EFFECTS OF ROCK PROPERTIES ON SLOPE STABILITY OF SELECTED QUARRIES IN ONDO AND OGUN STATES, NIGERIA

Abstract

At any surface operation, some instability can be expected from minor bench ravelling to massive slope failures. Fatalities occur most often at stone mines follow by coal, sand and gravel. Slope failures may occur rapidly or progress slowly over a period of years. It is very important to understand rock failure mechanism and the many factors of the mode of rock failure in particular the nature of the applied stress and the nature of the rock. Twenty samples each were collected from each face of the study areas for the laboratory determination of mechanical and physical properties of the selected rocks. The determined mechanical properties are uniaxial compressive strength, point load index, Schmidt rebound hardness and shear strength while physical properties are dry densities, dry unit weight and porosity. Modelling of slope stability using RS2 software was carried out. Geological mapping was carried out to measure the orientations of discontinuities. DIPS 7.0 was used to performed kinematics analyses for mode of failure. Two major joint sets were identified each of the faces of Sagamu quarry with average orientations of   60 / 049 and   87 /134 for main face,   63 / 046 and   87 /138 for Lagos end while at Sagamu end three major joint sets were identified with average orientations of   88 /139 ,   17 / 276 and   60 / 047 . Two major joint sets were identified in the quarry face of Zibo FM with average orientations of   55 / 233 and   49 /186 for face 1 and   33 /178 and   39 / 220 for face 3. The shear strength parameters for the kinematic analyses were obtained using Roclab 1.0 from Rocscience. This gives friction angles of  26.16 ,  31.86 and  28.98 and cohesion of 3.187 MPa, 5.625 MPa and 4.148MPa for Sagamu main face, Lagos end and Sagamu end respectively. Zibo FM face 1 and face 3 have friction angles of  34.74 and  34.74 , cohesion of 10.808 MPa and 10.856 MPa respectively. The results of the stability analyses carried out show that the five quarry faces are exposed to only planar failure. The results of the relationship between rock properties and strength reduction factor indicate that when the value of the rock properties increase the shear reduction factors obtained from stability analyses also increase