淋溶时间对红黏土物理力学特性的影响

Effect of leaching time on physical and mechanical characteristics of lateritic soil

以湖北省鄂州市庙岭镇的红黏土为研究对象,以化学选择溶解法结合淋溶作用为处理手段,将原状土样中的游离氧化铁按梯度去除,获得连二亚硫酸钠-柠檬酸钠-碳酸氢钠(DCB)溶液淋溶时间与除铁率的关系,并分析了不同淋溶时间对红黏土物理力学特性及微观孔隙结构的影响。试验结果表明,DCB溶液淋溶时间与除铁率相关性较强,除铁率与时间呈先快速增长后逐渐稳定的关系。由于游离氧化铁在土颗粒间主要起胶结作用,故淋溶时间对红黏土的物理力学特性有较大影响。随着淋溶时间的增长,黏粒与胶粒含量逐渐增大,耐热性小幅提升,无侧限抗压强度显著减小,且无侧限抗压强度变化整体趋势为前期急剧降低至后期趋于平稳。核磁共振、差热分析和电镜扫描的结果表明,随着淋溶时间的增大,庙岭红黏土内部孔隙增大,自由水减少,结合水增多,微观形态上团粒结构遭到破坏,胶结物质明显减少,结构形式从紧凑的粒团堆叠结构逐渐转化为聚集体-松散颗粒状结构。

Taking the lateritic soil collected from Miaoling town, Ezhou city, Hubei province as the study object, the free iron oxide in the undisturbed clay was removed by chemical selective dissolution combined with leaching as the treatment method in gradient,and the relationship between the drenching time of dithionite-citrate-bicarbonate(DCB) solution and the iron removal rate was achieved, and the effects of different leaching times on the physical, mechanical properties and the microscopic pore structure of the lateritic soil were analyzed. The experimental results show that the leaching time of DCB solution has a strong correlation with the iron removal rate, and the iron removal rate first increases rapidly and then gradually stabilizes with the time. Since the free iron oxide primarily plays the role of cementation between lateritic soil, the drenching time has a great influence on the physical and mechanical properties of lateritic soil. With the increase of drenching time, the contents of clay particles and colloidal particles gradually increase, the heat resistance increases marginally, and the unconfined compressive strength decreases significantly, while the overall trend of unconfined compressive strength decreases sharply in the early stage and tends to be stable in the later stage.Results of nuclear magnetic resonance(NMR), differential thermal analysis(DTA) and scanning electron microscopy(SEM) reveal that as the leaching time increases, the internal pores of the Miaoling lateritic soil enlarge, the free water diminishes, the bound water increases, the microscopic morphology of the agglomerate structure is destroyed, the cemented material is significantly reduced, and the structural form gradually converts from a compact granule stacking structure to an aggregate-loose granular structure.