Performance-cost analysis of stabilized undercut subgrades

An approach for comparatively evaluating the performance cost of undercut subgrade stabilization measures is presented. The performance-cost analysis coupled results from laboratory cyclic load testing with material prices and estimated cost factors for stabilization alternatives. The study utilized data from 22 simulated undercut sections with different stabilization configurations over a soft subgrade with a California bearing ratio of approximately 2.0%. The computed cost factors are normalized with respect to the rut-depth magnitude and subgrade strength. Sections with lime-stabilized subgrade were the most economical with respect to initial and postrut repair cycles. Unreinforced aggregate based course (ABC) sections between 356 and 508 mm (14 and 20 in.) in thickness were economical during initial cycles. Sections with geosynthetic reinforcement showed that once enough rut depth is induced to mobilize the strength of the reinforcement, economical performance was comparable with other stabilization measures excluding lime-stabilized subgrade. When the ABC layer was thicker [between 457 and 508 mm (18 and 20 in.)], differences in the reinforcement type were less significant. Tests with 914 mm (36 in.) select fill overlaid by 76 mm (3 in.) ABC stabilization exhibited a high unit cost but were moderately economical. This study shows the advantage of including performance aspects, such as rut depth and subgrade strength, when considering the overall cost of stabilization.