Experimental and Cost Analysis of the Stabilization Techniques for a Tunnel Section of the Topcam Highway

The objective of this study is to compare the effectiveness of traditional high-calcium lime and a commercial ammonium chloride-based additive Consolid system (Consolid444+Solidry) in stabilizing high-swelling bentonite clay for subgrade improvement. The study examines a 400 m tunnel section of the Ordu–Ulubey Intersection–Topcam Highway in northern Türkiye. Clay was treated with 5%, 7%, and 10% lime and 1%, 2%, and 3% Consolid system by dry weight of soil. The geotechnical properties analyzed include consistency limits, compaction characteristics, swelling potential, linear shrinkage, unconfined compressive strength, and undrained shear strength. Additionally, the California bearing ratio (CBR) test was performed to evaluate the load-bearing capacity. The effects of curing time and freeze–thaw cycles on strength, as well as deformation properties through consolidation and resilient modulus tests, were also assessed. Triaxial compression tests were used to determine changes in cohesion and friction angle. The study further evaluates the implications of stabilization methods for pavement design, considering pavement layers and the associated direct construction costs. Results show that the Consolid additive is more effective than lime in enhancing CBR strength, providing faster strength improvement and a more significant decrease in void ratios, although lime remains more cost-effective.