Mechanical Properties of Unsaturated Expansive Soils Treated with Eco-Friendly Sodium Alginate Biopolymer

Seasonal variations in moisture and suction have considerable influence on the mechanical performance of soils in the vadose zone, especially swelling soils. Our study explores the use of sodium alginate (SA) biopolymer as an additive to decrease soil-swelling potential while assessing its effects on soil shear strength and water potential. We tested two types of cohesive swelling soils from Egypt, varying the SA from 1 to 4% using both wet and dry methods. Our experimental testing program included comprehensive testing: compaction, swelling tests, soil matric suction tests, and triaxial shear tests. Based on the loaded swell test, the two tested soils were categorized as having high and low swelling potential. Soil matric suction was measured using the indirect filter paper method. Our results indicate that the impact of SA additives varies with soil type and treatment method. For instance, when treating high-swelling soil with a swelling pressure of 1656 kPa, the addition of a mere 2% SA decreased swelling potential by 40% and 22% for wet and dry methods, respectively. Concurrently, the addition of 2% SA enhanced the undrained shear strength and soil modulus by about 38%, underscoring the potential of biopolymers in improving swelling soils. While the addition of SA, in any concentration, to the low swelling potential soil exhibited a less favorable influence on its swelling potential.