Carleton University - CIVE 3208 Lab 3: Compaction

Summary

This geotechnical engineering tutorial guides students through the process of determining the optimal moisture content for soil compaction. It explains the significance of density in soil properties, such as shear strength and hydraulic conductivity. The lab involves conducting standard and modified Proctor tests, using a specific hammer weight and drop height to compact soil layers in a mold. Students measure and record soil mass at varying moisture levels to identify the maximum dry density, plotting these findings to determine the ideal moisture content for soil compaction.

Takeaways

• 🌟 The purpose of the geotechnical engineering compaction test lab is to determine the water content that results in a maximum dry density of soil.
• 🔍 Density is a critical factor in soil as it influences properties such as shear strength, compressibility, settlement, and hydraulic conductivity.
• 📈 A denser soil will exhibit higher shear strength, less settlement, less compressibility, and lower hydraulic conductivity.
• 🧪 The lab involves conducting compaction tests, specifically standard and modified Proctor tests, to find the optimal moisture content for maximum dry density.
• 📏 The test requires about 6 pounds (3 kilograms) of dry soil passing through sieve number four.
• 💧 Water is added to the soil sample to achieve a specific moisture content, starting at about 5%.
• 🔨 The Proctor mold is used to compact the soil in layers, with a 5.5-pound hammer for the standard test and a 10-pound hammer for the modified test.
• 📏 Compaction is performed by dropping the hammer from a height of 12 inches for the standard test and 18 inches for the modified test.
• 🔄 The process is repeated with increasing moisture content until the maximum density is found, indicated by a drop in the total mass of the compacted sample plus the mold.
• ⏱ After 24 hours of drying in an oven, the mass of the soil is recorded to calculate the soil density and moisture content.
• 📊 A graph is plotted with density on the y-axis and moisture content on the x-axis to determine the optimal moisture content for maximum dry density.

Q & A

What is the main objective of the compaction test lab in geotechnical engineering?

The main objective of the compaction test lab in geotechnical engineering is to determine the water content that results in a maximum dry density of soil, which is crucial for understanding soil attributes like shear strength, compressibility, settlement, and hydraulic conductivity.

Why is soil density important in geotechnical engineering?

Soil density is important in geotechnical engineering because it governs various soil attributes such as shear strength, compressibility, settlement, and hydraulic conductivity. A denser soil will have higher shear strength, less settlement, less compressibility, and lower hydraulic conductivity.

What does the density-water content curve typically look like?

The density-water content curve typically shows that at lower water contents, soil grains are locked together, and compaction energy has less effect. As water is added, soil grains can move more freely, leading to a peak density. Adding more water after the peak results in a reduction of overall soil density due to saturation.

What are the standard and modified Proctor tests?

The standard and modified Proctor tests are compaction tests used to determine the maximum dry density of a soil sample at various moisture contents. The standard Proctor test uses a 5.5 pound hammer dropped from a height of 12 inches, while the modified Proctor test uses a 10-pound hammer dropped from a height of 18 inches, applying more compaction energy.

How much soil is needed for the compaction tests in this lab?

About 6 pounds (approximately 3 kilograms) of dry soil passing sieve number four is needed for the compaction tests in this lab.

How is the moisture content of the soil sample calculated?

The moisture content of the soil sample is calculated by multiplying the dry mass of the soil by the desired moisture percentage. For example, for a 5% moisture content, the amount of water needed is calculated by multiplying the dry mass by 0.05.

What is the purpose of the Proctor mold in the compaction test?

The Proctor mold is used to contain the soil sample during the compaction tests. It ensures that the soil is compacted within a standardized volume and allows for consistent application of compaction energy.

How many layers of soil are compacted in the standard Proctor test?

In the standard Proctor test, the soil is compacted in three layers within the Proctor mold.

How many drops of the hammer are needed to compact each layer in the standard Proctor test?

In the standard Proctor test, 25 drops of the 5.5 pound hammer are needed to compact each layer of soil.

How is the moisture content increased for subsequent tests after the initial compaction test?

For subsequent tests after the initial compaction test, the moisture content of the soil sample is increased by roughly 2 to 3 percent. This is achieved by adding additional water to the soil and mixing it to ensure uniformity.

How is the maximum density of soil determined during the compaction tests?

The maximum density of soil is determined when the total mass of the compacted sample plus the mold begins to drop after reaching a peak. This indicates that the soil has reached its maximum density at the corresponding moisture content.