cement is just one of the ingredients of a concrete mix.
The truck can be loaded with dry materials and water, and the mixing occurs en route to
the job site, since concrete generally has a limited time before it begins to cure.
Concrete is often placed directly from the truck using a chute, but that’s not always the easiest
way. Concrete pumps are used to pump concrete to job site locations that are hard to access with
a truck, often with a huge overhead boom. Since concrete is more than twice as dense as water,
these pumps operate at extremely high pressures, sometimes over 100 times atmospheric pressure!
Finishing concrete is mostly a hand-tool job, but there are some machines for big jobs, like ride-on
trowels, that speed up the job of floating a slab smooth once it has started to set up.
Big jobs with lots of concrete might just mix it onsite with a mobile batching plant.
This is helpful if you need to produce vast volumes of concrete over a long period in a
way that would be too inconvenient or maybe even impossible for mixer trucks to handle.
Sometimes concrete needs to be placed on a sloped or vertical surface to stabilize a rock face,
shore up a tunnel, or even just install a pool! The catch-all term for the various varieties of
sprayed concrete is shotcrete (although some pool installers might disagree). Shotcrete
machines use compressed air to apply concrete to all kinds of surfaces in the construction world.
When projects require the installation of new or additional utility lines in areas that are
already built up, the traditional method of digging trenches isn’t feasible. This kind of
job calls for a directional drilling machine. While these are technically boring tools,
they are anything but uninteresting. I actually have a dedicated video just
to talk about how they work, and specifically how they steer that
bit below the ground. Go check that out after this if you want to learn more.
Hopefully there have been a few machines in the list so far that are new to you, but if not,
I have a few more specialized machines you might be lucky enough to spot on a site:
Fans of the channel might recognize a soil nail rig, a specialized machine that drills out more
or less horizontal shafts in an earthen slope and then adds soil nails to greatly enhance stability.
Jobs that require grout often use mobile batch plants, called grout plants. You can even inject
ground into the ground at high pressures using a hydraulic pump to fill voids and stabilize soils.
A wick drain machine installs prefabricated vertical drains into the soil at regular
intervals to speed up drainage of water in clay soils which helps speed up the
inevitable settling of the soil so construction can get started faster.
One option for repairing existing pipelines in place without trenching is cured-in-place pipe
lining. Inverting a liner impregnated with epoxy-resin into an existing pipeline using
air pressure essentially puts a brand new pipe inside an old or damaged line.
One of the least boring machines that you’d be really lucky to see above ground
is a tunnel boring machine. These behemoths use a complicated face of various cutting tools followed
by a material removal and shoring installation apparatus to efficiently bore full scale tunnels!
Obviously I can’t be exhaustive here. The construction industry is just full of machines.
There is such a variety in the type and scale of projects that manufacturers are always coming up
with new and improved equipment that can get a particular job done better. And lots of industries
outside of construction use heavy machinery, including mines, oil and gas, and railroads.
Let me know what you think I missed or if you want a similar list within a different industry.
But I think this is a good starting point for any burgeoning construction spotter,
and I hope it’s exhaustive enough that if you see something that didn’t make the list,
you can puzzle out its purpose on your own. That part of the satisfaction of
construction spotting anyway, so get out there and see what kinds of machines you can find.
I am obviously fascinated by the machines that both build and make up our constructed
environment, from the oldest to the most modern. I think it’s interesting that a
lot of the differences we see in vehicles comes down to how efficient they are at
doing a very specific task. For example, my friend Brian from the Real Engineering channel
just released a video all about maglev trains, and he explains why there is only one commercial high
speed maglev line in the world, even though the technology seems ready to revolutionize
train travel. I had no idea how travel time factors into the economics of these projects.
Maybe you’ve noticed what I have over the past few years: my old favorite TV networks are just
running reality shows, and the best video content that I actually enjoy watching is being made my
independent creators. There’s just something different about a small team who is passionate
about their topic instead of being told what to do by some studio executive looking at ratings
numbers. You can catch the Real Engineering video on maglev trains on YouTube when it comes out
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