Abstract: In the pipeline transportation of unclassified tailings slurry， the bottom of the slurry pipeline is worn out， which greatly affects the service life of the slurry pipeline. Based on the filling status of the L-shaped pipeline of a tailings slurry of an iron mine in Tangshan，the minimum pressure loss of L-shaped pipeline was taken as the principle to conduct study work.The filling slurry with the ratio of cement to sand ratio of 1∶4，1∶6，1∶8，slurry concentration was 54%，58%，62%，and the test was carried out at 3，5，7 m/s is the slurry flow rate.The pressure loss of the pipe diameters of 70，80，90，100 mm is calculated based on the 3D numerical model by using COMSOL Multiphysics numerical simulation software，besides that，the influence factors of pressure loss were analyzed and optimized.The study results show that the larger the diameter of the pipe，the greater the pressure of the 45° section，and the pressure loss of the L-shaped pipe is quadratic polynomial function；the diameter of the pipe is reduced to 70 mm or increased to 100 mm，which will accelerate the abrasion of the bottom of the L-shaped pipe.In order to extend the service time of the L-shaped pipeline in the mine and minimize the wear of the bottom of the pipeline，it is suggested that diameter of the L-shaped filling slurry conveying pipeline of the mine can be determined as 85 mm ，the slurry flow rate is 3 m/s，the cement-sand ratio is 1∶4 and the mass concentration is 64%.

Key words: fill mining, L-shaped pipe, pressure loss, numerical simulation, slurry transport, pipe diameter