Effect of Granular Layer Properties on the Stabilisation of Weak Subgrade with Geosynthetics

Weak and soft subgrades present significant challenges for road pavements construction and conventional stabilization methods have become outdated due to environmental and economic concerns. The use of geosynthetics has become increasingly popular as a sustainable technique for subgrade improvement. However, limited research has been conducted focusing on the quantification of factors affecting on the stiffness improvement of weak subgrades with a granular layer and composite geogrids. This study focuses on examining the effect of gravel type on subgrade stabilization using model box tests conducted in a scaled model pavement steel box measuring length, width, and height as 1 m, 1 m and 1.2 m, respectively. The subgrade condition was kept constant for all tests and constructed to a thickness of 500 mm, maintaining CBR value as 2.5%. The gravel “Type 2.1 and Type 2.5” specified as the best and lowest quality gravel in “MRTS05- Unbound pavements” were used in 200 mm thick gravel layer for each test, respectively. Composite geogrid was placed at the gravel-subgrade interface in these tests. All the tests were subjected to a monotonic load applied on the top surface using a 200 mm diameter circular plate until reaching the point of ultimate failure obtaining parameters; vertical deformation and stress distribution to analyze the load bearing capacity and stiffness. The outcomes of the study verified the effect of granular layer properties on designing stabilized subgrades with geosynthetic reinforcement.