Unconfined Compression Test
The Unconfined Compression Test (UCT) is a fundamental geotechnical laboratory test used to determine the strength of rock samples. Here's a concise explanation of the test:
Purpose:
- To measure the unconfined compressive strength of rock specimens
- To assess the stress-strain behavior of rock under uniaxial loading
Key aspects:
1. Sample preparation:
- Cylindrical rock core specimens are prepared with specific height-to-diameter ratios (typically 2:1 to 2.5:1)
- Ends are carefully trimmed to ensure they are flat and parallel
2. Test setup:
- The sample is placed between two rigid platens in a compression testing machine
- No confining pressure is applied (hence "unconfined")
3. Loading conditions:
- Axial load is applied at a constant rate until failure occurs
- Loading rate is typically between 0.5 to 1.0 MPa/s
4. Measurements:
- Applied load
- Axial deformation
- Time
5. Calculations:
- Stress = Applied load / Cross-sectional area
- Strain = Axial deformation / Original length
- Unconfined compressive strength (UCS) = Maximum stress at failure
6. Data analysis:
- Stress-strain curve
- Young's modulus
- Failure mode observation
7. Applications:
- Rock mass classification
- Design of underground structures
- Slope stability analysis