2.1. Engineering News Formula

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.

During the installation of precast piles, they experience significant stresses due to two primary factors: handling and driving. Handling stresses occur when the piles are being transported and positioned, while driving stresses happen when the pile is hammered into the ground. It is crucial to consider these stresses in the design phase because the strongest stresses occur during driving, rather than when the pile is in service. This understanding is vital for ensuring the integrity and durability of the piles.

Think of a soda can being opened. When you pull the tab to open it, the can experiences a sudden stress in that specific area, similar to the stresses a pile faces when being driven into the ground. If the can was designed to withstand just the pressures it experiences after being opened (like being filled with soda), it would likely fail when the tab is pulled, similar to how a poorly designed pile might fail during the installation.

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.

One effective way to manage driving stresses is to use cushioning materials between the pile and the hammer (the equipment that drives the pile into the ground). This cushioning protects the pile from excessive impact forces, which are particularly damaging to concrete piles due to their brittleness. Common cushioning materials include wood, and it's essential to select a thickness that is adequate to absorb shocks effectively, preferably never below 10 centimeters in thickness.

Imagine using a pillow when hitting a rubber ball. The pillow absorbs the impact, preventing the ball from bursting or being damaged. Similarly, using cushioning material between the pile and the hammer serves to 'absorb' the stress that would otherwise damage the concrete pile.

So, 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.

The stress that a pile experiences during driving is directly related to how fast the hammer strikes it. This speed is affected by the hammer’s weight and the height from which it falls (the stroke height). The formula for blow energy is given as the product of weight (W) and height (H), which means that heavier hammers falling shorter distances can create sufficient energy without causing overly high impact velocities, thus protecting the pile from damage.

Consider a strong baseball player hitting a ball. If he swings a heavy bat and connects with the ball at a short distance, the ball will go far without being damaged. Similarly, using a heavy hammer at a shorter height effectively delivers energy to the pile without greatly increasing the impact velocity that could cause damage.

So, now let us see with how to determine the safe load on the piles? ... the 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.

The Engineering News Formula is a widely accepted method to calculate the safe load on piles and the driving energy required. It is derived from the principle that the energy from the hammer impacts must equal the work done against the soil resistance. The formula is expressed as R = (2 * W * H) / (S + 0.1), where R is the safe load, W is the weight of the hammer, H is the height of free fall, and S is the penetration of the pile. This formula essentially balances the energy provided by the hammer with the energy required to penetrate the ground.

Imagine trying to push an umbrella into the ground; you need to apply a certain amount of force (energy) to get it to penetrate the soil. The Engineering News Formula helps engineers calculate how much force (or load) a pile can handle before it 'breaks' just like knowing how hard you can push the umbrella without bending it.

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.

Selecting the appropriate pile hammer is crucial and depends on various factors such as the size, weight, and material type of the pile, as well as site conditions and the number of piles to be driven. The weight of the hammer should ideally match or be a significant fraction of the pile's weight. Additionally, the soil type and conditions, space available for equipment, and project timelines also influence this decision.

Think of choosing the right tool for a job. If you're using a hammer to drive nails into different materials (like wood or concrete), the size and weight of the hammer must match the task. If the hammer is too light, it won't drive the nail in; if too heavy, it might break the wood. Similarly, engineers must select the appropriate hammer for driving different types of piles under specific conditions.

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