Slope factor of safety during road construction

Abstract

Road construction is one of the longitudinal geological-geotechnical works that may consider thousands of kms, where a diversity of embankment slopes and cut slopes are made to implement the way of the desired road. Due to the heterogeneity and variability of the geological and geotechnical surroundings, local slope instabilities are a common geotechnical hazard. To minimize the economic impact and the unavoidable delays due to such happenings it is very important to plan ahead an observation system that insures a safe road construction. One of the key instruments to install is the inclinometer that is used to monitor the evolution of horizontal displacements at specific locations and depths. The purpose of this study is to generalize the procedures developed in 1995 by Salgado (1), assuming initial horizontal ground conditions, to estimate the local factor of safety value at the location of specific inclinometer measurements, to a more realistic and common condition where initial sloping ground conditions prevail. The procedures follow the original work (1) where the boundary conditions between two consecutive inclinometer readings, in depth, are associated to the boundary conditions of the simple shear test. By comparison with the simple shear test results it is possible to assess a factor of safety value based on the level of the shear strain estimated from the inclinometer readings. To extrapolate to different confining stresses the procedures were expanded in 1997 by Carvalho (2) and optimized in 1998 by Salgado & Carvalho (3) considering the hyperbolic stress-strain model formulation. To extrapolate to initial slope ground conditions, new procedures were developed by Salgado (4, 5) to take into account the initial static bias imposed by the in situ sloping ground.