SWELLING AND SHRINKAGE BEHAVIOUR OF EXPANSIVE SOIL AMELIORATED BY CALCIUM LIGNOSULPHONATE DURING WETTING-DRYING CYCLES

According to a field investigation,expansive soil disasters such as building damage and slope failure happened in the area of Nanyang Basin in Henan Province as a result of extreme climate condition—persistent rains and drought,threatening people's property and lives. This paper aims to study the effect of calcium lignosulphonate for improving the swelling and shrinkage characteristics of weak expansive soil. The soil specimens mixed with calcium lignosulphonate at various percentages(0.5%,0.75%,1%,1.25%) by dry weight,and the free swell test were performed after specimens cured for 0,3,7,11,14,and 28 days to explore the optimum value of calcium lignosulphonate. The laboratory test results indicate that the specimen mixed with 0.75% calcium lignosulphonate and cured for 14 days has the lowest free swelling ratio. Based on the optimum values of calcium lignosulphonate(0.75%),unloaded expansion test and shrinkage test were conducted under cyclic drying and wetting condition. The results show that the addition of calcium lignosulfonate can effectively reduce the absolute expansion rate and the absolute shrinkage rate of weak expansive soil during the wetting-drying cycle. The maximum absolute expansion rate decreases from 29% to 3%,and the maximum absolute shrinkage rate decreases from 17% to 2%. The relative expansion rate and shrinkage rate of ameliorated soils keep steady with the increase of the wetting-drying cycle,which indicates that calcium lignosulfonate can effectively ameliorate the stability of swelling and shrinkage property of weak expansive soil during wetting and drying cycles. The increased drying-wetting cycle has no effect on the improved effectiveness of calcium lignosulphonate. By analyzing the crack development pattern of test specimens,calcium lignosulfonate primarily inhibits crack development,improves soil cementation ability,and causes the soil to form a more compact structure,allowing weak expansive soil to maintain its swelling and shrinkage characteristics stability during the drying-wetting cycle.