Overview and Working Principle

The fully automatic rock triaxial apparatus is an advanced laboratory instrument used to evaluate the mechanical behavior of rocks under simulated in-situ stress conditions. It is essential for various applications in rock mechanics, geotechnical engineering, tunneling, mining, and petroleum reservoir studies. This apparatus helps determine critical rock properties such as compressive strength, cohesion, internal friction angle, Young’s modulus, and Poisson’s ratio with high accuracy. The system comprises several key components. At its core is the triaxial cell, a high-pressure chamber that houses the cylindrical rock specimen and applies uniform confining pressure using hydraulic oil or gas. The axial load frame features a servo-controlled actuator that delivers vertical stress to the specimen. The pressure controller regulates cell pressure. The automatic data acquisition system captures real-time measurements of load, displacement, pressure, and strain with high precision. For accurate deformation measurement, the sample is equipped with sensors such as strain gauges and LVDTs (Linear Variable Differential Transformers).

The test begins with sample preparation, where a cylindrical rock core—typically 38–54 mm in diameter with a height-to-diameter ratio of approximately 2:1—is encased in a rubber jacket and placed inside the triaxial cell. Confining pressure is then applied to simulate the rock's natural environment, similar to conditions found deep underground. After this, axial stress is applied at a controlled rate by the actuator, either under constant confining pressure (conventional triaxial test) or with varying pressures (true triaxial test). The system monitors the specimen continuously, recording parameters such as stress, strain, and pore pressure until the rock fails. Finally, the recorded data is analyzed to generate results like the Mohr-Coulomb failure envelope, elastic constants, and strength criteria of the rock. The fully automatic system offers several benefits, including high precision and repeatability, minimal human error, time efficiency, and real-time data logging, making it a preferred choice for modern rock testing laboratories.