Study on pillar's plastic zone based on elasto-visco-plastic theory

To evaluate the long-term strength and stability of a pillar, the pillar's stress and displacement distributions and the width of visco-plastic zone based on elasto-visco-plastic theory and unified strength theory are presented theoretically in this paper combined with the concept of strain softening. The effects of several major factors, such as interface friction angle, pillar's compressive strength, underground pressure and the selection of yield criterion et al, on the width of visco-plastic zone are analyzed in detail. Some experimental results are explained. The proper size of pillar is discussed and several problems concerning mining methods are also pointed out.