Abstract
This study investigates the correlation of the uniaxial compressive strength (UCS) and the point load test (PLT) index Is(50), bulk density, water absorption and the RQD properties of the Sudanese Nubian sandstone formation. The UCS being is the rock property needed in engineering practice but its determination is tedious, time consuming and expensive. Alternatively, the UCS may be indirectly evaluated through establishing relationships with rock parameters which are easier, cheaper and more convenient to determine in the laboratory or in the field. An extensive laboratory testing was executed to determine the above rock properties for many NSF samples taken from Khartoum State and other areas. Statistical analysis was performed on the test data and a reliable linear regression equation has been developed with a UCS to PLT Is(50) conversion factor of 10.18 and may be applied to estimate the strength of the Sudanese sandstone formation. The developed correlation is in good agreement with few of the many methods published for similar rock types which indicates that large errors may result in from applying an inappropriate UCS prediction method. Thus, it is important to establish separate correlations or validate published correlations to check their suitability for a specific rock types and local geologies. Useful correlation relationships of reasonable accuracy were also established for rough estimation of the UCS from the bulk density, water absorption and the RQD properties of the Nubian sandstone formation.
Highlights
Evaluation of the shear strength characteristics of rocks is an important aspect in most geotechnical investigations related to engineering problems
Rock strength is normally evaluated in terms of the uniaxial compressive strength (UCS) which can be directly and accurately determined from laboratory testing
The UCS may be indirectly estimated from the results of point load test (PLT) or other rock properties
Summary
Evaluation of the shear strength characteristics of rocks is an important aspect in most geotechnical investigations related to engineering problems. Rock strength is normally evaluated in terms of the uniaxial compressive strength (UCS) which can be directly and accurately determined from laboratory testing. Retrieval of high quality samples is a prerequisite for testing which is often difficult to obtain for weak and highly weathered rocks and the test is time-consuming and expensive. The UCS may be indirectly estimated from the results of point load test (PLT) or other rock properties. Many empirical methods have been proposed by researchers from different countries to estimate the UCS from the PLT strength Index Is(50). The reliability of these relationships depends on the type, location and degree of weathering of rocks
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