Calculation model on the mud dosing amount for backtow drag reduction in horizontal directional drilling

In backtow operation of HDD crossing pipeline, residual buoyancy of mud imposed on backtow's pipelineoften generates a squeezed extrusion contact between pipeline and sidewall, and accordingly results in an increase inpipeline frictional drag and negative impacts on smooth engineering implementation. This paper studies stress state ofbacktow pipeline. The main study method is to construct a force model for bending/straight pipeline sections and analyzeand calculate the forces using the model. It puts forth a functional relationship between mud dosing amount and pipelinebacktow time, realizing dynamic adjustments of mud dosing amount in the backtow process of large-diameter pipeline. Incases analysis, the calculation results of the functional relationship enables operator to balance the residual buoyancy of mudimposed on pipeline, reduce pipeline drag resistance, and further provide sufficient theoretical basis and proposals to thepipeline backtow process.