Transport of large solids in sewer pipes.

This paper presents a method for determining the conditions under which large solids (i.e., solids with a vertical dimension greater than the depth of water) are able to move in a pipe. Depending on the value of a dimensionless number [s(d/y) - 1], where s 5 specific gravity of the solids, d = water depth, and y = height of solids, motion will occur if a sufficient velocity (also reported as a Froude number or modified "solids" Froude number) is exceeded. Flume experiments were used to determine the coefficients to be used in the design. The velocity required to reach fluid movement was approximately 0.6 to 1.0 m/s (2 to 3 ft/s), which is consistent, although slightly higher than values generally used in conventional sewer design practice. However, it was demonstrated that increasing the pipe slope to achieve a higher velocity does not ensure that the solid will move. Water Environ. Res., 81, 709 (2009).