铁离子作用下膨胀土干湿循环裂隙演化机制

Evolution mechanism of dry-wet cycle fracture in expansive soil under action of iron ion

为探究重金属Fe 3+作用下膨胀土干湿循环裂隙演化机制,以不同浓度Fe 2(SO 4)3溶液作用的饱和膨胀土为对象,开展干湿循环裂隙试验、扫描电镜(SEM)试验与X射线衍射(XRD)试验,研究Fe 3+作用下膨胀土干湿循环裂隙、微观结构和矿物成分的演化规律及机制。结果表明:相同干湿次数下,随Fe 3+浓度增加,土体裂隙面积率下降;随干湿次数增加,相同浓度土体裂隙面积率总体上升;Fe 3+作用下,粒间孔隙波动性微变,黏土矿物晶体结构损伤,晶层间距减小;干湿作用后,粒间孔隙剧增,土体结构破坏,晶体损伤加剧。总结出Fe 3+作用下膨胀土干湿循环裂隙演化机制为:水分子在土体内反复迁移,劣化土体结构,形成拉应力,导致裂隙产生;Fe 3+则在一定程度上缩小颗粒间距,增强抗拉强度,降低拉应力,抑制了裂隙发育。

In order to investigate the mechanism of dry and wet cycle fracture evolution of swelling soils under the action of Fe 3+,saturated swelling soils contaminated by different concentrations of Fe 2(SO 4)3 solution were subjected to dry and wet cycle fracture tests,scanning electron microscopy(SEM)tests and X-ray diffraction(XRD)tests to investigate the evolution of dry and wet cycle fracture,microstructure and mineral composition of swelling soils under the action of Fe 3+.The results show that under the same dry and wet times,the soil fracture area rate decreases when the Fe 3+concentration increases;when the dry and wet times increase,the soil fracture area rate of the same Fe 3+concentration increases in general;after the contamination of Fe 3+solution,the intergranular pore fluctuation changes slightly,the clay mineral crystal structure is damaged and the crystal layer spacing decreases;after the dry and wet action,the intergranular pore space increases dramatically,the soil structure is damaged and the crystal damage is intensified.Comprehensive experimental results and analysis conclude that the mechanism of dry and wet cycle fracture evolution of swelling soil under the action of Fe 3+is as follows:water molecules repeatedly migrate in the soil body,deteriorate the soil structure,form tensile stress and lead to fracture generation;Fe 3+,on the other hand,reduces particle space to a certain extent,enhances tensile strength,reduces tensile stress and inhibits fracture development.