Effect of Relative Compaction on Water Absorption and Gypsum Dissolution in Gypsum-Rich Clayey CBR Samples

A clayey gypsiferous soil of CL group according to the Unified Soil Classification System was studied for the effect of relative compaction on water absorption and gypsum dissolution during long-term soaking. The soil has a gypsum content of about 33%. Two sets of soil samples were prepared at optimum moisture content of 11.75% of the modified Proctor compaction test. The first set received 100%, while the second received about 93.5% relative compaction with respect to modified Proctor. These samples were soaked for 4, 7, 15, 30, and 120 days under 40 lbs (178 N) surcharge load. The moisture content was determined at top, quarter points, midpoint, and bottom of each soil sample. The test results revealed that for each compaction effort, the moisture content along each soaked soil sample is not uniform and increased with increasing soaking period. This increase in moisture content is greater for soil samples compacted at the lower compaction effort. The moisture content at top of each soil sample is greater than at the bottom, and the least moisture content took place at the middle of the sample. The dissolution of gypsum, at the top of soil samples, was greater than that at the middle. A multiple regression equation was developed relating strongly the decrease in gypsum content along the clayey CBR samples, with compaction effort and increase in average moisture content along the samples due to soaking. Similarly, strong correlation was obtained from the multiple regression developed between absorbed water, soaking period, and compaction effort. The paper shows that the water absorption and gypsum dissolution decrease with increasing relative compaction as the soil becomes denser.