Ihab Saad – Hydraulic Excavators
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AI: Transcript ©
Welcome to another lecture in construction equipment, and today
we're going to talk about hydraulic excavators. We're going
to start talking about different types of equipment, their
production rates, their cycle times, etc. We're going to have a
few ideas about what are these equipment used for and how to
maximize the efficiency of their use. So the first piece of
equipment that we're going to start talking about is a set of
types of equipment called hydraulic excavators, used
primarily for excavation.
So what are they? They're an excavator is a power driven
digging machine, so the primary use is to dig or to excavate.
Major types include hydraulic excavators, shovels, drag lines,
hose or back hose and clam shells. All of these are considered under
one major group of equipment called hydraulic excavators, A
is other equipment, such as dozers, loaders and scrapers may
also use, be used as excavators, although that's not the primary
use of these equipment. So if we do not have any of the first type
or first group, backhoes, shovels, clamshells, drag lights and so on.
To a certain extent, we can use the bulldozers or the loaders or
the scrapers in an A sub optimal use, just to excavate, although
that's not their primary use, as I just mentioned.
So here are some samples. Here we have a drag line.
This is a backhoe.
And this is a clamshell, as you can see, all of them are used for
excavation for different types of soils, for different types of
projects.
Now we start, we need to start talking about the production of
the excavator. How can we measure its production? The production of
an excavator can be simply calculated from the equation,
production per hour is equal to volume per cycle times cycles per
hour. So depending on the volume that you can achieve per cycle,
whether it's on the bucket or the drag line or the clamshell, its
capacity times, how many cycles per hour? How many repetitive
cycles can we achieve per hour?
The volume per cycle depends on the rated bucket capacity and the
bucket fill factor. So there are two major elements here. Rated
bucket capacity, which is the size of the bucket and the bucket fill
factor, how far can you fill it?
And here we have a couple of tables that show, for different
types of machines, what would be the rated bucket capacity, and for
different types of materials, what would be the bucket fill factor.
So for example, for a backhoe or shovel, that's cable,
the rated bucket capacity is the struck volume. So if the bucket
size is, let's say, two cubic yards, the struck volume means
that there's no heap just at the surface of the bucket. That's the
maximum capacity. And if it's a hydraulic backhoe or shovel, then
the heaped volume at a one to one angle of repose. So there's going
to be a heap on top of the rated capacity of the bucket, plus that,
that heap, which is going to be something like a cone or a
pyramid, at that angle of slope of one to one, which is the angle
where the soil can support itself without without any additional
support. For clam shells, it's going to be the plate line, or
water line volume for the drag line, 90%
of the struck volume, and we're going to see why. Because once you
drag that bucket and you start lifting it, some soil is going to
fall down. So that amount for about 10% of the volume of the
bucket. And for a loader, which is a front loader, not a backhoe,
front loader lifts from the front, is going to be a heap volume at
two to one angle of repose. So with the hydraulic backhoe, is
going to be one to one angle of repose. With the loader, it's
going to be two to one angle of repose. Now, based on the material
itself that we're going to carry inside that bucket,
the more the finer the grain of that material, the more volume we
can carry. Of course, the coarser the grain, the less volume. So we
can see here, for example,
for common earth or loan with very fine particles, the bucket fill
factor is going to be anywhere between point eight to 1.1
the capacity or the size of that bucket for sand or gravel is going
to be anywhere between point nine and one for hard clay, point six,
five to point nine, five is.
For wet clay. Point five, 2.9
for rock that's well blasted. Point seven, 2.9
for rock that's poorly blasted is going to be much less than that.
Point four, 2.7 because of the angular shape of these rock parts
or parts of rock, and the amount of air that's going to be in
between, because they're not going to be interlocking together in an
efficient way.
So let's look at an example. Here estimate the hourly production of
a loader with a bucket heaped capacity of five cubic yards. The
soil is sand, and the load factor, which is to convert from loose to
bank volume that's going to take care of the swell, is point eight.
The Cycle Time for the loader is one minute and 30 seconds, which
is basically 90 seconds. And the job efficiency is 80% which means
out of every hour we can use 80% which is 48 minutes.
So to solve this problem, we need to get the number of cycles per
hour times the bucket capacity.
The bucket load is going to be equal to the fill factor times the
bucket heat capacity, which is point nine times 4.5 here we have
we're going to look at the table that's going to give us that point
nine and the bucket heat capacity was five cubic yards, and that's
going to be in loose cubic yards. Then to convert from loose cubic
yards to bank cubic yards, we multiply by the load factor. So
4.5 lose cubic yards times point eight gives us 3.6 bank cubic
yards. So the capacity per cycle is 3.6 bank cubic yards. The next
part is, how many cycles can we have per hour? Number of cycles
per hour is 60 minutes divided by the cycle time in minutes, but we
were given the cycle times in minutes, in seconds, which is 90
seconds, or in minutes, which is 1.5 minutes. So 60 divided by 1.5
gives 40 cycles per hour. However, that's assuming that we're working
60 minutes per hour. We know that we're not going to be working 60
minutes per hour, but only 48 so we have to multiply by the
efficiency, which is point eight, and that gives us a total of 115.2
bank cubic yards per hour. Now remember that this point nine came
from
a table like this. We were looking at Sand and Gravel. It's anywhere
between point nine and 1.0
and here we are told that,
what type of soil do we have? The soil is sand, so that's why we use
the point nine.
Okay, so here's the the table that we used, which is the point nine
to get that point nine here at the top. So the total production per
hour is going to be 115 bank cubic yards per hour. If the question
was to calculate that hourly production in loose cubic yards.
We wouldn't have to multiply by the load factor in this case, so
it's going to be 4.5
loose cubic yards instead of 3.6
times 40 cycles, times point eight. And that would give a
different number that's going to be in loose cubic yards per hour.
So always make sure what the question is asking about. Is it
asking about bank cubic yards or loose cubic yards
for the hydraulic excavators, also, we have something called a
hydraulic hoe or hydraulic excavator backhoe, depending on
whether the bucket is lifting forward, or is it lifting
backward?
It digs by pulling the dipper back towards the machine. If it's a
backhoe,
when the dipper is filled, it's curled, curled up to reduce the
spillage so that it can maintain the maximum volume of soil inside
that bucket. And here's the example. This is the dipper or the
bucket. So you extend the arm you dig, and then you drag the arm
backwards and lift the bucket to maintain the soil in the bucket.
This, of course, is hydraulically driven. So all of these are
hydraulic pumps
or cylinders. So
what is it used for? It's used for trenching work, if you want to dig
a trench, and the best production is going to be if the trench has
the same width as the width of the bucket itself. It can also lay
pipes, pull trench shields or sheet piles and backfill.
The Trench by placing the soil back after laying the pipes,
the dipping width of the bucket should match the trench width to
maximize the production.
We can also have telescoping booms, which are going to replace
the articulated booms. In the previous picture, we had an
articulated boom. But you can also have telescoping booms that can
extend hydraulically as well.
The production rate for that excavator is going to be the
generic equation is going to be production in loose cubic yards
per hour. Notice now, now that this is in loose cubic yards per
hour is equal to C times s times v, times b, times E. Let's learn
about each one of these symbols.
C is the number of cycles per hour. Basically, the production is
going to be volume per cycle times number of cycles per hour. This is
the in a nutshell, how we calculate the production. But what
are the details? Now the C is the number of cycles per hour.
S is the swing depth factor. We're going to see that in a table in
just a second. V is the heat bucket volume. B is the bucket
fill factor, which would vary from one type of soil to another. And E
is the job efficiency. How many minutes can we work per hour? If
that efficiency is 80% then it's 48 minutes. If it's 75% that is 45
minutes and so on. How do we get the number of minutes by
multiplying that factor times 60. So 80% is 80 times 60, which gives
48 minutes. 75% 75.75
times 60, which gives the 45 minutes.
So the effect of job conditions. Now this is something that you as
a project manager can control on site to improve the production
rate of that equipment. So we have different job conditions, varying
from accident to severe, which is extremely poor, depending on the
backhoe bucket side size, we can estimate the cycle time.
So under excellent conditions, let's say we have a two cubic yard
bucket. The two cubic yards going to be somewhere in between these
two. So under excellent conditions, the cycle time is
going to be anywhere between 15 to 16 seconds. So 15 and a half would
be fine. 15 would be fine. 16 would be fine. Above Average,
which is not excellent. A little bit longer it's going to take 17
instead of 15 seconds, severe, that's the worst type of
conditions. Is going to take 25 seconds instead of 15 Now imagine
if every cycle is extended by 10 seconds. That means that you're
going to have a total reduced number of cycles per hour, which
is going to reduce the total production rate. Here is an
example of what do we mean by excellent and and so on. So
excellent conditions are characterized as easy digging,
unpacked Earth, including sand ditch cleaning, etc, some loose
soil digging to less than 40% of the machines maximum digging
depth. So again, you're not going to extend the boom to the ex to
the maximum swing angles less than 30% when you swing the piece of
equipment to dump the soil into a truck or somewhere else,
dump into a soil spoiled pile, so not into a truck, for example,
because if you're dumping into a truck, you have To adjust to make
sure that your your topic exactly in the in a proper location. But
if you're dumping into spoiled pile, you have more latitude, no
obstruction, so there's no fence, and you can see clearly the area
where you're going to be dumping. The soil that would be excellent
conditions. With any change of these conditions, it's going to
reduce the the the efficiency and increase the cycle time above
average. Conditions are characterized as medium digging.
Here it was easy. Now it's medium, packed Earth, dry clay, soiled
with less than 25% truck content. The depth also, instead of being
only 40% of the maximum being depth. Now it's 50, up to 50% of
the maximum big depth.
The angle the swing ended here was only 30% here it has increased to
60%
large dump target and a few obstructions. So that's going to
increase the cycle time and reduce production rate and so on. You can
see, with the average, we're gonna have hard packed soil that 70% is
instead of 50 swing angle 90 degrees, instead of 30 or 60 and
so on, under severe conditions characterized as tough digging,
sandstone, shale, limestone, hard thrust, depth over 90%
Is going to affect the cycle time with a factor so if the angle of
swing,
and if the optimum depth is 40%
of the maximum, and the swing angle is 90 degrees, then that's
going to have a factor of point eight. It's going to reduce your
production rate by a factor of point eight. If the angle is is 45
degrees, the reduction is going to be only 7% this is a reduction of
20% this is only 7%
if the maximum depth,
if the optimum depth, is 160%
as you can see, we're going to have here
different production rates
on the job conditions, which is, which is, again, something that
you can control, like, for example, cleaning the site, having
no obstacles, having a clear line of sight or line of view for the
operator, having the equipment close to the to to your Excavator
or your your shovel, so that to minimize any travel time. So if
it's excellent, you get point eight, 4%
if it's poor, you get point seven, 2%
and so on. So these are the job conditions, and these are the
management conditions. The management conditions, again,
these are, these are something that you can control as a project
manager. Let's
look at an example again. To make things much clearer, a contractor
has a project to excavate an apartment complex and must
construct a three foot compacted fill to support a parking garage.
The borrow site where you're going to get your soil is three miles
from the construction site.
A 10 cubic yard dump truck will be used, and 10 cubic yard dump
trucks will be used to haul the needed fill.
A two cubic yard shovel would be used to load the dump trucks. So
how many cycles is it going to take for the shovel to fill the
truck. This is two cubic yards. This is 10 cubic yards. We're
talking about five cycles to fill one truck.
The material is tough, dry clay with a swell of 35%
the height of the cut at the bottom side is 11.6 feet, and the
angle of swing of the shovel is 150 degrees. That's quite large.
Estimate the ideal production using the table and estimate the
actual production for good job and management conditions. The optimum
digging depth of the soil of the shovel is 9.8 feet. Optimum
digging depth is 9.8 feet, and the actual depth of cut is going to be
11.6 feet.
So the ideal production from the table is 265,
band cubic yards per hour.
Let's see. Look at that table.
So we have two cubic yards bucket and we have tough clay. Therefore
the ideal production rate is going to be 265
bank cubic yards per hour.
The fill factor
is for that tough clay, as we have seen before, in the table, is 1.05
that's an average
the cycle time for
the
average job conditions for two cubic yards, which is going to be
somewhere between one to two and two to three. We're going to take
the average of the two. So between 20 seconds and 22 seconds, we
selected 21 seconds, which is average. Therefore the production
is going to be equal to the bucket capacity times the field factor
divided by the ideal cycle time. The Bucket capacity two cubic
yards, the feed factor 1.05 depending on the type of soil,
and divided by the cycle time, which is 21 seconds that we
obtained from here.
And we basically 21 divided by 33 3600 to convert from seconds to
hours. So we put the 3600 above here,
divided also by the
load factor to convert from loose to bank cubic yards, based on the
swell factor that we already had, which is 35% so the percent of
optimum depth for this excavating operation is now we have the
optimum is 9.8 the actual is 11.8 so that's equivalent to 120% of
the optimum.
Are capable of digging at higher depth. So you can,
you can descend it into a well, for example, or a shaft, and you
can grab the soil and lift it vertically.
It lacks positive digging action and lateral control of the shovel
or backhoe. So the backhoe and the shovel are much better for lateral
control and positive digging action, which means hitting with a
certain force. This relies primarily on the weight of the
clamshell itself,
used for excavating vertical shafts and footings. So again,
same machine as we had with the drag line. The only difference
here is that we're going to drop this vertically, which is the clam
shell, and it's going to grab the soil. You're going to lift it,
turn and dump it wherever you need to.
And that's, again, is a magnified view of the clamshell itself.
Here it shows that it can
dig, especially in marine conditions and in wet conditions,
a clamshell would be a very good
machine to use.
Production is based on the equation, again, same generic
equation, volume per cycle, time, cycles per hour.
The maximum load should be limited to 80% of safe lifting capacity
for rubber tired equipment and 90% for crawler mounted equipment.
Just because of issues of stability of the equipment itself,
we don't want it to again, tip over.
Other factors to improve the production rate for the clam shell
include having the dumping radius same as the digging radius. So
again, you're not going to move the clamshell along the boom.
You're gonna lift the soil, turn and dump the soil in a truck or a
soil pile, kicking, keeping the machine level to avoid swinging
uphill or downhill, which is going to affect issues of stability and
issues of production rate as well.
So based on the angle of swing, as you can see, if it's a 90 degree,
that's going to give you the optimum
swing. If it's less than that, it's going to increase the
production rate because of a shorter swing cycle.
And again, similar to what we have seen before, depending on
the ideal production rate is going to depend on the bucket size and
the type of soil that you are digging.
So let's look at an example one more time, a contractor has
decided to use a two cubic yard clamshell mounted on a crawler
crane to excavate for the foundations of three concrete
piers for a highway bridge. The excavated material will be dumped
in stockpiles for later use in backfilling. The material is
common earth, and the average angle of swing is 120, degrees.
Job and management conditions are good. What's the estimated
productivity of the clamshell in bank cubic yards per hour.
So the estimated ideal productivity for a two cubic yard,
two cubic yard for Common Earth is 160
bank cubic yards per hour.
The angle of swing for is 120 degrees. So the correction factor
for the angle of swing is point nine, one,
and the good job and management conditions from the previous
tables is point seven, five. Therefore the production rate is
going to be 160 band cubic yards per hour times point nine, one
times point seven, five, and that gives 109 bank cubic yards per
hour.
So
in this lecture, we have learned about what are the different types
of
excavation equipment, earth moving equipment for excavation,
primarily, we talked about the shovel, the backhoe, the dragline
and the clamshell. We looked at the different factors affecting
their production rate, and how many of these factors can be
controlled by the project manager, by improving the site layout and
improving the location of the equipment and the dumping
equipment and so on and so forth. So all of this is within your
control,
and I'll be glad to answer any questions related to that in
class. Well, thank you and see you next time in another lecture. You.