Estimation of the strength of Nubian sandstone formation from point load test index and other simple parameters

¹ Building and Road Research Institute, University of Khartoum, Khartoum, Sudan
² General Administration for Buildings, Ministry of Physical Planning, Khartoum State Khartoum, Sudan

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 I_s(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.