<p>Granular material for underdrains should be clear crushed 50 mm diameter stone graded in accordance with ASTM D 2940. The void space ratio shall be 0.4 .</p> | <p>Granular material for underdrains should be clear crushed 50 mm diameter stone graded in accordance with ASTM D 2940. The void space ratio shall be 0.4 .</p> |