INFLUENCE OF MINERAL TYPE AND DENSITY ON THE PERMEABILITY OF SUBBASE MATERIALS

Abstract

The permeability of granular material used in road construction has a significant effect on stiffness and pavement performance and therefore should influence the design thickness for base, subbase or capping layers. While designing these layers, particular attention should be given to providing adequate permeability and load bearing properties. Open gradings lead to high permeability and reduced stiffness while well graded material increases the stiffness and reduces the permeability. Open gradings with good drainage will also reduce frost heave and capillary rise. However, for construction purposes some fines are required. Keeping in view all the above factors, unbound granular material with grading envelopes ranging from open graded to well graded have been selected. A permeameter was built in accordance to the Department of Transport Highways and Traffic Advice Note HA 41/90. Laboratory investigations have been carried out using this permeameter to determine the horizontal permeability of base, subbase and capping layer materials under constant head and to study the effect of particle size distribution and maximum dry density on the permeability of unbound crushed aggregates used in flexible pavements. A significant relationship have been developed as a result of statistical analysis on material gradings, voids ratio and their corresponding permeabilities. Subsequently this relationship will be used to control the permeability from the material gradings for roads construction in Northern Ireland (U.K.)