7.2. Basic Principle of Pile Driving

And if you are not able to predict the length requirement accurately, we can make some adjustments at this site but for the precast piles which are made in the factory. So, such kind of adjustments are not possible at the site, you can go for either cutting or splicing, and that is very difficult with the concrete piles. That is why when you go for precast piles, we have to accurately determine the length of the pile needed.

It’s crucial to accurately determine the length of precast piles before they are manufactured in a factory. Unlike other types of piles, precast piles are not easy to adjust at the construction site once they have been cast. If the length is uncertain, it can lead to complications and additional challenges when installing them. For instance, cutting or splicing precast concrete piles is difficult because concrete is not easily altered once set. Thus, precise length estimation is vital.

Think of precast piles like a pre-measured cake layer that you ordered for a birthday party. If you guess the height incorrectly, it’ll either be too short or too tall when placed between other layers, and altering that cake once it’s baked is nearly impossible!

So, that is why we need to do a thorough prior investigation you have to carry out the pile testing program. So, you have to do some preliminary pile testing to know the exact length needed and also to assess the load bearing capacity of the pile. And also, you should know some geotechnical investigations to know the complete soil profile.

Before beginning pile driving, it's vital to conduct thorough investigations of the soil. This includes a testing program that can help ascertain the necessary length for the piles and ensure they can support the loads they’ll encounter. The understanding of soil characteristics—such as its composition and strength—allows engineers to make informed decisions about the type and dimensions of piles needed for each specific project.

Imagine planning to build a house. You wouldn’t just choose any foundation without checking if the ground is solid. Just as you’d assess soil stability before building, engineers need to understand the soil profile before determining how deep and strong to make their piles.

So, in addition to this, there is also other methods where, they use this bentonite slurry for the piling method. What they do is? They use of bentonite slurry to act like a foam up to the soil. So, this will be more cost-effective when compared to the steel formwork. So, soil has a pore bearing capacity, they use this bentonite slurry, so that it will help to stabilize your soil and prevent the collapse of the soil.

Bentonite slurry is used as a material in the piling process to both support and stabilize the soil around the pile during installation. It’s particularly beneficial because it can help prevent soil collapse, maintaining the integrity of the site. Furthermore, using bentonite slurry can be more economical than constructing a steel formwork around piles, reducing material costs.

Picture how a well-blended batter in a cake pan helps the cake keep its shape while baking; the bentonite acts similarly by holding the soil in place while the piles are driven into the ground, ensuring everything stays stable during the construction process.

So, now we are going to discuss about the precast concrete piles. So, they are going to be made in the factory in control condition. Since it is made in the factory you will have a good quality control, you will have a good control over the quality of the concrete than at the construction project site and you will be requiring less time only productivity will be high in the factory.

Precast concrete piles are manufactured in controlled factory conditions, which allows for strict quality control and reduction in variability compared to on-site casting. This streamlined process leads to a quicker turnaround and higher productivity since the piles can be produced rapidly and with consistent quality.

Think about how factory-manufactured car parts are consistently better in shape and quality than parts made in a garage. Similarly, precast concrete piles from a factory will generally perform better and require less time to produce than trying to form them on-site under less-than-ideal conditions.

But what will be their demerit? Demerit is these concrete piles are likely to be very huge, so it will be very heavy. Handling of the piles is very difficult, so particularly, when you handle the concrete piles, they are likely to be subjected to more amount of handling stresses and they are likely to be damaged.

While precast concrete piles offer many advantages, they also have some drawbacks. Their larger size and weight make them difficult to handle safely during transportation and installation. If not managed properly, they can suffer damage due to the handling stresses they are subjected to, which can compromise their structural integrity.

Imagine trying to carry a large and heavy suitcase; if not careful, you might drop it, causing damage. Similarly, if the heavy precast piles are not handled with care during installation, they risk cracking or breaking.

To improve its load bearing capacity and to improve its resistance to handling stresses, and it is improved implement in resistance to the deflection we can go for pre-stressing method. Pre-stressed concrete piles are very common.

Pre-stressing is a technique used to improve the load-bearing capacity of concrete piles. This involves introducing internal stresses to the concrete before it is applied to external loads. By doing so, concrete piles can withstand higher loads and more handling stress without sustaining damage.

Think of pre-stressing like a balloon: when you inflate it, the internal pressure allows it to handle external forces better and resist being squished. Similarly, pre-stressing concrete piles allows them to better endure the loads they'll face once installed.

So, what is this basic concept of pre-stressing? I will just introduce to you what is the basic concept. Basically, what we are trying to do is we are deliberately introducing some internal stresses in the concrete. So, that before the external load application...

Pre-stressing involves applying tension to tendons within the concrete before it is loaded, allowing the concrete to counteract any external forces it may experience later. This internal tension is created using equipment known as stressing jacks, and it helps enhance the structural integrity and performance of the piles under different load scenarios.

This process is similar to how a stretched rubber band can withstand being pulled on more effectively than if it’s slack. By pre-stressing the concrete like a rubber band, the pile can resist future loads better and function more effectively.

If you are going to apply the tension before the concrete casting is done, it is called as pre-tensioning. If you are going to apply the stress after the concrete casting is done, it is called as post-tensioning.

There are two main methods of pre-stressing: pre-tensioning and post-tensioning. In pre-tensioning, tension is applied to tendons before the concrete is cast. In post-tensioning, tension is introduced after the concrete has cured. Both methods achieve the goal of enhancing the load-bearing capacity of the concrete and are used depending on specific project requirements.

Think of pre-tensioning and post-tensioning like stretching a slingshot: in pre-tensioning, you pull it back before loading a rock, while in post-tensioning, you add tension after you’ve placed the rock. Both allow the slingshot to launch better but in different ways!

Basically when you go for this pre-stressing method, you can increase the length of the pile. Because as I told you concrete piles, say for example, the precast concrete piles, it is a normal conventional reinforced concrete pile...

By employing pre-stressing methods, engineers can increase the lengths of concrete piles beyond standard limitations. For instance, while typical precast concrete piles might have a maximum length of 15 meters, pre-stressed versions can reach lengths of 30 meters or more. This enhancement opens the possibility for more versatile construction applications.

Imagine a long elastic band. When stretched (like pre-stressing), it can extend and reach further, allowing it to cover more distance than a normal band that cannot stretch. Pre-stressing allows piles to reach deeper depths where they’re needed.

So, I have just given you a brief overview about the pile types, because we are going to spend more time to learn about the pile driving equipment in this particular course.

This section offered a concise understanding of various pile types and the basics of pile driving. Understanding these principles sets the foundation for later discussions regarding specific equipment and techniques used in pile driving operations.

Think of this segment as an introduction to a larger book: understanding the chapter’s key themes (the types of piles and principles of driving) helps lay the groundwork for deeper dives into the more complex topics (the equipment and methods) that will follow.

--