# Ihab Saad – Hydraulic Excavators

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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.