冻融作用下水泥改良土未冻水含量及孔隙特征试验研究

Experiment research on unfrozen water content and pore characteristic of cement improved soil under freeze-thaw cycle

水泥基材料注浆是控制人工冻结地层冻融变形普遍有效的措施。基于核磁共振技术,对冻融作用下不同水泥掺量的粉质黏土未冻水含量及冻融前后孔隙特征进行测试,结合扫描电镜和压汞技术分析了冻融前后水泥改良土的孔隙特征变化规律及冻融损伤微观机理。结果表明:①含水量一定时,随着水泥掺量的增大,孔隙中水分子磁化程度对温度的敏感性先增大后减小;②当水泥掺量为0~10%时,正融过程同一温度下,随着水泥掺量的增加,冻结土体中未冻水含量先减小后增大;③相比于未掺水泥的粉质黏土,水泥改良粉质黏土冻融前后孔隙的变化程度较小,当水泥掺量为5%时,其孔隙特征及微观结构受冻融循环影响较小。研究结果可为改良土体抗冻融损伤研究及人工冻结工程地层冻胀融沉稳定性控制提供参考。

Grouting with cementitious materials is a commonly-recognized measure to control the freezing and thawing deformation of artificial freezing strata.This study investigated the unfrozen water content of silty clay with different cement content under freeze-thaw condition,as well as the pore characteristics of the silty clay before and after freeze-thaw cycle based on nuclear magnetic resonance.It analyzed pore characteristics variation patterns of cement improved soil before and after freeze-thaw cycle and the mi-cro-mechanism of freeze-thaw damage through scanning electron microscopy and mercury intrusion poro-simetry.Results showed that:①With the same water content,the increase of cement content would lead to the initial increase and subsequent decrease in the sensitivity to temperature of water molecule mag-netization in the pores.②When the cement content is between 0%~10%and at the same temperature during thawing process,the increase of cement content would lead to the initial decrease and subsequent increase of the unfrozen water content in the frozen soil.③Compared with the silty clay without cement,cement improved silty clay shows little changes in its pores before and after the freeze-thaw cycle.The pore characteristics and microstructure of improved silty clay with cement content of 5%are less affect-ed by freeze-thaw cycle.This research can provide references for the study of freeze-thaw resistance of improved soil and the stability control of strata frost heave and thaw settlement in artificial frozen engi-neering.