Abstract: With the widespread application of the staged backfill mining method in mines，a deeper understanding has been gained of the stress state changes of the first-step filling body during the second�step ore room mining process. During the mining process，the stress state of the filling body changes from three-dimensional compression to two-dimensional compression，and mining disturbances are prone to cause the filling body to collapse and fail at the exposure surface. To address this issue，the failure mecha⁃ nism of the lateral exposure surface collapse was analyzed in depth，and the original filling scheme of the mine was optimized and regulated by adding control layers. Through the FLAC3D numerical simulation tech⁃ nology，the variation laws of the development of the plastic zone，stress field，horizontal displacement and exposure surface displacement of the single-sided exposure cemented filling body with control layers under the condition of a main body sand ratio of 1∶9 were studied in detail. At the same time，the safety of the filling scheme was analyzed. The research results show that under the unilateral exposure condition，the filling body generates longitudinal cracks under the vertical stress，thereby deteriorating the performance of the cemented filling body. The introduction of the control layer can effectively reduce the formation of the plastic zone by 19.2%，and by blocking large-scale plastic zones，it effectively reduces the deforma⁃ tion and failure of the filling body. In addition，the application of the control layer makes the filling body with a main body sand ratio of 1∶9 have similar overall strength to the filling body without a control layer with a sand ratio of 1∶8. This technology not only successfully controlls the failure of the unilateral open faces，but also enhances the stability of the filling body，reduces cost.

Key words: cemented filling body, single-sided exposure, control layer, numerical simulation