Document Type : Original Article


1 Mining Engineering Department, Khartoum University, Sudan

2 Building and Road Research Institute, Khartoum University, Sudan


Basalt and rhyolite rock masses are widespread through the north east part of Sabaloka plateau, 80 km north of Khartoum. The geological history of this area with the repeated changes in the volcanic activity, alternated with destructive events, caldera collapses, produced a very complex system. The variation in lithology, in the degree of tectonization and disturbance determined a wide spectrum of geotechnical materials, ranging from hard lavas to poorly welded pyroclastic deposits. Quarries, tunnels and other infrastructures were and will be constructed in these rock masses. This paper deals with determining the rock mass strength and deformability of these rocks in Sabaloka, in order to characterize them for the engineering purpose. The estimate of rock mass strength and deformability is reasonably well predicted through the use of empirical failure criteria such as the Hoek –Brown failure criterion which has gained broad acceptance in the rock mechanics community, and in situ test and empirical expressions to predict deformability. The rock mass properties and modulus of deformations of these rocks have been carefully assessed based on laboratory tests (uniaxial compressive, tensile test, triaxial test), and field investigations. The rock mass characterization approaches, Geological Strength Index (GSI) systems have been applied extensively to predict and evaluate the rock mass properties and support design. Numerical modeling studies (RocLab) based on field and laboratory data, have been used to evaluate the performance of these rock masses. Generally the main objective of the work reported in this paper was to increase knowledge of intact rock and defect properties of jointed basalt and rhyolite rock masses, develop reliable rock mass data and improve the ability to estimate the rock mass strength of these rocks.