English：

Horizontal directional drilling is a trenchless technologywidely used in underground pipelinelaying. In recent years, the technology is continuously developed in the direction of large diameter andlong distance crossing. However, the increase of borehole diameter will significantly reduce the mud flowrate and weaken its rock carrying capacity, resulting in incomplete cleaning of boreholes,which will leadto engineering accidents such as pipe sticking, drill pipe fracture and even pipe laying failure. In order tosolve the problem of hole cleaning in the construction of large-diameter horizontal directional drilling, thehole cleaning performance of horizontal directional drilling mud is taken as the research object. Combinedwith the characteristics of large-diameter horizontal directional drilling engineering, the annular mud flowequations are established. It is found that the larger the diameter of the flow core area is, the smaller thepressure drop gradient is, and the better the hole cleaning performance is. Fitting the rheological modelof mud, it is found that the Herschel-Bulkley model can accurately describe the rheological properties ofmud, and the specific particle size of drilling cuttings can increase the dynamic shear force. Thenumerical simulation shows that the ratio of inlet velocity to annulus diameter can improve the holecleaning efficiency.