A study on the impact Soil degree of Compactness on Soil Physical Quality index for Soils with varying gypsum content

Laboratory experiments were conducted to study the impact of soil compaction degree (DC%) defined as the ratio between natural bulk density (BD natural) and critical bulk density (BD critical) on Soil Physical Quality index (S-index) for seven soil samples with different gypsum content 61.1(G1), 104 (G2), 151 (G3), 214 (G4), 279 (G5), 363 (G6), and 414 g kg⁻¹(G7). The water retention curve for each soil sample was determined at matric suctions of 0, 3, 8, 33, 200, 500, 700, 1000, and 1500 kPa after compacting the soil samples to bulk densities of 1.3, 1.5, and 1.7 Mg m⁻³. The physical soil quality index (S-index) was calculated using the van Genuchten-Mualem equation implemented in the RETC program.The results revealed that the critical bulk density (Proctor density) decreased with increasing soil gypsum content. A positive exponential relationship was observed between the S-index and soil gypsum content, indicating that higher gypsum content improved the physical soil quality index. A negative polynomial relationship was found between soil gypsum content and compaction degree (DC%). Furthermore, the S-index was negatively correlated with both bulk density and compaction degree (DC%).