摘要
基于三轴剪切试验与可溶盐含量测试,探究高分子活性剂掺量与养护时间对硫酸型盐渍土力学性能与可溶盐含量的影响,揭示土体微观特性及其改良机理.结果表明:CLI型高分子活性剂的掺入能有效提升硫酸型盐渍土的力学强度和抗变形能力,其最佳掺量为8%;活性剂与盐渍土发生置换反应,从而增强盐渍土的保水性能,有效降低盐渍土的可溶盐含量,CLI型高分子活性剂掺量越大,改良效果越好;养护时间达到7 d时,盐渍土的可溶盐含量趋于稳定.
硫酸型盐渍土可作为路基工程中的主要填筑材料,由于土体中存在大量的可溶盐,其侵蚀作用易造成土体溶陷破坏或结构件损
综上所述,改良盐渍土作为建筑材料使用时需要对其强度性能进行改良.因此,本文引入一种CLI型高分子活性剂对新疆地区盐渍土进行改良,探究该活性剂对盐渍土力学性能和含盐量改良的可行性,为新疆地区盐渍土区域工程建设提供一定的参考依据.通过设置不同活性剂掺量与养护时间,探究改良盐渍土力学强度及含盐量的变化规律,并通过微观测试来揭示其改良机理,为盐渍土的地基及路基处理设计提供理论和实践指导.
试验所用土体均取自新疆巴音郭楞蒙古自治州尉犁县农二师三十三团某工地,取土深度约为1 m.经测试得到原状土中含多种盐分,其中无水硫酸钠的含
Specific gravity | Dry density/(g·c | Optimum moisture content(by mass)/% | Liquid limit(by mass)/% | Plastic limit(by mass)/% |
---|---|---|---|---|
2.72 | 1.73 | 14.12 | 25.52 | 15.32 |
采用一种自制的CLI型高分子活性剂(后文简称CLI)对盐渍土进行改良.CLI由造纸废液提纯并干燥后制得,在常温条件下呈棕黄色粉末状,其基本物理参数如
Appearance | Relative molecular mass | Solid content(by mass)/% | Specific gravity | Water insoluble content(by mass)/% | PH value | Water content(by mass)/% |
---|---|---|---|---|---|---|
Brownish yellow powder | 2 500 | 45 | 1.2 | 0.5 | 7 | 1.0 |
在试样制备过程中,根据设置的土体干密度(ρd,ρd=1.5、1.6、1.7、1.8、1.9 g/c
通过三轴剪切试验研究不同CLI掺量及养护时间下盐渍土的强度(峰值偏应力).所设围压分别为100、200、300 kPa,试验过程按照GB/T 50123—2019《土工试验方法标准》进行,控制剪切仪的应变速率为0.8 mm/min.试验所用仪器为TSZ‑1型全自动三轴剪切仪.
参照文献[
将经三轴剪切试验后的盐渍土试样破碎后烘干,取其中尺寸为10 mm×10 mm×2 mm的碎片进行微观测试.采用SU3500扫描电子显微镜(SEM)观察盐渍土改良前后的微观特征,并结合能谱(EDS)测试,确定盐渍土改良前后的元素组成.
通过行星式研磨机对试样碎片进行研磨,采用DX‑2700型X射线衍射仪(XRD)对研磨后的盐渍土粉末进行观测,对比分析盐渍土试样改良前后的矿物成分变化.
不同围压条件下养护1 d时各试样偏应力-轴向应变曲线如

图1 不同围压条件下养护1 d时各试样偏应力-轴向应变曲线
Fig.1 Deviatoric stress‑axial strain curves of samples after curing for 1 day under various confining pressures
不同养护时间及围压下各试样的峰值偏应力如
Confining pressure/kPa | Curing time/d | Peak deviatoric stress/kPa | |||
---|---|---|---|---|---|
S0 | S4 | S8 | S12 | ||
100 | 1 | 437.25 | 553.01 | 974.48 | 605.53 |
3 | 444.22 | 528.37 | 1 159.71 | 1 004.82 | |
7 | 532.38 | 658.66 | 1 294.08 | 1 111.63 | |
14 | 501.67 | 708.78 | 1 292.26 | 1 167.07 | |
200 | 1 | 625.73 | 680.43 | 1 269.43 | 753.54 |
3 | 632.36 | 753.06 | 1 442.02 | 1 172.51 | |
7 | 678.27 | 890.29 | 1 629.68 | 1 378.64 | |
14 | 703.57 | 1 048.52 | 1 766.22 | 1 460.54 | |
300 | 1 | 764.28 | 954.71 | 1 463.43 | 924.96 |
3 | 819.92 | 1 003.92 | 1 707.21 | 1 443.21 | |
7 | 859.43 | 1 169.89 | 1 927.41 | 1 531.76 | |
14 | 857.73 | 1 165.35 | 1 950.86 | 1 546.77 |

图2 不同养护时间和CLI掺量下试样的内聚力和内摩擦角
Fig.2 Cohesions and internal friction angles of samples with different curing times and CLI contents
由
改良后试样内聚力的增长幅度明显高于内摩擦角,说明CLI主要通过在颗粒间建立聚合物线束或聚合物膜来增强颗粒间的胶结作用,从而引起试样内聚力的显著提升;并且聚合物的粒间胶结及表面黏附使得颗粒咬合程度和表面摩擦角提升,从而引起内摩擦角的增大.
养护7 d时,不同干密度下改良盐渍土试样S8的内聚力与内摩擦角见

图3 不同干密度下改良盐渍土试样S8的内聚力与内摩擦角
Fig.3 Cohesions and internal friction angles of sample S8 with different dry densities(7 d)

图4 各试样的含水率与可溶盐含量
Fig.4 Moisture content and soluble salt content of samples
由
为了确认CLI与硫酸型盐渍土作用是否有新的矿物生成,对改良前后的盐渍土试样S0、S8(养护时间为7 d)进行XRD和EDS分析,结果如图

图5 试样S0和S8的XRD图谱
Fig.5 XRD patterns of S0 and S8 samples(7 d)

图6 试样S0和S8的EDS扫描分析
Fig.6 EDS scanning analysis of S0 and S8 samples(7 d)
由
由

图7 试样S0和S8的SEM照片
Fig.7 SEM images of S0 and S8 samples(7 d)
根据土壤的双电层理论,当黏土颗粒表面电荷恒定时,离子浓度越高,离子价数越大,土颗粒的双电层厚度越

图8 硫酸型盐渍土与CLI反应原理示意图
Fig.8 Schematic diagram of reaction between sulphuric acid saline soil and CLI
CLI掺量对盐渍土Zeta电位的影响如

图9 CLI掺量对盐渍土Zeta电位的影响
Fig.9 Effect of different contents of CLI polymer active agent on the Zeta potential of saline soil(7 d)
当土壤中的CLI掺量过高时,CLI将与土颗粒发生过量反应,导致短时间内团聚体数量剧增,反而在一定程度上增大了土壤的孔隙度,降低了土壤结构的整体稳定性,从而提升了水分的蒸发量,并使试样的强度降低.
此外,在水、土及电解质环境中,游离的钙离子能够与钠离子发生置换反应而形成硫酸钙沉淀(见
(1)CLI型高分子活性剂的掺入可以有效提升硫酸型盐渍土的力学强度,其最佳掺量为8%,此时试样的内聚力较素土试样最大可提升113.77 kPa.
(2)养护时间对CLI型高分子活性剂改良效果有重要影响,随着养护时间的延长,改良后的试样力学性能呈先增加后稳定的趋势,养护7 d时试样力学性能基本稳定.
(3)改良盐渍土保水性能随CLI型高分子活化剂掺量增加而先增大后减小,掺量为8%时试样保水性能最强,其含水率较素土试样提升约69.02%.
(4)CLI型高分子活化剂可以有效地降低盐渍土的含盐量.其掺量越高,离子置换反应能力越强,随养护时间的增加,置换效果在7 d后趋于稳定.
(5)CLI型高分子活化剂降低了土颗粒双电层厚度,增加了颗粒间的静电作用和离子桥接,改善了盐渍土的力学性质,生成的絮凝物质可填充孔隙,增强土体结构,提升其保水性能.
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