Trucks
Hello everyone I welcome you all to the lecture 15 of this course construction methods andequipment management. So, in this series of lecture on the earth moving equipment today we aregoing to discuss about the trucks.(Refer Slide Time: 00:44)
So, in the last lecture we discussed about the fixed position excavators that is front shovels andthe backhoes. So, let us look into the outline of today's presentation, in today's presentation wewill be discussing about the types of trucks and we will define what is the production cycle of thetruck, what are all the components of the production cycle, let us see how to estimate theproductivity of trucks.
And we will work out some problems on how to balance the interdependent machines. So, as youknow that the trucks and the loaders are going to work together, how to balance size of themachines and how to balance the number of trucks for the loader? So, we will work with someexamples in this regard.(Refer Slide Time: 01:20)
So, basically for any earth moving equipment we are more concerned about the economic hauldistance of the equipment.
So, this is the picture of the off highway quarry truck. As I told you it is commonly used inquarry, it is not permitted on public highways because it is size and weight is greater than thelimitations allowed for the public highways. And one thing you can note that is, it will not have atailgate, so that is why you can see that the body floor will be sloping upward, you can see it issloping upward. This kind of arrangement facilitates easy loading of the truck with the loader, sothat is why it has this shape.(Refer Slide Time: 04:46)
So, the next type is based on the frame. As we mentioned earlier, we have rigid frame andarticulated frame. Basically articulated frame is there will be a pivot joint, so the machine will behinged between the front part and rear part, that permits the articulation, it will have a betterturning ability when compared to the rigid frame. So, you have a articulated joint and anoscillating ring between the tractor and the dumb body, so this is the dump body.
So, between the tractor and the dumb body you have the articulated joint, so that will facilitatebetter articulation. So, this is commonly used for poor underfoot conditions, so poor underfootconditions in the sense the terrain is very bad and you have to climb steeper grades. In that caseyou have to go for this articulated truck for tough conditions if the mission has to climb steepergrade or the terrain is to it is a clay area.
So, which is not possible for a rigid frame to maneuver, in that case you can go for thearticulated trucks. They are basically designed for tough underfoot conditions, so they can claimsteeper grades up to 35% while the rigid frame is commonly used for only up to 10% slope, I amtalking about the slope. But another limitation of this articulated truck is, it is designed for poorunderfoot conditions, so these trucks will have a limitation on it is capacity and the speed.
So, it is capacity as well as the speed will be lesser than the rigid frame truck, so depending uponyour requirement whether it can go for rigid frame or articulated truck. And also in confined
areas it is easy to work with this machine which has a better turning ability. So, based upon yourrequirement you have to make the selection but obviously articulated trucks are costlier whencompared to rigid frame. So, but you have to justify the cost based upon the application.(Refer Slide Time: 06:39)
And the next one is your highway rear dump truck. So, you can see the picture the material isbeing dumped through the tailgate in the rear end. So, you can see the machine will be having ahydraulic jack system with that you can lift the dumb body and dump the material at the end. So,this is the one which is commonly seen, the commonly used one is rear dump truck. But if youlook into the dump time, so basically when you go for real dumping, so it takes little bit moretime.
This is because since you are dumping at the rear end you have to correctly locate the locationwhere you have to dump it. Sometimes you have to travel some back distance to exactly locatethe place and then dump it. So, this may increase the dump time, so for the rear dumpmechanism the dump time is slightly higher. Obviously it depends upon your type of materialalso, some material maybe easily flowing, in that case dumping will be relatively easier.
It also depends upon the capacity of your truck your truck capacity, the type of material all thesethings will influence the dump time. But basically rear dumping takes more time because you
have to exactly locate the location and then you may have to even travel in a backward directionto locate that location and then you have to dump it. (Video Starts: 07:58)
This video shows you the how the rear dump truck unloads the material you can see that with thehelp of this hydraulic jack system. So, the dumb body is lifted, so this is lifting it you can seethat, it is lifting the dump body and the material can be unloaded through the tailgate. (VideoEnds: 08:24)(Refer Slide Time: 08:28)
So, the next is about the bottom dump trailers. So, here you can see that dumping will be fromthe bottom opening. See you have a facility to unload the material to the bottom opening, sowhen compared to rear dumping this bottom dumping it will have a lesser time. So, this isbecause basically we go for these trailers this bottom dump trailers when you have to dump thematerial over a large area, you have to dump it and as well as spread it.
Actually the machine will be moving and dumping together, the machine will be traveling anddumping together both the operations will be done in one stage. So, the machine will keep onmoving as well as it will be keep on dumping the material through the bottom end. So, for thatyou need a larger dumping area, you need a larger dumping site, so that this trailer can easilydeposit the material in windrows they call it as windrows.
So, you can deposit the material in layers uniformly with this bottom dump trailers. Whereveryou want to dump the material over a larger area and spread it uniformly and spread it in layersthen you can go for this bottom dump trailer. Since it is moving as well as dumping you can seethat the dumping time is relatively lesser when compared to the rear dumping trucks.
So, in this case since the number of bucket loads is lesser than the balanced number ofbucket loads it is called as short load.
So, the truck load is not equal to the truck full capacity, here how to calculate the truck load? It isnothing but number of your bucket loads multiplied by the bucket volume, number of bucketloads multiplied by the bucket volume will give you the truck load. And this is not going to beequal to the full capacity of a truck as you know.(Refer Slide Time: 17:45)
Now the next case is say the number of bucket loads which we are going to adopt is greater thanthe balanced number of loads. So, now we have rounded it to the higher end say instead of I got4.2 and I am rounding it to 5, say for example I am rounding it to 5. In this case it means I amtrying to load the truck beyond it is capacity, so obviously there will be spillage of material.
So, if number of bucket loads rounded to next higher integer higher than the balanced number ofloads either the excess material will spill off the truck or some portion of material will remain inthe bucket of excavator itself. So, either way it can happen but one thing you should know thatwhat you can load only to the truck capacity, we cannot load beyond that, excess material willdefinitely will spill off. So, here you have to take the truck load is full and it will be equal to thetruck volumetric capacity.(Refer Slide Time: 18:55)
Your truck load is full here and it will be equal to the truck volumetric capacity, you should nottake it as the number of bucket loads multiplied by the bucket volume as you did for earlier.Number of bucket loads by bucket volume you are not going to follow that earlier formula. Thisway you should not calculate for this, because here the number of bucket loads are more than thebalance number of loads.
But even though it is more than the balanced number of loads I cannot load it beyond thecapacity of the truck, truck maximum capacity will be the limiting capacity. So, in this case youshould not go by this the truck load will be equal to truck volumetric capacity only, you have tofollow that.(Refer Slide Time: 19:42)
But the loading time will be number of bucket loads multiplied by the bucket cycle time.(Refer Slide Time: 19:46)
Another important thing you have to keep in mind is for any machine whatever maybe themission we have discussed about different types of machines so far. All the machines we areconcerned about the safe gravimetric capacity of the machine. For every machine what is thissafe operating load in terms of weight is given by the manufacturer, so that we call it as agravimetric capacity.
So, only that capacity your machine can take because the structural frame of the machine isdesigned to handle that particular load only. So, we are not supposed to load the machine beyond
the gravimetric capacity. So, since the density of material can vary from case to case, it is alwaysadvisable to check whether the load weight is within the safe gravimetric capacity. Check theload weight against the gravimetric capacity of the truck, how to check that?
For that you need to know what is the unit weight of your material, if you know the density ofyour material you can multiplied by the volumetric load you will get the actual weight ofmaterial in the truck, you will get the truck load. That should be within the rated gravimetriccapacity of the machine given by the manufacturer, check truck load is less than ratedgravimetric payload.
See many times you can see that people will put these side boards, and in the trucks commonlyyou can see they put the side boards and try to increase the volume of the truck. If the materialwhich you are going to handle is less denser, in that case it will not create much problem, youhave to check whether the loaded weight in the truck is within the gravimetric capacity.
But if the material is going to be denser like wet sand or other denser material, what happens isthere are more chances that your machine maybe overloaded. That means the weight of materialin the truck will be above the safe gravimetric capacity defined by the manufacturer. In that caseit will result in lot of wear and tear to the machine, so particularly your tires will flex and it willresult in abusing of tires.
Say for example I am getting the balance number say 7.4 whether I should round it to 7 or Ishould round it to 8 trucks, we have to decide, how to decide that? We have to work out theeconomics, if I go for 7 trucks for 1 loader or 1 excavator. If I go for 8 trucks for 1 excavator,what is the unit production cost associated with that. You consider both the cases and then makea decision, that will be more logical.(Refer Slide Time: 28:36)
Now let us consider the case say the number of trucks lower than the balance number. Say I amgoing to round it to lower number, say I got 7.4 now I am going to round it to 7. When I round itto lower than the balanced number that means trucks are less than what is needed. So, trucks aremore critical for the production, so here the loader will have the idle time, loader will be waitingfor the truck, so truck cycle time will control the productivity of this stream.
So, the truck productivity will be controlling, so production, how to estimate the production inthis case? Truck load multiplied by number of trucks divided by the truck cycle time. So, heretruck cycle time I have taken in minutes, so I am converting it to hour, because I need theproductivity loose cubic meter per hour, so I am just multiplying by 60 minutes.
In the case when I round it to the number greater than the balanced number. So, instead ofrounding it to 7 I am rounding it to 8, my balance number is 7.4 I am rounding it to higher end 8.In this case number of trucks are greater than the balance number, so the trucks will have the idletime, truck will be waiting for the loader, loader will be critical here. Beyond the balance numberyou can see that the productivity will be controlled by the loader cycle time.
Unless the loader is available though the trucks are more in number they cannot do the job. So,the production is going to be controlled by loader, loader cycle time or excavator whateverexcavator cycle time. Now how to estimate the productivity? Truck load divided by the
excavator cycle time it is in minutes, so converting into hour I need to multiply by 60 minutes,this will give the production of the system when the number of trucks are greater than thebalance number.
If I choose, if we round it to number greater than the balanced number. But very commonly youcan see that people prefer to round it to lower than balanced number. One reason is basicallywhen it is lower than the balance number you can engage the excavator or the loader to addressthe loading site and it will get ready for the next truck. And people also do not prefer workingwith loader continuously, because if the loader or excavator works continuously and if it breaksdown it will severely affect your entire system.
Say for example you have only one excavator and if the excavator breaks down that will hamperyour project seriously. But the trucks are more in number even if the truck breaks down, if onetruck breaks down it will affect the production but that would not be as serious as the breakdownof a loader or the excavator, that you have to always keep in mind. That is why routinemaintenance of the loader or the excavator is very important for the continuous running of thesystem.
That is why people always prefer rounding it to lower number, but the logical way is to work outthe economics of both the cases and then take a decision, that will be more logical.(Refer Slide Time: 31:53)
Now let us work on the problem on balancing the interdependent machines. So, here a loader isoperating at 90 meter cube per hour and it has a 2.2 heap capacity bucket, and operates on 1.1minute load cycle. The cycle time of the bucket is given as 1.1 minute, a cycle time per cycle it is1.1 minute for the bucket of the loader. Truck will be loaded by the loader and the truck'scapacity is 10.3 meter cube capacity and 34 minute dump + haul + return time.
Other than loading what is the time needed for dumping, hauling and returning is given directlyto you. If it is not given then you have to go for the performance chart to find out the haul timeand the return time and you can go by the manufacturer's data for the dump time. Truck fillfactor is estimated at 100%, so based upon the filling ability of the material it is given as 100%for truck but for the bucket it is given as 90% based upon the filling ability of the material.
So, whatever the rated heaped capacity given by the manufacturer I have to adjust with the fillfactor. Say for the loader bucket it is 2.2 meter cube, this is the rated heaped capacity given bythe manufacturer adjacent with the bucket fill factor 90% 0.9. Similarly for the truck it is 10.3meter cube, here the filling factor is 1 that is it. So, you have to get the realistic estimate of theload volume by adjusting the rated heaped volume with the bucket fill factor or the truck fillfactors accordingly.
The efficiency estimate is 50 minute per hour the job efficiency is given that means the machineis working for 50 minutes in a hour. Find out the optimum number of trucks required for eachloader. So, we are going to find the balance number at which your productivity is going to beoptimum. Also calculate the unit cost of production using the following hourly rates the hourlyrate or the hourly cost associated with the loader including the operator cost is given as rupees2700 per hour and for the truck it is given as rupees thousand 650 per hour.(Refer Slide Time: 34:26)
Now let us work out the solution, the first step will be to find the balance number of the bucketloads needed to fill the truck. How will you find the balance number of bucket loads needed tofill the truck? It depends upon your truck capacity by your bucket capacity, so what is your truckcapacity? It was given as 10.3 meter cube, you adjust it with the fill factor, truck fill factor isgiven as 1.
Now let us find the balance number of trucks needed for one loader. So, that depends upon yourthe balance number of trucks per loader going to be serve by one loader is equal to your truckcycle time divided by load of cycle time. So, you have estimated the truck cycle time earlier, soestimated it is 39.5.(Refer Slide Time: 39:23)
The truck cycle time is 39.5 and the loader cycle time is 5.5, we have calculated the loader cycletime as 5.5. So, this gives me the balance number of 7.18, here also I did not get the old number,so I have to do the rounding either I can round it to 7 or I can round it to 8. So, but the logicalthing is you have to work with the economics of both the cases and then take the decision. So,here I am going to work out the economics of both the cases.
So, just to give you a better explanation I am just working out what will be the economics when Igo for different number of trucks. Say if I go for 5 number of trucks 6, 7, 8 and 9, how theproductivity will vary, how the unit production cost will vary? We will work it out and see, sothat will get a clear picture on what is the effect of number of trucks, and what is the effect ofincreasing the number of trucks beyond the balance number on the unit production cost.
So, we will do in-depth analysis by working out for all the number of trucks. So, basically howto estimate the job production? So, it is nothing but your single truck productivity multiplied bynumber of trucks, that will give you the job production. So, provided the number of trucks arelesser than the balance number. In that case you can calculate by that, because when the trucksare lesser than the balance number or equal to balance number your truck cycle time will governthe productivity.
But when the number of trucks are this is your balance number say 7, so actual balance numberis 7.18. So, when the numbers of trucks are lesser than the balance number say 5 trucks, 5 intoproductivity of your truck, individual truck productivity is 12.53 meter cube per hour. So, thatgives me the value is 62.65 meter cube per hour, this is what you got. Similarly when the numberof trucks is 6, 6 into 12.53 meter cube per hour that will give me the answer is 75.18.
When the number of trucks equal to 7, 7 into 12.53 gives me the productivity as 87.71 metercube per hour. When the number of trucks is 8, 8 into 12.53, I am getting the value as 100.24meter cube per hour. But I cannot go by this productivity, this is because when the trucks arelesser than the balance number equal to balanced number your truck will be controlling theproductivity of the system.
Beyond the balance number, so you can see that number of trucks are more so the truck will bewaiting for the loader unless the loader is available your truck cannot do the job. So, theproductivity here will be controlled by your loader. So, beyond the balance number you can seethat you cannot go beyond the productivity of the loader because the load of cycle time willcontrol the productivity of the system, for cases above the balance number.
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Say for first for 5 number of trucks, how will you calculate the total cost? Total cost is nothingbut 5 into what is the hourly cost of truck 1650 plus there is only one loader 1 multiplied by2700. So, this gives me the cost is 10950 rupees, this will be the cost associated with the 5trucks. Similarly for the 6 trucks, 6 into 1650 + 1 into 2700, so this gives me the cost is rupees12600, you can get this.
Similarly for the 7 trucks, 7 into 1650 + 2700, this gives me the cost is the rupees 14250 perhour. Like this you keep calculating for 8 trucks and 9 trucks you can calculate the cost, totalcost per hour. Now your productivity already you have estimated the productivity in the earliertable 62.65, 75.18, 87.71, but you have to note that beyond the balance number the productivitywill be only 90, I cannot go beyond 90.
Because beyond the balance number the productivity is controlled by loader whose productivityis 90 meter cube per hour. So, that is why you can say the productivity is only 90 beyond thebalance number. Now you have to calculate the unit cost of production, how to estimate the unitcost of production?(Refer Slide Time: 47:18)
Unit cost of production is nothing but cost per hour divided by productivity per hour. So, for thenumber of trucks 5, so for 5 trucks what is the total cost 10950 divided by productivity is 62.65.
So, this gives me the answer as rupees 174.78 per meter cube, this is the unit production costassociated with 5 trucks, similarly for 6 trucks you have to calculate, 6 trucks.(Refer Slide Time: 48:14)
It is nothing but 12600 divided by 75.18 gives me the value is 167.60, you can see here.Similarly you find the unit production cost by dividing total cost by productivity, you will get theunit production cost for all the cases you can just find it for all the cases 5 trucks, 6, 7, 8 and 9.(Refer Slide Time: 48:57)
So, one important thing you have to note here is when the number of trucks is 5 though the totalcost is less in this case, but the productivity is also less, that is why you can see that the unit costis high. But as your number of truck increases you can see that the productivity increases
significantly, that is why your unit cost of production reduces, it is reducing. But beyond thebalance number 7 when I try to increase the number of trucks, there is no increase inproductivity.
Because the productivity is limited by loader, I cannot go beyond 90, but your truck causesunnecessarily increasing. So, because of that I can see that the unit cost increases significantly,unit production cost increases significantly, that is why it is not advisable to go beyond thebalance number.(Refer Slide Time: 49:44)
So, graphically you can see this, so when the number of trucks or less your unit protection cost isless when the number of trucks is 5, when the number of trucks is less the unit production cost ishigher than the optimum value. You can see the optimum value for the number of trucks 7 theunit production cost is 162.47. But when you go for 5 trucks you can see that the unit productioncost is higher than the optimum value, why it is higher than the optimum value?
Because here productivity is less in this case, but when you increase the number of trucks youcan see that the productivity will increase significantly, so your unit production costs keepreducing. And when you reach the balance number you can see that you can have the minimumunit production cost. But when you try to increase number of trucks beyond the balance number,what is happening? There is no increase in productivity.
Beyond the balance number the productivity is limited by the loader, so I cannot go beyond 90meter cube per hour that was the productivity of the loader I cannot go beyond 90 meter cube perhour.(Refer Slide Time: 51:08)
But and your cost of the truck is increasing that is why you can see that unit production costsignificantly increases. So, it is always preferable to go by the balance number, but in this caseour balance number was 7.18, it was 7.18. So, whether to round it to lower number or round it tohigher number, whether I should go for 7 or whether I should go for 8. If I go for 7 my unitproduction cost is 162.47.(Refer Slide Time: 51:29)
If I go for 8 trucks my unit production cost is 176.67, so it is preferable to round it to the lowernumber, rounding to lower number is preferable. As I told you this is what is commonlyfollowed, when you round it to lower number you can avoid you can give some break time foryour loader. That is also one way good, the loader will help you in clearing the addressing thesite as I told you.
The site as well as there will be some break time for the loader, and it will get ready to load thenext truck. That is why people always prefer to round it to lower number, but anyway it is alwayspreferable to work out the economics of both the cases, I have worked out and showed you. Youcan see that for lower number of trucks the unit production cost is very less for 7 in this case.
For when you go for 8 there is no significant increase in productivity that is why you can see thatthe unit production cost increases significantly. So, whether you go for 8 trucks or 9 trucks therewill not be increase in productivity, there will be just increase in the truck cost, that is the reasonwhich is significantly increasing.(Refer Slide Time: 52:45)
So, we have come to the end of this lecture, let me now summarize. We have discussed about thedifferent types of trucks and I told you the importance of checking the payload the weight of loadinside the truck against the rated gravimetric capacity. You should never overload the machinewhich will result in premature aging of your truck as well as the tires. And dumping time whenyou calculate, you should know that it depends upon the mode of dumping whether you aregoing for rear dump trucks or bottom dump trucks.
And the material type easy flowing or tough material and also it depends upon the congestion inthe dump area, all these things are going to affect your dumping time. So, when you work in ateam with machines, so basically the all the interdependent machines should be balanced in theirsize as well as it should be balanced in number. Excavator and truck should be of compatiblecapacities.
Based on studies they found that truck capacity should be 4 to 5 times the bucket capacity of theexcavator, that is the ideal case. So, then the number of machines also to be balanced at thebalance number of machines you can see that both the loading unit and the hauling unit willoperate at the same production level, you will get your maximum efficiency at the balancenumber, the waiting time will be minimum.
And always whether you are going to round it to a lower number or round it to the highernumber, work out the economics. Work out the unit production cost associated with both thecases and then evaluate the balance number and decide your selection. Estimation of job cost Ihave done it already by evaluating the equipment balance.(Refer Slide Time: 54:31)
So, these are the references which I have referred for this lecture, you can try to procure thesetextbooks for preparation. In the next lecture we will be discussing about the piles and the piledriving methods, thank you.
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