Abstract Hydrotransport of solids through a pipe is a cost and energy efficient method to transport granular solid materials over long distances. A problem in the hydrotransport of fine particle slurries is the possible presence in the pipe of undesirable large materials, such as rocks or metal fragments broken off of shovels, which may enter the slurry pipe through breaks in screens. This large material can damage booster pumps and downstream equipment resulting in costly repairs and loss of production. Acoustic sensors along with signal analysis techniques can be used for online detection of oversized material in a hydrotransport system. Acoustic detection methods are ideal, since they are non-invasive and any probe located within the pipe would be unlikely to survive the harsh conditions present within the line. The objective of this study was to model the motion behaviour of large materials, such as rocks, travelling through a horizontal hydrotransport pipe. This information can then be used to determine optimum locations for the acoustic sensors to ensure that rocks are detected quickly and effectively.