The apparatus used to conduct the Unconfined Compression Test consists of the following parts: Therefore, moisture recorded in the field should also be preserved until testing.Īt least 5 samples are required to achieve a reliable value of the UCS. The purpose of the procedure is to preserve the in-situ properties of the sample until the test is conducted. In particular, the sample’s ends must be leveled within a 0.02 millimeters tolerance and they should not depart from perpendicularity by more than 0.06 degrees. The cylindrical surfaces are prepared in order to be flat and smooth. The samples’ length to diameter ratio (L/D) must be between 2.0 and 2.5, according to ASTM (American Society for Testing and Materials) and 2.5-3.0 according to ISRM (International Society for Rock Mechanics). The minimum diameter of a specimen must be at least 47 millimeters and 10 times larger than the size of the largest mineral grain (or 6 times larger for weaker rocks e.g. Samples are retrieved by drill cores and are selected cautiously in order be representative of the original rock formation. On a large scale, the rockmass properties are highly affected by other factors including discontinuities, faults and weathering.ĭuring the test, apart from the axial load, axial and lateral deformation are commonly measured to derive the sample’s elastic modulus and Poisson’s ratio. UCS is a parameter widely used in geotechnical design, but may not represent the strength in-situ. Due to the fact that stress is applied along the longitudinal axis, the Unconfined Compression Test is also known as Uniaxial Compression Test.
Unconfirmed Compressive Strength (UCS) stands for the maximum axial compressive stress that a specimen can bear under zero confining stress. Two models Logarithmic and exponential were found to be appropriate and recommended for application at Lugoba Quarry.The Unconfined Compression Test is a laboratory test used to derive the Unconfirmed Compressive Strength (UCS) of a rock specimen. This implies that RHN accounted between 93 and 95% of the total variation of the UCS and the relationships were very strong. The values of obtained in this study were found to be between 0.93 and 0.95, which are comparable with other studies.
Regression Analysis using SPSS software was carried out to develop 5 regression models of UCS vs.RHN.
The obtained results of UCS ranging from 105 to 132.5 MPa and RHN from 44.90 to 49.5 were found to be comparable with values of other granitic rocks in other parts of the world. The tests were done horizontally on two scanline's geotechnical domains of the rock mass on the footwall side of the quarry. The rebound hammer test was carried out using testing hammer type N.
Data for direct uniaxial compressive strength were obtained from uniaxial compressive strength test carried out on 20 core samples at the Dar es Salaam Institute of Technology Geotechnical Laboratory using ISMR Standard Procedures. This study aims at establishing the empirical models of uniaxial compressive strength fits on rebound hammer number that can be used to predict uniaxial compressive strength of granitic rock at Lugoba Quarry. In quarries, uniaxial compressive strength is a crucial parameter in the analysis of geotechnical problems involving rock stability and rock blasting design. Rebound hammer test is widely used as an indirect measure of uniaxial compressive strength for engineering materials such as concrete, soil, and rock in both civil and mining engineering works.