Lithological heterogeneity in sedimentary rocks and its impact on the stability of hillsides and slopesThe present work seeks to understand and comprehend the role of physical weathering by slaking in soft sedimentary rocks, which are part of a lithological heterogeneity. In many cases, slaking progresses with time and is imperceptible to the professional but when an external agent acts by overcoming the resistance of weathered material, it can generate very important stability problems.The investigation was in development at the Los Ajos mine owned by Ladrillera Santafé S.A.S, which is found localizate inside of Bogota formation. Within the mine, two slopes were selected in claystones that show the process of physical weathering by slaking; however, its development and preservation over time is different based on the external factors that interfere with it.With the aim to understand how the process of slaking evolves and comprehend its incidence in the stability of each of the slopes, monitoring was carried out on each slope by placing checkpoints on the face of each slope. At these points, deformation measurements were made on during expansion and contraction cycles on the slope face and in furrows with great progress to understanding the slaking process. In addition, geomechanical and mineralogical characterization of the degraded claystone and slightly weathered claystone were carried out.Based on the geomechanical characterization and mineralogical composition of the claystone of each slope, thicknesses of material affected by the slaking process were established and the following parameters were proposed: slaking intensity for Slope 1 and erosion-transport-deposition rates for Slope 2.

The mechanical behavior of rock containing parallel non-persistent joint sets was studied using a numerical model. The numerical analysis was performed using the discrete element software UDEC. The use of fictitious joints allowed the inclusion of non-persistent joints in the model domain and simulating the progressive failure due to propagation of existing fractures. The material and joint mechanical parameters used in the model were obtained from experimental results. The results of the numerical model showed good agreement with the strength and failure modes observed in the laboratory. The results showed the large anisotropy in the strength resulting from variation of the joint orientation. Lower strength of the specimens was caused by the coalescence of fractures belonging to parallel joint sets. A correlation was found between geometrical parameters of the joint sets and the contribution of the joint sets strength in the global strength of the specimen. The results suggest that for the same dip angle with respect to the principal stresses; the uniaxial strength depends primarily on the joint spacing and the angle between joints tips and less on the length of the rock bridges (persistency). A relation between joint geometrical parameters was found from which the resulting failure mode can be predicted.

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