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Exercise F - Changing Uplift Pressure by Changing
Length of Flow Lines
The pressure at any point along a flow line, and for that matter, pressure at any point
along the submerged perimeter of a structure, changes with any change of the
overall length of the flow line. This fact is often used to reduce the uplift pressure on
structures by stretching out the flow lines. This can be done with vertical or horizontal
impermeable membranes (aprons). In most instances these are located upstream of
the structure.
The influence of the flow line length on uplift pressure can be easily demonstrated. In
Exercise E - Uplift Pressure on Foundation of Structures
, simply change the depth of
penetration into the sand of the impermeable vertical screen.
For each of several depths the uplift pressures registered in the standpipes can be
recorded and the flow lines visualised in the ordinary way.