干湿循环前后不同改性黄土的微观特性

Microstructure Characteristics of Modified Loess before and after Drying-wetting Cycle

黄土化学加固系利用素黄土与改良剂反应生成的物质胶结土粒和填充孔隙,从而达到改善土体工程地质特性的目的,得到广泛应用。通过X衍射、电镜扫描、压汞试验对比分析木质素磺酸钙、木质素磺酸钠、硅酸钠、生石灰改性黄土和压实素黄土在矿物成分、微观特性和强度指标上的差异以探究不同固化黄土的改性机制,并进行不同改性黄土干湿循环试验,从微观孔隙特征和强度角度探究不同改性黄土的水稳性。试验结果表明:素黄土进行改性后其原有矿物成分之斜绿泥石和锌硅钠石消失,主要矿物成分石英和钠长石占比从70%增长至78%以上。添加剂致使土体微观结构显著变化,主要表现为孔隙含量的减小、孔隙分布的改变和土骨架颗粒连接方式的转变。面孔隙度和孔隙总体积的变化和无侧限抗压强度之间呈较好的负相关关系,表明添加剂在很大程度上是通过改变土体的孔隙度来影响土体强度特性的。经历10次干湿循环后,不同改性黄土孔隙累积体积降低、平均孔隙直径和孔隙分布发生改变,无侧限抗压强度降低,微观结构和宏观性质的改变均表明干湿作用对土体的弱化作用。干湿作用下硅酸钠和生石灰改性土强度劣化现象显著,木钠改性土试样表面完整性较差,木钙改性土试样完整性好且仍然保持较高强度,水稳性良好,表明木钙在运用于提高黄土力学性能和抗干湿循环方面具有明显的作用,具有广阔应用前景。

The chemical solidification of loess utilizes the substances generated by the reaction between the soil particles and the additives to improve the engineering geological characteristics of the soil,which has been widely used.The X-ray diffraction test,scanning electron microscope(SEM)test and mercury intrusion porosimetry(MIP)test were conducted to investigate the mineral compositions,microstructures and strengths of loess soils modified with calcium lignosulfonate,sodium lignosulfonate,sodium silicate and quick lime,and compacted loess.The drying-wetting cycle tests were performed to assess the water stability of modified loess soils.The results show that the clinochlore and gaultite that existed in compacted loess were undetected,and the mass per cent of quartz and albite in modified loess was increased from 70%to above 78%.The obvious microstructure change would result from the addition of various modifiers in loess,characterized by the decrease of pore contents,redistribution of pores and transformation of connection between soil particles.There is a negative correlation between unconfined compression strength and plane porosity.After 10 cycles of drying-wetting,the cumulative pore volume of modified loess soils was decreased,but the mean pore diameter and pore distribution showed different trends.The unconfined compression strength of modified soils decreased overall following drying-wetting cycles.Collectively,the results from both the micro-and macro-analyses indicated that the drying-wetting cycle would cause the deterioration of the geotechnical properties of modified and compacter loess.However,the calcium lignosulfonate-modified loess exhibits good surface integrity and its strength remains reasonably high after 10 drying-wetting cycles,suggesting that calcium lignosulfonate has an important function in improving the mechanical properties and resistance to drying-wetting cycles of loess.