School of Mining，Liaoning Technical University，Fuxin ，China

In order to solve the difficult problem of optimizing the morphological parameters of soft rock open pit slope in composite coal seam, based on the understanding of the key factors affecting the stability of slope, a method of combining rigid limit equilibrium software and FLAC3D numerical simulation software was adopted. From the top-down level of horizontal formation, a stage-by-stage optimization method for the sloped layered slope parameters is proposed. The method is applied to the northern slope of No. 1 Baiyinhua open-pit mine. It is optimized in four stages to study the spatial pattern of the soft rock open pit slope of the composite coal seam in the northern part of the mine. The results show that the landslide mode of the northern slope of the No. 1 Baiyinhua open-pit mine is a cut-sliding slip with the shear arc as the side interface and the weak layer of coal seam top and bottom as the bottom interface. The bottom slope of the weak layer above the coal floor is 12°, the width of Stage 1 slope platform is 25 m; the angle of step slope above the weak seam of coal is 22°, the width of Stage 2 slope is 30 m; the angle of step slope above weak seam of the No. 3-1 coal floor is 15°, the width of Stage 3 slope flat panel is 54 m; the angle of step slope above the weak seam of No.3-2 coal floor is 14°. The width of the flat plate of Section 4 is 25 m; the ultimate design slope angle of the northern slope is raised from 13° to 15° from the original design. The amount of coal to be mined is 4.43 million tons, and the amount of multi-stripping rock is 1.67 million m3. The research results can be used to optimize the design of the slope parameters of the composite coal seam soft rock open pit mine, to make up for the lack of slope angle caused by the traditional method design and to maximize the economic benefits.

国家自然科学基金资助项目（51874160）；辽宁省高等学校创新团队支持计划资助项目(LT2018008)；辽宁省高等学校创新人才支持计划资助项目（LR2016039）