3 Phase Diagrams Part 1

Summary

Professor Kitch's webcast from the 'Introduction to Geotechnical Engineering' course delves into the particulate nature of soils and the use of three-phase diagrams. It covers the three phases of soil: solid particles, water, and air, explaining how to compute various properties such as unit weight, dry unit weight, void ratio, porosity, degree of saturation, and moisture content. The session demonstrates how to use these diagrams to solve problems involving soil properties, offering a step-by-step example involving a cylindrical specimen of soil. By following this approach, students can solve similar problems efficiently and with fewer errors.

Takeaways

• 😀 The three-phase nature of soil includes solid mineral particles, air/gases, and water/liquids, and can be represented through a diagram.
• 😀 The three-phase diagram includes weight and volume sides to represent the different phases of soil using units like pounds, kilotons, cubic feet, and cubic meters.
• 😀 The mass version of the three-phase diagram, often used in SI units, involves using grams for mass and cubic centimeters for volume.
• 😀 There are two types of problems when working with phase diagrams: one involving exact quantities for the soil phases and the other involving relative quantities like water content and porosity.
• 😀 The first problem type, discussed in the webcast, involves given exact quantities such as total weight and volume to compute various parameters.
• 😀 In a sample problem, a cylindrical soil specimen’s weight and dimensions are used to calculate the total unit weight, dry unit weight, void ratio, porosity, and water content.
• 😀 A three-phase diagram is created by calculating weights (such as total weight, weight of solids, and weight of water) and volumes (such as total volume, volume of solids, water, and air).
• 😀 The volume of water is computed by dividing its weight by the unit weight of water (62.4 lb per cubic foot), and similarly, the volume of solids is found using the specific gravity of solids.
• 😀 The volume of air is determined by subtracting the volumes of solids and water from the total volume, and the void volume is the sum of the water and air volumes.
• 😀 After the diagram is complete, key parameters such as unit weight, void ratio, porosity, degree of saturation, and moisture content are computed using the three-phase diagram for better accuracy and understanding.

Q & A

What is the primary focus of this webcast?

The webcast focuses on understanding the particulate nature of soils and how to use three-phase diagrams to solve weight and volume problems in geotechnical engineering, specifically covering sections 4.1 to 4.3 of the textbook.

What are the three main phases in soil represented in the three-phase diagram?

The three main phases in soil are the solid mineral particles, air or gases, and water or other liquids.

How are the weights of the soil phases represented in the diagram?

The weights of the soil phases are represented on the left side of the diagram using W Subs: W_subs for the weight of solids, W_subw for the weight of water, and W_subt for the total weight.

What are the units used for volume representation in the three-phase diagram?

The volumes are represented on the right side of the diagram, with units in cubic feet or cubic meters.

How do you calculate the volume of solids in the three-phase diagram?

The volume of solids is calculated using the weight of the solids divided by the unit weight of the solids, where the specific gravity of the solids is also used in the formula.

What is the formula to compute the total unit weight of the soil?

The total unit weight is calculated by dividing the total weight of the soil by the total volume of the soil.

What is the void ratio, and how is it calculated?

The void ratio is the ratio of the volume of voids to the volume of solids. It is calculated as the volume of voids divided by the volume of solids.

How do you calculate the porosity of the soil?

Porosity is calculated by dividing the volume of voids by the total volume of the soil and is usually expressed as a percentage.

What is the degree of saturation, and how is it computed?

The degree of saturation is the ratio of the volume of water to the volume of voids. It is computed as (volume of water / volume of voids) * 100%.

How do you calculate the moisture content or water content?

The moisture content (or water content) is calculated by dividing the mass of water by the mass of solids, and it is usually expressed as a percentage.