Expansive clay subgrade soil improvement using municipal solid waste fly ash: Experimental and numerical approach

Abstract

The expansive soil under investigation has caused damage to lightweight structures due to its swelling and shrinkage characteristics in response to changing moisture content. The study aims to assess the impact of municipal solid waste (MSW) fly ash on the engineering properties of subgrade expansive soils and its influence on pavement structure deformation. The influence of municipal solid waste fly ash on expansive soils was evaluated using laboratory tests and finite element methods. The Abaqus software was used to investigate the effects of MSW fly ash on pavement structure deformation. The input parameters employed for this analysis were elastic modulus, Poisson ratio, load, contact area dimension, and pavement layer thickness. To mitigate this issue, MSW fly ash was used as a stabilizing agent at varying percentages (5 %, 10 %, 15 %, 20 %, 25 %, and 30 % of the dry mass of the soil sample).According to the AASHTO soil classification, the soil is classified as A-7, has a high free swell, a low soaked CBR value, and a high soaked CBR swell, and does not meet the ERA manual standard for subgrade materials. The laboratory tests shown several improvements in the engineering properties of expansive soil when MSW fly ash were mixed. These improvements included a reduction of soaked CBR swelling, free swell index, plasticity index, specific gravity, optimum moisture content. Additionally, the maximum dry density and soaked CBR values increased. Numerical analysis using Abaqus software focused on vertical deformation of the pavement structure. The results showed that as the percentage of MSW fly ash in form 0 % to 25 % of soil dry weight, the vertical deformation of the pavement structure decreased from 0.84 mm to 0.67 mm. This demonstrates that the addition of MSW fly ash reduced the deformation of expansive sub-grade soil and improved the engineering qualities of pavement structure. In conclusion, the study revealed that the use of MSW fly ash as stabilizing agent effectively reduced the deformation of expansive subgrade soil and improved the engineering qualities of pavement structure.