7.3. Blow Efficiency in 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.

Accurately predicting the length of a pile is crucial, especially for precast piles, which are made in a factory and cannot be easily modified on-site. If the length is not accurately determined, significant difficulties can arise in cutting or splicing the concrete piles to ensure they fit the necessary specifications. Therefore, it is essential to conduct thorough investigations to ascertain the required length before commencing the piling operations.

Imagine trying to assemble a pre-made piece of furniture. If the instructions incorrectly specify the length of a shelf, you'll struggle to fit it into place, much as precast piles cannot be easily resized on-site.

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. So, you need to know the various end bearing strata and also you need to know carryout all the tests.

Before installing piles, conducting a thorough investigation and tests is critical. This includes preliminary tests to determine the necessary length of the pile and to evaluate its load-bearing capacity. Geotechnical investigations also play a role in understanding the soil profile and the various strata that affect how the pile will behave when installed. This information is fundamental to making informed decisions regarding pile design.

Think of this process like preparing to build a house. Before starting, you would want to know the local building codes, the soil type, and whether your construction will be stable—just as engineers must know the soil and load requirements before designing piles.

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 employed in piling methods as a stabilizing agent. It acts like a foam that stabilizes the soil, preventing its collapse during the pile installation process. This method is often seen as more cost-effective than using steel formwork. The bentonite slurry not only supports the surrounding soil but also facilitates the flushing of the borehole, which ensures that debris does not interfere with the pile’s load-bearing capacity.

Consider how a lifeguard uses flotation devices to help a struggling swimmer stay afloat. Similarly, bentonite slurry helps the soil 'stay afloat' and stable around the pile, allowing for successful installation.

So far we have discussed about the cast in situ concrete piles. So, there are two ways you can go for the displacement method there is the driving method or you can go for the non-displacement that is boring method, and we have discussed about the auger boring. 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.

In the context of piling, we can differentiate between two main methods: cast in situ and precast concrete piles. Cast in situ piles are made on the site using displacement or boring methods, while precast concrete piles are manufactured in a controlled factory environment. This controlled manufacturing process often leads to better quality control and faster production times compared to on-site methods.

Think of baking cookies from scratch versus buying store-made cookies. The store-made cookies are produced in a controlled environment where quality is consistently maintained, similar to how precast piles are manufactured.

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 benefits in terms of quality and time, there are significant challenges related to handling them. Because these piles are typically large and heavy, they can experience significant handling stresses that may lead to damage if they are not moved carefully. Thus, additional care is required during transportation and installation to prevent such damages.

Imagine trying to lift and move a heavy piece of furniture without proper tools or a team of people. It’s likely to get scratched or even broken, much as precast concrete piles can be damaged if not handled correctly.

And another important thing is, it is very difficult to do cutting and splicing with a concrete pile. That is why we have to accurately predict the length needed. So, properly do the soil investigation to look at the end bearing strata and decide the length of the pile because there is difficulty in changing the lengths at the site.

Pre-stressing is a technique used to enhance the performance of concrete piles. Since concrete is weak in tension and handling longer piles can lead to difficulty, pre-stressing introduces internal stresses to improve the pile's load-bearing capacity and resistance to deflection. This method allows for longer piles without increasing the risk of damage during handling.

Consider a stretched rubber band that can withstand additional force without breaking, similar to how pre-stressing provides extra resilience to concrete piles under stress.

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, we are introducing some internal stresses.

The basic concept of pre-stressing involves intentionally introducing internal stresses in concrete piles prior to any external load being applied. This process enhances the structure's ability to withstand load and minimizes deflection and handling stress. Pre-stressing can improve the overall longevity and capacity of the piles, enabling longer lengths than would be feasible with regular concrete piles.

Think of a bow and arrow; pulling back on the string creates tension that allows the arrow to fly further and more accurately. This is like pre-stressing, where we create tension in concrete to enable it to support higher loads.

So, you can have a thorough flushing of the borehole. So, that there would not be any muck or the left-out material at the bottom end which may reduce the end bearing capacity of the pile, so that is advantage of going for bentonite slurry. So, this is also one of the commonly accepted methods for cast in situ concrete piles.

Blow efficiency in pile driving refers to the proportion of energy from the hammer blow that effectively contributes to driving the pile into the ground. It is essential to maximize blow efficiency to enhance productivity during pile installation. Factors influencing blow efficiency include the weight of the hammer, the height of its drop, and the energy lost through friction and heat.

Just as a strong swing of a bat hits a baseball further, maximizing the energy delivered through the hammer helps drive the pile deeper into the ground, which is critical for ensuring stability.

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