Research on non-full pipeline flow transportation and prevention method of coal gangue cemented backfill

The coal gangue cemented backfill slurry has high quality concentration.If the pipeline layout and transportation parameters are unreasonable,non-full pipeline flow and pipeline transportation failures are likely to occur during the backfilling process.In order to clarify the causes and hazards of non-full pipeline flow of coal gangue cemented backfill pipelines,corresponding prevention measures are proposed,combined with the practice of gangue high-concentration backfill slurry pipeline transportation,a pump-backfill pipeline transportation model is established.Based on the basic theory of slurry pipeline transportation,the causes of the non-full pipeline flow are studied,and the theoretical discriminant of the dissatisfied pipe flow state is proposed.According to the movement characteristics of the slurry in the process of dissatisfied pipe flow,the effect of dissatisfied pipe flow on the pipeline transportation system was discussed.Combining case analysis,the prevention and treatment methods of the non-full pipeline flow status are analyzed and proposed.The results show that the main factors affecting the transport state of the filling slurry are the backfill flow rate,the geometric parameters and layout of the pipeline,the rheological properties and density of the slurry.During the transportation process,the filling slurry and the transportation parameters are unreasonably matched.At the top of the vertical drilled pipe,the high-concentration slurry will break off and change from one continuum to a discontinuity,resulting in a non-full pipeline flow status in pipeline transportation.With the further development of the slurry pull-off zone,an empty pipe section appears on the upper part of the vertical drilled pipe and presents a certain degree of vacuum,which is in a negative pressure state.The backfill slurry changes from a solid,liquid two-phase flow state to solid,liquid and gas three-phase flow state.The change of the slurry state deteriorates the stability of the filling pipeline transportation,and has obvious impact and harm on the pipeline transportation system,including "water hammer" impact,erosion and wear on the pipe wall,horizontal pipeline vibration,slurry siltation clogging,and filling pump damage.In order to avoid the occurrence of pipeline flow dissatisfaction,the vertical drilling position should be selected reasonably during the pipeline construction.In the actual filling work,the slurry concentration can be appropriately increased or the inner diameter of the non-main pipeline can be reduced to increase the friction resistance of the pipeline to maintain the state of full pipe flow of slurry.