EVALUATION OF SIEVE AND PERMEAMETER ANALYSES METHODS FOR SUBSURFACE DRAIN ENVELOPE LABORATORY RESEARCH IN PAKISTAN

Properly designed gravel envelopes for subsurface horizontal drain pip es did not give satisfactory results in the Fourth Drainage Project (F DP), Faisalabad, Pakistan. Poor handling and placing of the granular e nvelopes were considered the main reasons for failure. This study inve stigates whether the failure was also because of the existing selectio n procedures for gravel envelopes or not. USER design criteria (sieve analysis) were used for distinguishing between the good and poor envel opes. Permeameter experiments for selecting the envelopes for subsurfa ce drain pipes based on these permeameter test results have now been s tarted at SCARF Monitoring Organisation (SMO) in collaboration with th e Netherlands Research Assistance Project (NRAP), International Waterl ogging and Salinity Research Institute (IWASRI), Lahore. A one-dimensi onal upward how permeameter with four rectangular perforated drain pla tes was used for testing the subsurface drain envelopes. Another hypot hesis for this study was to verify the methodology adopted in permeame ter experiments. The effects of sieve and permeameter analyses methods on selection of subsurface drain envelope selection is reported. Foll owing is a recommendation for comparing the permeameter test results o btained in Pakistan with those obtained in Belgium and Canada for worl dwide use. This paper also accomplishes the objective of distinguishin g between good and poor drain envelopes in a more simple way.