2.5. Guidelines for Soft and Medium Cohesive Soil

Today, we’re going to talk about how to choose the right type of hammer for different pile materials. Can anyone tell me why a heavier hammer is recommended for concrete piles?

Maybe it's to reduce the height of fall and driving stresses?

Exactly! A heavier hammer helps minimize those stresses. Now, what about timber piles?

Do we still use a drop hammer for timber as well?

Correct! Drop or single acting hammers are good for timber piles too. Now, can anyone explain what types of hammers are used for steel piles?

I think we can use double acting hammers for faster blows?

That's right! Double acting hammers are suitable for steel piles due to their rapid blow rate. Let's remember: 'Concrete = Heavy Hammer, Timber = Drop or Single Acting, Steel = Double Acting'.

Can you remind us again about the productivity impact?

Good question! For productivity, single acting hammers can be preferred over drop hammers due to their efficiency in some conditions.

In summary, selecting the right hammer depends on pile type: Concrete uses heavier hammers to reduce fall height, timber prefers lighter hammers, and steel utilizes double acting for increased speed.

Now, let’s delve into soil types and how they influence our hammer choice. What do we know about cohesive and non-cohesive soils?

Cohesive soils tend to stick together, while non-cohesive soils like sand don't.

Exactly! And how does this affect the blow energy needed for pile driving?

More blows mean tougher soil will require heavier hammers, right?

Right again! For loose sand, we might opt for double acting hammers, but for very stiff cohesive soil, heavier, single acting hammers are preferable. Why do you think that is?

Because they can provide the necessary energy to overcome the resistance?

Exactly! Remember: 'Heavier Hammer = Tougher Soil'. It's essential to assess soil type accurately before hammer selection.

In summary, cohesive vs. non-cohesive soils affects hammer choice: loose sand might allow for double acting hammers, while stiff cohesive soils will need the heavy hitters.

Next, let’s introduce the guidelines from the U.S. Army Corps of Engineers regarding hammer selection. What’s the guideline for very loose soil conditions?

For loose sand, both concrete and wood piles can use double acting hammers, but generally single acting is preferred?

Exactly! Even though single acting hammers are generally recommended for concrete piles, exceptions are made in very loose conditions. What should we use for steel piles in similar conditions?

It’s common to use double acting as well, right?

Correct! The guidelines provide flexibility based on the soil's state. For medium non-cohesive sand, what about the suggesting hammer type for concrete and steel piles?

Single acting for concrete and either double acting or vibratory for steel?

Well done! These guidelines help ensure we select the right tools for the job considering existing soil and material conditions.

To wrap up, remember the U.S. guidelines emphasize concrete requires single acting in most cases, while loose soils permit using double acting for flexibility.

Finally, let’s talk about hammer size and the relationship between its weight and blow energy. How do we calculate blow energy?

Is it the weight of the hammer times the height of the fall?

Correct! Blow energy is given by W multiplied by H. What do you think happens to blow energy requirements as pile length increases?

It increases, I assume? Heavier, longer piles would need more energy.

Exactly! The relationship is linear. For very tough soil conditions, you will need higher blow energy. Remember: 'Longer and Heavier = More Energy!' Can anyone remind us again how weight affects our selection?

Concrete piles need higher blow energy compared to timber or steel piles, right?

Right! In summary, understanding the correlation between hammer weight and required energy is vital for effective hammer selection. A heavier hammer reduces fall height and driving stresses, especially in challenging conditions.