水玻璃固化硫酸盐渍土强度特性及固化机制研究

盐渍土化学固化法是解决盐渍土盐胀、溶陷和腐蚀等不良工程问题的有效方法之一。通过无侧限抗压强度试验、X射线衍射试验、化学成分分析和扫描电镜试验研究了石灰粉、煤灰、水玻璃联合固化硫酸盐渍土的强度特征,分析探讨了其固化机制。试验结果表明：石灰含量小于8%时,石灰、粉煤灰、水玻璃联合固化硫酸盐渍土的抗压和抗剪强度较石灰粉煤灰固化土有大幅度提升,固化土强度随水玻璃浓度几乎呈线性增长。水玻璃固化硫酸盐渍土强度增加的机制在于：水玻璃的碱激发粉煤灰作用和水玻璃与盐渍土中化学成分的吸附作用所生成各类凝胶的填充和包裹,使得骨架颗粒的接触面积增大,颗粒之间的孔隙逐步减小,骨架颗粒由点接触变为面接触,固化盐渍土通过凝胶而黏结成为一个紧密的空间网状整体结构,土体强度得以提高。同时,复杂的物理化学作用大幅度降低了固化盐渍土中 含量,有效地抑制了硫酸盐渍土的盐胀特性。     

硅酸钠改良水泥基稳定磷石膏在路面基层中的试验研究

磷石膏是一种固体废弃材料,磷石膏的堆存浪费大量土地资源,严重污染土壤与水环境,并可能引发滑坡溃坝,因此进行磷石膏的资源化利用迫在眉睫。本文采用硅酸钠改良水泥基稳定磷石膏,开展路面基层试验研究。通过无侧限抗压强度试验、水稳定性试验、干缩试验及扫描电镜试验,研究了硅酸钠在不同掺量、掺入方式、养护龄期条件下改良水泥基稳定磷石膏的物理力学特性,揭示了硅酸钠促进水泥水化并产生水化硅酸钙,从而提高混合料强度的改良机理。试验结果表明,当溶于水的硅酸钠掺量为2%~4%时,可有效改良水泥基稳定磷石膏混合料的抗压强度、水稳定性能、失水率及干缩应变,并提出在路面基层施工后的4~5 d内,是有效控制路面基层失水与干缩的最佳时间,从而可避免因水分快速散失导致裂缝的产生。     

石灰及其外加剂固化天津滨海软土的试验研究

天津滨海软土力学性质较差,不能直接满足工程需要,在软土中加入固化剂能有效提高软土的工程力学性能,但若在固化剂中再添加适量外加剂,又能再次提高固化土的强度。本文以石灰作为主剂,水泥、石膏作为辅剂改良天津滨海软土,以无侧限抗压强度作为固化效果判断标准,同时进行相应的微观结构测试,并对破坏后的试样进行抗压试验。试验结果表明:水泥的最佳掺量仅随石灰掺量不同而变化,如12%的石灰固化土中,水泥掺量不超过3%可以最好地提高石灰固化土强度; 石膏则不能改善土体强度,并且会使土体水稳定性差,遇水开裂。纯石灰固化土及掺外加剂的石灰固化土都是低压缩性土,各种力学性质都得到明显提高,其破坏形式为脆性破坏,破坏后强度很低且不能恢复,在实践中值得重视。微观结构分析表明:固化土中有CSH网状胶凝(水化硅酸钙)、针状钙矾石、无定形文石(CaCO3)、Ca(OH)2晶体等能够填充孔隙、胶结颗粒的物质生成,有效、适量的生成物有利于固化土强度的提高。土体中总孔隙个数及总颗粒个数都随荷载的增加而增多,孔隙面积、孔隙等效直径及颗粒等效直径都随荷载的增加而减少。     

Compressive and Tensile Behavior of Polymer Treated Sulfate Contaminated CL Soil

In this study, the compressive and tensile behavior of polymer treated sulfate contaminated CL soil was investigated. Based on the information in the literature, a field soil was contaminated with up to 4 % (40,000 ppm) of calcium sulfate in this study. In addition to characterizing the behavior of sulfate contaminated CL soil, the effect of treating the soil with a polymer solution was investigated and the performance was compared to 6 % lime treated soil. In treating the soil, acrylamide polymer solution (15 g of polymer dissolved in 85 g of water) content was varied up to 15 % (by dry soil weight). Addition of 4 % calcium sulfate to the soil decreased the compressive and tensile strengths of the compacted soils by 22 and 33 % respectively with the formation of calcium silicate sulfate [ternesite Ca₅(SiO₄)₂SO₄)], magnesium silicate sulfate (Mg₅(SiO₄)₂SO₄) and calcium-magnesium silicate (merwinite Ca₃Mg(SiO₄)₂). With the polymer treatment the strength properties of sulfate contaminated CL soil was substantially improved. Polymer treated sulfate soils had higher compressive and tensile strengths and enhanced compressive stress–strain relationships compared to the lime treated soils. Also polymer treated soils gained strength more rapidly than lime treated soil. With 10 % of polymer solution treatment, the maximum unconfined compressive and splitting tensile strengths for 4 % of calcium sulfate soil were 625 kPa (91 psi) and 131 kPa (19 psi) respectively in 1 day of curing. Similar improvement in the compressive modulus was observed with polymer treated sulfate contaminated CL soil. The variation of the compacted compressive strength and tensile strength with calcium sulfate concentrations for the treated soils were quantified and the parameters were related to calcium sulfate content in the soil and polymer content. Compressive stress–strain relationships of the sulfate soil, with and without lime and polymer treatment, have been quantified using two nonlinear constitutive models. The constitutive model parameters were sensitive to the calcium sulfate content and the type of treatment.     

Lime stabilization of clay minerals and soils

Clay soil can be stabilized by the addition of small percentages, by weight, of lime, thereby enhancing many of the engineering properties of the soil and producing an improved construction material. In order to illustrate such improvements, three of the most frequently occurring minerals in clay deposits, namely, kaolinite, montmorillonite and quartz were subjected to a series of tests. As lime stabilization is most often used in relation to road construction, the tests were chosen with this in mind. Till and laminated clay were treated in similar fashion. With the addition of lime, the plasticity of montmorillonite was reduced whilst that of kaolinite and quartz was increased somewhat. However, the addition of lime to the till had little influence on its plasticity but a significant reduction occurred in that of the laminated clay. All materials experienced an increase in their optimum moisture content and a decrease in their maximum dry density, as well as enhanced California bearing ratio, on addition of lime. Some notable increases in strength and Young's Modulus occurred in these materials when they were treated with lime. Length of time curing and temperature at which curing took place had an important influence on the amount of strength developed.     

电阻率法评价膨胀土改良的物化过程

掺石灰、粉煤灰是工程中通常采用的改良膨胀土的方法。土电阻率是土的基本物理指标之一,其变化可反映土的其他物理性质指标的变化。通过掺灰改良膨胀土不同养护龄期下的电阻率测试以及膨胀量、膨胀力及无侧限抗压强度等试验研究,探讨了掺灰改良膨胀土养护过程中的物理化学反应过程。根据养护过程中的电阻率随龄期的变化规律,可将改良膨胀土的物理化学反应过程划分为瞬时反应阶段、主体反应阶段、残余反应阶段和稳定阶段4个不同阶段。针对改良膨胀土质量控制和评价体系中存在的不足,提出了基于电阻率指标的改性膨胀土的质量评价方法,通过试验证实了该方法的有效性和实用性。     

干湿循环对石灰粉煤灰固化石油污染土抗压强度的影响

中国北部沿海地区夏季多雨,春季干燥多风,土体吸水膨胀、脱水收缩,降低了固化土的抗压强度,研究固化土干湿交替条件下的力学稳定性是实现其工程利用的前提。室内模拟干湿循环,借助无侧限抗压强度指标探究石灰粉煤灰固化石油污染土的力学分布规律。结果表明:经历干湿循环后固化污染土的质量前6次下降较小,7~8次下降明显,9次后趋于稳定,最大下降幅度为4.5%;固化污染土的抗压强度随干湿循环次数的增加而增强,3次循环后抗压强度较初始强度增加了35%,之后逐渐减弱,7次循环后强度趋于稳定,稳定时强度达到初始强度的70%;固化污染土强度的水稳性随含油率的提高逐渐降低,破坏形态随干湿循环次数的增加由软化型逐渐向硬化型转变;当二灰比为0.75,抗干湿循环稳定性较好。石油污染土重新利用时应注意干湿循环对工程的影响。     

Effect of polypropylene fibre and lime admixture on engineering properties of clayey soil

In order to reduce the brittleness of soil stabilized by lime only, a recent study of a newly proposed mixture of polypropylene fibre and lime for ground improvement is described and reported in the paper. To investigate and understand the influence of the mixture of polypropylene fibre and lime on the engineering properties of a clayey soil, nine groups of treated soil specimens were prepared and tested at three different percentages of fibre content (i.e. 0.05%, 0.15%, 0.25% by weight of the parent soil) and three different percentages of lime (i.e. 2%, 5%, 8% by weight of the parent soil). These treated specimens were subjected to unconfined compression, direct shear, swelling and shrinkage tests. Through scanning electron microscopy (SEM) analysis of the specimens after shearing, the improving mechanisms of polypropylene fibre and lime in the soil were discussed and the observed test results were explained. It was found that fibre content, lime content and curing duration had significant influence on the engineering properties of the fibre–lime treated soil. An increase in lime content resulted in an initial increase followed by a slight decrease in unconfined compressive strength, cohesion and angle of internal friction of the clayey soil. On the other hand, an increase in lime content led to a reduction of swelling and shrinkage potential. However, an increase in fibre content caused an increase in strength and shrinkage potential but brought on the reduction of swelling potential. An increase in curing duration improved the unconfined compressive strength and shear strength parameters of the stabilized soil significantly. Based on the SEM analysis, it was found that the presence of fibre contributed to physical interaction between fibre and soil whereas the use of lime produced chemical reaction between lime and soil and changed soil fabric significantly.     

冻融循环对硅酸钠固化黄土力学性质的影响

硅酸钠作为一种灌浆材料,常被用于湿陷性黄土的固化工程。冻融循环会影响季节冻土区固化黄土的结构,从而导致其力学性质发生变化。以兰州黄土为研究对象,分别对冻融循环前后掺量为3%的硅酸钠固化黄土进行压汞试验和力学强度试验,从强度、刚度、能量耗散和土体微观孔隙结构等方面探讨冻融循环作用对硅酸钠固化黄土力学特性的影响。结果表明：一方面,冻融作用会增大土中平均孔隙直径,降低微孔隙含量,导致土样产生裂隙;另一方面,硅酸钠反应生成的Na⁺在水分梯度作用下迁移至土样和裂隙表面并重结晶,上述作用破坏了土颗粒间胶结,最终大幅度劣化了固化黄土力学性能。随着冻融次数的增加,硅酸钠固化黄土无侧限抗压强度在单轴加卸载过程中的能耗值、弹性变形量和滞回环回弹模量均呈现下降趋势,冻融20次后强度降幅高达85.33%,而能耗均值与回弹模量均值分别为未冻融状态下的8.68%和20.70%,即固化土消振性与刚度大幅劣化。鉴于此情况,季节冻土区盐渍黄土硅酸钠的固化处理措施应慎重使用。     

Shear Strength Parameters of Improved Peat by Chemical Stabilizer

The present research aimed to discuss the applicability of cationic grouts in geotechnical engineering. The effects of several cationic stabilizers such as monovalent (sodium silicate), divalent (calcium oxide and calcium chloride), and trivalent (aluminum hydroxide) were investigated on shear strength improvement of tropical peat samples. The unconfined compressive strength (UCS) tests were performed after the time frame of 7, 21, and 30 days as curing time, respectively. Apart from the physicochemical characteristics of the stabilized peat, scanning electron microscopy and energy-dispersive X-ray spectroscopy tests were also carried out to study the ongoing microstructural changes. It is to be noted that the shear strength values for peat samples rose to 8, 6, 6, and 4 % of sodium silicate, calcium oxide, calcium chloride, and aluminum hydroxide, respectively. The highest observed UCS outcome is the one taken from the calcium oxide where the UCS of treated peat after 30-day curing time increased to 76 kPa. The strength changes resulted from the various cationic stabilizers can best be explained via the consideration within the mineralogical composition as well as those physicochemical changes happening in the peat.     

重塑石灰土的力学特征与性能劣化机制分析

石灰土在公路等工程中应用很广泛,随着公路改扩建等工程的迅速增多,面临如何处理与利用废弃石灰土的难题。通过对比分析素土、石灰土、重塑石灰土的压缩、强度等力学指标,探讨重塑石灰土的力学特征。结果表明,重塑石灰土压缩系数与石灰土相比提高了2～3倍,无侧限抗压强度损失了30%～40%,内摩擦角增大了1.2倍,黏聚力降低了40%。提出用劣化系数评价重塑石灰土的力学特性劣化程度,并从石灰处治红黏土的团粒化、碳化、灰结机制等角度分析了重塑石灰土性能劣化的本质原因。与素土相比,石灰土的黏粒（d <0.002 mm）含量减少而粗粒（d >0.074 mm）含量增加,从而提高了石灰土的内摩擦角。但重塑过程则破化了石灰土中的胶结结构致使重塑石灰土的黏聚力降低,从而影响重塑石灰土的其他力学性能指标。     

Utilization of lime,slag and fly ash for improvement of a colluvial soil in New South Wales,Australia

In Australia, colluvial soils form large terrains which are often subjected to considerable erosion and mass movement. This study presents a laboratory evaluation of the improvement effected by hydrated lime, milled blast furnace slag and fly ash on a fine grained (erosive) colluvial soil in New South Wales, Australia. Geotechnical tests were conducted to determine the compaction and consolidation characteristics and the compressive and shear strength properties of the blended and natural soil specimens. The effect of these additives on the Atterberg limits and pH levels is also investigated. As large amounts of fly ash and steel slag are produced in New South Wales, it is economically attractive to utilize these industrial by-products for ground improvement rather than employing conventional methods such as lime treatment. This study demonstrates that for the colluvial soil tested, milled slag is the most effective in terms of improving the internal friction angle of the treated soil, while lime is the most suitable for achieving the optimum compressive strength. Non-pozzolanic fly ash is found to be inappropriate as a soil improving agent. The cost of ground treatment using the various additives is also estimated and compared.     

重塑石灰土的强度恢复方法与机制初探

石灰稳定土工程翻修改造后会产生大量的石灰土弃渣,为避免污染环境和节约工程投资,需重新利用破碎的石灰土进行填筑。但石灰土破碎后强度急剧降低,需要添加胶凝材料提升其力学性能。以重塑石灰土为研究对象,通过添加5%石灰或水泥进行再改良,对比分析两种再改良土的强度和压缩性等力学指标,结果表明,石灰再改良土的力学特性优于水泥再改良土。借助粒度分析、电镜扫描、X衍射和热重分析试验手段揭示了石灰再改良土性能优越的内在机制,发现石灰再改良土中的石灰和石灰土团粒能形成很好的胶结;但水泥未能和石灰土团粒形成有效胶结,自身形成了边-面和边-边接触的片状多孔架构。重塑石灰土残存的氢氧化钙是引起水泥再改良土性能劣于石灰再改良土的主要诱因。     

工业废渣加固土强度特性

工业废渣的资源化是解决工业废渣环境污染的有效途径之一。以粉煤灰和高炉矿渣为固化剂,石灰为碱性激发剂,对黏土进行加固。通过室内试验的方法,分析固化剂掺入量、养护龄期等对固化土无侧限抗压强度、pH值和饱和度等发展规律的影响。试验结果表明,固化土的无侧限抗压强度随固化剂掺入量的增加而增大,随养护龄期的增加而增大,提出一个综合反映固化剂掺入量、养护龄期和压实度等因素对固化土强度影响规律的综合影响因子,固化土强度与综合影响因子呈负指数函数关系;粉煤灰+石灰和高炉矿渣+石灰可有效改良土体无侧限抗压强度特性;石灰是一种有效的碱性激发剂,可提供工业废渣发生火山灰反应的高碱性环境。试验成果为工业废渣改良不良土质的设计提供试验依据。     

滨海盐渍土的固化方法及固化土的偏应力-应变

滨海盐渍土可使用水泥、石灰、粉煤灰和高分子材料SH固土剂单独及联合固化,以提高土的强度、抗变形能力和水稳性。为研究各种固化方法固化盐渍土的抗变形能力和偏应力-应变特征,通过三轴UU压缩试验得到盐渍土和6种固化盐渍土的偏应力-应变曲线。曲线显示：水泥＋石灰类固化土呈应变软化型、石灰＋粉煤灰类固化土呈应变软化型、石灰类固化土呈应变硬化型。掺入SH固土剂,提高了固化土的浸水前后的强度,同时也增强了固化土的水稳性。掺入SH固土剂使固化土达到偏应力峰值所需的应变增加,即抗变形能力增强;0.9%SH固土剂+12%石灰+36%粉煤灰固化土具有适中的强度、良好的弹性变形和水稳性的优点,作为轻质路堤填料使用,还可减少滨海地区软土路基的沉降量,这使其成为滨海盐渍土的6种固化方案中的最适宜方案。     

Improvement of Clayey Soil with Lime and Industrial Sludge

Industrial waste generation has reached up to millions of tons yearly. One way to solve the problems of the large accumulating amount of waste could be to incorporate it into the soil; thus, finding a way for the use of industrial waste could be a quest for soil improvement studies. Industrial sludge in certain pozzolanic form reacts with soil and possesses cementitious properties. This paper illustrates the utilization of lime, steel and copper sludge in improvement of high plasticity clayey soil. The influence of stabilizer type, different curing times and various ratios of lime to sludge are evaluated by Atterberg limits, standard proctor compaction, unconfined compressive strength and unconsolidated undrained strength in triaxial test. The  test results show that adding lime and sludge results in an increase in maximum strength. Moreover, the strength of soil increases with the increase of curing time. Utilizing stabilizers also influences plasticity index and compaction parameters. Finally, the results demonstrate that steel sludge has better performance than that of copper sludge in term of strength development.     

冻融循环对二灰和改性聚乙烯醇固化盐渍土力学性能的影响

随季节性变化的冻融循环作用对土体结构有显著的影响。为降低盐渍土对环境温度的敏感性并将其应用于工程中,提出以石灰、粉煤灰和改性聚乙烯醇(MPA)为固化材料的联合固化方法。先通过无侧限抗压强度(UCS)和微观扫描试验评价固化效果,构建固化材料的参数范围,再将抗剪强度(黏聚力和内摩擦角)与正交试验相结合,分析各因素的影响,明确最佳组合参数。结果表明:石灰+粉煤灰+MPA联合固化有助于提高盐渍土的强度,联合固化盐渍土的UCS为1 130.25 kPa,是盐渍土(218 k Pa)的5.18倍;联合固化盐渍土的冻融强度满足工程规范(JTG 3430-2020)要求。冻融循环作用下联合固化盐渍土的UCS稳定值为700k Pa,且3次循环后的波动范围在5%左右。适宜配比下联合固化盐渍土的抗剪强度(黏聚力和内摩擦角)在3次冻融循环后为208.2 kPa和38.56°。各因素的敏感性由高到低依次为养护时间、石灰掺量、MPA掺量、干密度、含盐量和冻融循环次数,随石灰、粉煤灰和MPA掺量的增加,联合固化盐渍土强度增大并趋于稳定,固化参数的优化可有效弱化冻融作用对滨海盐渍土的影响。结合抗压及抗剪强度试验结果,...     

Some geotechnical properties of a lime-stabilized laterite containing a high proportion of aluminium oxide

The engineering properties of many soils can be improved by lime stabilization. Not all such soils, however, show improved strength. Such non-reactive soils will show no strength increase regardless of lime type and percentage, curing environment and duration of treatment.The type and amount of minerals and elements may either facilitate or inhibit increase in strength. The strength of soils possessing high proportions of aluminium oxide could be reduced when stabilized with lime and cured over a long period at a high temperature. This decrease in strength is due to the type of reaction products formed.A Kenyan laterite with a high proportion of aluminium oxide was stabilized with different percentages of lime and cured over periods of uo to 28 days. The results show that with a lower percentage of lime, the unconfined strength decreases with increase in curing time. However, when the amount of lime is increased, there is an increase in strength with curing time. The immediate California Bearing Ratio (C.B.R.) values are observed to be functions of density and moisture content. The higher the density, the greater the C.B.R. values.     

Classification,shear strength,and durability of expansive clayey soil stabilized with lime and perlite

An experimental study was performed to investigate the effect of perlite and perlite–lime admixtures on classification, shear strength, and durability properties of an expansive soil containing smectite clay minerals. Two types of mixtures, namely soil–perlite and soil–perlite–lime, were prepared with different percentages of perlite and compacted with standard Proctor energy at their optimum water contents. Samples of 38 mm diameter and 76 mm height for durability tests and square samples of 60 mm edge for shear box test were taken and preserved until test time in a desiccator. Disturbed samples were also taken to determine liquid and plastic limits. The expansive soil shows behavior of fine sand and silt due to pozzolanic reactions in microstructure caused by addition of lime and perlite. Although apparent cohesion of treated soil decreased with increasing amount of perlite for both types of samples, perlite–lime-treated samples had higher apparent cohesion than only perlite-treated samples. Large increments in angle of shearing resistance were obtained with increasing usage of perlite. Samples stabilized with only perlite could not show enough durability at the durability tests based on volumetric stability and unconfined compression strength. However, samples stabilized with lime and more than 30 % perlite proved to have enough durability and shear strength.     

Physico-Chemical and Shrinkage Properties of Highly Organic Soil Treated with Non-traditional Additives

The changes in the shrinkage and physicochemical properties of untreated and treated organic soil using several chemical additives were investigated. In order to evaluate the effect of each chemical solution on the peaty soil environment different experiments namely; shrinkage limit, unconfined compressive strength (UCS), pH test, and water content were undertaken. The results of the laboratory experiments are further proved and interpreted using the X-ray diffraction, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy tests. The result unveils the structure of the treated soil significantly changed depending upon the used additive type and concentrations. The rate of shrinkage largely decreased when sodium silicate additives are used. In addition, it was observed that UCS value increased up to 500% and water content reduced up to 50% in comparison with untreated samples, depend on the amount of used non-traditional additives. The SEM micrographs of the sample before and after treatment validate the results obtained and analyzed from experiments.