So, everyone knows particularly the precast piles or likely to be subjected to more amount of stress while driving it. They are subjected to more amount of handling stresses as well as when you drive the pile into the ground they are subjected to more amount of driving stresses. That is why all the stresses should be taken into account when you design your pile. So, highest stress across in the pile mainly during it is driving than when compare to during it is service life.

So, mainly during the driving it is being subjected to more amount of stress. So, how to control the driving stress? So, the commonly adopted method is, we have to introduce some cushioning material between the pile and the bile hammer so that is a basic thing we can do it. Particularly for the concrete piles as you know, concrete piles are weak in tension and they are more brittle. They are likely to be shattered very easily when you subject it to a very high impact, that is why we have to protect the concrete pile from the driving stress by using adequate cushioning material.

So, commonly used cushion is wood timber cushion so you have to choose a sufficient thickness depending upon the length of the pile needed, so we should never go below 10-centimeter thickness. And we should replace the cushion at regular intervals as gets worn out.

So, this is a common 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 is your hammer cushion. And there is also a H shaped helmet which helps you to distribute the load uniformly over the head of the pile, so that there is no stress concentration at a particular point on the pile head, so we can distribute the stresses uniformly using this arrangement.

So, another important guideline which you should keep in mind to control the driving stress is, the driving stress is will be very high when the impact velocity is high, that depends upon your height of fall. So, as everyone knows the blow energy is nothing but your product of W into H, W is your weight of hammer and H is your height of fall or the stroke.

So, if you want to increase the blow energy of your pile, it is preferable to increase the weight of hammer but do not increase the height of fall. Because if you increase the height of fall this will increase your impact velocity and your pile head is subjected to a lot of stresses. This may result in damage of your pile, if you increase its impact velocity, that is why it is preferable to go for a heavier hammer and shorter stroke.

So, the driving stresses are proportional to the ram impact velocity and your impact velocity depends upon your height of fall v = √2𝑔𝐻, H is your height of fall. So, that is why and the studies of found that your blow efficiency already we have discussed what is blow efficiency. Blow efficiency is nothing but the ratio of transmitted energy to input energy, so this will be high if the height of fall is less.

So, now let us see with how to determine the safe load on the piles? As a piles are likely to be subjected to more amount of stress during driving. We need to determine what is the safe load allowable on the pile that is very important. There are many popular relationships of formulae which have been derived already in this context.

We just go to discuss one such formula 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 energy needed for the pile, both these since I can determine from this engineering news formula.

And this is basically derived from the elementary pile driving formula which is nothing but your hammer energy equal to the work of soil resistance. That means what is the function of a pile hammer, it is going to offer you the required blow energy to drive the pile into the ground.

So, basically in this formula they have incorporated a fact of safety 6, that means 6 times load will be supported by the pile. So, R is the safe load on the pile in pounds, w is the weight of the hammer that is a falling mass in pounds, H is a height of free fall for the mass w in feet and S is a average penetration per blow for last few blows say 5 to 10 blows in inches.

So, now let us see what are all the basic factors which governs the pile hammer selection. So, obviously we have to select the pile hammer depending upon the type of a pile. So, what will be the size of a pile, weight of a pile according to that you have to choose a weight of the hammer.

So, we need a blowing energy requirement will vary. And as you know for this piling process we need a lot of supporting equipment like crane to hold the pile, to hold the hammer everything in position and to lift it.

So, we need to check. And based on the type of crane available, the crane should have the lifting capacity, sufficient lifting capacity, lift your pile, to lift your hammer and even lift your need which will help you to hold everything in proper alignment.

So, also you have to check the location of a project whether you are going to do the driving operation on land or in water. Say if it is going to be in water you may need to have some equipment with closed coverings. Noise restrictions, say you know that when you drive the pile into the ground with a hammer, it is going to produce a lot of noise.

So, we have come to the end of this lecture, let me now summarize what we have discussed so far earlier. So, we have discussed about different types of piles, so classification based on its use, based upon the load transfer, based upon the material type and based upon the course of fabrication.