Lab 3 Triaxial Loading Test

Summary

In this lab, students perform triaxial measurements to determine the elastic properties of rocks. They apply axial stress and confining stress using fluid pressure, measuring the rock's response. The process involves preparing the sample, setting up the loading frame, fracturing the rock, and analyzing data to find stress-strain relationships, modulus of elasticity, and rock strength. The experiment aims to understand how confining pressure affects rock behavior.

Takeaways

• 🪨 The lab focuses on triaxial measurements to determine the elastic properties of rock under confined conditions.
• 📏 Similar to laboratory one, axial stress is applied, but the main difference is the use of a confining vessel filled with fluid.
• 💧 A fluid pump is used to apply confining pressure, with differential stress being the difference between axial and confining stresses.
• 🔧 The workflow involves measuring the sample, preparing the assembly, fracturing the rock, and analyzing the data.
• ⚙️ A membrane is used to isolate the sample from the confining fluid, and components like end caps, plastic o-rings, and vacuum grease are crucial for sealing.
• 🚰 Once the sample is prepared and placed in the vessel, air is removed from the system to ensure only water remains in the confining chamber.
• 🔍 The key measurements in the process include load and displacement, which help determine elastic properties and the point of rock fracture.
• 📉 The analysis focuses on converting force and displacement into stress and strain to calculate Young's modulus during loading and unloading.
• 📐 By performing several measurements, more circles can be combined to estimate the rock's cohesion and internal friction angle.
• 💥 The peak stress during fracture represents the maximum axial stress, and the angle at which the rock fractures can be predicted based on confining pressure.

Q & A

What is the main objective of Laboratory Number Three?

The main objective of Laboratory Number Three is to perform triaxial measurements to determine the elastic properties of the rock.

How is the principle used in Laboratory Number Three similar to Laboratory One?

The principle used in Laboratory Number Three is similar to Laboratory One in that both involve applying axial stress to a rock sample to induce deformation and fracturing.

What is the role of the confining stress in the triaxial measurements?

In triaxial measurements, confining stress is applied through a fluid to the rock sample, influencing the actual stress and vertical strain experienced by the rock.

What is the differential stress and how does it relate to the axial stress and confining stress?

Differential stress is the difference between the axial stress and the confining stress, which is a crucial parameter in analyzing the rock's behavior under stress.

What is the purpose of the fluid pump in the laboratory setup?

The fluid pump is used to increase the confining pressure in the system by allowing the confining fluid to be pressurized.

What are the steps involved in measuring the rock sample in Laboratory Number Three?

The steps include ensuring the sample is straight, measuring the diameter at different points, checking that the interfaces are parallel, and weighing the sample.

How is the rock sample prepared for the triaxial test?

The sample is placed in a membrane within a vessel, with components such as end caps, o-rings, vacuum grease, and water added to isolate it from the confining fluid.

What is the significance of the bleed valve and pump valve during the setup?

The bleed valve and pump valve are used to control the air pressure within the vessel, ensuring that air is displaced and the system is filled with water.

How is the confining pressure applied and monitored during the test?

The confining pressure is applied by connecting the vessel to the pump and using it to increase pressure. It is monitored by observing the pressure readings on the console.

What is the purpose of the strain gauge in the laboratory setup?

The strain gauge is used to measure the displacement of the rock sample during the test, which is crucial for determining the rock's elastic properties.

How is the data from the triaxial test analyzed to determine the rock's properties?

The data from the test is analyzed by converting the measurements of force and displacement into stress and strain. This allows for the calculation of the rock's elastic modulus and peak strength at different confining pressures.