This study conducted an experimental and numerical investigation on the stabilization of clayey subgrades using nano-silica and geogrid reinforcement. Nano-silica was incorporated in varying contents (0-4%) to assess its effects on Atterberg limits, compaction behavior, shear strength, and California bearing ratio. The results showed optimal performance at 2.5% nano-silica, with reduced plasticity index and enhanced dry density, cohesion, friction angle, and bearing capacity. A three-dimensional finite element model was developed to simulate subgrade behavior under cyclic loading, incorporating the effects of both nano-silica and geogrid layers. The model was calibrated using laboratory data to reflect observed settlement and stress distribution. The numerical results confirmed that nano-silica reduced settlement significantly up to the optimal content, while geogrid reinforcement further enhanced load distribution and reduced displacement. The combination of nano-silica and geogrid resulted in improved mechanical performance of the subgrade. These findings demonstrate the effectiveness of integrating chemical stabilization and mechanical reinforcement in clayey soils to improve structural capacity and reduce long-term deformation, providing a viable solution for pavement subgrade enhancement.

Road infrastructure plays an important role in strengthening transportation and driving the economic advancement of countries. However, the increasing traffic volume has accelerated road deterioration, particularly at critical points like bridge-road junctions. Traditional repair methods involving demolition and reconstruction lead to extended closures and high costs. This study explores the polyurethane (PU) foam injection technique as an alternative solution, which can reduce both repair time and costs. The research evaluates the application of PU foam in various road projects across Thailand, highlighting its ability to repair pavement surfaces and structures, even in severely damaged areas. Despite its advantages, the use of PU foam faces challenges due to a lack of standardized quality control. This paper proposes a set of working guidelines for PU foam injection, aimed at key stakeholders such as the Department of Highways, the Department of Rural Roads, and the Department of Local Administration. The findings underline the importance of establishing standardized methods to ensure the long-term effectiveness of PU foam in road maintenance. Future research should focus on refining these guidelines for diverse road conditions to support the sustainable development of national transportation infrastructure.