Stabilization of Expansive Soil with Cement Kiln Dust and RBI Grade 81 at Subgrade Level

The present research work deals with an expansive high plastic clayey soil with cement kiln dust (CKD) and stabilizer (RBI Grade 81). The physical and engineering properties of soil are plasticity, compaction, unconfined compressive strength (UCS), consolidation and California bearing ratio (CBR) of the clayey soil and clay treated with CKD and stabilizer were determined. Soil chemistry was examined before and after treatment using scanning electron microscope (SEM) and elemental dispersive spectrometer. The clay mixed with CKD, CKD and RBI Grade 81 was found that optimum contents are 10 % (CKD), 15 % CKD with 4 % RBI Grade 81, respectively. The result indicates that CKD alone will decrease maximum dry density and increase optimum moisture content. CKD with RBI Grade 81 slightly increases maximum dry density and decreases optimum moisture content. UCS increased with CKD alone and CKD with RBI Grade 81 from 88.3 to 976 kN/m², respectively. CBR values were increased by the addition of CKD, CKD with RBI Grade 81 from 1.65 to 21.7 %. With the curing time of 3, 14 and 28 days, UCS and CBR values were increased due to pozzolanic reaction from cementations material. The treated soil has considerable reduction in compression index. SEM images clearly indicate the formation of CSH and CAH gel.     

膨胀土与红黏土石灰改性对比试验研究

为探讨石灰改性膨胀土与红黏土的强度发展规律,以生石灰与消石灰改性的南阳膨胀土与郴州红黏土为研究对象,进行了无侧限抗压、固结快速直剪和固结压缩试验的对比研究。研究发现：在1 a养生龄期内,石灰改性的南阳膨胀土与郴州红黏土无侧限抗压强度与养生龄期的对数基本呈线性关系;按大于最佳含水率3%制样的强度在养生28 d以后高于按最佳含水率制样;生石灰改性效果比消石灰改性效果好,由于矿物成分不同,石灰改性南阳膨胀土的效果比石灰改性郴州红黏土好     

Shear strength characteristics of Irbid clayey soil mixed with iron filling and iron filling–cement mixture

Iron filling and iron filling–cement mixture were used to improve the shear strength characteristics of Irbid clayey soil. For this purpose, five types of Irbid clay soils were obtained and mixed with iron filling and iron filling–cement mixture at different percentages. Two sets of prepared samples were mixed with the admixture. The first set was prepared by mixing the soil samples with iron filling alone at 2.5, 5.0, 7.5, and 10% by dry weight of the soil. The second set was prepared by mixing with iron filling–cement mixture at equal ratio of the same percentages of the first set. An unconfined compression test was performed in this study to measure the shear strength properties of the soils. The test results showed that the increase in the percentages of the iron filling and iron filling–cement mixture up to 10% will result in increasing the maximum dry density of the soil and increase the unconfined compressive strength and the secant of modulus of elasticity of the clayey soil. Also, the addition of iron filling–cement mixture increased the unconfined compressive strength and secant modulus of elasticity of the clayey soil higher than the addition of iron filling alone.     

含盐量对石灰固化滨海盐渍土力学强度影响试验研究

随含盐量的增加,滨海盐渍土中的盐分结晶形成了许多晶体颗粒,改变了土的颗粒级配和微结构形式,使土的力学强度发生变化。无侧限抗压试验和三轴压缩试验结果表明,随含盐量的增加,石灰固化土的无侧限抗压强度和抗剪强度降低;随养护龄期的增加,石灰固化土的无侧限抗压强度和抗剪强度增加;随含盐量的增加,固化土试样浸水和不浸水无侧限抗压强度之间的差值越来越小。工程应用滨海盐渍土时需控制土的含盐量。     

Strength behavior and microstructural characteristics of tropical laterite soil treated with sodium silicate-based liquid stabilizer

Although the effects of nontraditional stabilizers on the geotechnical properties of tropical soils has been the issue of investigation in recent years, the micro-structural characteristics of nontraditional soil additives and in particular selected additive (TX-85) have not been fully studied. Nontraditional soil stabilization additives are widely used for stabilizing marginal materials. These additives are low-cost alternatives to traditional construction materials and have different compositions. They also differ from one another while interacting with soil. In line with that, it was the objective of this research to investigate the strength properties and physicochemical mechanisms related to tropical laterite soil mixed with the liquid stabilizer TX-85. Macro-structure study, i.e., compaction, and unconfined compression strength test were used to assess the engineering and shear properties of the stabilized laterite soil. In addition, the possible mechanisms that contributed to the stabilization process were discussed using various spectroscopic and microscopic techniques such as X-ray diffractometry (XRD), energy-dispersive X-ray spectrometry, scanning electron microscopy, and Fourier transform infrared spectroscopy. From engineering point of view, the results indicated that the strength of TX-85 stabilized laterite soil improved significantly. The degree of improvement was approximately four times stronger than natural soil after a 7-day curing period. The XRD showed no crystalline products (gel form). Moreover, weathering effects were obvious in TX-85 treated samples in most of clay minerals’ peak intensities. These effects were reduced especially for kaolinite mineral inside the soil with curing time.     

基于生物酶的固土技术在香港的应用研究

传统加固土体的方法主要是通过在土中加入一定量的高性能掺合剂使之成为一种强度较高的复合土体,但这种方法需要较长的养护时间,且不经济。利用一种新型实用的生物酶固化技术,针对香港地区3种常见的海洋黏土、完全风化花岗岩和完全风化凝灰岩,开展了土体加固试验研究。试验结果表明,生物酶对海洋土的加固效果最好,强度增加最高可达20%,而生物酶对完全风化花岗岩的加固效果则不太理想,抗剪强度指标只有少许改变。此外,海洋土和完全风化凝灰岩的压缩性因为生物酶的作用反而有所增强。最后,从微观上分析了生物酶固土作用的本质,指出固土效果主要缘自于生物酶分子与土中的黏土矿物分子发生相互作用产生的胶结作用。     

Evaluation of Engineering and Cement–Stabilization Parameters of Clayey–Sand Mixtures under Soaked Conditions

Clay soils, especially clay soils of high or very high swelling potential often present difficulties in construction operations. However, the engineering properties of these clay soils can be enhanced by the addition of cement, thereby producing an improved construction material. Higher strength loss of cement stabilized clay soils after soaking in water is attributed to water absorbing capacity of the clay fraction (e.g. montmorillonite). Kaolinite and illitic soils are largely inert and resist to water penetration. These clays generally develop satisfactory strengths resulting to low strength reduction [Croft, 1967]. The swelling clays such as bentonite soaked in water, due to environmental conditions, result to volume increase causing macro and micro-fracturing in engineering structures. These fractures accelerate water penetration and consequently cause greater strength loss [Sällfors and Öberg-Högsta, 2002]. The water intrusion during soaking creates swelling and disrupts the cement bonds. The development of internal and external force systems in soil mass, due to soaking conditions, establish the initiation of slaking. Internal force system of a stabilized clayey soil consists of the resultant stresses established by the bonding potential of a cementing agent and the swelling potential of a clay fraction. In an effort to study this influence of soaking conditions and final absorbed water content on the stabilization parameters (cement, compaction, curing time), both unconfined compressive strength and slaking (durability) tests were carried out on two different cement stabilized clayey mixtures consisted of active bentonite, kaolin and sand.     

固化风沙土强度特性及固化机制试验研究

通过PX固化剂对库布其沙漠风沙土进行加固。对不同含水状态、不同固化剂掺量、不同养护龄期下固化风沙土的强度特性进行试验研究。试验结果表明,不同含水状态下风沙土的强度特性是不同的,相同固化剂掺量、相同养护龄期时,固化风沙土在最优含水率下的无侧限抗压强度远远大于饱和含水率下的强度。相同含水状态下固化风沙土无侧限抗压强度随固化剂掺量增加、养护龄期延长而增大,且在养护初期强度增长较快,当固化剂掺量为8 %、养护龄期为28 d时,固化风沙土强度满足国际上对固沙强度的要求。最优含水率下固化风沙土抗剪强度较风沙土有较大提高;当固化剂掺量为8 %时,固化风沙土凝聚力和内摩擦角均达到最大,此时固化风沙土抗剪强度约为风沙土的1.8倍。进而,通过扫描电镜对风沙土固化前后微观结构变化进行试验研究。研究结果表明,风沙土中掺入PX固化剂后,颗粒间由原来的弱连接变为胶结连接,解释了固化风沙土较风沙土强度得以提高、稳定性得以改善的内在原因。     

非饱和红粘土和膨胀土抗剪强度的比较研究

红粘土是对环境湿热变化敏感的塑性粘土,具有一般膨胀土吸水膨胀失水收缩的特性。与普通粘性土相比,红粘土与膨胀土的强度特性更为复杂。它既是土体抵抗剪切破坏能力的表征,也是计算路堑、渠道、路堤、土坝等斜坡稳定性以及支挡构筑物土压力的重要参数。通过试验研究讨论了红粘土与膨胀土的强度特性以及与一般粘性土的差别及其各种影响因素,并探讨了非饱和红粘土与膨胀土的抗剪强度指标与含水量之间的相关关系。试验结果表明,红粘土与一般膨胀土的吸水膨胀规律完全相同。其试验结果可为红粘土与膨胀土地区工程设计与建设提供参考依据。     

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.     

碱激发材料固化低液限粉黏土路用性能及抗冻融特性研究

以伊犁地区S315线蜂场至尼勒克段低液限粉黏土为研究对象,以碱激发材料为固化剂,对粉质黏土和其固化土开展了路用性能指标试验与冻融循环试验,并利用电镜扫描试验(SEM)与X射线衍射试验(XRD)研究了固化土的微观特征,探讨了碱激发材料对粉质黏土路用性能指标与抗冻融特性的影响.试验结果表明,固化土的无侧限抗压强度与抗剪强度...     

Influence of grain size gradation of sand impurities on strength behaviour of cement-treated clay

In nature, soils are often composed of varying amounts of clay, silt and sand. Variation of the percentage of these compositions can affect the final strength of the soils when stabilised with cement. In this study, focus was placed on clayey soils with different gradation of sand impurities up to 40% in mass. An extensive study of such clayey soils treated with cement was investigated. For the results, it is noted that water:cement ratio was a major influence of strength development of cement-treated clayey soils. In contrast, the soil:cement ratio was found to have minor effects on the strength development. The presence of sand impurities has a significant reduction on the strength development of the cement-treated clayey soil mixture due to more free water available for hydration. The use of free-water:cement ratio is adopted which was shown to be capable of adjusting for such change in amount of free water and water holding capacity of the clay which is determined with Atterberg’s liquid limit tests. The effects of gradation (fine, coarse and well-graded) of the sand impurities were found to affect strength development minimally, owing to similarities in their liquid limits when mixed with clay. Ordinary Portland cement (OPC)-treated clayey soils produced a more rapid gain in strength but lower final strength at 28 days of curing as compared with Portland blast furnace cement (PBFC). This is found to be persistent for different gradation of sand impurities. A linear correlation can be established based on the log of the unconfined compressive strengths developed at different curing age, with slopes of these linear trends found to be similar for PBFC and OPC-treated clayey soil specimens. Finally, a strength prediction model comprising of these findings is developed. The parameters adopted in this model coincide with values proposed by past studies, thereby validating the robustness of the model. The practical benefits from this study offer a quality control scheme to forecast long-term performance of cement-treated clayey soils as well as optimise cement dosage in cement stabilisation to produce a more cost-effective and less environmental-invasive usage of the technology in geotechnical applications.

     

滇池固化淤泥重塑土的重塑时机及强度恢复特性试验

采用无侧限抗压强度试验和直剪试验,从单轴抗压强度、黏聚力、内摩擦角的角度探求了淤泥固化土重塑时导致的强度折减和重塑后土的强度恢复特性,并分析了重塑前养护龄期（T_前）、重塑后养护龄期（T_后）、水泥掺灰比（a_c）的影响。试验结果表明,重塑时机的选择对淤泥固化土的强度折减程度有显著的影响：T_前越长,破碎过程带来的强度折减越严重,且大致满足a_c越大、强度折减越严重的规律。从强度恢复特性来看：小水泥掺灰比的固化淤泥土经过T_后,其强度恢复较好;大掺灰比的重塑土其强度则较难恢复至固化土的水平,T_前越长,强度恢复越不利。从而得出了大掺灰比固化土宜早重塑,小掺灰比的重塑时间可适当延长的规律。     

Effects of soil pulverization quality on lime stabilization of an expansive clay

Lime stabilization is an effective way of stabilizing expansive clays, which cause significant environmental problems both as earth and foundation materials. There are considerable environmental benefits in using the in situ lime-stabilized expansive soils in the construction of road pavements, fill or foundations instead of importing valuable granular materials. However, due to high plastic nature of these clays, achieving appropriate pulverization in field applications is a difficult task. This paper presents the results of a laboratory investigation to determine the effects of soil pulverization quality on lime stabilization of a local expansive clay. Effect of mellowing the soil–lime mixtures for 24 h was also studied to find out whether this would compensate for poor pulverization. The clay studied had swelling pressures varying between 300 and 500 kN/m² and free swell potential as high as 19%. In this study, 3, 6 and 9% lime by dry weight were used for lime-stabilized samples. Unconfined compression strength, failure strain and Secant Elasticity Modulus values were measured through unconfined compression strength testing. The results of the study showed that lime stabilization improved plasticity, workability, compressive strength, elastic moduli and swelling and compressibility behavior of the expansive clay. While mellowing did not have a definite effect on the measured strength and moduli values, soil pulverization quality considerably affected the unconfined compression strength and Secant Elasticity Modulus values. The higher the percentage passing No. 4 sieve, the higher the effectiveness of lime treatment. Based on the data obtained in this study, two original equations were derived to assign Secant Elasticity Modulus based on unconfined compression strength, for different soil pulverization qualities. Microfabric investigations conducted by Environmental Scanning Electron Microscope and Mercury Intrusion Porosimetry exposed the effect of lime stabilization on fabric, porosity and pore size distributions. The results of the study clearly demonstrated that if enough time and effort were not given to soil pulverization process in lime stabilization works in field applications, lower performance and therefore increased environmental problems should be expected.     

土性对工程泥浆固化强度影响规律及微观机理

本文开展了一系列不同液限高分子吸水树脂固化工程泥浆无侧限抗压强度试验, 探讨了泥浆土液限对固化效率的影响规律, 对比研究了掺入高岭土对泥浆固化强度的改进程度, 最后基于XRD和SEM试验揭示了液限和高岭土对固化泥浆强度影响的微观机理。结果表明: 随着泥浆土液限的增大, 固化泥浆土强度逐渐降低, 固化效率随着泥浆土液限增大显著衰减, 当液限增加10%, 固化泥浆土强度qu平均减少48.2%。然而高岭土的掺入则显著提升了固化泥浆土的强度, 并且强度增长率随着龄期逐渐增大, 对于龄期为90天时, 增加40%高岭土能够提升固化泥浆土强度qu 1.17倍。微观结构试验表明泥浆土液限变化对水化产物产量的影响较小, 固化泥浆土强度随泥浆土液限减小主要是由于固化泥浆土孔隙随着泥浆土液限增大而增多, 使得微观结构松散从而导致强度降低。高岭土的掺入则显著提升了固化泥浆土的水化产物产量, 增强了固化泥浆土胶结强度, 从而提升了固化泥浆土强度。因此, 在实际工程中, 一方面可以通过调配泥浆土液限来提高固化效率; 另一方面可以通过掺入高岭土或者一些高岭土基废弃物(如高岭土尾矿)来提高固化强度, 实现“以废制废”绿色环保的理念。     

Use of Sewage Sludge Ash and Hydrated Lime to Improve the Engineering Properties of Clayey Soils

Using various additives has been considered as one of the most common stabilization methods for improvement of engineering properties of fine-grained soils. In this research the effect of sewage sludge ash (SSA) and hydrated lime (HL) on compressive strength of clayey soil was investigated. For this purpose, 16 kinds of mixtures or treatments were made by adding different amounts of SSA; 0, 5, 10 and 15% by weight and HL; 0, 1, 3 and 5% by weight of a clayey soil. First, compaction characteristics of the treatments were determined using Harvard compaction test apparatus. So that, 12 unconfined compressive strength test specimens were made using Harvard compaction mold from each treatments taking into account four different curing ages, including 7, 14, 28 and 90 days in three replications. Therefore, a total of 192 specimens were prepared and subjected to unconfined compressive strength tests. The results of this study showed that the maximum dry density of the treated soil samples decreases and their optimum water content increases by increasing the amount of SSA and hydrated lime in the mixtures. It is also found that the adding of HL and SSA individually would increase the compressive strength up to 3.8 and 1.5 times respectively. The application of HL and SSA with together could increases the compressive strength of a clayey soil more efficiently even up to 5 times.     

Stabilization of lateritic soils with phosphoric acid

Summary This paper describes a laboratory study on the stabilization of lateritic soils with phosphoric acid-H₃PO₄. This method is most promising for road and airport pavement construction in tropical regions where fine textured lateritic soils (red clays and silts) occur over large areas. The iron and aluminum phosphates formed are hard and insoluble. The main source of iron is free iron oxide, and the aluminum sources are free aluminum oxide, exchangeable cations and clay minerals (hydrated aluminum silicates). Four different soil samples were studied, but the most comprehensive study was carried out with a lateritic soil evolved from weathered basaltic bedrock. The variables of the test specimens were: percentage of acid, moulding water content, compaction energy, and curing time. Strength tests performed were the axial or unconfined compression test and the indirect tensile or diametrical compression test. With 5% of phosphoric acid to dry weight of soil, values of compressive strength around 4.0 MPa were obtained after 28 days curing.     

Sustainable Improvement of Tropical Residual Soil Using an Environmentally Friendly Additive

Many tropical residual laterites have relatively poor engineering properties due to the significant percentage of fine-grained soil particles that they contain, which are formed by the soil weathering process. The widespread presence of laterite soils in tropical regions often requires that some form of soil improvement be performed to allow for their use in various civil engineering applications, such as for road base or subbase construction. One of the most commonly utilized stabilization techniques for laterite soils is the application of additives that chemically react with the minerals that are present in soil to enhance its overall strength; effective soil stabilization can allow for the use of site-specific soils, and can consequently result in significant cost savings for a given project. With an increasing focus on the use of more environmentally friendly and sustainable materials in the built and natural environments, there is an emerging interest in eco-friendly additives that are an alternative to traditional chemical stabilizers. The current study examines the viability of xanthan gum as an environmentally friendly stabilizer that can improve the engineering properties of tropical residual laterite soil. Unconfined compressive strength (UCS) tests, standard direct shear tests, Brunauer, Emmett, and Teller (N₂-BET) surface area analysis tests and field emission scanning electron microscopy (FESEM) tests were used to investigate the effectiveness of xanthan gum for stabilization of a tropical laterite soil. The UCS test results showed that addition of 1.5% xanthan gum by weight yielded optimum stabilization, increasing the unconfined compressive strength of the laterite soil noticeably. Similarly, direct shear testing of 1.5% xanthan gum stabilized laterite specimens showed increasing Mohr–Coulomb shear strength parameters with increases in curing time. From the FESEM results, it was observed that the stabilization process modified the pore-network morphology of the laterite soil, while also forming new white layers on the surface of the clay particles. Analysis of the test results indicated that xanthan gum stabilization was effective for use on a tropical residual laterite soil, providing an eco-friendly and sustainable alternative to traditional soil stabilization additives such as cement or lime.     

STW型生态土壤稳定剂改良工程粘性土胀缩性试验研究

针对STW型生态土壤稳定剂改良粘性土的胀缩性进行了试验研究。实验结果表明:STW型土壤稳定剂可以有效地改良粘性土的胀缩性;土颗粒粒径的大小、稳定剂的掺量对改良粘性土的胀缩性均有不同程度的影响;在平均粒径为0.75mm时,改良土和素土的无荷膨胀率均达到最低值;改良土的胀缩性随着稳定剂掺量的增大而减小。     

侵蚀影响下水泥土的力学性质试验研究

港珠澳大桥拱北隧道地处沿海地区,其地下水与海水相连,隧道基底采用粉体喷射搅拌法和高压喷射注浆法等方法进行加固,加固产生的水泥土在海水侵蚀性离子作用下其强度和稳定性会发生变化,从而对工程安全产生影响。根据上述两种施工工艺,制作内部含侵蚀物质和不含侵蚀物质的两种水泥土试块,配制多种不同浓度的单组分的化学溶液来模拟海水侵蚀环境,将制备的水泥土试块置于侵蚀溶液中进行预定时间的短时（≤28 d）浸泡,通过无侧限抗压试验、电镜扫描以及离子色谱测定,分别得到了单组分侵蚀溶液短时浸泡下水泥土试块无侧限抗压强度、微观结构随侵蚀溶液浓度和侵蚀时间的变化规律,以及侵蚀环境中离子浓度随侵蚀时间的变化规律。基于海水化学成分,配制多种不同浓度的双组分的化学溶液来模拟海水侵蚀环境,将制备的内部含侵蚀物质的淤泥质土水泥土试块置于侵蚀溶液中进行预定时间的长时（≥90 d）浸泡,通过无侧限抗压试验得到了双组分侵蚀溶液长时浸泡下水泥土试块无侧限抗压强度变化规律。试验结果可为临时性及长期性水泥土工程的设计及安全维护提供一定参考依据。