The expansion of abandoned bamboo stand in the southern-western region of Japan is remarkable. In September 1998 in Kochi city, due to the heavy rainfall, on the slopes surrounding Kochi city: many slope failures and debris flow have occurred. At almost 1/3 site of disasters, bamboo stands were found very close to the site or on that point, and the bamboo stands seemed to have important role on the sediment related disasters.
Researches on the relation between the expansion of bamboo stand and the sediment related disasters are very few, though authors have the conviction that, in the near future, the bamboo and bamboo stands will cause one of the severe problems in the sediment related disasters. Once the bamboo slope is cut for the cultivation or another agricultural usage or house building at the foot of the slope, having the root-mat system good permeability, the infiltrated abundant rainwater through root-mat system will cause severe erosion and induces the slope instability. Authors have investigated the soil of the bamboo stand in the laboratory and executed the penetration test in-situ and subsequently, proposed three failure models of bamboo. These models will be useful for the treatment of the abandoned bamboo stand and for the measures of the instable slope on which bamboo grows.