Horizontal/Subsurface Infrastructure & Transportation

Sub-base course main function is drainage in a flexible pavement combination, but it has fines passing Seive no 200 up to 15 percent of the sample size. Would it still be a drainage or permeable layer? 

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Ejaz Khan S.M.ASCE
Director
Pakhtunkhawa Highways Authority
Islamabad
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The thickness of sub-base can range from 75 to 100 mm (3 to 4 in) for garden paths through 100 to 150 mm (4 to 6 in) for driveways and public footpaths, to 150 to 225 mm (6 to 9 in) for heavy used roads, and more for highways.

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Mohd Imran Aff.M.ASCE
Afzalgarh
9191 9540059257
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The rest of the gradation is also important.  Is the material well-graded or poorly graded?  A poorly graded material will drain faster than a well-graded material.  Well-graded materials tend to be stronger than poorly graded materials.

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Todd Lorenzen P.E., M.ASCE
Principal/President
Missoula MT
(406)830-0633
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The total gradation of the stone is important in determining if water will percolate through the material. There must also be someplace for the water to go once it reaches the bottom of the layer or you will have created a bath tub.  You need interconnected voids in the stone and sub-drains to provide a working system.

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DeWayne Heintz EI, A.M.ASCE
Project Manager
L.L. Pelling Company
North Liberty IA
(319)626-4600
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