Question

The hydraulic sand stowing pipeline layout should be such that

• A. the geometric profile must coincide with the hydraulic gradient line.
• B. the hydraulic profile should always be below the hydraulic gradient line.
• C. the hydraulic profile should always be above the hydraulic gradient line.
• D. the geometric profile should always be above the hydraulic gradient line.

Hint:

Always keep the pipeline below the hydraulic gradient line to maintain positive pressure and avoid slurry deposition.

Answer 1

The Correct Option is B

In hydraulic sand stowing, the flow of the sand-water slurry through the pipeline depends entirely on maintaining a continuous downward energy gradient. This gradient is represented by the hydraulic gradient line (HGL), which shows the pressure head available at every point along the pipe. For flow to occur without interruption, the pipe profile must always lie below the HGL. The reason is rooted in fluid mechanics: slurry flow in long pipelines experiences major head losses due to friction and minor losses due to bends, valves, and fittings. If the pipe rises above the HGL at any point, the pressure head becomes insufficient to sustain movement. When the available head falls below the critical value needed to overcome both elevation and frictional resistance, the flow velocity decreases abruptly. A velocity drop below the critical deposition velocity leads to rapid sedimentation of sand particles inside the pipe, forming a bed layer that thickens over time. This leads to choking of the pipeline, pipeline vibration due to intermittent movement of slurry, and a complete failure of hydraulic stowing operations. Clearing such blockages is extremely difficult and costly. Thus, the proper engineering principle is that the hydraulic profile (actual pipe elevation) must remain entirely below the hydraulic gradient line so that there is always positive pressure head along the pipeline. This ensures continuous, stable, non-depositing flow and prevents operational hazards. Therefore, option (B) is correct.