Granular envelope research in Pakistan

In 1989, research on granular envelope design for subsurface horizontal pipe drains was started when existing design procedures for envelope design did not result in successful application of a granular envelope (crushed rock) material at the Fourth Drainage Project. Although construction problems were, in part, the reason for the failure of the crushed rock envelope, it was also found that standard design criteria need additional rules to prevent a similar occurrence of failure. Tests were performed in the laboratory with permeameters, sieves, and other equipment and preliminary results are reported. The effect of number, size and arrangement of perforations on the test results are indicated. Test results of blended granular materials such as crushed rock, river-run gravel and sand from various sources in Pakistan are outlined.Proceedings of 5th International Drainage Workshop, Lahore, Pakistan, ICID-CIID, IWASRI, 1992, Vol. III, 5.38–5.49.