Optimization Research on the Inpit Haulage System Development Under Open Pit and Underground Mining Conditions XIAO Cangyan1, GUO Liwen2, CHEN Shuzhao3 1College of Light Industry, Hebei Polytechnic University, Tangshan, hebei 2College of Resource and Environment, Hebei Polytechnic University, Tangshan, hebei 3China University of Mining and Technology, Xuzhou, Jiangsu