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Classification of Piles

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Piles
Hello everyone, I welcome you all to the lecture 16 of this course construction methods andequipment management. In today's lecture we are going to discuss about the piles and the piledriving equipment.(Refer Slide Time: 00:39)
So, in the last lecture, we have discussed about the trucks, and how to balance the interdependentmachine safe trucks and the loaders. How to balance them in terms of size and number, so thatwe can optimize the productivity, that is what we have discussed in the last lecture. Now let uslook into the outline of today's presentation. In today's presentation, we are going to discussabout the different types of piles.
So, I will just give you a brief overview on what are all the different types of piles, because wecan classify them based on the application, based upon the material type, based upon the methodof fabrication, based upon the installation process. So, there are so many ways by which we canclassify them. So, I will just give you a overview of how to classify and what are the merits anddemerits of different types of piles.
So, then we will move on to what is the principle of the pile hammer. So, what is the principle ofpile driving operation, and as you know that particularly the precast piles, they are subjected tomore amount of driving stress. Say when you drive the pile into the ground, say we use a pilehammer, so for the driving mechanism, it is subjected to a huge amount of driving stress.
So, what are the methods to control the driving stress? That is what we are going to discuss. Andalso I will give you a brief overview on what are all the factors which governs the selection of apile hammer. So, based upon the type of the pile or based upon the size of your pile, so there aredifferent factors which are govern in the selection of the pile driving hammer, so we are going todiscuss about that in the upcoming slides.(Refer Slide Time: 02:07)
So, as everyone knows, the load of any structure is transferred to the ground to the foundation.So, this foundation can be a shallow foundation or deep foundation. Piles are deep foundationthey are examples for deep foundation. So, they are capable of transferring the load from thestructure through a weak strata and it can carry till the depth where a hard bearing strata isavailable.
So, the load of the structure is transmitted to the shallow or deep foundation as I discussed justnow. The deep foundation that is a pile is designed to transmit the structural load to underlying
strata. And the load transfer can be either on the basis of end bearing or basis of fiction, that weare going to discuss in the upcoming slides. So, basically your pile foundation you consider itwill act like a column, pile is like a column driven into the soil.
It transfers the load from the structure deep into the harder and stronger layer, which can bear theload. So, when do we go for the spell foundation? Basically when we have weak soils or soilwith poor bearing capacity, we need to transfer the load till we reach a depth where you confineda hard load bearing strata. So, till that depth we need to transfer the load, so for that we need adeep foundation like pile.
So, the other requirement maybe is a design load is very huge. Say for example you need todesign a foundation for a skyscraper or a multi storey building, where the design load is veryhuge. In that case people commonly go for the pile foundation.(Refer Slide Time: 03:38)
So, based on the application, so commonly, there are different types of uses of piles. So I am justgoing to discuss few common applications, so one is a sheet pile and other one is your endbearing pile and friction pile.(Refer Slide Time: 03:52)
First let us see what are these sheet piles? The sheet piles so we might have seen this kind ofsteel sheet piles, so they are with interlocking joints, you can see that. So, they act like a rigidbarrier for earth and water particularly during excavations or trenching. So, to protect the trenchfrom the collapse, to prevent the trench from the collapse of soil, we go for this kind of sheetpiles.
For excavation or the soil conditions requiring temporary or permanent bracing to support thelateral load imposed by the soil, we go for this kind of sheet piles. So, it acts like a rigid barriersupporting the lateral load from the soil, it can also be used in water, like an cofferdams. It helpsto act like a barrier for the water it provides a dry working area or dry working environment, soeliminating the need for dewatering, it can also be built in the water.
So, you can use any type of material like you can go for timber sheet piles or steel sheet piles orconcrete sheet piles, so it can be made out of different types of materials. So, commonly you cansee applications and retaining walls and cofferdams as I discussed just now.(Refer Slide Time: 05:02)
So, this is again a picture of your the steel sheet pile, you can see the interlocking joints. So, thisis mostly driven with the vibrating hammer, what is this vibrating hammer all these things? Wewill be discussing in the part 2 of this lecture, so where we will be discussing about differenttypes of pile hammer. So, this helps to support a lateral load from the soil, helps as a barrier tothe earth.(Refer Slide Time: 05:26)
This is the picture of the timber sheet pile as you know that timber is the oldest material. So,oldest building material we have been using this material for so many centuries, even now weuse it wherever the timber is abundant.(Refer Slide Time: 05:39)
So, other types of applications are end bearing file and the friction pile, based on the mode ofload transfer. So, particularly for the soil with poor bearing capacity and we go for this endbearing pile. So, the end bearing pile has to transfer the load through the weakest strata till itreaches it hard bearing strata which can carry the load. And the load is transferred through theend that is why it is called as the end bearing pile.
In the case of friction pile the load is transferred through the friction between the sides of the pileand the surrounding soil, so that is what is friction pile. So, if the end bearing strata the hardbearing strata is reachable it is within the reachable depth, then we can go for the end bearingpile otherwise we have to go for the friction pile only. If the hard bearing strata is at a verygreater depth, it is not reachable, then we can design a friction pile.
The most of the piles you can see that they can transfer the load both through the frictionmechanism as well as to the end bearing mechanism so that is also possible.(Refer Slide Time: 06:43)
So, this is what we discussed just now. Piles that reached a load bearing strata and transmit theload through the end are called the end bearing piles. Friction piles get the load bearing capacityfrom the friction between the pile sides and the earth.(Refer Slide Time: 07:00)
Now we have discussed the few types of piles based on the application or the use. Now let us seethe classification based on the material type. So, we can classify it into timber, concrete steel andcomposite piles.(Refer Slide Time: 07:13)
So, timber pile, as I told you this is the oldest material, so I can say it is the oldest deepfoundation known. So, it is very commonly used because easy to use, it is not expensive, easy tocut it and splice it, there are so many merits with it timber piles. How do you basically use it?You just use a trunk of the trees cut it, trim it and strip of the bark, why should we strip of thebark? When we use it as a friction pile there is possibility of slip between the bark and the trunk,so that is why we should strip of the bark.
And treat it with preservatives, that is very important because these piles are more susceptible torotting and insect attack as everyone knows. So, particularly when the timber piles are subjectedto fluctuating water table. So, you can see the issues of rotting and insect attack, this is becausefor the rotting mechanism, you need the presence of both water and the air. So, that is whytimber piles which are permanently submerged in the water, they are not susceptible to rotting.
They are not susceptible to insect attack; there are so many structures with the timber piles,which are servicing for so many years without any damage, without any rotting or insect attackwhen they are submerged in the water. But the problem arises only when it is subjected to thefluctuating water table because you know that the presence of water and air is necessary for thesemechanisms.
So, that is why in those cases where you know that it is going to be subjected to fluctuating watertable, you should definitely go for the preservatives to prevent it from rotting. So, if timber pilesremain permanently in the water, they can have a long service life, that is what we discussed justnow. And the untreated timber piles are subjected to insect attack and decay and they will lastonly for a few years.
So, both type of treatment we can offer to the timber piles to protect it from the insect attack androtting. So basically, in the olden days used to soak the timber in the natural saltwater. So, thenatural saltwater is best preservative, but nowadays we go for modern methods like this tocreosote with pressure treatment. So that is found to be very effective for the treatment for insectattack and the rotting.(Refer Slide Time: 09:34)
So, let us look into the merits and demerits of this timber piles. Basically the merit is, it isinexpensive, easy to cut and splice, that is a major advantage. But the demerit is obviously weknow that lot of defects was there, natural defect was there in the timber, let checks, splits, knotsand shakes. So, we have to quantify the amount of defects in the timber before assessing it issuitability for using it as a pile.
Where we have to quantify and whether the defects are within the permissible limit as given bythe standards, we have to check before it is used as a pile. And also there is a restriction on the
maximum length and the load carrying capability is limited, you know that when compared toconcrete or the steel piles, it is load carrying capacity is limited. So, that is why mostly we use itas a friction pile in sand, silt and clay.
We do not use it as a end bearing pile or we do not use it in very tough soil conditions like densegravel, we do not use it. Then timber pile is likely to get damaged easily when we drive it againsthigh resistance. So, when we driving soils with high resistance, it is likely to easily get damaged,that is why we use it only as friction piles in sand, slit and clay. It cannot be driven against highresistance without damage and hence not recommended in dense gravel or as end bearing piles torock.(Refer Slide Time: 10:55)
So, the next is about the concrete piles. Obviously, when it compared to the timber pile, it is loadbearing capacity is high, there is a high strength and as good resistance to decay, there is noissues of decay here. Now so there are based on the method of fabrication, you can either thecasted at your project site or you can make it in the factory. So, accordingly you call it a cast insitu concrete piles or precast concrete piles.(Refer Slide Time: 11:22)
So, what is this cast in situ concrete piles, what are the methods of making cast in situ concretepiles? Here also based on the process of installation, you can classify it further into displacementmethod and non displacement method. See, when you do the installation process, say if yourinstallation process is going to disturb the surrounding soil to a greater extent, say if it is going todisplace the surrounding soil to the greater extent, then it is called as displacement method.
So, if the disturbance to the surrounding soil is minimum, then it is called as non displacementmethod. So, basically there are two types of methods. Displacement method means, it willdisplace the surrounding soil to a relatively larger amount. So, say for example, doing thedriving, say in the case of cast in place concrete piles. So, you will be commonly driving yoursteel casing into the soil you have to drive the steel casing with a hammer.
So, what are the different types of hammer use? As I told you in the next lecture we will bediscussing in detail. As of now what you need to know is we will be blowing a hammer on thetop of the steel casing, so into the soil. When you do this driving operation, what happens is itwill displaces surrounding soil to a greater extent, say if it is going to be clay soil. So, due to thedisplacement you can see there will be huge buildup of pore water pressure in the claysurrounding the installation point.
 
Next is we are going to discuss about the cast in place concrete piles using displacement method.So, first is we are going to drive the steel casing into the ground, steel casing is nothing but thesteel pipe, it can be either open at the bottom or it can be closed at the bottom. So, drive the steelcasing into the ground this is your casing, you can see that.(Refer Slide Time: 20:33)
Now how do you drive it with the help of a hammer, you blow the hammer. Since there arechances are the casing may get damaged, and you have to reuse the casing for the further piling.
So, if you leave the casing it is called as cased pile or if you remove the casing it is called asuncased pile. So, basically when the casing is closed with bottom, so it means that you are goingto leave it permanent. So, the casing which is open at the bottom, we remove it and reuse it. So,this is a displacement method, because this driving mechanism will displace the surrounding soil.(Refer Slide Time: 21:53)
So, let me summarize what we discussed earlier the displacement method. So, cast in placeconcrete piles are constructed by driving the steel shell into the ground, shell is your casing and
the steel mandrel is attached to the pile driver is placed inside the steel shell. So, that before the external load application, we are introducing someinternal stresses So, that later the structure can counteract the external loads when it is subjectedto the load application.
So, these internal stresses will counteract the external load, that is what is a basic concept of thepre-stressing.
And we should replace the cushion at regular intervals as (()) (42:18) worn out. So, insertadequate cushioning material between the pile driver cap and the top of the pile. So, this is acommon setup which you can see to control the driving stress, so why we can see this is your
pile and this is your hammer. So, you have two cushions, one is your pile cushion, other one isyour hammer cushion.
And there is also a H shaped helmet which helps you to distribute the load uniformly over thehead of the pile. So, that there is no stress concentration at a particular point on the pile head, sowe can distribute the stresses uniformly using this arrangement. So, the pile helmet is needed todistribute the blow from the hammer uniformly to the head of the pile to cushion and protect thepile head. So, this is what is a common arrangement we follow for the now protection of aconcrete piles.
So, now let us see with how to determine the safe load on the piles? As a piles are likely to besubjected to more amount of stress during driving. We need to determine what is the safe loadallowable on the pile that is very important. There are very many popular relationships offormulae which have been derived already in this context. We just go into discuss one suchformula called as engineering news formula, it is very formula, engineering news.To determine what is a safe load on the piles and also you can find what is the driving energyneeded for the pile, both these since I can determine from this engineering news formula. A
The engineering news formula have been derived which is commonly accepted formula todetermine the safe load on the pile. This is nothing but 2 w H by S + 1 and this is for singleacting hammer, if it is going to be a double acting hammer where the mechanism is different, theformula has to be modified. So, the main objective is introduce to you that there are manyrelationships available to help you to find what is the safe mode available on the pile for differenttypes of hammers you can find different relationships available.
And you can make you suffer. So, basically in this formula they have incorporated a fact ofsafety 6, that means 6 times load will be supported by the pile. So, R is the safe load on the pilein pounds, w is the weight of the hammer that is a falling mass in pounds, H is a height of freefall for the mass w in feet and S is a average penetration per blow for last few blows say 5 to 10blows in inches, so this is a formula derived for single acting hammer.o, if you want to determine the safe load on the piles or if you want to know the desired drivingenergy needed, you can make use of this equation.
So, these are the important references which I have referred for this lecture. In the next lecture asI mentioned earlier we will be discussing about what are all the different types of the pilehammers available, their mechanism. And how to make the selection of the pile hammeraccording to the pile type and according to the soil type. So, how to make the selection? That iswhat we are going to discuss in the next lecture, thank you.
Hello everyone, I welcome you all to the lecture 16 of this course construction methods andequipment management. In today's lecture we are going to discuss about the piles and the piledriving equipment.(Refer Slide Time: 00:39)
So, in the last lecture, we have discussed about the trucks, and how to balance the interdependentmachine safe trucks and the loaders. How to balance them in terms of size and number, so thatwe can optimize the productivity, that is what we have discussed in the last lecture. Now let uslook into the outline of today's presentation. In today's presentation, we are going to discussabout the different types of piles.
So, I will just give you a brief overview on what are all the different types of piles, because wecan classify them based on the application, based upon the material type, based upon the methodof fabrication, based upon the installation process. So, there are so many ways by which we canclassify them. So, I will just give you a overview of how to classify and what are the merits anddemerits of different types of piles.
So, then we will move on to what is the principle of the pile hammer. So, what is the principle ofpile driving operation, and as you know that particularly the precast piles, they are subjected tomore amount of driving stress. Say when you drive the pile into the ground, say we use a pilehammer, so for the driving mechanism, it is subjected to a huge amount of driving stress.
So, what are the methods to control the driving stress? That is what we are going to discuss. Andalso I will give you a brief overview on what are all the factors which governs the selection of apile hammer. So, based upon the type of the pile or based upon the size of your pile, so there aredifferent factors which are govern in the selection of the pile driving hammer, so we are going todiscuss about that in the upcoming slides.
So, based on the application, so commonly, there are different types of uses of piles. So I am justgoing to discuss few common applications, so one is a sheet pile and other one is your endbearing pile and friction pile.(Refer Slide Time: 03:52)
First let us see what are these sheet piles? The sheet piles so we might have seen this kind ofsteel sheet piles, so they are with interlocking joints, you can see that. So, they act like a rigidbarrier for earth and water particularly during excavations or trenching. So, to protect the trenchfrom the collapse, to prevent the trench from the collapse of soil, we go for this kind of sheetpiles.
For excavation or the soil conditions requiring temporary or permanent bracing to support thelateral load imposed by the soil, we go for this kind of sheet piles. So, it acts like a rigid barriersupporting the lateral load from the soil, it can also be used in water, like an cofferdams. It helpsto act like a barrier for the water it provides a dry working area or dry working environment, soeliminating the need for dewatering, it can also be built in the water.
So, you can use any type of material like you can go for timber sheet piles or steel sheet piles orconcrete sheet piles, so it can be made out of different types of materials. So, commonly you cansee applications and retaining walls and cofferdams as I discussed just now.(Refer Slide Time: 05:02)
So, this is again a picture of your the steel sheet pile, you can see the interlocking joints. So, thisis mostly driven with the vibrating hammer, what is this vibrating hammer all these things? Wewill be discussing in the part 2 of this lecture, so where we will be discussing about differenttypes of pile hammer. So, this helps to support a lateral load from the soil, helps as a barrier tothe earth.(Refer Slide Time: 05:26)
This is the picture of the timber sheet pile as you know that timber is the oldest material. So,oldest building material we have been using this material for so many centuries, even now weuse it wherever the timber is abundant.(Refer Slide Time: 05:39)
So, other types of applications are end bearing file and the friction pile, based on the mode ofload transfer. So, particularly for the soil with poor bearing capacity and we go for this endbearing pile. So, the end bearing pile has to transfer the load through the weakest strata till itreaches it hard bearing strata which can carry the load. And the load is transferred through theend that is why it is called as the end bearing pile.
In the case of friction pile the load is transferred through the friction between the sides of the pileand the surrounding soil, so that is what is friction pile. So, if the end bearing strata the hardbearing strata is reachable it is within the reachable depth, then we can go for the end bearingpile otherwise we have to go for the friction pile only. If the hard bearing strata is at a verygreater depth, it is not reachable, then we can design a friction pile.
The most of the piles you can see that they can transfer the load both through the frictionmechanism as well as to the end bearing mechanism so that is also possible.(Refer Slide Time: 06:43)
So, this is what we discussed just now. Piles that reached a load bearing strata and transmit theload through the end are called the end bearing piles. Friction piles get the load bearing capacityfrom the friction between the pile sides and the earth
And treat it with preservatives, that is very important because these piles are more susceptible torotting and insect attack as everyone knows. So, particularly when the timber piles are subjectedto fluctuating water table. So, you can see the issues of rotting and insect attack, this is becausefor the rotting mechanism, you need the presence of both water and the air. So, that is whytimber piles which are permanently submerged in the water, they are not susceptible to rotting.
They are not susceptible to insect attack; there are so many structures with the timber piles,which are servicing for so many years without any damage, without any rotting or insect attackwhen they are submerged in the water. But the problem arises only when it is subjected to thefluctuating water table because you know that the presence of water and air is necessary for thesemechanisms.
So, that is why in those cases where you know that it is going to be subjected to fluctuating watertable, you should definitely go for the preservatives to prevent it from rotting. So, if timber pilesremain permanently in the water, they can have a long service life, that is what we discussed justnow. And the untreated timber piles are subjected to insect attack and decay and they will lastonly for a few years.
So, both type of treatment we can offer to the timber piles to protect it from the insect attack androtting. So basically, in the olden days used to soak the timber in the natural saltwater. So, thenatural saltwater is best preservative, but nowadays we go for modern methods like this tocreosote with pressure treatment. So that is found to be very effective for the treatment for insectattack and the rotting.(Refer Slide Time: 09:34)
So, let us look into the merits and demerits of this timber piles. Basically the merit is, it isinexpensive, easy to cut and splice, that is a major advantage. But the demerit is obviously weknow that lot of defects was there, natural defect was there in the timber, let checks, splits, knotsand shakes. So, we have to quantify the amount of defects in the timber before assessing it issuitability for using it as a pile.
Where we have to quantify and whether the defects are within the permissible limit as given bythe standards, we have to check before it is used as a pile. And also there is a restriction on the
maximum length and the load carrying capability is limited, you know that when compared toconcrete or the steel piles, it is load carrying capacity is limited. So, that is why mostly we use itas a friction pile in sand, silt and clay.
Because as I told you concrete piles, say for example, the precast concrete piles, it is a normalconventional reinforced concrete piles. If the length is say now commonly we do not go beyond15 meters. But if you go for pre-stressing method, we can even go up to 30  easily likely to get damaged, so that is why we have to be very carefulin selection of hammer for the concrete pile. So, when you discuss about the different types ofhammers you will understand these factors better. I am just introducing these factors to you. So,in the next lecture after we discussing detail about all the types of pile hammers we will againdiscuss how you are going to select the pile hammer for a particular soil type and for a particularpile type so.
So, what are the guidelines will be discussing again, these are just a brief overview before wemove onto part 2. So, you know that pile hammer selection is going to depend upon the size of apile, type of a pile that is material type, the weight of a pile and how many piles you are going todrive the productivity needed the project time schedule say everything is going to govern. That iswhat we are going to discuss in the next lecture, thank you.