The objective of this study is to measure the effect of Aggregate Base Coarse class A (BCA) gradation to permeability. In order to achieve this objective, an analysis related to the effect of compaction to gradation changes was conducted. In addition to analyzing the influence of average diameter (D₅₀) to horizontal permeability coefficient (k_h) and analyzing the influence of gradation coefficient (C_c) and uniformity coefficient (C_u) to k_h. The materials used were the BCA from Mount Kayangan and Katunun, South Borneo, and were compacted based on the OMC. Various mixed gradations were referred to the specifications of Bina Marga 2010 3^rd Revision. The method employed in this study was laboratory-scale permeability test with horizontal flow direction using fabrication equipment which calibrated by sand samples. Sieve analysis test was conducted after the compaction and permeability testing in order to measure the actual granules after the compaction.

The result of this study showed that the actual gradation would expand from the specification after the compaction due to the different abrasion values. Therefore, a design for reverse specification was required with expectation that the gradation would shrink into the specification. The equation y = 0.00018x² – 0.02674x + 0.95229 could be used for reverse gradation curve design. The average diameter (D₅₀) influenced the horizontal permeability coefficient (k_h). From these two materials, the graphics showed that the increase of D₅₀ was followed by the gradual increase and decrease of k_h and reached its maximum under condition of optimum D₅₀. Nevertheless, the gradation coefficient (C_c) and uniformity coefficient (C_u) did not significantly influence the horizontal permeability coefficient (k_h). BCA granular gradation affected the drainage quality. According to Holtz & Kovacs (1981) most of the researches showed bad quality of drainage, yet some were considered having good quality of drainage. Granular gradation that were restrained by Sieve No. 40 tended to have the highest permeability coefficient, i.e. 5.52 x 10^-2cm/s. During field implementation, with 3% slope of BCA surface on road class 1 with 7m width and 3.5m length of water trajectory, the puddles would disappear in 2.45 days. According to AASHTO (1993) the drainage was categorized as good to moderate quality.

Keywords: Aggregate Base Coarse class A (BCA), horizontal permeability, variation of gradation, abrasion.