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Highway drainage designs generally have been based upon empirical rules, and only in recent years has the importance of obtaining permeability data on granular materials been stressed for the design of sand drains and blanket courses used in embankments for assisting in the removal of water by consolidation of the subsoils. In 1952, the Bureau of Public Roads published a report on highway subdrainage. The report did not establish design criteria but it did present test methods, a new type of low-head drainage-lag permeameter, and data on the permeability and drainability of soils and their applications to highway subdrainage. This paper presents additional test data and information on the above-mentioned drainage-lag permeameter for the measurement of permeability coefficients of open-graded granular materials. Comparisons are made between the coefficients of permeability obtained by this device and an ordinary falling-head permeameter for eight gradings of granular material. The results of these tests indicate that the drainage-lag type of permeameter minimizes turbulence in permeability testing and can be used to measure higher permeability values than the ordinary falling-head type of permeameter.
Yemington, E. G.
Highway Physical Research Engineer, Bureau of Public Roads, Washington, D. C.,