Abstract: The erosion and bank collapse of soil bank slopes is currently the most prevalent and increasingly severe disaster problems in mountainous reservoir areas, and developing a geomechanical model for this event is the key to prediction and prevention of such disasters. This study constructs an erosion and bank collapse geomechanical model for simulating the soil bank slopes under erosion－through a combination of field investigations, theoretical analyses, laboratory geotechnical tests, and model tests－and applies it in a case study of the Wushan - Badong section of the Three Gorges reservoir area. We have found that the modes of soil bank collapse in the reservoir area can be clarified as two major types－collapse-slip and progressive erosion. Using the data of typical cases, we examine and summarize the characteristics of bank collapse and material composition of the two types. This model is validated under the conditions of the two collapse types with wave action. The results show that for the two types, the model predictions agree with our field observations, verifying the model￠s applicability and reliability. For the collapse-slip type, local wave scour niches are generated first; As these niches develop and come to connection, the bank slope under gravity collapses or slides eventually. In the case of progressive erosion failure, wave erosion niches are also formed in the initial stage due to wave scour. As the eroding process accelerates, wave abrasion eventually dominates. This study lays a basis for further study aimed at prediction and prevention of the bank collapse disasters in reservoir areas.

Key words: Three Gorges Reservoir area, geological hazard, bank collapse, geomechanical model, model test