Entrance resistance of plastic drain tubes

J. Wesseling, F. Homma
1967 Netherlands Journal of Agricultural Science  
The entrance resistance of plastic drain pipes with various amounts of longitudinal slits and covered with certain filter materials has been measured in a vertical sand tank model. It became apparent that the influence of an increasing amount of perfo rations on the lowering of the entrance resistance lessens at high perforation amounts. In general, a decrease of the entrance resistance can be better obtained by means of larger pipe diameters than by increasing the amount of perforations. For
more » ... perforations. For practical applications, a 4 cm pipe with 1 sheet of glass fibre requires about 450 mm 2 of per forations per running meter. The application of a single sheet of glass fibre has already a very favorable effect on the entrance resistance of the drains. This effect has to be ascribed to the devel opment of a more permeable layer rather than to its effect as a filter. Increasing the thickness of the filter (assuming it will retain its high permeability under field condi tions) will be more effective in decreasing the entrance resistance than increasing the pipe diameter. Some examples from practice show that, with the use of 4 cm pipes having 2 rows or 450 mm 2 of longitudinal slit perforations and covered with one sheet of glass fibre, the extra loss of head due to the entrance resistance is in most cases negligible. Only when the hydraulic conductivity of the backfill of the trench is low (about 10 cm/ day) this will not be the case. In such circumstances it is advisable to use a thicker filter or a larger pipe diameter. \ x \
doi:10.18174/njas.v15i3.17436 fatcat:w6rjm43wd5gq7elovg6dt6reym