Evaluation of the Effectiveness of Calcium Lignosulfonate for Loess Stabilization

Abstract

In recent years, lignin-based products have been increasingly investigated for soil improvement. In this study, calcium lignosulfonate (CLS) was adopted to enhance the mechanical behavior of loess. To quantify the effect of CLS on shear strength, specimens were prepared at a water content of 15% with three degrees of compaction (85%, 90%, and 95%). Six CLS dosages (0, 0.25%, 0.5%, 1%, 2%, and 4% by dry soil mass) were considered, and direct shear tests were conducted under normal stresses of 100, 200, 300, and 400 kPa. The results show that CLS addition effectively increased the shear strength of loess, mitigated post-peak softening, and improved the residual shear resistance, accompanied by notable enhancements in the shear strength parameters. A quadratic regression model for the peak shear stress ( τp ) was developed using a Box–Behnken response surface design. The model was highly significant overall, and the relative contribution of the factors followed the order: normal stress > degree of compaction > CLS dosage. Overall, the strength gain induced by CLS was primarily attributed to an increase in cohesion. Under the tested conditions, a low dosage of 0.25% CLS, combined with a higher degree of compaction, is recommended to achieve a more stable improvement in shear strength.