Types of Shovels
Hello everyone, I welcome you all to the lecture 14 of this course construction methods and
equipment management. So, in this lecture we will be discussing about the fixed position
excavating equipments like front shovel and back hoe.
(Refer Slide Time: 00:44)
So, in the last lecture we have discussed about the loaders. And we also discuss about the
different types of loaders and how to estimate the collectivity of loader. So, let us look into
the outline of today's presentation. In today's presentation, we will be discussing about the
front shovel, its applications and factors affecting the selection of the front shovel and the
productivity of front shovel and the productivity of front shove and how to estimate the
productivity.
Then, we will be discussing about the backhoe, its applications and what are all the possible
attachments which can be used for different applications of backhoe and how to make the
selection of the backhoe. So, these are the things which are going to discuss in the upcoming
slides.
(Refer Slide Time: 01:20)
So, basically, shovels can be divided into 2 types based upon the digging motion of the
bucket. So, in the first picture, you can see that the digging motion of the bucket is in upward
direction. So, it is an upward direction. So, that means the bucket is moving away from the
machine. So, that is called as a front shovel, in backhoe or the back shovel, you can see that
the digging motion of the bucket is a downward direction.
That is the bucket is moving towards the machine. So, that is called as a back shovel or
backhoe. Basically maybe want to go for digging above the ground level at or above the
ground level, then we prefer front shovel. So, when you want to go for digging below the
ground level, so, for dipper digging below the ground level, you go for the back shovel. So,
this is how we have to choose whether will go for a front shovel or a back shovel.
So, wherever you want to do the excavation at or above the ground level go for front shovel.
So, for the dipper excavations where we want to do the digging below the ground level, you
go for the backhoe or the back shovel.
(Refer Slide Time: 02:28)
So, let us first discuss about front shovel this picture shows you the front shovel of the very
huge capacity. So, basically these shovels are fixed position excavating machines that means
they are not designed for much mobility. So, from the loading to dumping position, basically
it is not design to move, it will just swing its boom, it will just swing it boom from loading to
dumping position. So, that is why we call them as fixed position excavating machine.
(Refer Slide Time: 02:58)
So, as I told you, this front shovel is generally needed when you want hard digging, hard
digging a rock say, you can handle the rock easily with this machine, so at or above the
ground level. So, this machine is the right choice. So, this is useful when considerable hard
digging of rock from a bank that will start with a vertical face. So, that means this machine
will give you a very good productivity when it is used for excavating a material which is
standing like a vertical wall, perpendicular to the ground.
Say for example, you are going for a hill cutting it stands vertical, perpendicular to the
ground. In that case, it will be very convenient to use a front shovel. So, it can be used to
excavate any bank of material or in a quarry, very commonly, you can see this machine in the
quarry. So, whatever rocks you are blasted using the blasting method. So, those blasted rock
pieces as a short rock can be excavated with the help of the front shovel.
So, it is a using quarry work for loading of the short rock, so but it is purely dependent on a
truck or any hauling machine for hauling the material. So, basically, this shovel will swing it
is boom from loading to dumping position and dumped the material into the truck, it is not
designed for high mobility. So, it is used for quarry work or side hill cutting. So, basically if
you want to use this material for excavating below the ground level, then what are you
supposed to do?
You have to do the ramping down that means the shovel must dig a ramp down into the
material until a digging face of desired height is obtained. So, then only it will be easier to
use a front shovel. So, if you want to excavate the material below the ground level, basically
what they adopt is they will construct the ramp down into the material. There and though till
they reach a digging phase, which is the desirable to cut with a front shovel. So, that is how
they do for excavation below the ground level, if you want to use a front shovel.
(Refer Slide Time: 05:05)
So, this picture shows you the basic operating paths of the front shovel. So, basically the
substructure is a mounting mostly you can see crawler mounting and the superstructure is the
operator cab along with the engine. So, you can see the boom, this is a boom you can see the
boom and this is a stick or the dipper arm and this one is a bucket or the dipper. So, these are
basically hydraulic machines, they were based on hydraulic power.
So, you will be having the ICBs diesel engines to operate the hydraulic pump, motor and the
hydraulic cylinders which is going to deliver the power for digging operation. There are
different types of cylinders you can see, the one which is connected to the boom is causing
boom cylinder. So, this is the hoist cylinder or boom cylinder. So, other one which is
connected to the dipper arm is called a dipper arm cylinder, this is a dipper arm cylinder.
And the one which is connected to the bucket is called as a bucket or dipper cylinder. So,
there are many hydraulic cylinders you can see, these hydraulic cylinders are only going to
deliver the hydraulic power which is needed for digging the material , it will be able to
generate the breakout force and dig the material because of the hydraulic power generator.
So, let us see how the front shovel will function. So, basically, when you want to excavate the
material, first place the shovel bucket with the bucket facing the material which is to be
excavated, so, low it to the base of the material, which is going to be excavated, now curl the
bucket through the material to be excavated, the bucket will get loaded, once a bucket gets
loaded, now lift it.
Now lift the bucket to the desired height, then swing the bucket to the dumping position. So,
basically a truck should come and stand closer to the shovel till you reach the truck, you have
to swing the boom. Now as a boom reaches a truck to dump the material into the truck. So,
very commonly, you can see bottom dump buckets, which will facilitate the material to be
dumped in the downward direction.
So, through a bottom there will be opening which will facilitate you to dump the material.
But the main limitation of the bottom dump is these buckets are heavier. So, that will limit
the lifting capacity of the bucket. Otherwise, the advantage is you can easily dump the
material without much spillage. So, that is a advantage with the bottom dump bucket. Once
you dump the material, then what to do is you have to swing it back, you have to go for the
return swing, swing it back to the original position then lower it.
So, that you can start the cutting again from the base of the material which is to be excavated.
So, this is the common production cycle of the front shovel.
(Refer Slide Time: 08:02)
So, what are the elements of production cycle? First is we are going to load the bucket with
the material you have to dig it, once the bucket is loaded, you raise your bucket, swing it till it
reaches the truck, then dump the load into the bucket, then return spring back to the original
question. So, all these things makes up the production cycle of the shovel. So, one thing have
to noted here is from loading to dumping position, basically this machine is not designed to
move, it will just swing its boom. So, that is why it is called as fixed position excavator.
(Refer Slide Time: 08:38)
How to select this spring shovel for a particular job? So, you know some important
parameters related to the machine. So, that you can make the choice of the machine for the
particular job. So, basically for every shovel, the manufacturer will provide you information
on what is a maximum cutting height for the shovel, what is the maximum digging depth for
the shovel and what is the maximum dumping height for the shovel and what is the maximum
digging reach for the shovel.
So, all these informations I can get it from the manufacturer, this depends upon the dimension
of you shovel. So, what is digging reach? It is a distance between the centerline of this swing.
You know that this superstructure have a 360 degree rotation about the sliding ring which is
fixed to below it. So, the distance between the centerline of the swing to the end of the
bucket. So that is called as a maximum digging reach, a completely stretch your boom or the
arm.
You completely stretch the boom, so that you will get what is the maximum digging reach
possible. So, you completely stretch the boom, then you can find what is the maximum
digging reach possible with this machine. It depends upon the dimension of the boom , and
you can get this data from the manufacturer, it will help you to know what is the maximum
working radius possible with this particular machine based upon that you can make the
selection.
And another thing is what is the maximum cutting height possible with the machine? So, you
can see what is the maximum cutting height and this is the maximum dumping height. So,
this information is important because accordingly how to select the truck, because the truck
and the shovel they are interdependent machines. So, the dimension of the shovel should be
sufficient enough to reach the top of your truck.
So, that it can dump the material that is why we need to know what is the maximum dumping
height with this machine. So, based upon our requirements, you have to make the selection of
the machine. This information I will be getting from the manufacturer. So, for your project,
what is the maximum digging reach needed, what is the working radius needed you know,
what is the maximum dumping height needed depending upon truck available.
What is the maximum cutting height needed; you know it for your project. Accordingly now
you can make this the selection of the shovel, match your job requirements with the machine
specifications and make the selection.
(Refer Slide Time: 11:15)
Apart from the above factors there are also the fundamental factors which govern the shovel
selection. So, the important factor as everyone knows is the cost per meter cube of
excavation, the unit cost of excavation that is very important for any job, what is it unit cost
of production is a very important parameter, which we need to estimate. This is because
based upon the unit cost only we are going to make the selection of the machine.
So, whenever we have different options of machines for selection, we will generally go with
option which will give you the minimum unit cost of production for the minimum unit cost of
excavation. So, for that we need to estimate this parameter. So, how to estimate that you need
to know the cost associated with the machine and we need to know the productivity of the
machine hourly productivity.
If you know these 2 data, I can find a unit cost of excavation associated with the machine,
whichever machine is going to give me the minimum unit cost I will select it accordingly. So,
basically you have to select the machine based upon the size of your job obviously, you know
that. So, for a machine which has to handle a very huge quantity of material, I have to go for
a bigger shovel, the size of the jobs will dictate the size of the machine.
Obviously, when you go for a bigger machine, its mobilization cost is going to be high,
though with a bigger machine you can get a high productivity, but the mobilization cost is
also going to high, that you have to take into account when you work out the economics,
when you decide the selection of the machine. And another important thing you have to know
that is when you go for a bigger size shovel.
So, you know that very commonly we use the shovel for quarry work b. So, when I go for a
bigger shovel, the bucket will be able to handle bigger pieces of rocks. So, accordingly I can
change my drilling and blasting pattern. So, I can have the drilling and blasting pattern
economical pattern in such a way that the rock pieces can be bigger, because a bucket is
bigger, it can handle bigger pieces of rock.
So, that is advantage of going for the bigger machine, it will reduce your drilling and blasting
cost. So, all these things you have to work out the economics and select your machine. . So,
apart from this, the other job conditions, which is going to affect a selection is for particularly
as I told you earlier, when you are going to handle the blasted rock, you need more effort,
you need more breakout force to loosen the material and dig it and load it into the bucket.
So, for that it is preferable to go for larger sized shovel, which can deliver more breakout
force. So, that it can easily do the digging operation. So, for blasted rock preferable to go for
larger size shovel and another thing you have to always keep in mind is that we have to
balance a interdependent machines. Based upon your interdependent machine you have to
make the selection.
As you know, your hauling unit truck and a shovel they must be compatible, because they
work in team. So, you should not have a very big shovel and a small truck or a bigger truck or
a smaller shovel. In both cases, you can see that there will be always some wastage of cycle
time. So, that will affect your productivity. So, based upon the studies people have found out,
it is always advisable to go for a truck with approximately 5 times the excavator bucket size.
So go for a truck with 5 times the bucket size. So, that is the ideal selection. So, that will help
you to give the optimum productivity for both the machines. And you should also to select
the machine the shovel dimensions in such a way that it will be able to reach your truck, that
is why the maximum bucket dumping height, dumping height is also very important when
you select a trucker or the shovel. All these basic guidelines you should keep in mind when
you select the shovel for the particular job.
(Refer Slide Time: 15:18)
So, what are the other factors which affect the output of the shovel? Let us see class of
material, height of cut, angle of swing, size of the hauling unit, scale of the operator, haul unit
exchange time. So, all these things are going to affect the output of a shovel. Just before we
discuss about the size of hauling unit, the hauling unit and your shovel should be compatible
with each other.
So, the truck capacity should be 5 times your bucket size that is a right combination to have
the maximum productivity and operator skill even that will also affect your cycle time in the
productivity of the machine. Now, it is discussed all these factors one by one in the coming
slides.
(Refer Slide Time: 16:02)
The first thing which we are going to discuss is about the class of material. So, how the
material type will affect the productivity of technician, obviously when you are going to
handle some easy flowing material like loose flowing material like sand. So, you can easily
fill the bucket in a very shorter sweep, but if it is going to be a sticky material or raw chunky
material. So, in that case, it may take more time to load the bucket.
So, it depends upon the flowing ability of the material. So, that is going to affect the cycle
time and the productivity of your machine. Loose flowing material will fill the digging
bucket in somewhat shorter sweep than sticky and chunky material. So, an another important
thing you already know is just like what we discussed for the loaders, here also we can get
the rater heap bucket capacity from the manufacturer.
So, the manufacturer has done the rating of the bucket under standard condition say the
particular angle of repose say 1 is to 1. And they have given you the rated heaped bucket
capacity, but you have to adjust the bucket capacity according to the filling ability of the
material, which you are going to handle a project site, says because some materials can easily
fill into the bucket, but some material will have a poor filling ability.
So, rocks may have poor filling ability, sand will have good filling ability, accordingly, the
actual load volume in the bucket will vary. So, we are supposed to adjust the rater bucket
volume given by the manufacturer according to the material type which we are going to
handle at our project site. Rated heaped bucket capacity must be corrected by multiplying by
a bucket fill factor based on the characteristics of the material being handled at the project
site.
(Refer Slide Time: 18:04)
Now the another important factor which we are going to discuss is about the height of cut,
how this factor is going to affect the productivity let us see. So, every shovel can give its
maximum productivity or optimum productivity at a particular height of cut of material. So,
the machine will give you optimal productivity only at optimum height of cut. So that optimal
height of cut for the particular machine will depend upon that dimension of your machine. , it
depends upon the dimension of your machine.
Say if I am using a shovel for cutting a very smaller height material. So, buckets optimum
height of cut is needed is more, but the actual height of cut of material in my project site is
smaller than the optimum height of cut needed for the particular machine. In that case, you
can see that you would not be able to fill the bucket in one sweep, you may have to go for
another sweep to fill the bucket.
This will increase your cycle time. So, similar note you can see that when the height of cut in
your project site there is actual height of cut is greater than the optimum height of cut for the
particular dimension of the machine . In that case also your cycle time will be more, this is
because your bucket has to maneuver for the interior height of cut, so that it can fill its
bucket, , and there will be spillage also.
And all these things will result in increasing cycle time. So, what I am trying to say here is
there is a optimum height of cut for every machine which depends upon the dimension of the
machine. If your actual height of cut in your project is less than the optimum height of cut
needed for the particular machine. In the case also you would not be able to fill the bucket in
one sweep.
So, your cycle time will be more, cycle time will increase. Similarly, if the actual height of
cut in your project site is going to be greater than the optimum height of cut needed for the
machine; in the case also cycle time will be more, you have to maneuver the entire height. So,
only at optimum height of cut, it will give you the maximum productivity. So, that is what is
discussed in this slide.
So, the most efficient production is obtained with power excavator working at its optimal
height of cut. Digging at this depth of cut requires no re-digging for full bucket nor spillage.
That means when the machine is working at the optimal height of cut when the actual height
of cut of material in a project site is equal to the optimum height of cut needed for the
machine you can fill the bucket in shorter sweep.
So, there is no need for re-digging again to fill the bucket and there would not be spillage
also. All these things will improve your productivity of the machine. So, basically what is this
optimum height of cut, the vertical distance that permits a bucket to obtain a full load without
overcrowding the bucket or under crowding is known as optimum height of cut. So, at this
particular height of cut, I can fill the bucket in one sweep without overcrowding the bucket or
under corroding the bucket. So, that they can give me optimum productivity or maximum
productivity.
(Refer Slide Time: 22:04)
Now, let us see how to know the optimum height of cut for the machine. So, optimum height
of cut require for a particular machine depends upon the dimension of the machine as I told
you. So, this will be equal to based on studies they found that it is equal to 30 to 50% of
maximum cutting height obviously, you know that for every machine for every shovel, I can
get the information on what is the maximum cutting height from the manufacturer , what is
the maximum cutting height.
What is the dumping height, what is the maximum digging reach, all these information I can
get it from the manufacturer and I should know that at its maximum cutting height, definitely
it would not give you maximum productivity. So, the optimal height of cut will be 30 to 50%
of the maximum cutting height for the particular machine. Now, how to design whether it is
30% or 50% that is going to depend upon the material type.
Material type, say if you are going to handle some easy flowing material, like sand, or loose
earth, in that case, a 30% of maximum cutting height, I can easily fill the bucket, but if you
are going to have some hard materials like rock or clay, in that case I need 50% of the
maximum cutting height to fill my bucket. So, it depends upon the material type, for easy
flowing material, I can take the optimal height of cut as 30% of maximum cutting height.
That is what is given here. So, for basically the optimal height of cut is from 30 to 50% of the
maximum digging height. This information I can get it from the manufacturer depending
upon the machine dimension and I should go for lower percentage there is 30% for material
which are easy to handle, easy to load like sand, gravel, loam, loose earth, etc. I can go for
30%.
For hard to load material like sticky clay, blasted rock, I should go for higher percentage say
50%, for common year you can take it as 40%. This is how you have to find your optimal
height of cut for the particular machine. So, basically, it depends upon the maximum cutting
height possible for the machine as well as depends upon the material type. So based upon that
I can find the optimum height of cut.
So, we have determined the optimal height of cut for your machine depending upon the
material type and depending upon the maximum cutting height for the particular machine, but
in your project, the actual height of cut may be different from the optimal height of cut. So,
now if it is going to be as I told you, if the actual height of cut is lesser than the optimum
height of cut also it will affect the productivity.
If the actual height of cutting a project site is greater than the optimal rate of cut in that case
also it will affect your productivity. So, how it is going to affect the productivity we need to
assess. So, we need to apply some correction factor to the productivity depending upon the
actual height of cut in your project site. So, that is what we are going to do now.
So, the optimal height of cut percentage is nothing but actual height of cut divided by
optimum height for the given material and for the given bucket that means for the given
dimension of the shovel, so based upon that you can find the optimum height of cut
percentage. Say for example, for a particular front shovel the optimum height of cut needed is
4 meter, optimum height of cut needed for a particular shovel it is 4 meter based upon the
material type as well as based upon the maximum cutting height.
We found that it is 4 meter, but the actual height of cut in your project site is a 2 meter. Now,
what is the optimal height of cut percentage is equal to 2 meter divided by 4 meter into 100.
So, this is going to give me 50%. So, the optimum height of cut is only 50%. So, that means
your productivity is going to be affected because the height of cut is less than the optimal
height of cut actual height of cut is less than the optimal height of cut.
This correction I have to do for the productivity estimation. So, I will tell you later how to do
the productivity estimation in the upcoming slides.
(Refer Slide Time: 26:52)
Another important factor you should know that which is going to affect your productivity is
the angle of swing. So, basically the angle of swing is nothing but the horizontal angle
between the loading and the dumping position, that is your horizontal angle between your
bucket and the truck, it will vary depending upon the position of your truck. As I told you for
ideal conditions, it is preferable to place a truck close to the excavator, this is because these
machines just not good at mobility.
They have poor mobility. So, that is why it is preferable to place a truck very close to the
excavator. So, very commonly you can see that the truck is placed at 90 degree. So, the truck
is placed at 90 degree, this will be 90 to the bucket position. So, this is a common position.
So, basically angle of swing is nothing but the horizontal angle between the digging and the
dumping position between the loading and the dumping position.
As the truck moves further away, your angle of swing would increase as the angle of swing
increases. As the angle of swing increases, you can see that your cycle time will increase, the
productivity will decrease. So, angle of swing is the horizontal angle between the degree and
the dumping positions of the bucket, if the angle of spring is increased, the cycle time
increases you know it.
So, ideal condition ideal production of shovel is based on 90 degrees swing that is what I told
you, the truck will replace it 90 degree is ideal condition and the actual height of cut in your
project site should be same as optimal height of cut, that combination that will give you ideal
production .
(Refer Slide Time: 28:55)
Now, let us see what are all the adjustment factors, we have to apply while doing the
productivity estimation based upon the height of the cut of material actual height of cut of
material in your project site and based upon the angle of swing that is going to depend upon
the position of your truck relative to the position of your excavator. So, adjustment factors for
the height of cut and the angle of swing for the shovel.
So, as I told you, if the actual height of cut is same as optimum height of cut, it means the
percentage is 100%how do you calculate the percentage actual height of cut divided by
optimal height of cut for the particular machine. If this percentage is going to be 100% it
means actual height of cut and optimum height of cut are same. So, in that case, you need not
apply any correction factor.
Similarly, the ideal condition what we assume is the truck is placed at 90 degree to the
excavator. , So the angle of swing is 90 degree for both these cases the correction factor is 1,
that means I need not apply any correction factor based on height of swing because it is an
ideal condition, but if your actual project condition is going to differ or vary from the ideal
condition, then in that case you have to apply the correction factor.
Say if you are going to do the cutting operation and the height of cut is say lesser than the
optimum height of cut, say it is only 60% of the optimal height of cut, you can see you have
to apply this correction factor. Similarly, when it is 160% also apply this correction factor.
So, thing you have to notice is, when the height of cut is less correction factor is also less,
that means the productivity is going to be reduced.
When the height of cut is more your correction factor in the case also it is less, the
productivity is going to be less. Similarly, when you consider the angle of swing when the
angle of swing is more than 90 degree, you can see that the correction factor is reducing, it
shows that your productivity will reduce, but if your angle of swing is lesser than 90 degree,
you can see that the correction factor is increasing.
That means it shows that your productivity is increasing. So, if possible to keep your truck at
an angle of swing lesser than 90 degree, it will be better than the ideal condition. That means
because the correction factor is increasing. So, that is going to increase the productivity. So,
depending upon the angle of swing in your project site and depending upon the actual height
of cut of the material, which you are going to cut, based upon that you have to apply the
correction factor while you do the estimation of your productivity.
(Refer Slide Time: 31:55)
Another thing to be noted is truck spotting clearance. That means, as I told you, it is
preferable to place a truck closer to the excavator. But at the same time, note that there should
be some space left for the tail swing of the shovel. That means now you can have a complete
360 degree swing, you have a swing ring here, you can have a complete 360 degree rotation
about the mounting.
So when it rotates, you should make sure that the tail of this shovel should not collate with
the truck which is placed too close to the truck that is why there should be some space left for
the tail swing of the shovel that is called this truck spotting clearance.
(Refer Slide Time: 32:41)
Other important factor is haul unit exchange time. That means the time needed for the loaded
truck to leave its position. And for a new truck that is an empty truck to take the position.
That is called as a haul unit exchange time. So, this is also going to affect the productivity. If
your truck is not readily available for the loader to load the material or to dump the material
into the truck if you do not have a truck readily available, then the loader has to wait for the
truck.
So, that will increase the cycle time. So, it is nothing but a total time required for the loaded
truck to clear its loading position and for the next empty truck to the position for loadi
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