Abstract：The occurring mechanism of unloading crannies during excavating soil-like material slopes is analyzed. It is shown that the excavation changes stress in the soil or rock masses，and during the excavation，an extra lateral stress in the direction to the slope surface will act on the slopes. The generation of new crannies and the splaying of existing crannies are attributed to the extra stress. The characteristics of unloading crannies and the influencing factors of their displacements are summarized through centrifugal tests in test chamber about the excavation in silt，clay，and completely weathered mudstone. From the tests，it is concluded that deformations of the existing crannies will increase with the accretion of its obliquity，depth and approaching to unloaded surface. The relations of stretch and obliquity of cranny，deformation modulus and angle to unloading direction of cranny are put forward The method of determining the width of unloading zones is presented for practical engineering projects，and feasibility of the method is proved through an application in the bank of Yangtze River in Chongqing City.
