Abstract: Dispersive clay is a type of water-sensitive soil, which has the characteristics of dispersivity and material loss when encountering water. The influential factors and modification mechanism of dispersive clay modified by calcium lignosulfonate (CL) were studied using dispersivity test, mechanical property test, chemical property test, microstructure test and simulated rainfall scouring test. The test results indicated that with the increase in CL content, the dispersivity, slake durability and erosion resistance of the modified soil were gradually improved, and it had a good modification effect when the CL content reached 3.0%. The unconfined compressive strength (UCS) first increased and then decreased, while the coefficient of consolidation first decreased and then increased, and both achieved extreme values at the CL content of 0.5%. With the increase in curing age, the dispersivity and slake durability of the modified soil decreased gradually, the coefficient of consolidation reduced significantly, while the UCS increased gradually. At the curing age of 28 d, the UCS values of the modified soil with the CL contents of 0.5% and 3.0% increased by 50% and 20%, respectively, compared with that of dispersive clay. The engineering properties of dispersive clay were improved by the addition of CL mainly through reduction of thickness of electric double layer, cation bridging, particle cementation and hydrophobic effect of hydrophobic group. However, when the CL content was too high, the CL would preferentially combine with itself and weaken the attraction between soil particles, which would increase the porosity and decrease the mechanical properties of soil. It is concluded that CL has a good modification effect on the dispersive clay, in terms of significant improvement of water sensitivity, water stability and erosion resistance of dispersive clay.

Key words: dispersive clay, lignosulfonate, mechanical properties, modification mechanism, simulated rainfall scouring