Lime stabilization to improve clay-textured forest soil road subgrades

Lime is the oldest known traditional soil stabilizer, especially for clay soils. In the Hyrcanian forest in northern Iran, clay-textured soils are widespread and cause many problems for infrastructure development, particularly forest roads. Therefore, the current study investigated the stabilization effect of different percentages (5%, 7%, and 9% by weight) of lime on a typical clay with high plasticity. Laboratory tests were Atterberg limits, standard Proctor, and unconfined compressive strength (UCS) and were used to determine the extent of stabilization. Lime decreased the liquid limit and plasticity index, but increased the plastic limit. The greatest decrease in liquid limit and plasticity index was 48% and 94%, respectively, for the 9% lime treatment and the greatest increase in plastic limit was approximately 39% when 7% lime was added. Furthermore, the greatest decrease in maximum dry density was 5% with the 9% lime addition and the greatest increase in optimum moisture content was 9% when lime was added at both 5% and 7%. Lime treatments generally had a positive effect on soil compressive strength, except when added at the 7% rate. At 7% lime, compressive strength decreased as compared with the control soil. The best improvement in soil strength was achieved with 9% lime treatment; with a 39.45 kN/m2 (6%) increase in the strength. Based on these laboratory findings, lime can improve the engineering properties of expanding clay soils in a forest road. However, further field studies are necessary to determine if the effects of our laboratory study are similar to road subgrades.