A Numerical Modelling Approach for Designing of Capping Layer on Weak Subgrades with Geogrids

Abstract A capping layer is a conventional mechanism used to stabilize weak subgrade, particularly in platform design in the pavement industry, facilitating the operation of heavy machinery. The thickness of the capping layer depends on the in-situ CBR strength and the target strength and stiffness properties of the working platform. Geogrid reinforcement in subgrade stabilization has emerged as a sustainable solution, reducing the demand for quarry aggregates by decreasing the thickness of the capping layer. However, designing the capping layer on a weak subgrade when the strength is below 5% of California Bearing Ratio (CBR) is difficult since conducting laboratory tests to investigate the properties of the weak subgrade proves challenging due to its poor workability and inconsistent behaviors. Therefore, this study used numerical analysis to assess the strength and stiffness with the parameters load bearing capacity and strain modulus of stabilized subgrades with a capping layer and, with and without geogrid in the interface of the subgrade and capping layer. The investigation focused on exploring different subgrade properties, considering various CBR values below 5%, and altering the thickness of the granular capping layer. To validate the developed numerical models, experimental data from large-scale model box tests were employed. The obtained results were further analyzed to introduce an efficient and effective mechanism for designing a capping layer thickness with and without geogrids, based on the subgrade strength conditions. The design curves are ultimately applicable to optimizing capping layer design on the weak subgrade of CBR below 5%.