电化学法改善蒙脱土膨胀性试验研究

基于电化学特点,提出一种可实现原位处理膨胀土的新思路,以室内配制具有高电荷的羟基铝离子溶液为电解质,在外加电场作用下,羟基铝离子进入土体实现对蒙脱土的改性。从宏观角度,对电化学改性前后的蒙脱土进行颗粒分析、界限含水率及膨胀特性试验研究,表明改性后蒙脱土膨胀特性指标显著下降,阳极区土体达到非膨胀土的性能要求。从微观层面,进行X射线衍射试验,改性后蒙脱土矿物晶格层间吸湿敏感性明显降低,表明羟基铝离子进入晶层间置换了层间阳离子,降低了矿物晶格的亲水性;通过热分析试验研究不同温度下改性前后蒙脱土的失重变化,表明羟基铝离子进入双电层交换出水化阳离子并且附着在黏土颗粒表面,减小了双电层厚度,降低了蒙脱土的膨胀性。     

离子土固化剂对膨胀土结合水影响机制研究

以河南安阳弱膨胀土为对象，通过“水汽等温吸附–热失重、差热分析”对膨胀土表面吸附结合水类型进行界定，比较分析离子土固化剂（ISS）改性前后，膨胀土结合水分布形态及数量变化，并基于傅里叶红外光谱，从水分子结构振动信息角度对膨胀土吸附结合水类型界定方法进行定性验证；结合ISS改性前后黏土矿物组分、表面理化性质的变化，解释分析了不同水汽湿度区间内，ISS对膨胀土水合行为的作用模型及改性机理。结果表明：达到一定的水汽“特征”湿度段，土表面水合状态和结合水性质将发生转变，根据热曲线的脱失温度区间可将结合水界定划分为三种类型：强结合水，“过渡”结合水和弱结合水。ISS作用后，土吸附强结合水量无明显改变，“过渡”结合水及弱结合水含量显著降低。ISS通过对膨胀性黏土矿物表面及层间的物化作用，弱化黏土矿物部分“水合活性中心”能量，从而抑制了膨胀土水化膨胀势。     

阳离子型化合物改良膨胀土试验研究

为探究不同阳离子化合物改良膨胀土工程特性的实际效果,并确定最佳复合配比,分别选用硅酸钠(Na₂SiO₃)和阳离子聚丙烯酰胺(CPAM)作为改良剂,对改良土样进行一系列物理力学性能研究。结果表明:随着两种改良剂的掺入,膨胀土的液塑限、胀缩率、强度均有明显改善与提高;界限含水率指标上,两种改良剂改善效果相差不大;CPAM更有效降低土的膨胀性;Na₂SiO₃在降低土的收缩性和提高抗剪强度方面效果更明显。选用0.6% CPAM与Na₂SiO₃进行复掺,随着Na₂SiO₃掺量的增加,改良土的无侧限抗压强度呈现先增长后降低的趋势,4% Na₂SiO₃和0.6% CPAM复掺效果最佳且水稳性更优,扫描电镜(SEM)显示复掺改良后膨胀土由弯曲起皱片状结构转为块状结构,提高了土体的密实性和强度。     

PAM固化土体的微观特性试验分析

采用红外光谱、元素分析、XRD测试、比表面积测试、扫描电镜等微观试验,分析PAM固化剂的材料属性和固化土的固化机理。研究表明:PAM固化剂主要含有C、N、H 3种元素,其固化剂土体未产生新的矿物。PAM固化剂含有有利于土颗粒加固的链式结构,可以增强土颗粒间的粘结力。PAM掺量越多,比表面积减少,但固化土体的强度越强。     

酸雨入渗膨胀土的水土化学试验与作用机理分析

弄清酸雨入渗膨胀土所产生的水土化学作用,对获取酸雨区浅表层膨胀土基本性能劣化机理及分析边坡的稳定性非常重要。为此,取广西酸雨重灾区的百色原状膨胀土,研制循环饱水试验装置并模拟不同pH值的雨水入渗环境,开展酸雨入渗膨胀土水土化学试验;运用多种微观测试技术,探究膨胀土的矿物与化学成分演变规律;采用地球化学模拟软件(PHREEQC)及水土化学理论,分析膨胀土与酸雨间水土化学作用机理。结果表明：相比静态水饱和状态,降雨入渗动态水饱和环境能促进膨胀土中矿物质的溶蚀与淋滤,加速土体结构的破坏;酸雨入渗后膨胀土中CaO、Fe₂O₃、K₂O明显大于Si O₂、Al₂O₃等氧化物的溶蚀与淋滤量;雨水的pH值越小,膨胀土片状微结构间溶蚀的方解石及游离氧化物等胶结物越多,离子交换作用增强;酸雨与土中矿物的相互作用加剧,部分伊利石脱钾转变为蒙脱石黏土矿物,导致伊利石含量减小,蒙脱石含量增加,土的亲水性增强而结构不稳定性变大,不利于膨胀土边坡的稳定。     

合肥膨胀土阳离子改良试验及微观机制分析

以合肥典型膨胀土为研究对象,利用石灰与十六烷基三甲基溴化铵(CTMAB)混合物作为添加剂对膨胀土进行改良,通过界限含水率试验、直剪试验、不固结不排水三轴压缩试验、自由膨胀率试验和扫描电镜(SEM)试验,对比分析了两种不同膨胀潜势膨胀土改良前、后基本物理力学性质变化情况和改良效果,并基于双电层理论进行改良微观机制分析。试验研究结果表明:膨胀土改良后,黏粒含量减小,粉粒含量增多,塑性指数降低,亲水性减弱,膨胀潜势得到有效抑制,自由膨胀率低于40%,变为非膨胀土,抗剪强度得到提高。通过SEM观察微观结构发现:改良土土粒产生团聚作用并胶结成整体,土颗粒间胶结力增强,水稳定性提高。CTMAB与石灰相互促进、激发,形成协同作用,通过离子交换、吸附、包裹、胶结等一系列复杂的表面物化反应,使土粒扩散层厚度变薄,膨胀土对水"敏感性"降低,强度提高,工程性质得到明显改善。     

含盐量对极细颗粒黏土强度影响的试验研究

 为深入研究滨海盐渍土等极细颗粒黏土的不良工程特性产生的物理化学机制,探讨在水的作用下由可溶盐离子引起土颗粒表面微电场的变化对极细颗粒黏土抗剪强度的影响,首先对一系列含盐量即不同孔隙液离子浓度下的人工土(膨润土、高岭土与膨润土的混合土、石英)进行常规直剪与液塑限试验,同时测试人工土的阳离子交换量与比表面积等微细观参数用于计算颗粒的表面电位,建立抗剪强度与表面电位之间的关系。测试结果表明,可溶盐离子通过扩散的双电层改变土颗粒表面电位,引起结合水膜厚度的变化致使土颗粒之间的变形阻力发生改变,在宏观上表现为土体强度的变化。结合科威特Bubiyan岛的海港盐渍土软基加固工程,研究可溶盐含量对当地滨海盐渍土的强度与液塑限的影响,证实孔隙液离子浓度对人工土的强度的影响机制与变化规律同样适用于天然极细颗粒黏土,为从微细观角度揭示盐渍土的不良工程特性提供理论解释与试验基础。     

脂肪族离子固化剂改性水泥土的机理研究

水泥基材料加固土(水泥土)存在早期强度低、易开裂变形等性能缺陷。为对其改性,在水泥土中掺入含水率体积1/300～1/50不等的新型土壤固化材料,离子固化剂(ISS)。通过无侧限抗压强度试验、体积化学减缩试验,探究了ISS改性水泥土的可行性,并通过对表面吸附特性、物相构成演变、微结构特性的表征及分析,对ISS改性水泥土的机理进行了系统的研究。结果表明:ISS分子对于水泥土各组分具有显著的选择吸附性;ISS掺入水泥土后,能够提升体系内各组分的分散性并降低黏土矿物结合水的能力,进而加速土体内水化反应产物的生成,优化土体孔隙结构,提升土体强度并增大体积化学减缩;最优ISS掺量为1/150,过量的掺入会减弱ISS的改性效果,但可降低水泥土体积的化学减缩。相关成果可为离子固化剂应用于水泥土的改性提供一定的参照。     

离子固化剂改性蒙脱土吸附水特性及持水模型研究

采用不同浓度离子固化剂对天然钙蒙脱土进行改性处理,开展素土与改性土在相对湿度(P/P0)0.01～0.95区间的水汽等温吸—脱附试验,通过持水速率曲线、晶层d001演化曲线及红外光谱特征峰解析蒙脱土吸附水进程中主控因素的演化规律,据此提出水合状态变化的界限相对湿度区间,在此基础上,分别从阳离子水化能和晶层表面水合能角度,建立了离子固化剂改性蒙脱土微观持水方程。试验结果表明:对于钙蒙脱土,在0P/P00.15～0.2,阳离子与水分子结合形成单层"水化壳";在0.15～0.2P/P00.45～0.5,阳离子形成2层"水化壳";当0.45～0.5P/P00.8～0.9,晶层基面进一步吸附水分子形成2层完整水化膜。在极高吸力段(ψ200 MPa),蒙脱土持水能力只受控于层间阳离子水化作用,而在中高吸力段(15 MPaψ200 MPa),晶层基面与水之间的分子作用力是影响蒙脱土表面水合能及持水性状的主要因素。在特定吸力范围内,离子固化剂通过改变相应的物化性质参数(阳离子交换量、比表面积)从而弱化蒙脱土持水能力。基于微观水合机制所构建的持水方程能够很好预测本次试验及文献报道的数据结果,不同吸力段的持水模型可量化表征离子固化剂对蒙脱土吸附水性状的调控机理。     

阳离子型添加剂改良膨胀土研究

根据膨胀土颗粒表面的带电原理、膨胀土的胀缩机理,用自行研制的阳离子型添加剂对膨胀土进行改性,详细分析了改性膨胀土的改性机理,通过不同条件对改良后的膨胀土进行保养前和保养后的强度及水稳定性试验,并和素膨胀土进行了对比。试验结果表明:改良膨胀土的水稳定性大大优于素膨胀土,浸水后的强度高于对应素膨胀土;从添加剂的特性看,它对提高土体强度的作用不明显,但能大幅度地提高膨胀土的水稳定性;在加入添加剂的初期,土体的水稳定性不是很高,但随着龄期的增长,添加剂的作用愈加显示出来,并有良好效果。     

Inhibition effect of swelling characteristics of expansive soil using cohesive non-swelling soil layer under unidirectional seepage

Cohesive non-swelling soil (CNS) cushion technology is widely used to solve swelling deformation problems in expansive soil areas. However, the swelling inhibition mechanism is still not fully understood. In this study, the inhibition effect on expansive soil using a CNS layer was studied by performing five types of laboratory model tests under unidirectional seepage. The results showed that CNS cushion technology produced a sound inhibition effect on the swelling characteristics of expansive soil. It was shown that the cations in the CNS layer moved downward and accumulated on the surface of solids and produced an electrical environment inside the expansive soil. In this process, the adsorbed hydrated cations participated in ion exchange with the expansive soil, leading to the modification effect on its swelling potential. Meanwhile, the adsorbed water membrane surrounding the expansive soil aggregates formed by the hydrated cations obstructed further adsorption of water molecules, which inhibited the swelling development of expansive soil. Therefore, the swelling inhibition mechanism can be attributed to three factors: (i) modification effect, (ii) electrical environment, and (iii) deadweight of the CNS layer. The combined contribution of modification effect and electrical environment can be considered as an electric charge effect, which mainly controls the swelling characteristics of expansive soil.     

阳离子改性剂改良膨胀土试验研究

膨胀土化学改性是化学岩土工程中的一项重要课题,受到广大岩土工程师的重视。结合云南某高速公路路堤工程,采用一种阳离子改性剂对膨胀土进行化学改良试验,探讨了改性剂的改性机理和效果。结果表明:改性剂可以彻底改变膨胀土的亲水性、胀缩性,降低自由膨胀率,大大改善膨胀土的颗粒级配、强度特性、水理特性等物理力学性质。改性后的膨胀土黏粒减少,粉粒增多,孔隙明显减少,结构更加致密,改性剂的"团聚"、"凝胶"效果显著。改性后的膨胀土干密度随含水率变化较小,水稳性提高,可以满足设计施工要求,降低了工程造价,可见该改性剂对膨胀土的工程性质有很大程度的改善。     

Prediction of expansive soil swelling based on four micro-scale properties

A comprehensive study of expansive soil behavior includes understanding the surface phenomena of clay particles within the soil matrix. This research studies four micro-scale properties of four remolded expansive soils––matric suction, pH, surface conductance and percentage of montmorillonite––in order to predict soil swelling. An approach to approximate surface conductance is presented. Linear regression analyses were undertaken in an attempt to predict percent swell and swell pressure based on each of these micro-scale properties. Matric suction was found to be the most accurate predictor of the swelling behavior of the studied soils, which were initially compacted at optimum moisture content. Surface conductance, which is a combination of specific surface area, cation exchange capacity and cation mobility, also gave good predictions, except for one soil with high acidity.     

膨胀土的自由膨胀比试验研究

自由膨胀率是膨胀土判别与分类的一项重要指标,由于自由膨胀率的测试人为干扰因素较多,自由膨胀率的科学性和可靠性被广泛质疑,因此,寻求一种人为干扰因素少,又能反映膨胀土本质的合理而适用的指标具有重要意义。为此,引进了一种新的试验方法即自由膨胀比试验,膨胀比是10g烘干土样分别在盛有蒸馏水和煤油(或CCl4)的标准量筒(通常为50mL)中沉积稳定时的体积之比。阐述该指标的意义和试验方法,系统开展自由膨胀比试验和膨胀土物理力学指标试验,试验表明:相对自由膨胀率而言,自由膨胀比与阳离子交换量、比表面积、蒙脱石含量具有更好的相关性,能较好反映膨胀土的胀缩特性;将自由膨胀比与公路规范中常用的指标液限、塑性指数、标准吸湿含水量进行对比分析,发现自由膨胀比作为膨胀土判别与分类指标具有更高的可信度,同时自由膨胀比与这些指标相关关系也较好,可将其结合起来用于膨胀土的判别分类中。     

膨胀土填料改良试验研究

结合合宁线肥东试验段工程实践，从改良前后土的颗粒分析、物理性质、水理性质、强度试验和土的膨胀性指标测定等入手，着重阐述了石灰改良膨胀土的效果。     

Model test study on the protection of expansive soil slope with polymer waterproof coating

Polymer Waterproof Coating (PWC) is proposed to protect expansive soil slopes. Three groups of slope test models are developed to compare the efficiency of PWC, and the laws of water content, pore water pressure, soil deformation, and slope surface morphology change under repeated cycles of precipitation-evaporation environment are monitored and analyzed. The mechanism and effect of PWC protection on the expansive soil slope are discussed. The test results show that cyclic precipitation-evaporation has a significant impact on the water content, deformation, and slope surface shape of shallow layer of expansive soil slope. The change of water content and pore water pressure of slope caused by rainfall infiltration has hysteresis. The PWC-protected slope has significantly less soil deformation and water change than bare slope. The PWC protective layer blocks the water exchange between inside and outside the slope, keeping the slope water in a "dynamic and stable" state and inhibiting the slope surface cracking. The PWC protective layer significantly reduces the erosion of slope surface due to rainwater and has a significant effect on improving the integrity and strength of the slope soil. The PWC protection slope continues to have great stability even after numerous simulations of extremely harsh climates.     

Changes in the soil sorption complex of forest soils in Poland over the past 27 years

Soil acidification due to natural factors and acid deposition is expressed in changes in soil properties such as pH, cation exchange capacity (CEC) and Al saturation. The aim of this work was to establish whether the soil sorption complex of forest soils in Poland was subject to changes over the period 1978-2005. The removal of base cations from the soil sorption complex was observed. The intensity of cation leaching depends, inter alia, on the soil type and vegetation cover. Changes occurring over the past 27 years are best recognized in the saturation of CEC with base and acid cations. The composition of CEC, expressed as series of decreasing proportions of cations, showed replacement of Ca with H ions in the Rustic Podzol; a shift of Ca and Mg towards lower percentages and an increase in the proportion of H in the Eutric Cambisol and a drastic decrease in the Mg contribution in the Haplic Podzol. This suggests that the ion composition of CEC may be used as an efficient index for evaluating the acidification process.