This paper evaluates porosity changes in compacted soil subjected to acidic leachate percolation through different dry unit weights. The porosity of compacted soil is presented in different nominal porosities or dry unit weights (41.9% and 15.5 kN/m3, 43.8% and 15.0 kN/m³, and 45.7% and 14.5 kN/m³) percolated with a sulfuric acid solution under a constant vertical stress of 280 kPa. Porosity was evaluated via X-ray microtomography (μ-CT) and mercury intrusion porosimetry (MIP). The results demonstrated that percolation by a 2% sulfuric acid solution in compacted clay soil caused changes in pore size distribution, increased the pore diameter in all specimens’ layers, and increased the porosity in specimens’ upper layers due to acidic attack on the soil’s microstructure. The porosity assessed by mercury intrusion showed a good correlation with the macroscopically measured porosity. The same behavior was not observed via μ-CT due to the limited resolution of the images and the inability to characterize the micropores.