Tests of thick fiberglass filters for subsurface drains

A series of tests was made to evaluate the use of thick fiberglass materials as a substitute for gravel filters around subsurface drains and to study the effect of perforation spacing on inflow to filtered drain pipe.

From the results of the experiments and studies of the background information, the following is concluded:

Within the range of loading ordinarily expected under field conditions, the thickness of the fiberglass filter materials tested is greatly reduced from that measured in the uncompressed state. This change in thickness depends on (a) initial thickness, (b) initial density, and (c) to some extent, manufacturing processes.

The hydraulic conductivity of the fiberglass materials was high and essentially varied little with load or samples of different thicknesses and densities. All “K” values measured were within the range given by other workers for clean sands or mixtures of clean sands and gravels.

For ponded water conditions, inflow to a filtered drain is greater than that to a nonfiltered drain with a similar perforation arrangement. Inflow to the filtered drain was affected very little by perforation spacing, whereas inflow to the nonfiltered drain varied considerably. Experimental results were influenced by a time effect not related to perforation spacing.