Triaxial

Summary

This educational video, presented by Rian Saputra from the Department of Civil and Environmental Engineering at IPB, focuses on the laboratory testing of soil shear strength, specifically the triaxial test. The video explains the principles, types, and procedures of the test, detailing the equipment used, such as the triaxial test chamber and pressure gauges. It highlights the two main phases: consolidation and shear loading, with variations in drainage conditions (drained and undrained) influencing the results. The video also outlines the three main testing conditions (UU, CD, and CU), emphasizing the significance of effective stress and failure envelopes in soil analysis.

Takeaways

• 😀 The video explains the triaxial soil testing method in civil engineering, covering its principles and laboratory procedure.
• 😀 The goal of the learning session is for students to understand the principles of triaxial testing, types of tests, procedures, and be able to perform the test in a laboratory.
• 😀 The triaxial testing apparatus consists of a sample chamber where the soil sample is placed, surrounded by a rubber membrane to prevent damage during testing.
• 😀 Two pressure gauges are used in the triaxial test to measure cell pressure and pore water pressure, with drainage control provided by a drainage valve.
• 😀 During testing, axial loading is applied to the soil sample, with displacement measured to observe deformation during the process.
• 😀 There are two main phases in the triaxial test: consolidation and shear loading. Consolidation involves increasing the cell pressure to compress the soil, while shear loading involves applying axial force to test the soil's shear strength.
• 😀 The consolidation phase can occur under either drained or undrained conditions, affecting the soil’s response and volume change during the test.
• 😀 Shear loading in the triaxial test can occur under drained or undrained conditions, with different effects on pore water pressure and soil volume.
• 😀 The three types of triaxial tests are: UU (undrained, unconsolidated), CD (consolidated, drained), and CU (consolidated, undrained). These tests differ in terms of drainage conditions and applied pressures during the test.
• 😀 The results of the triaxial test can be used to plot the failure envelope and determine the soil's cohesion and internal friction angle based on the stress-strain response.
• 😀 The video concludes by emphasizing the importance of understanding the types of triaxial tests, their procedures, and their ability to perform these tests in a lab setting.

Q & A

What is the main objective of the triaxial test in soil mechanics?

The main objective of the triaxial test is to determine the shear strength properties of soil, particularly the relationship between stress and strain under different conditions of drainage.

What are the three main conditions under which the triaxial test is conducted?

The three main conditions for the triaxial test are: UU (Undrained Unconsolidated), CD (Consolidated Drained), and CU (Consolidated Undrained).

What does the UU condition signify in a triaxial test?

The UU condition, or Undrained Unconsolidated, occurs when the drainage valve is closed during both consolidation and shear loading, which means that no water is allowed to escape from the sample during testing.

What happens during the CD condition in the triaxial test?

In the CD condition, the soil sample is consolidated with the drainage valve open, allowing water to escape. After consolidation, axial loading is applied slowly, and the sample undergoes shear testing.

How is the CU condition different from CD?

In the CU condition (Consolidated Undrained), the soil is first consolidated with the drainage valve open, but during shear testing, the valve is closed to prevent water drainage, causing pore water pressure to increase.

What is the purpose of the drainage valve in the triaxial test?

The drainage valve controls the flow of water during the test. When it is open, water can exit the sample, simulating drained conditions, while closing it prevents drainage, simulating undrained conditions.

What does the term 'shear stress' refer to in the triaxial test?

Shear stress refers to the force applied to the soil sample in the direction that causes the soil to deform or shear. It is measured during the axial loading phase of the triaxial test.

How is the failure envelope in the triaxial test determined?

The failure envelope is determined by plotting the deviator stress (difference between axial and confining stress) against the normal stress at failure. The envelope is drawn as a tangent line to the failure points in the stress space.

What is the role of pore water pressure in the triaxial test?

Pore water pressure is monitored to understand how water within the soil behaves during loading. It is particularly important in the UU and CU tests, where the presence or absence of drainage affects the pore pressure buildup.

What is the significance of the angle of internal friction in the triaxial test?

The angle of internal friction, determined from the slope of the failure envelope, represents the soil's resistance to shear. It is crucial for understanding the soil's shear strength under various loading conditions.