Rock Slope Stability of the Abu Ghaylan Formation under Varying Water ‎Contents and Slope Angles, Gharyan, NW Libya

Abstract

Road slope stability is affected by rock properties, slope geometry, weathering, and water infiltration. This study evaluates the stability of Abu ghaylanFormation outcrops parallel to the Abu Ghaylan mountain road in Gharyan, northwestern Libya, focusing on increasing water content. Field investigations documented slope geometry and surface conditions, while limestone samples were tested by direct shear under three water conditions corresponding to rainfall amounts of 5, 25, and 50 mm. Water contents were 9.15%, 14.7%, and 19%, respectively. Cohesion decreased from 18.23 to 12.50 and 8.34 t/m², while the friction angle decreased from 42.86° to 25.4° and 19.6%. These parameters were used in RocPlane analyses at slope angles of 85° and 40°. At 85°, the factor of safety decreased from 11.0027 to 6.66206 and 3.96693 with increasing water content. At 40°, the corresponding values were 29.143, 17.5742, and 10.4693, with zero calculated probability of failure. Increasing water content reduces resisting force and factor of safety, while the 40° slope is more stable. Recommendations include monitoring water conditions, removing rock debris, and constructing a concrete barrier.