Abstract

The highway designers prefer using open-graded, highly permeable layers to overcome the problem of drainage adequacy (Nchrp 1998). So the material specifications should be checked to assure that Hydraulic conductivity, strength, load-distribution, and construction stability requirements are met. The present work purposes is to accumulate main factors effecting on predict the coefficient of Hydraulic conductivity of different stratification layers and gradation of granular materials used as base and subbase courses by constant-head Hydraulic conductivity tests, within the range of validity of Darcy's law for laminar flow condition. Three types and other four types of sand-gravel mixtures are selected as base and subbase course respectively, locally available and currently used in Iraq as pavement construction materials, brought from Al-niba’i quarry near Baghdad, conform to the general specification for road and bridges (SORB, 2003), which based on the BS, AASHTO, or ASTM specifications in gradation and physical properties. Set up depending in this work, comply with Darcy law for laminar flow with porous media and comply with the requirements of ASTM D2434 and AASHTO T215 for determining of Hydraulic conductivity of the granular materials (Al-saoudi and Shubber, 2008, 2012). Where, granular material was speared in layers with compaction sequentially, confirm with required void ratio percent. Water starts to covering prepared sample gradually and slowly until reach 20 cm height above it, then samples left for 24hr to ensure saturation. A hydraulic gradients create of (i= 0.2, 0.25, and 0.3). The rate of flow was checking each 20 sec, constant rate indicating the validity of the steady state flow. The samples were tested at different voids ratio (e1/e2= 0.6, 0.75, 1.0, 1.25, &1.5) and thickness percent (T1/T2= 0.5, 0.66, 1, 1.5, 2) for stratified layers.