Identifying the effect of subgrade layer thickness of soil stabilized with waste foundry sand and fly ash on bearing capacity

The issue of subgrade soil often involves unstable soil properties, such as low bearing capacity, susceptibility to expansion and shrinkage, and vulnerability to erosion and deformation due to traffic loads and weather conditions. Unstable subgrade soil can cause various infrastructure problems, including cracks, settlement, and damage to road surfaces. Therefore, stabilizing subgrade soil is an important step to ensure the reliability and longevity of highways. One effective and sustainable method for subgrade soil stabilization is by utilizing local waste materials. The use of local waste materials such as fly ash (FA) and waste foundry sand (WFS) not only improves the physical and mechanical properties of the soil but also helps reduce environmental impact by repurposing pollutants. This study aims to analyze the effect of the thickness of subgrade layers stabilized with FA and WFS on bearing capacity. The initial stage includes examining the physical and mechanical properties of natural soil and soil stabilized with FA and WFS. The waste content used is 9 % FA and 15 % WFS by dry weight of the soil. Subgrade modeling was conducted using a steel box measuring 60×60×60 cm with a soil thickness of 30 cm. Load testing was carried out on 5 layer variants that had undergone 4 days of curing. The study results found that the ultimate bearing capacity (qult) of 890 kPa was produced by the V4 layer, which is a subgrade with a 30 cm thick layer of soil stabilized with FA and WFS at a settlement of 6 mm. The bearing capacity ratio of 2.87 means that the subgrade with a 30 cm thick layer of soil stabilized with FA and WFS experienced an improvement in bearing capacity of 2.87 times that of the subgrade with untreated soil material. The results obtained can be applied in practice to the local geotechnical conditions of the project site in West Java, including natural soil properties and seasonal changes