In this work, 2D squat cohesive columns failing under gravity are simulated with the Contact Dynamics algorithm and a robust criteria is established to investigate the failure event in time and space by detecting the grains movement. To differentiate macroscopic flow motion from creeping motion, a cumulative displacement threshold is first defined for each grain. The grains whose cumulative displacement exceed this threshold are treated as “mobile” grains. We study the instantaneous number of grains exceeding the displacement threshold, by which a characteristic moment is defined as the initiation of the failure; the failure aging can be characterized. Next, the failure plane, the interface between the “mobile” grains and the “immobile” grains is plotted with time : We find that the time evolution of the orientation of the failure plane over time bespeaks different erosion efficiencies at the free surface and the bottom of cohesive granular step. Then we investigate the dependency between the height of the cohesive granular columns and the orientation of failure. The results are coherent with the experimental results found by Gans et al 2020.