Experiment research on unfrozen water content and pore characteristic of cement improved soil under freeze-thaw cycle
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摘要: 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。Abstract: 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 micro-mechanism of freeze-thaw damage through scanning electron microscopy and mercury intrusion porosimetry. 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 magnetization 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 affected 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 engineering.
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图 3 不同水泥掺量粉质黏土的NMR信号量与温度关系
Figure 3. NMR signal population-temperature of improved silty clay with different cement content
图 4 不同水泥掺量改良粉质黏土正融过程未冻水含量-温度关系曲线
Figure 4. Relationship curves between unfrozen water content-temperature of improved silty clay with different cement content during thawing process
图 5 不同水泥掺量的改良粉质黏土冻融前后孔隙水T2分布
Figure 5. T2 distribution curves of pore water in improved silty clay with different cement content before and after freeze-thaw cycle
图 6 不同水泥掺量改良粉质黏土冻融前后孔隙特征参数变化曲线
Figure 6. Variation curves of pore characteristic parameters of improved silty clay with different cement content before and after freeze-thaw cycle
图 7 不同水泥掺量改良粉质黏土冻融前后电镜扫描结果
Figure 7. SEM results of improved silty clay with different cement content before and after freeze-thaw cycle
图 8 不同水泥掺量改良粉质黏土冻融前后孔隙孔径体积占比分布
Figure 8. Distribution of pore size proportion of improved silty clay with different cement content before and after freeze-thaw cycle
图 9 5%水泥改良粉质黏土冻融前后NMR及MIP结果
Figure 9. NMR and MIP results of improved silty clay with 5% cement content before and after freeze-thaw cycle
表 1 土样基本物理性质指标
Table 1. Basic physical property index of soil
土类 天然含水率/% 天然干密度/(g·cm-3) 孔隙比 液限 塑限 粉质黏土 28.92 1.54 0.72 32.9 18.7 
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表 2 不同水泥掺量改良粉质黏土顺磁回归线参数
Table 2. Paramagnetic regression parameters of improved silty clay with different cement content
参数 土样 试样A 试样B 试样C 试样D 试样E a -43.64 -50.53 -65.38 -50.17 -47.76 b 19 968.22 21 366.12 22 272.32 22 231.37 22 372.91 w/% 28.93 29.04 28.86 29.12 28.98
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表 3 不同水泥掺量改良粉质黏土冻融前后总孔隙率及孔径中值(MIP)
Table 3. Total porosity and median pore diameter of improved silty clay with different cement content before and after freeze-thaw cycle(MIP)
特征参数 A冻融前 A冻融后 C冻融前 C冻融后 E冻融前 E冻融后 总孔隙率/% 34.21 35.77 32.96 33.23 30.59 29.16 孔径中值/μm 3.58 3.43 3.42 2.37 2.32 2.10 冻融前后总孔隙率变化率/% 4.56 0.81 -4.67 冻融前后孔径中值变化率/% -4.19 -30.70 -9.48
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