Abstract: Understanding the interactions between pillars and backfill is an important issue for optimization and safety design of the backfill body and pillars. The effects of the lateral stress and the backfill ratio on the interactions between the pillar and backfill were studied by biaxial compression tests. The result showe that when the filling body meets the roof， it can bring its own strength into full play and directly participate in the roof support. At this time， the bearing capacity of the pillar-filling body support system can be maximum；when the filling body does not touch the roof， that the support force of the pillar-filling body increases under the action of a certain lateral stress are mainly due to the friction between the two interfaces. The lateral confinement effect of the backfill body has not an obvious impact on pillar strength. Therefore， a higher filling rate means a larger contact area at the pillar-filling interface， and a greater frictional force at the interface will be generated under a certain lateral stress， resulting in a greater bearing capacity of the system. By comparing the experimental results with the test results in Xincheng Gold Mine， it is proved that this study has certain guiding significance for the stability analysis of the second-step stope in Xincheng Gold Mine.

Key words: Cemented backfill, Interaction, Loading unit, Pillar, Frictional force