This study examined the behaviour of two completion aggregates that were placed on a silty sandy formation material and subjected to repeated loading in a large-scale testing rig. The completion aggregates were (i) a good quality limestone, and (ii) a poor quality schist, and are used in the construction of unbound forest roads in Ireland. The schist was tested on its own and in combination with the completion limestone aggregate for up to 150,000 load applications with a maximum loading pressure of 1000 kPa. Measurements of surface deflections and formation pressures were made during each test. A combination of a 200 rum layer of the limestone aggregate placed on top of a 250 mm layer of the schist aggregate produced the lowest permanent deformations, resilient deflections, and resilient pressures under dry and wet undrained conditions. (C) 2009 ISTVS. Published by Elsevier Ltd. All rights reserved.