الفهرس 
AcknowledgementOnly 14 pages are availabe for public view
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Abstract
Considering the importance of drain envelope materials for the efficient performance of subsurface drainage systems, a field study was carried out to evaluate the performance of some synthetic envelope materials in unstable soils in Haress pilot area. This area is considered to be representative for the soils of the fringes of Western Delta of Egypt.
Three locally made polypropylene (thick) sheet envelopes and one imported knitted (thin) sheet synthetic envelope were evaluated.The synthetic envelope materials were evaluated according to their mechanical and hydraulic functions.
The sedimentation height and the cross sectional area closed by sediments are the criteria that used to evaluate the mechanical function. The obtained results of the mechanical evaluation revealed that all the sedimentations that found inside the pipes of all the tested materials are insignificant and all the synthetic envelope types performed satisfactorily the mechanical function.
The head loss ratio, the entrance resistance and the resistance constant of each envelope material are the criteria that used to evaluate the hydraulic function. The obtained results of the hydraulic evaluation revealed that a significant difference was obtained between the local made thick envelopes and the imported thin envelope. The local made thick envelopes (pp360) and (pp290) give the best results followed by the local made thick envelope (pp310) while the imported thin envelope (sock 100) gave the worst results.