Effect Of Clay Minerals On Swelling Of Collapsed Soil Under Different Ion Concentrations

Collapse is a typical soil erosion in the red soil region of southern China.The swelling and shrinkage characteristics of the collapsed hill during the process of water change have a significant impact on the development of collapsing erosion.This study selected a typical collapsed hill in Anxi County,Fujian Province and collected the red soil layer,sand layer and debris layer on the collapsed wall as the research object of this experiment.By adding clay mineral content and different ion content as well as setting the number of dry and wet cycles,then took the soil samples to expansion tests,exploring under the different ion content and the number of dry and wet cycles,the relationship between clay mineral content and soil expansion strength.The results showed that:(1)The unloaded expansion rate has a nonlinear relationship with the change of time under different clay mineral contents in the three soil layers.The expansion process can be roughly divided into three phases:the rapid expansion phase,the slow expansion phase and the expansion stabilization phase.The water absorption amount was basically saturated until 12 hours.With the increase of clay mineral content,the final unloaded expansion rate of the collapsed soil layers first decreased and then increased.As the soil layer deepens,the speed of rapid expansion increased,and the duration of rapid expansion was shortened.The final unloaded expansion rate at 12 h was:red soil layer>sand layer>debris layer.(2)Considering that the amount of cations adsorbed on the surface of the colloid was another important factor affecting soil expansion,so studying under the different ions(K~+,Na~+),the relationship of clay mineral content and soil expansion.Under the same clay mineral content,with the growth of K~+,the unloaded expansion rate of soil in each soil layer decreased.Under the constant K~+,unloaded expansion rate of each clay mineral content both were smaller than the unloaded expansion rate of the air-dried soil.It was indicated that the combination of K~+and clay mineral content inhibited the expansion capacity of the collapsed soil.Na~+showed the opposite result to K~+.Under the same clay mineral content,the final unloaded expansion rate of soil in each soil layer of the collapsed hill increased with the growth of Na~+.The expansion rate was significantly correlated with the concentration of Na~+.The probable reason was that the Na~+characteristic accelerated the dispersion of fine particles in the soil.So it can promote soil expansion.(3)The frequent swelling and shrinking process were the driving factor for the expansion of the soil.Therefore,through the study of dry and wet cycles was ordered to explore the mechanism of its influence on the swelling of various soil layers.Under the same clay mineral content,the final unloaded expansion rate was increases with the number of dry and wet cycles in the red soil layer after ion adsorbed.The first dry-wet cycle was the most important contribution to the swelling of the red soil layer and the expansion rate in the subsequent cycles became slowly.Under the same conditions,the sand layer and the debris layer showed that the unloaded expansion rate decreased with the number of dry and wet cycles without adding clay minerals.With the increase of clay mineral content,the unloaded expansion rate increased significantly with the number of cycles,especially after the third cycle.Similarly,as the number of dry and wet cycles continues to increase,the unloaded expansion rate of the two soil layers appeared to be stable.