Laboratory experiments were carried out to study erosional processes of landslide dam failure due to piping phenomenon with an evaluation of landslides and landslide dam triggered by 2011 Typhoon in Nara and Wakayama Prefectures of western Japan. Landslide dam models were built in a flume box with flume bed slope of 5°. To initiate piping, cylindrical pipe was laid in the dam at different horizontal and vertical locations. Four erosional stages were observed from the experiments. They include: appearance of wet spot/pipe development, continuation, progression, and breach. Stability and longevity of landslide dams due to piping were analyzed by varying heights of dams (HD), downstream slope angles, and horizontal positions of pipe. Results obtained show that stability and longevity of landslide dams depend on downstream slope angle, height and size of dams, and the erosive forces acting on the dam material. Results obtained from petrologic analysis of rock samples from the landslide and landslide dam sites show that the geomaterial of the areas are grain-supported which could lead to initiation of internal erosion and pipe formation.