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Pile Hammers
Hello everyone, I welcome you all to the lecture 17 of this course construction methods andequipment management. In this lecture we are going to discuss about the pile driving equipment.So, let us have a recap of what we discussed in the last lecture, the last lecture we discussedabout the different types of piles merits and demerits of different types of piles.(Refer Slide Time: 00:45)
And about the basic pile driving principle and the methods of how to control the pile drivingstress and how to determine the safe load on the pile. So, these are the important things which wehave discussed in the last lecture. Now, let us look into the outline of today's presentation. Intoday's presentation, we will be discussing about the different types of pile hammers, and we willbe also discussing about the guidelines for selection of the pile hammer.
So, how to select the pile hammer for a particular type of soil and for a particular the length ofpile and weight of pile for a particular material type, how to make the selection of pile hammerwe are going to discuss in this lecture.(Refer Slide Time: 01:29)
So, there are different types of pile hammer ranging from the oldest drop hammer method to themodern vibratory the pile drivers. So, we are going to discuss all these types of pile hammers oneby one in this lecture. So firstly we will be discussing about the drop hammer followed by thesteam hammers, then we will be discussing about diesel hammer and the vibratory pile drivers.(Refer Slide Time: 01:52)
So, first is about the drop hammer. So, basically and this is nothing but a heavy metal weight, sothis has to be lifted with some lifting mechanism. You can go for any lifting mechanismdepending upon your project size, depending upon your project budget or the availability ofequipment. So, you can go for any lifting mechanism, you can go for a simple pulley and ropemechanism or you can go for a crane.
So, depending upon the availability of a equipment and a project budget, so you can go for thelifting mechanism. So basically you are going to lift the hammer, that hammer is nothing but aheavy metal object. So, we are going to lift it with some lifting mechanism to a particular height,then allow it to fall on the pile height by gravity, allow it to freely fall on the height of the pile.So, you can look into this setup, so basically this is your hammer.
And this is your pile, you can see the pile, in between the hammer and pile, you have the pilecushion to control the pile driving stress to protect the pile head from the damage, you put thepile cushion. So, you are going to lift this hammer with some lifting mechanism and then allow itto fall on the pile. So, and you can see some more supporting arrangement this is called as theleader or lead.
So, this frame structure, it is going to help you to place everything in right position, it helps youto hold the pile, pile hammer, everything in the right position helps you to maintain thealignment. So, for that you need the supporting arrangement called as leader so this is yourleader, lead or leader. So, these are the supporting equipments you need. So, as I told you for thepile driving, we cannot just do the pile driving only with the pile hammer.
We need the supporting equipment like we may need some lifting equipment like crane, and youneed a structural frame like leader to hold everything in position. So, what is this drop hammer,let me summarize what we discussed just now. Drop hammer is heavy metal weight, raised bywinching, powered by diesel or electric motor and then released and allowed to fall on to the topof the pile.
So winching mechanism, winching mechanism is a lifting mechanism as everyone knows.Basically it is nothing but a rotating drum, this drum will be rotated by any motor diesel motor orelectric motor, on this rotating drum, you can see the rope winding over. So, with the help of thisrotating drum, I can either pulling the rope or pull out rope. So, this is a common mechanismwhich we use in the crane also. So, basically with any pulley, rope and winch mechanism, so you
can just lift the hammer to a particular height and allow it to freely fall by gravity on the pileheight, so that is what is a drop hammer.(Refer Slide Time: 04:43)
So, as I told you it needs some supporting frame structure to hold everything in position, so thatyou can maintain the proper alignment of the pile, so for that you need help of the needles. So, itis necessary to hold the pile and the hammer in position and guide them during installation. So,for that we need the frame known as lead, it has a rails, you can see it has the rail kind ofarrangement, it is used as a support system for the pile driving operation.
And one more important thing you need to know that whatever lifting mechanism, you are goingto use maybe a crane. If you are going to use a crane, you have to check for this lifting capacityof the crane whether the crane has a sufficient lifting capacity to lift your pile, to lift your pilehammer and to hold your lead everything in position. So, for that the crane should have thesufficient capacity, crane must have the sufficient capacity to support the weight of pile, pilehammer and the leads.
So, the capacity of the crane should be sufficient to support a maximum load at the operatingradius. So, operating radius is nothing but distance from the center of axis of rotation of the craneto the load line, that is a operating radius. This operating radius keeps varying depending upon
your boom, crane boom inclination, just by changing the angle of inclination of the boom I canvary the operating radius.
I can either reduce the radius or I can increase operating radius by changing the angle ofinclination of the boom. So, you know that when you reduce the operating radius, that means youare going to bring the load line towards the center of the crane. In that case the crane will be in amore stable position, so it is lifting capacity will be high. But when you are moving your loadline away from the center of the crane, that means your operating rate is more.
In that case your crane will be relatively unstable, it is stability is relatively poor, so the liftingcapacity will also be less. So, that is why we need to check whether the crane has a sufficientlifting capacity to lift your pile, pile hammer and the lead, so at various operating radius that weneed to check before making the selection of your crane for the pile driving operation.
So, the hoisting equipment must also provide you the required horizontal and the verticalreaches. So, you need what is the working range needed, what is the horizontal and the verticalreach needed? And the crane what you are going to use must be able to satisfy that requirement.Accordingly you have to make the selection of the supporting equipment for pile drivingoperation.(Refer Slide Time: 07:21)
So, hammer is hung from a rope running over a pulley. So, the whole arrangement is supportedon a strong frame called leader. Hammer is raised by winching and that is powered by eitherdiesel motor or electric motor and hammer is allowed to drop under free fall on the pile. So,basically when you select a weight of the hammer, it is advisable to select the weight of thehammer at least equal to the weight of your pile.
So, that you can get your desired blow energy. So, if your hammer weight is going to be lesser,then in that case you have to increase the height of fall to get the desired blow energy. So, youknow the impact already when you increase the height of fall the impact velocity will be more.So, that is likely to create more driving stresses on your pile height particularly for the concretepile we should be very careful with respect to the driving stresses and we have to restrict thestroke or the height of fall.
So, we have to select a heavy hammer at least equal to the weight of pile. So, for this drophammer as per the literature you can see the hammer weight should be from 0.5 to two times thepile weight depending upon the availability of your hammer and you can make the selection.And the height of drop varies from 5 to 20 feet. So, like depending upon the material type therewill be restriction on the height of fall. As I told you concrete is weak in tension it is more easilysusceptible to shattering while ramming it the driving the pile.(Refer Slide Time: 08:55)
So, that is why for concrete piles the limitation of height of fall is given for the drop hammer as 8feet, for timber pile it is 15 feet. And one more important thing to be noted is, this drop hammermethod is very slow, it is fairly slow. So, if you have to drive only few piles, if you do not have avery tight deadline, so if you are not very much concerned about the productivity, if you do nothave a tight deadline.
In that case, you can go for the drop hammer method, because this is basically a slow method.So, you can see the blow rate number of blows you can make is only 4 to 8 blows per minute, theblow rate is relatively very less. So, that is why you can go for the drop hammer, if you haveonly very few piles to be driven, and if you do not have a very tight deadline, in that case youcan go for the drop hammer method. It is a oldest method, nowadays we have lot of advancedtechniques.(Refer Slide Time: 09:48)
Next is your single acting steam hammer, so this is an improvement over the drop hammer. As aname indicates steam hammer, so it means you are going to use a steam energy, you can eithergo for steam energy or you can go for compressed air also. So accordingly you may need a steamboiler or air compressor for this method. So, the name says single acting, that means you aregoing to use the steam energy only in the upward stroke.
That means when you are lifting the hammer that is called as a upward stroke, only during theupward stroke I make use of the steam energy. So, the downward stroke that means when youallow the hammer to fall, it will fall freely by gravity, so that is why it is called a single actingsteam hammer. So, the hammer is raised by steam or compressed air instead of winching, andyou can see the setup.
So, this setup you can see you have a sliding cylinder which can move over the frame, this is ahollow piston rod you can see the hollow piston rod and the piston. So, this is the control levelwhich can control the air inlet and the air exhaust. So, first what you are supposed to do is, forthe upward stroke, so you need to allow the entry of air into the piston rod. So, allow the airentry through the piston rod as the air fills the chamber, what happens?
Due to the pressure the ram is raised up, your cylinder is raised up, so due to the air pressure. So,to complete a upward stroke what you supposed to do is you allow the air entry into the chamber.Once the air enters into the chamber, you can say as the air starts filling the chamber, yourhammer will be raised up due to the air pressure. So, now your upward stroke is complete. So, letme summarize.
So, the setup as a hollow piston rod and a sliding cylinder, this is a sliding cylinder it can moveup and down. But the piston rod is fixed, only the cylinder can move up and down. Steam or theair is admitted into the piston rod through the valve, you can see the inlet valve. So, you canadjust the control lever, so that the air can enter through this inlet and into the piston rod. So,now as a air enters the chamber, the cylinder is raised up, so that is your upward stroke yourcylinder is raised due to the entry of air into the chamber due to the air pressure.(Refer Slide Time: 12:14)
Now let us see how the downward stroke is done. Now what you do is you control the lever insuch a way that the air inlet is shut off, you close the air inlet and all the air from the cylinderwill be expelled out of the exhaust valve, so all the air now comes out of the exhaust. As the airis released out of the chamber, the hammer will fall down, so hammer falls down, so that is adownward stroke.
So, your lever is released and the air inlet valve is shut off, and the exhaust valve is opened. So,now you stop the entry of air into the inlet valve and you open exhaust valve, so all the air fromthe cylinder will go out. Now this will result in the fall of your cylinder, cylinder will fall down,that is a downward stroke. So, you are providing a safety valve also, mainly to prevent theoverrunning of the hammer to prevent the excessive buildup of the air pressure. So, we have asafety valve to prevent overrunning of the hammer.(Refer Slide Time: 13:10)
So, when you compare the productivity of your single acting hammer with the drop hammer, sayearlier we discuss the blow rate of the drop hammer is 4 to 8 blows per minute. But your singleacting hammer has a better productivity, it can go of a 1 blow per second. That means the blowrate is almost 40 to 60 blows per minute, even the smaller will more faster, when compared tothe larger units.
So, when compared to the drop hammer you can see that the blow rate is significantly high. Thatis why when you are concerned about your productivity of your job, if you have a tight deadline,it is preferable to go for single acting hammer.(Refer Slide Time: 13:48)
And again the guidelines are given for single acting hammer. So, as I told you the basic rule isselect a hammer having a weight approximately equal to that of the pile. So, at least a hammerweight which should be equal to that of the pile. But sometimes certain concrete piles are tooheavier, we do not have equivalent size hammer in the market. In that case, the worst case weshould make sure that the hammer weight should not be less than one third of the weight of thepile.
So, that is a minimum requirement and the height of the drop should be limited to 4 feet. So,particularly for the concrete piles, we have to restrict the height for the single acting hammer ithas mentioned there you should restrict it to 4 feet.(Refer Slide Time: 14:26)
So, whatever hammers we discussed so far, a drop hammer, single acting hammer, all theseimpact hammers are noisy hammers, that means it results in lot of noise prediction during thedriving operation. So, the impact hammers produces the highest sound pressure levels. So, thereare different types of noises, I can say. One is because of the hammer the ramming against a pilehead, that results in one type of noise.
The other type of noise is due to running of your air compressor or steam boiler, all these thingsalso results in production of noise. So, there are basically 2 types of noise which are produced by
impact hammer, one is your impact noise produced by the ram striking the pile, and other one isproduced by the operating steam air, or the diesel exhaust as it is exhausted from the cylinder.(Refer Slide Time: 15:21)
So, it is work out a simple problem on the hammer selection. A single acting hammer is used todrive concrete pile which weighs 15,000 kg, so the weight of the concrete pile is given as 15,000kg, you are going to recommend the hammer weight needed, recommended hammer weight andthe minimum hammer weight required. As I told you the basic rule for the single acting hammeris hammer weight should be equal to the weight of the pile.
So, the concrete weight pile is 15,000 kg, so recommended hammer weight is nothing but 15,000kg. In the worst case, if 15,000 kgs of heavy hammer is not available in the market. In that case,the minimum requirement is you should never go below one third of the weight of your pile.That means minimum weight needed is 0.33 into weight of pile, 0.33 into 15,000 kg 1 by 3 into15,000 kg gives you 4950 kg, at least we should never go below this. So, this is the minimumrequirement needed, you cannot go below this. So, this is a basic guideline that we should keepin mind.(Refer Slide Time: 16:41)
So, we have discussed about the single acting hammer, now let us move onto double actingsteam hammer. As the name indicates double acting, so you are going to use the steam energyfor both the upward stroke as well as for the downward stroke. So, that means you are going touse the steam energy for rising of the hammer as well as for the falling of the hammer. So, thefreefall impact as well as additional energy or obtained on the downward stroke.
That means you are using the steam energy for the downward stroke also. Here the valve systemis little bit more complex than the single acting hammer. If you look into the setup I will showyou in the next slide. Basically there are 2 cylinders here, upper cylinder and the lower cylinder.Alternatively you will be supplying to the upper cylinder and the lower cylinder and to carry outthe upward stroke and the downward stroke. So, air or steam is admitted into upper and lowercylinders alternatively.(Refer Slide Time: 17:37)
So, basically what to do here is, so this is a setup of the double acting steam hammer, you cansee two cylinders one is the upper cylinder, other one is a lowest cylinder. Now in the upwardstroke what you do is, you supply air into the lower cylinder. So, when you supply into this, thisis a lowest cylinder, when you supply air into the lower cylinder, the hammer which was earlierin the lower cylinder will be pushed up into the upper cylinder.
So, the hammer is pushed up into the upper cylinder, the air which was already there in the uppercylinder will expel out to the exhaust. So, the air which was already there in the upper cylinderwill be expelled out through the exhaust. So, basically what you are doing here is you supply airinto the lower cylinder. So, that will push your hammer upward into the upper cylinder and theair which is already in the upper cylinder will be released through the exhaust, now your upwardstroke is complete.
So, what are you doing the downward cylinder? You supply air through the inlet into the uppercylinder. So, when you are supply air into the upper cylinder, the hammer which was alreadythere will be pushed into the lower cylinder. And air which was already in the lower cylinder willbe expelled out through the exhaust. So, now that completes a downward stroke, so alternativelyyou are supplying air into a upper cylinder and the lower cylinder, so that you can have the risingand falling.
So, that was explained here in upward stroke air is supplied to the lower cylinder, your piston israised, when the piston raises and occupies upper cylinder all the air which was in the uppercylinder will be expelled out. Similarly in the downward stroke what you do, air is supplied tothe upper cylinder and the hammer will be pushed into the lower cylinder. And the air which wasalready in the lower cylinder will be expelled out, so this is how you do it.(Refer Slide Time: 19:32)
So, the striking ram is driven by compressed air or steam, when both rising and falling.(Refer Slide Time: 19:40)
So, another important thing we need to know with respect to double acting hammer is in thismost of the blow energy is the derived from the steam energy. Both for the upward stroke as well
as for the downward stroke, the blow energy is derived mainly from the steam energy. So, 90%of the blow energy is derived from the action of air or the steam. So, that is why, for the doubleacting hammer we need not for a heavier hammer.
We can go for lighter hammers, smaller in size and you can go for the shorter stroke or shorterheight of fall. So, these hammers are basically designed to be lighter in weight. So, because mostof the energy is derived for the upward stroke as well as for the downward stroke is derived fromthe steam energy. We are not mainly dependent upon the weight of the hammer, so we can go forlighter hammers in this case.
And this hammer is basically designed for I can say lighter conditions, lighter conditions in thesense. So, it is basically designed for light to medium weight piles and for soil with normalfrictional resistance. So, very tight clay, hardened clay with very high frictional resistance, so weare not supposed to use these double acting hammers. Because these double acting hammers aredesigned for lighter conditions, that means for light to medium weight piles and for the normalsoil with normal frictional resistance.
So, it is basically designed for this kind of conditions only, and you should never use this doubleacting hammer for concrete pile. Because these double acting hammers, they basically have avery high blow rate, if you look into the blow rate, you can see that the blow rate will be 95 to300 blows per minute. So, it is very high when compared to the single acting hammer. So, such ahigh blow rate may can easily damage your the concrete pile.
So, that is why it is not recommended for the concrete pile. So, let me summarize what wediscussed, so your use of steam energy in driving the ram allows use of shorter stroke andcompact hammer than single acting hammer. So, when compared to single acting hammer thesehammers are more compact smaller in size, lighter in weight and they have a shorter stroke.
And they are designed for lighter conditions, they can deliver a blow rate of 95 to 300 blows.This lighter ram and highest striking velocity maybe suitable for driving light to medium weightpiles into soil having normal frictional resistance. So, we cannot recommend this hammer for a
tough soil condition with very high frictional resistance. And not always preferable for concretepiles, as I told you high blow rate can result in damage of your concrete pile , which is basicallyweaken tension. So, it is not recommended for concrete pile but you can use it for steel piles.(Refer Slide Time: 22:41)
So, we have completed the double acting stream hammer, now let us move on to diesel hammer.So, basically this diesel hammer is a self contained unit, that means everything is containedwithin a single assembly, I do not need a separate accessory a steam boiler or air compressor aswe need it for the steam hammers. Everything is contained within a single unit you can see, sowhat will be the advantage?
So, it will be more compact and easy to move it in the site from one place to another, it ismobilization is very easier when compared to steam hammers which need a separate steam boileror air compressor. So, now let us look into the operation of the diesel hammer. So, basically herewhat we do is, the ramp is lifted with some lifting mechanism to initiate the operation, any liftingmechanism you can use.
So, if you are going for a crane, so first with the help of a crane, you lift the hammer or the rampto the required height and allow it to fall by gravity. So, you can see there is a fuel tank and afuel pump and this is called as the combustion chamber, this is your combustion chamber. So,
basically what happens is as the hammer moves down, it activates the fuel pump and the fuelpump will spray the fuel into the combustion chamber.
This is a combustion chamber, the fuel is sprayed into this combustion chamber. Now as theramp compresses the mixture of air and the fuel in the combustion chamber, so as it moves downit will compress the mixture of the air and the fuel mixture. So, what happens, it will result inignition or explosion. So, this explosive energy what will happen? It will help you in drivingyour pile downward and also it helps you the rebound of you hammer.
So, it helps you in the rebound of your hammer. So, this explosive energy helps for both drivinga pile downward as well as for the rebound of your hammer. So, the next cycle will continue onit is own, you need not lift it again with any lifting mechanism or crane. So, based upon therebound, it will continue on it is own, the cycle will continue on it is own till the fuel is available.So, another important thing to be noted here is, this rebound will depend upon the soil type, thishammer is more suitable for the cohesive soil.
So, basically if the soil is more cohesive, the frictional resistance will be very high. So, thedriving resistance will be very high, so that will result in a greater rebound of the hammer, thatwill deliver more energy from pile training. So, that is why in cohesive soil the cycle cancontinue easily when compared to lose sand.(Refer Slide Time: 25:30)
Let us see the picture of this diesel hammer you can see, this is a picture of the diesel hammerlifted by a crane. So, it is driving a steel pile, you can see this is a diesel hammer, this is a pile, itis lifted with the help of your crane.(Refer Slide Time: 25:47)
So, let me summarize the operation of the diesel hammer, this process is initiated by raising theram and then it is allowed to fall. You have to raise the ram with help of any lifting mechanismthe crane. As the ram nears the end of the downward stroke it activates a fuel pump, and the fuelis injected into the combustion chamber between the ram and the anvil. So, further continueddownward stroke of the ram compresses the air and the fuel mixture, so that will impact theenergy.
The resulting exposure, so not only drives the pile downward, but also lift your hammer of theram upward to repeat it stroke, and the gases are expelled through the exhaust ports. So, if youwant to stop the operation, there is a slack rope provided to disengage the fuel pump to stop thediesel hammer operation. So, there is a provision to stop the functioning of the hammer, so this ishow the diesel hammer work.(Refer Slide Time: 26:44)
The main advantage is it does not require a separate air compressor or steam boiler and hencevery compact as I told you. And the available input energy per blow is doubled for the givenweight of ram, how it is double? Because of the explosive energy we get additional energy fordriving, so it can be also either single acting or double acting. So, as I told you in a soft ground,the initiation of the process is difficult.
If the pile resistance is going to be greater, if the soil is more cohesive, if the driving resistance ismore that will result in a better stroke, that will result in better rebound, that will result in moreenergy delivery. Hence more energy is delivered to the pile when the resistance to the drivingincreases, so this will happen in cohesive soil. So, diesel has performed well in cohesive soil thanin soft ground.(Refer Slide Time: 27:37)
So, the last type of pile which we are going to discuss is about the vibratory pile driver. So, forwhatever we discuss on impact hammers, which results in lot of noise production as wediscussed earlier. And this method may not be feasible, if you are going to do a pile drivingoperation in a residential colony or near schools or hospitals where we need silent pile drivingmethod.
Your vibratory pile driver is one such quiet method of pile driving method. So, basically how doyou create the vibration? So, this vibratory pile driver we have a casing, inside the casing therewill be a shaft with rotating eccentric weights. These weights will be rotating in the oppositedirection. So, this rotating eccentric weights it is rotating with the help of a electric or hydraulicmotor.
These are the references which I have referred for the lecture preparation. So, in the next lecturewe will be discussing about the cranes, the lifting equipment cranes. So, what is the liftingmechanism of the crane? What are all the different types of cranes merits and demerits, all thosethings we are going to discuss in the next lecture, thank you.