Effects of the attitude of dominant joints on the mobility of translational landslides

Abstract

Geological structures and ground undulation affect the mobility of translational landslides. Combining field investigation, back-analysis, and numerical simulation, we explore the role of dominant joint dip angle in controlling the mobility of translational landslides. First, the attitudes of the geological structures are revealed by aerial photography measurements. The pre-failure slope surface of the Wolong landslide, Southeastern Tibetan Plateau, is estimated from the contours of the adjacent stable hillslopes and the deposit bottom boundary. Then, to back-analyze cohesion and internal fraction angle of the landslide, we fit a maximum stable relief limit based on Culmann’s model to the upper envelope of 96 rock scars and 37 previously published landslides. Next, we design eight scenarios (S1–S8) for the simulation of landslide mobility, respectively, corresponding to the eight joint dip angles between 20° and 60°. The mobility index H/L increases with the dip angle β, as confirmed by the best-fit line H/L = 0.288 ln(β) − 0.698. The numerical results of the runout characteristics, velocity, and energy consumption of the simulated landslides in the eight scenarios indicate that (1) the momentum losses at slope break are closely related to the joint dip, apparent friction angle, and height of the mass center; (2) local undulations in substrate have an inapparent effect on mobility of large and long runout landslides; and (3) conventional mobility indexes need to be improved or modified when high mobile landslides encounter high obstacles at slope bottom, opposite hills, or mountains. This study will be useful for hazard evaluations of translational landslides in mountainous regions.