Lessons from Revisiting Three Cases of Slope Failure

Three old failures of geotechnical projects are analyzed, where some original design uncertainties were lately discovered. The first case concerns the failure during construction of a slope at the portal area of a tunnel in Greece, due to unexpected excessive water pressures. The failure was restricted to the upper weathered zone of flysh formation. Due to difficulties in performing laboratory tests with such hard soil material necessitated the estimation of shear strength parameters on the basis of the rockmass classification systems. The next case deals with an extensive failure of an open pit mine slope in Greece. The ground consists of alternations of lignite layers with very stiff clay. Despite the detailed investigation on the peculiar nature of shear strength, the unavoidable scatter of the values in combination with the applied low safety factors and the development of excessive pore pressures, lead to this failure. The last case refers to the well known failure in Kimola Canal and addresses the probable failure mode and the proper analysis method. The analyses of the slope stability in formation of post glacial clays had been carried out with φ=0 and the use of undrained shear strength. The failure surface was developed upwards to a great distance and it could interpreted on the basis of the effective stresses analyses, taking into consideration the influence of the shear strength anisotropy