4.2 - Performance of Diesel Hammers in Cohesive Soil
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Interactive Audio Lesson
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Introduction to Hammer Selection
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Today we are going to learn about how to choose the right hammer for piling. Can anyone tell me why the choice of hammer is important?
I think it depends on the type of pile used.
Exactly! The material type of your pile greatly influences the hammer you should select. For example, concrete piles need a heavier hammer to prevent damage.
What kind of hammer should we use for concrete piles?
For concrete piles, we typically use drop or single acting hammers. They are heavier and help to reduce stresses on the pile head.
Understanding Soil Types
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Soil can be categorized into cohesive and non-cohesive types. Do you remember how we classify the soil based on penetration tests?
Yes! Based on the number of blows needed for penetration.
Right! Non-cohesive soils are categorized from very loose to dense sands based on the number of blows. The tougher the condition, the heavier the hammer needed.
What about cohesive soils?
Cohesive soils are also rated based on blow counts. For very stiff soils, we always choose heavy single acting hammers for every type of pile.
Hammer Types Explained
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Now let's discuss the performance of diesel hammers in cohesive soil. Why do you think diesel hammers are effective?
Probably because they give strong energy for driving?
Exactly! Diesel hammers perform very well when the soil conditions are tough due to their ability to deliver substantial energy to the pile.
Can they be used in all soil conditions?
They are not ideal for all conditions. For example, in loose or water-saturated soils, vibratory hammers are better suited.
Selecting Hammer Size
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Let's talk about hammer sizes. Hammer size is defined by blow energy. Can someone explain how we calculate that?
Is it the weight of the hammer times the height it falls?
Exactly! The formula is W x H. As the pile length or weight increases, so does the blow energy requirement. Hence, we need larger hammers for tougher conditions.
Does that mean lighter conditions allow smaller hammers?
Yes, for lighter conditions, you can use lighter, double acting hammers.
Summary and Application of Knowledge
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To summarize, hammer selection is based on pile materials and soil types. Can anyone list the types of hammers we discussed today?
Drop hammers, single acting hammers, and double acting hammers.
Plus diesel hammers for tough cohesive soils!
Great! And remember, always check soil conditions before selecting your hammer to ensure effective driving.
What if we have noise restrictions?
In that case, you should consider vibratory methods or quieter hammers!
Introduction & Overview
Read summaries of the section's main ideas at different levels of detail.
Quick Overview
Standard
The section highlights the importance of hammer selection based on pile material type and soil conditions, detailing guidelines for different hammer types and their effectiveness in various types of soil, especially in cohesive soils. It emphasizes the need for heavier hammers in tough soil conditions, particularly the performance of diesel hammers.
Detailed
Performance of Diesel Hammers in Cohesive Soil
In this section, we explore the performance of various types of pile hammers and the criteria for their selection based on both pile material type and soil conditions. Notably, diesel hammers excel in cohesive soil conditions due to their high driving resistance.
Hammer Selection Criteria
- Concrete Piles: It is vital to choose heavier hammers, specifically drop or single acting hammers, to minimize driving stresses on the pile head. Recommended height of fall for effective use is less than 0.5 meters.
- Timber Piles: Similar to concrete, drop or single acting hammers are preferable.
- Steel and Sheet Piles: Double acting hammers are recommended for their rapid blow rate, while vibratory methods can be applied for noise-sensitive projects.
Soil Classification & Hammer Guidelines
Soils are categorized based on standard penetration tests, classifying them primarily into cohesive and non-cohesive types.
- Non-Cohesive Soil: This includes various levels of loose to dense sands defined by the number of blows during penetration tests. Heavier hammers are ideal for tougher soil conditions, with lighter conditions allowing for double acting hammers.
- Cohesive Soil: Cohesive soils are also divided based on blow counts, with varying guidelines:
- Very Stiff to Hard Soil (15-30+ blows): Use heavy single acting hammers for all pile types.
- Stiff Soil (8-15 blows): Single acting for concrete and wood piles; double acting for steel piles.
- Soft to Medium Cohesive Soil (0-8 blows): Can utilize vibratory methods or double acting hammers for effective driving.
Hammer Size and Blow Energy
The size of the hammer correlates with required blow energy, which is determined by the formula: W x H (Weight x Height of Fall). In tougher soil conditions or longer pile lengths, the blow energy requirement increases, necessitating the selection of a suitably sized hammer. It's crucial to avoid using double acting hammers for concrete piles due to their rapid blow rate which could damage the pile.
Conclusion
Diesel hammers deliver effective performance in cohesive soil by providing substantial energy to overcome high driving resistance. A comprehensive geotechnical investigation helps in hammer selection based on material type, soil conditions, pile length, and anticipated noise restrictions.
Audio Book
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Introduction to Hammer Selection
Chapter 1 of 5
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Chapter Content
So, we have discussed about the functioning of different types of hammers and let us discuss about how to make the hammer selection. Your pile material type, the soil type everything is going to govern your selection of your pile hammer.
Detailed Explanation
This chunk introduces the importance of selecting the right hammer for pile driving. Factors such as pile material (e.g., concrete, timber, steel) and soil type (e.g., cohesive or non-cohesive) play vital roles in determining the hammer choice. Practically, if the soil is very hard or cohesive, heavier hammers are preferred to effectively drive the piles into the ground.
Examples & Analogies
Think of hammer selection like choosing the right tool for a job. Just like you wouldn't use a small screwdriver for tightening a large screw, you wouldn’t use a lightweight hammer for driving heavy concrete piles into tough soil.
Classification of Soil Types
Chapter 2 of 5
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Chapter Content
Now how to make the pile hammer selection with respect to your soil type, as I told you we can classify the soil into different categories. So, based upon there are some standard tests to categorize the soil into different categories. Like once this test is your standard penetration test where you find what is the number of blows needed for the standard penetration.
Detailed Explanation
Soils are classified based on their cohesiveness and how much energy is needed to penetrate them. For instance, non-cohesive soils include sands of varying densities, and cohesive soils include clay with different stiffness levels. Standard penetration testing determines the blow count needed to penetrate the soil, which helps categorize the soil type.
Examples & Analogies
Imagine trying to push a stick into the ground. If the soil is loose sand, it’s easy to push; but if it’s dense clay, it takes much more effort. The energy required to push the stick reflects the hammer's selection in construction.
Recommendations for Hammer Selection
Chapter 3 of 5
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Chapter Content
For very tough soil conditions, it is preferable always go for heavier hammer, which is nothing but your drop hammer or single acting hammer that is always heavier, single acting hammer for tough soil condition and for the heavier pile.
Detailed Explanation
Heavier hammers are recommended for challenging soil conditions because they can generate more force and energy to effectively drive piles into the ground. Lighter hammers are not effective in such conditions because they may not deliver enough power to penetrate the soil adequately.
Examples & Analogies
Consider how a heavyweight boxer can deliver a stronger punch compared to a lightweight boxer. In construction, the heavier hammer delivers a more powerful 'punch' to drive pilings deep into tough soil.
Specific Recommendations Based on Soil Conditions
Chapter 4 of 5
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Chapter Content
So, with this basic guideline let us discuss what are the guidelines available from U.S army corps of engineers. For very loose to loose sand, it is given that for concrete pile or the wood pile you can go for double acting.
Detailed Explanation
The U.S. Army Corps of Engineers provides guidelines on hammer selection based on specific soil conditions. For example, in very loose sand, it's acceptable to use double-acting hammers for concrete and wooden piles. These hammers deliver rapid blows, which can help drive piles more efficiently in such material.
Examples & Analogies
When playing with a soft ball, if you hit it gently, it moves slowly, but if you hit it fast and hard, it can go farther. Similarly, double-acting hammers replicate this concept by delivering fast, powerful blows, allowing for effective pile driving in loose soil.
Performance of Diesel Hammers in Cohesive Soil
Chapter 5 of 5
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Chapter Content
DieEachers perform well in cohesive soil, as I told you in the tough soil conditions where the driving resistance is high that will result in greater rebound of the hammer which will offer more energy for pile driving.
Detailed Explanation
Diesel hammers excel when working in cohesive soils because the dense nature of cohesive soil can create significant driving resistance. In these scenarios, the rebound effect of the hammer during its drive phase stores and then releases more energy for the next blow, making it more efficient.
Examples & Analogies
Imagine a basketball player bouncing a ball on a hard court versus a soft grassy field. On a hard court, the ball rebounds higher and faster, similar to how a diesel hammer reacts more vigorously on dense soil, resulting in greater energy transfer with each blow.
Key Concepts
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Hammer Selection: The choice of hammer depends on pile material and soil conditions.
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Cohesive vs Non-Cohesive Soil: Soil types differ in terms of how they respond to hammering.
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Blow Energy Requirement: Determined by the weight of the hammer and the height from which it falls.
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Heavy Hammers for Tough Soil: For tougher soil conditions, heavier hammers are necessary.
Examples & Applications
For concrete piles in rigid soil conditions, a heavy single acting hammer reduces the risk of pile damage.
In loose sand, double acting hammers may perform better due to their rapid striking capabilities.
Memory Aids
Interactive tools to help you remember key concepts
Rhymes
For heavy piles where soil's tough, a single hammer is the right stuff.
Stories
Imagine a construction site where workers are trying to drive piles into tough clay soil. They learn that using a heavy hammer helps them drive the piles deeper without cracking them, ensuring their structure stays strong.
Memory Tools
C-H-A-M-P for remembering hammer types: Concrete = Heavy, Hammers for All types of Piles.
Acronyms
H.E.A.V.Y. - Hammer for Effective And Valuable Yields.
Flash Cards
Glossary
- Single Acting Hammer
A hammer that delivers a blow to the pile in one direction, typically using gravity or steam pressure.
- Double Acting Hammer
A hammer that can deliver blows in both directions, allowing for a shorter stroke and more compact design.
- Cohesive Soil
Soil that has the ability to stick together due to water content, often referred to in categories of stiffness based on penetration test results.
- Drop Hammer
A simple hammer that is dropped from a height to drive a pile into the ground.
- Vibratory Hammer
A type of hammer that uses vibration to reduce friction and allows faster pile driving in certain soil types.
- Blow Energy
The energy delivered to a pile during the impact of the hammer, calculated as weight times height of fall.
Reference links
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