2.1. Guidelines for Loose to Medium Non-Cohesive Sand

So, you can classify the soils into different categories depending upon a number of blows. For 0 to 10 blows, it is very loose to loose sand; for 10 to 30 it is medium non-cohesive sand; for 30 to 50 plus blows it is dense non-cohesive sand.

Soils can be identified and classified based on how many blows are needed for a standard penetration test. This test measures how easily a hammer drives into the soil. If it takes 0 to 10 blows, the soil is categorized as very loose to loose sand. If it takes 10 to 30 blows, this soil is medium non-cohesive sand, and if it takes between 30 to 50 blows, it indicates dense non-cohesive sand. Essentially, as the number of blows increases, it means the soil is becoming more compact and dense.

Think of it like pressing down on a sponge. If you press lightly (0 to 10 times), it squishes down easily — that's like very loose sand. If you press a bit harder (10 to 30 times), it resists a bit more, like medium sand. Finally, if you're pressing really hard (30 to 50 times), the sponge is very tight and compact, much like dense sand.

For very loose to loose sand, for concrete piles or wood piles, you can go for double acting. For steel piles, you can either go for double acting or vibratory hammer.

Different types of piles will require specific hammers depending on the soil conditions. In very loose sand, while concrete piles usually prefer heavier single acting hammers, a double acting hammer is acceptable. For steel piles, a double acting or vibratory hammer can be used, which generates a higher blow rate effective for the lesser density of the soil.

Imagine you are driving a nail into different types of wood. With soft wood (comparable to very loose sand), you can use a lighter hammer (double acting hammer) without much force. But if you are working with denser wood (like medium or dense sand), you'd need a stronger, heavier hammer (single acting) to get it in properly.

For medium non-cohesive sand, a single acting hammer should be used for concrete piles; double acting hammers should not be used for concrete piles. Steel piles can use either double acting or vibratory hammers.

When dealing with medium non-cohesive sand, it's important to use the right hammer for pile driving. Single acting hammers are recommended for concrete piles because they offer a more controlled blow, crucial for driving into moderately dense soil. However, double acting hammers are allowed for steel piles since they can handle the push and pull efficiently. Vibratory hammers can also be a good option in sandy conditions.

Think of this as using different tools when building something. For a delicate procedure (like driving a concrete pile), you'd want a precise tool (like a single acting hammer) to avoid damages. But for a sturdier construction (steel piles), you can use a multi-purpose tool (double acting hammer) that can handle the task with a bit more strength and speed.

As the densification of the sand increases, indicated by the increase in number of blows, the guidelines change. For wood or concrete piles go for single acting hammer; for higher blow counts (50+), you can switch to single acting hammer for steel piles as well.

When the number of blows increases to 50 or more, indicating denser sand, the recommendation is to keep using single acting hammers for concrete and wood piles, ensuring effective driving with sufficient energy. Interestingly, even for denser steel piles, where a double acting hammer is commonly recommended, a single acting hammer can be used when the sand is more compact.

Consider how you would drive different types of stakes into the ground. If the ground is soft (low blows), a regular thin stake (concrete pile) with a rubber mallet (single acting hammer) works fine. But as the ground gets tougher (high blows), you still use the rubber mallet for softer stakes, but might adapt to a heavier tool for the denser areas, to make sure you're getting the job done.

Hammer selection should consider the weight of your pile, its length, and the material type, as well as noise restrictions and overhead space for equipment.

The selection of the hammer is critical and involves a combination of factors including the weight and length of the pile and its material type. In dense conditions where vibration restrictions might apply, a vibratory hammer might not be ideal. These factors all interact to determine the best choice for driving piles effectively and safely.

It's like preparing for a road trip: you wouldn't choose the same vehicle (hammer) if you're hauling a heavy trailer (heavy pile) versus going solo (light pile). Additionally, you consider road conditions (soil type) and possible detours (space restrictions) to ensure a smooth journey without issues.

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