Medical Journal of the Chinese People's Armed Police Forces

Journal of Changjiang River Scientific Research Institute >

2025 , Vol. 42 >Issue 9: 131 - 138

DOI: https://doi.org/10.11988/ckyyb.20240765

Rock Soil Engineering

Experimental Study of Cohesive Non-swelling Soil Stabilized with Hydroxy-Aluminum Solution for the Treatment of Expansive Soil

  • SHE Jian-bo , 1, 2, 3 ,
  • LI Shuai 2 ,
  • TANG You-sheng 4 ,
  • XIAN Shao-hua 5 ,
  • LU Zheng 3 ,
  • YAO Hai-lin 3 ,
  • ZHOU Yong-wei 2
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  • 1 Hubei Institute of Urban Geological Engineering, Wuhan 430050, China
  • 2 Hubei Dijian Construction Co., Ltd., Wuhan 430050, China
  • 3 State Key Laboratory of Geomechanics and Geotechnical Engineering Safety, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan 430071, China
  • 4 China United Engineering Corporation Limited, Hangzhou 310052, China
  • 5 Wuhan Municipal Engineering Design & Research Institute Co., Ltd, Wuhan 430023, China

Received date: 2024-07-22

  Revised date: 2024-10-24

  Online published: 2025-01-23

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Abstract

[Objective] Cohesive non-swelling soil (CNS) covering technology, when applied to the in-situ treatment of expansive soil foundations and slopes, frequently necessitates the modification of the expansive soil with traditional additives like lime to prepare suitable CNS materials. Research on the treatment of expansive soil using hydroxy-aluminum remains limited, and its application as an in-situ CNS material has not yet been reported. This study aims to ascertain the viability of using chemically stabilized soil (CSS) with hydroxy-aluminum solution as a CNS cushion layer material through laboratory experiments. [Methods] A series of basic physical-mechanical, chemical, and microstructural tests were carried out. Changes in particle size distribution, Atterberg limits, and compaction indices of soils were analyzed to evaluate the modification effect of hydroxy-aluminum on expansive soil. Subsequently, the permeability, shear strength, and swelling characteristics of the expansive soil (ES), CSS, and CNS were investigated under varying degrees of compaction (85%, 90%, 95%, 100%). Ion concentration analysis of soils and microstructural analyses (XRD, SEM) were also conducted to assess the overall performance of CSS and validate its potential as a CNS cushion layer material. [Results] (1) Following the addition of the hydroxy-aluminum solution, flocculation and agglomeration occurred between the hydroxy-aluminum and the clay particles of expansive soil. This process resulted in a reduction in the dispersibility and hydrophilicity of expansive soil, leading to denser particle packing. Consequently, the particle size distribution of expansive soil shifted, with an increase in silt content from 31% to approximately 46%, and a decrease in clay content from 65% to 51%, indicating a trend toward silty soil. (2) Plasticity index exhibited a substantial decrease, with a 43.5% reduction from 38.06 to 21.49. This decline resulted in a transformation of the soil classification from high-liquid-limit clay (CH) to low-liquid-limit clay (CL). These changes demonstrated a marked improvement in the basic physical properties of expansive soil. (3) Under varying degrees of compaction, the CSS exhibited substantial improvements in permeability, shear strength, and swelling characteristics compared to expansive soil. The permeability coefficient increased from 10-8 to 10-9 cm/s to the order of 10-7 cm/s, reaching a level comparable to that observed in the CNS. The shear strength parameters were enhanced; notably, at high compaction degree (K=100%), the shear strength of CSS even exceeded that of CNS. The swelling potential of CSS was significantly reduced, with the development of swelling deformation following the same trend as CNS. The swelling percentage decreased from 16%-24% to 8%-15%, representing a reduction of 37.5%-50%, which was slightly higher than CNS but still within the range of non-swelling soil. [Conclusion] Overall, the comprehensive performance of CSS was found to be essentially equivalent to that of CNS. The modification of expansive soil by hydroxy-aluminum solution primarily involved physicochemical reactions, including adsorption, ion exchange, and flocculation-agglomeration. The concentrations of K+, Na+, Ca2+, and Mg2+ of CSS all showed a significant increase. The findings suggest that CSS has a better potential for the inhibition of the swelling behavior of expansive soil. The results demonstrate the feasibility of utilizing CSS as a CNS cushion layer material for expansive soil.

Key words： expansive soil; hydroxy-aluminum solution; chemically stabilized soil; cohesive non-swelling soil; cushion layer technology

Cite this article

SHE Jian-bo , LI Shuai , TANG You-sheng , XIAN Shao-hua , LU Zheng , YAO Hai-lin , ZHOU Yong-wei . Experimental Study of Cohesive Non-swelling Soil Stabilized with Hydroxy-Aluminum Solution for the Treatment of Expansive Soil[J]. Journal of Changjiang River Scientific Research Institute, 2025 , 42(9) : 131 -138 . DOI: 10.11988/ckyyb.20240765

开放科学(资源服务)标识码(OSID):

0 引言

膨胀土(Expansive Soil,ES)是自然地质形成过程中产生的一种多裂隙并具有显著胀缩性的特殊黏土,对各类浅表层轻型工程建设均有特殊的危害作用。为了有效抑制或减轻膨胀土的这种胀缩效应,非膨胀性黏土(Cohesive Non-swelling Soil, CNS)覆盖技术(又称包边法)作为一种施工简单、安全环保的方法,在工程中得到了广泛的应用[1-5]。印度学者Katti等[2-3]通过多个现场试验和工程应用案例,提出了膨胀土灾害治理的CNS工法技术指南。国内何漓江等[6-7]、孔令伟等[8]、陈善雄等[9]、刘观仕等[10]、杨和平等[11]学者也开展了大量的研究工作,并总结出了CNS技术的工程设计方法。在团队前期的研究中,发现CNS覆盖层中的阳离子会在注水饱和过程中向膨胀土层迁移富集,产生的电荷作用对膨胀土的抑制效果比覆盖层的自重作用更为显著[12-13]。这表明CNS中富含的离子成分是决定CNS技术应用效果的重要因素。在实际应用时,寻找合适的天然CNS材料往往费时费力,工程中常以化学改性土(Chemically Stabilized Soil,CSS)作为非膨胀性的包边土,如在膨胀土中加入石灰、水泥、粉煤灰等就地拌合改良使用[1,9,14 -15],但由于膨胀土结构成团,现场很难拌合均匀,施工效率低下,应用效果不佳。对于地基和边坡等原位膨胀土而言,通过添加石灰等外加剂进行原位处治存在诸多困难;已经运行的既有工程出现病害,CNS技术也难以适用。因此,亟需寻求一种新型的化学改良剂以及处治应用技术。
在团队多年的研究中,发现羟基铝溶液作为一种离子型改性剂,和蒙脱土胶结后可以显著降低蒙脱土的膨胀性,改善其物理力学性能[16-17]。羟基铝中的Al13([AlO4Al12(OH)24(H2O)12]7+,[Al13]7+)被认为是膨胀性黏土矿物中理想的插层剂和化学稳定剂[18]。Bottero等[19]发现Al13聚合物是羟基铝溶液与蒙脱石交联后吸附在层间的主要Al 成分,可以形成牢固的热稳定柱撑剂,且Al13在晶层间形成的这种柱撑物是不可逆的[20]。羟基铝溶液对膨胀土也有很好的改良效果,可以显著降低膨胀土的自由膨胀率[21]。在用于分散性土的改性时,改性后的基本物理性质甚至优于石灰改性土[22-24]。此外,有学者还通过电化学方法利用羟基铝溶液对膨胀土进行原位改性,处治后膨胀土的基本物理性质以及膨胀性能均得到了明显的改善[25-26]。
可见,相较于传统改性剂,羟基铝溶液由于具有高电荷性、水溶性、导电性的特点,不仅可以通过现场搅拌、混合等方式与膨胀土产生胶结反应,从而对膨胀土进行改良;还可以通过钻孔灌注、表面喷洒等物理手段结合电渗等电化学方法实现对膨胀土的原位处治,达到浅层膨胀土改性、深层膨胀土抑制的协同处治效果,具有很好的工程应用前景。此项技术如能研究成功,将突破传统CNS技术的局限性,对提高膨胀土地区灾害治理的水平具有重要的理论意义和实践价值。
目前关于羟基铝处治膨胀土的研究尚处于初步阶段,以羟基铝改性膨胀土作为非膨胀性包边土的文献还未见报道。基于此,本文通过羟基铝溶液制备化学改性膨胀土CSS,并以天然CNS为对照,研究膨胀土改性前后在颗粒组成、界限含水率和击实指标方面的变化,分析羟基铝的改性效果;然后研究不同压实度下ES、CSS和CNS的渗透性、抗剪强度以及膨胀特性的变化规律,结合化学成分和微观结构分析,探讨以CSS替代CNS作为膨胀土包边覆盖层的可行性,为后期进一步开展CSS原位包边技术的应用研究奠定基础。

1 试验材料

1.1 土样性质

为了分析CSS替代天然CNS的可行性,本文试验所用的膨胀土ES和CNS与文献[12]和文献[13]保持一致,土样的物理性质指标如表1所示。
表1 土样物理性质指标

Table 1 Physical properties of soil samples

土样 粒度含量/% 相对
密度		 界限含水率/% 土定
名		 自由膨
胀率/%
砂粒 粉粒 黏粒 液限 塑限
CNS 1.40 64.20 34.40 2.73 37.23 20.10 CL 24.50
ES 3.90 31.70 64.40 2.70 63.00 24.94 CH 65.50

注:CL表示低液限黏土;CH表示高液限黏土。

从表1可以看到,ES为高液限黏土,CNS为低液限黏土。在前期的研究中,已经证明了所用CNS覆盖层对膨胀土的膨胀具有明显的抑制效果[12-13]。

1.2 羟基铝溶液的配制

羟基铝是铝离子达到水解平衡后形成的各种铝形态的统称,一般由AlCl3溶液和NaOH溶液在一定条件下进行碱中和滴定制得。而Al13([Al13]7+)具有高电荷和中等尺寸(约9.5Å),是对膨胀性黏土矿物具有显著改性效果的主要铝形态,Al13在土体中的离子交换能力顺序为:[Al13]7+>Ba2+>Ca2+>Mg2+>K+> Na+>Li[21]。Yao等[17]通过试验给出了制备高浓度含量Al13的羟基铝溶液具体参数,本文参照文献[17]进行羟基铝溶液的制备,相关配制参数与文献[23]保持一致。

1.3 羟基铝改性膨胀土

根据团队前期的研究以及刘亮等[21]的研究结论,本文将羟基铝溶液与膨胀土混合的铝土比(Al的摩尔量/膨胀土的干土质量)控制在0.18 mmol/g,拌和均匀后在室温下老化4 周,去除上清液后,对胶结土样进行风干即为羟基铝改性膨胀土CSS。

2 试验方法

2.1 基本物理力学试验

根据《公路土工试验规程》(JTG 3430—2020)[27]的有关规定,开展颗粒分析、界限含水率、击实、渗透、抗剪强度和膨胀性试验。其中,抗剪强度试验采用快剪试验方式,在应变控制式直剪仪中进行,施加的垂直压力分别为50、100、200、400 kPa,剪切速率为0.8 mm/min;膨胀性试验分为自由膨胀率试验和无荷膨胀率试验。
将自然风干后的膨胀土ES、非膨胀性黏土CNS以及羟基铝改性膨胀土CSS进行磨碎过2 mm以及0.5 mm筛备用。然后进行颗粒分析、界限含水率、击实以及自由膨胀率试验。同时,对ES、CNS和CSS按照最优含水率,100%、95%、90%、85%四个压实度进行环刀样的制备,在渗透和直剪试验开始之前,将环刀试样放入真空缸内进行抽气注水饱和。

2.2 浸出液离子浓度试验

参照《公路土工试验规程》(JTG 3430—2020)[27]的规定,将土样烘干磨碎过1 mm标准筛后,按照土水比1∶1制备浸出液,通过美国哈希公司生产的HACH DR1900 分光光度计和HACH HQD 多参数分析仪进行K+、Na+、Ca2+、Mg2+四种阳离子的测定,测试方法按照HACH 公司出版的水质分析手册[28]进行。

2.3 微观分析试验

微观分析试验主要包括X射线衍射(X-Ray Diffraction, XRD)试验和扫描电镜(Scanning Electron Microscope, SEM)试验,利用中国科学院武汉岩土力学研究所的D8 Advance X-射线衍射仪和FEI Quanta 250 扫描电子显微镜进行,衍射仪采用Cu Kα 源,管电压为40 kV,管电流为40 mA,SEM试验的加速电压控制在20 kV。

3 试验结果与分析

3.1 羟基铝对膨胀土的基本物理性质影响

3.1.1 粒径分布

图1给出了膨胀土ES、非膨胀性黏土CNS以及羟基铝改性膨胀土CSS的粒径分布曲线。根据《土的工程分类标准》(GB/T 50145—2007)[29],CNS的黏粒含量最低,为34%左右,而粉粒含量最高,达64%左右。膨胀土中黏粒含量为65%左右,粉粒含量为31%左右,改性后黏粒含量降低至51%,粉粒含量增加至46%左右。这说明羟基铝溶液的加入使膨胀土出现了粉土化,土的比表面积降低、亲水性和分散性变弱,黏土颗粒之间产生团聚胶结作用,造成粉粒含量增大而黏粒含量降低。
图1 土样粒径分布曲线

Fig.1 Particle size distribution curves of soil samples

3.1.2 界限含水率

图2给出了ES、CNS以及CSS的液塑限以及塑性图。CNS的液限和塑限分别为37.23%、20.10%,塑性指数为17.13,根据《土的工程分类标准》(GB/T 50145—2007)[29]定义为低液限黏土。而膨胀土改性后由高液限黏土变为低液限黏土,其中塑限变化不大,而液限从63%降为45.01%,塑性指数从38.06降低至21.49,下降了43.5%,说明羟基铝的加入使膨胀土在可塑状态下所能吸附的弱结合水含量变少,黏土颗粒表面的扩散双电层厚度变小,双电层斥力变弱,结合水膜变薄,宏观上就会表现为颗粒出现团聚胶结而黏粒含量降低、粉粒含量增大,这与颗粒分析试验的结果一致。
图2 土样的液塑限及塑性

注:CL为低液限黏土;CLO为有机质低液限黏土;CH为高液限黏土;CHO为有机质高液限黏土;ML为低液限粉土;MLO为有机质低液限粉土;MH为高液限粉土;MHO为有机质高液限粉土。

Fig.2 Atterberg limits and plasticity chart of soil samples

3.1.3 击实特性

3种土样的干密度和含水率关系曲线如图3所示。其中CNS 的最大干密度为1.92 g/cm3,最优含水率为13.8%。膨胀土的最大干密度为1.80 g/cm3,最优含水率16.2%;经过改性后最大干密度和最优含水率分别出现了轻微增大和降低。这说明羟基铝加入后使黏土颗粒产生絮凝和团聚,比表面积降低,颗粒之间连接更加紧密,因此最优含水率降低而最大干密度变大,这与Turkoz等[30]的发现一致。
图3 土样的干密度-含水率关系

Fig.3 Dry density-moisture content relationship of soil samples

从上述试验结果来看,羟基铝与膨胀土黏土颗粒产生絮凝团聚作用,导致土体的颗粒组成出现变化,粉粒含量增大而黏粒含量降低,降低了膨胀土的分散性和持水能力。由此可见,经过羟基铝改性后,膨胀土的物理性能得到了明显的提升。

3.2 不同压实度下土样的性能变化

3.2.1 渗透特性

不同压实度K下CNS、ES和CSS的渗透系数如表2所示。
表2 不同压实度下土样的渗透系数

Table 2 Permeability coefficients of soil samples at different degrees of compaction

压实度/% 渗透系数/(cm·s-1)
CNS ES CSS
85 2.87×10-7 4.86×10-8 7.29×10-7
90 1.96×10-7 1.58×10-8 5.14×10-7
95 1.14×10-7 8.11×10-9 3.38×10-7
100 9.23×10-8 4.57×10-9 2.77×10-7
由表2可知, 随着压实度的增大,由于土体内部连通的大孔隙被破坏、压实转化成连通性较差的小孔隙,而水分的渗透运移主要与内部连通性较好的大孔隙有关[31],故试样的渗透系数不断降低。其中膨胀土的渗透系数最小,在10-8~10-9 cm/s之间,透水性较差。在经过羟基铝改性后,渗透系数提高了1~2个数量级,说明羟基铝的加入使得膨胀土膨胀性变弱,土颗粒粒径变大,内部连通的大孔隙变多,促进了水分在土体中的运移速度,因而渗透性明显提高。而CNS 的渗透系数居中,在10-7~10-8 cm/s之间,比CSS的略低。需要注意的是,由于CNS的最大干密度高于CSS,CNS在压实度为85%~95%时的干密度基本上与CSS在90%~100%时等同,此时两者的渗透系数处在同一个数量级。这表明膨胀土在经过羟基铝改性后,其渗透性能已经达到了与天然非膨胀性黏土相同的水平。

3.2.2 抗剪性能

图4给出了ES、CNS以及CSS在不同压实度K下抗剪强度的变化关系。
图4 土样在不同压实度下的抗剪强度变化

Fig.4 Changes in shear strength of soil samples under different degrees of compaction

由图4可知,3种土样的抗剪强度与压实度均呈正相关,压实度越大,抗剪强度则越大。在压实度较低(K=85%)时,由于膨胀土内部存在较多孔隙,在抽气饱和过程中吸水膨胀,颗粒间的联结力变弱,导致土体软化、强度变低,相应的黏聚力和内摩擦角也最小。随着压实度的增大(K=90~100%),土体的初始干密度增加,内部孔隙空间变小,膨胀土吸水产生的膨胀在一定程度上被限制,故表现为强度的增大。与CNS相比,膨胀土黏聚力较高,而内摩擦角则较低,这与CNS的黏粒含量最少、粉粒含量最高,土颗粒间的胶结力较弱,颗粒粒径较大有关。
经过羟基铝改性后,膨胀土的抗剪强度变大,黏聚力和内摩擦角增大,这是由于羟基铝中Al13等聚合物被吸附在黏土颗粒表面后,使得结合水膜变薄,颗粒间的联结力增强,故黏聚力变大;同时黏土颗粒之间产生絮凝团聚,粉粒等粗颗粒含量增大,增加了抵抗剪切破坏的能力,表现为内摩擦角的增大。可见,羟基铝溶液可以显著提高膨胀土的抗剪强度,在压实度较高(K=100%)时,CSS的强度甚至超过了CNS。

3.2.3 膨胀性能

为了对比3种土样的膨胀特性,本文先根据《公路土工试验规程》(JTG 3430—2020)[27]的规定,利用自由膨胀率指标判别土样的膨胀性;然后采用无荷膨胀率试验进一步分析土样的膨胀性能。经测试,CNS的自由膨胀率为24.5%,膨胀土的自由膨胀率为65.5%,改性后降低至30%,下降了54.2%。根据《膨胀土地区建筑技术规范》(GB 50112—2013)[32]的规定,膨胀土初判为中等膨胀土,而CNS和CSS的自由膨胀率均小于40%,故为非膨胀土。
图5为土样在不同压实度下的无荷膨胀率。从图5中的(a)—(c)可知,3种土样的无荷膨胀率随时间呈非线性增长,注水初期膨胀率增长较快,后期逐渐趋于稳定。其中,在不同压实度下,膨胀土的变形发展差异较大。在压实度较低(K=85%~90%)时,由于土样内部孔隙空间较大,水分能很快渗入,故注水初期膨胀土的变形增长迅速,在50~100 min便达到基本稳定。随着压实度的增大,土体内部流通孔隙变少,渗透性降低,从而阻碍了前期膨胀率的增长,相应的变形稳定时间随之变长。对于CSS和CNS而言,在不同压实度下的无荷膨胀率变化曲线基本类似,分别在400 min和300 min时达到基本稳定,表明膨胀土改性后分散性和亲水性降低,膨胀受到抑制,导致二者膨胀变形发展规律相同,这与渗透试验结果相吻合。
图5 土样在不同压实度下的无荷膨胀率

Fig.5 Free swelling ratio of soil samples at different degrees of compaction

由图5(d)可知,CNS的无荷膨胀率最小,在5%~12%之间,而膨胀土的无荷膨胀率最大,达到16%~24%,经过羟基铝改性后无荷膨胀率降低了37.5%~50%,在8%~15%之间,比CNS略高,与自由膨胀率的试验结果一致。总体上看,CSS虽然表现出比CNS略高的膨胀性,但仍处于非膨胀性黏土的范畴。
综上,膨胀土在经过羟基铝改性后,其渗透性、抗剪强度以及膨胀性能均得到了明显的改善。这与前述颗粒分析、界限含水率以及击实试验的结果一致。CSS的膨胀性虽然比CNS略高,但渗透性和抗剪强度达到了与CNS相同的水平,整体性能与CNS基本相当,具备作为包边覆盖层的可行性。

3.3 浸出液离子浓度分析

土样浸出液离子浓度如表3所示,土水质量比为1∶1。
表3 土样浸出液的离子浓度

Table 3 Ion concentration in leachate of soil samples

试验土样 离子浓度/(mg·L-1)
K+ Na+ Ca2+ Mg2+
CNS 20 7.5 217.5 75
ES 10 12.5 405.5 35
CSS 59 4 094.55 754.85 72.75
从表3可以看出,膨胀土和CNS的浸出液中主要为Ca2+,其次是Mg2+,而K+、Na+浓度较低。膨胀土经过羟基铝改性后,浸出液中K+、Na+、Ca2+、Mg2+四种离子的浓度均出现明显增加,这归功于羟基铝加入后,Al13等铝聚合物与黏土颗粒之间产生离子交换作用,置换出了低价K+、Na+、Ca2+、Mg2+离子,从而使浓度增加。其中CSS中Na+含量出现了异常增加,还有可能是因为在配置羟基铝溶液时NaOH碱溶液含有的Na+所致。与CNS相比,CSS中除Mg2+相差不大外,K+、Na+、Ca2+浓度均要高于CNS,根据团队前期的研究,CSS中富含的离子成分可能会比CNS表现出对膨胀土更好的抑制效果[12-13]。

3.4 微观结构分析

3.4.1 矿物成分

由图6可知,CNS的矿物成分以石英、高岭石为主,含有少量的蒙脱石、伊利石和钠长石。ES和CSS的主要矿物成分为石英、伊利石、蒙脱石和高岭石,改性前后矿物成分基本没有发生变化,说明羟基铝对膨胀土的改性主要为吸附、离子交换、絮凝团聚等理化反应。此外,CSS中出现了少量岩盐(NaCl),这可能是由于羟基铝溶液加入后,溶液自身含有的NaCl以及与黏土颗粒产生离子交换作用置换出的Na+在干燥过程中发生了结晶所致,与前述土样浸出液离子浓度分析的结果一致。
图6 土样的XRD图谱

Fig.6 XRD patterns of soil samples

3.4.2 微观结构形貌

对羟基铝改性前后的膨胀土进行SEM试验,如图7所示。膨胀土主要为层状薄片结构,黏土矿物薄片呈现卷曲状,为典型的蒙脱石、伊利石形态特征。经过羟基铝改性后,黏土颗粒转变为以凝聚-堆叠状结构为主,卷曲状的薄片结构基本消失,颗粒之间相互叠聚形成团聚体,结构表面呈现粗糙化和致密化,并伴有孔隙产生。这说明羟基铝对膨胀土的团聚胶结作用降低了黏土颗粒的比表面积和亲水性,土体的颗粒级配和结构形态得到改善,膨胀性受到抑制。这与前述颗粒分析、界限含水率、击实试验的结果相吻合,也从微观上解释了CSS的渗透性能和抗剪强度得到明显改善的原因。
图7 土样的SEM 图谱

Fig.7 SEM images of soil samples

4 结论

本文以天然非膨胀性黏土CNS为对照,通过羟基铝溶液制备化学改性膨胀土CSS,研究膨胀土在改性前后以及不同压实度下的基本物理力学性质和膨胀特性的变化规律,并结合化学和微观结构分析,探讨以CSS替代CNS作为膨胀土包边覆盖层的可行性,为后期进一步开展CSS原位包边技术的应用研究提供参考。得到的结论如下:
(1)在膨胀土中加入羟基铝溶液对黏土颗粒产生絮凝团聚作用,土体的颗粒级配发生变化,粉粒含量增大而黏粒含量降低,呈现出粉土化,塑性指数下降了43.5%,膨胀土从高液限黏土变成低液限黏土,分散性和亲水性出现明显减弱,基本物理性能得到明显提升。
(2)羟基铝对膨胀土的改性主要以吸附、离子交换、絮凝团聚等理化反应为主。改性后黏土颗粒从卷曲状的薄片结构转变为以凝聚-堆叠状结构为主,颗粒之间相互叠聚形成团聚体,结构表面呈现粗糙化和致密化,并伴有孔隙产生。
(3)膨胀土在经过羟基铝改性后,其渗透性提高了1~2个数量级,自由膨胀率降低至30%,无荷膨胀率下降37.5%~50%,抗剪强度得到明显增强。在不同压实度下,CSS的渗透性能和力学强度达到了与CNS相同的水平,虽然膨胀性略高,但仍处于非膨胀性黏土的范畴,整体性能与CNS基本相当,且CSS中含有比CNS更高浓度的K+、Na+、Ca2+等离子成分,具备作为包边覆盖层的潜力。

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