粉煤灰加固软土地基的室内配方试验研究

粉煤灰是一种强度较高的工业废弃物,可用来加固软土地基。本文进行了粉煤灰加固土的室内配方试验,分别将生石灰或水泥与粉煤灰按照不同的比例干拌均匀后,再与不同含水量的软土人工拌和均匀,测定了4个龄期的无侧限抗压强度,并进一步分析了其加固机理,旨在为其进一步的研究和工程应用提供参考。     

生石灰与粉煤灰桩加固软土地基的微观分析

采用压汞试验和扫描的电镜的手段，分析了生石灰与粉煤灰桩加固软土地基前后土的微观结构和孔隙特征的变化，发现加固后特大孔隙和大孔隙减少，小孔隙和微孔隙增加，不同的土质存在着不同的孔隙阈界值，且孔隙阈界值在加固后明显降低，对加固前后不同土的微观结构进行分类，从微观上解释了生石灰与粉煤灰桩加固软土的机理。     

水泥粉煤灰加固有机质土的试验研究

对于高有机质含量的泻湖相软土,单纯采用水泥不能有效提高该软土的力学性能,因此提出了采用水泥和粉煤灰作为固化剂的加固方法。通过不同水泥掺入量、粉煤灰掺入量和龄期下水泥土的无侧限抗压强度试验,分析了水泥粉煤灰固化土的强度规律和变形规律,探讨了水泥和粉煤灰加固高有机质含量软土的机理。结果表明,粉煤灰对于水泥试块的早期强度影响较小,对后期强度影响较大;粉煤灰最佳掺入量为12％,超过此掺入量水泥土强度反而会降低,粉煤灰水泥土的破坏应变、E50也在粉煤灰掺量为12％时分别达到最低值和最大值。水泥掺加粉煤灰可有效地提高高有机质含量软土的强度。     

粉煤灰桩加固软基特性的室内试验研究

通过粉煤灰桩的室内模型试验,分析了粉煤灰桩的变形破坏特性,桩土应力的变化规律及其加固软土地基的作用机理,随着荷载的增加,桩间土应力逐渐增大,桩体应力增长较快,达到峰值时桩体屈服,复合地基开始发生破坏,桩体应力下降;桩土应力比随着荷载和时间的变化而变化,并与桩土模量比,桩的长径比有关,在桩基设计时应把桩土应力比作为一个变值来考虑,粉煤灰桩强度较高且透水性好,加固软基时其挤密作用,置换作用和时间效应都     

高钙粉煤灰加固促淤地基机理和性状试验研究

结合高钙粉煤灰与上海浦东国际机场工期促淤软土拌和后加固土体的室内外试验,指出高钙粉煤灰足加固促淤软土地基的一种新型材料。基于在不同掺灰量、不同游离氧化钙含量和添加不同激发剂情形下拌和灰土的室内物理力学性能试验,探讨了高钙粉煤灰加固促淤软土的固化机理和工程特性,加固后土体在无侧限抗压强度、变形、渗透特性以及抗液化能力等方面均有明显改善,指出灰土强度与掺灰量、土体改性激发剂的品种和数量以及养护龄期有关,高钙灰与土体拌和后自膨胀特性下降为12％,消除了高钙灰的体积不稳定问题。现场进行粉喷桩加固软土地基试验表明,复合软土地基的极限承载力达到240kPa以上,可以替代水泥土搅拌桩,桩间土体强度和变形也得到改善。加固场地地下水质分析表明,高钙灰加固促淤软土地基不会影响地下水质和环境。     

粉体喷射搅拌桩机理及施工技术

粉体喷射搅拌桩机理及施工技术湖北省第三探矿工程大队谢俊粉体喷射搅拌桩是采用搅拌机械，直接将粉体材料（如水泥或生石灰粉等）与天然地基土就地强制搅拌，从而形成固体混合物的一种软土地基加固措施。近几年来该项施工工艺应用于上海软土地基加固极为广泛。从设计角度...     

钙基液态水硬性加固剂用于潮湿土遗址的加固保护

通过对钙基液态水硬性加固剂的研制,对潮湿环境土遗址的加固保护进行了探索性研究。X射线衍射（XRD）和扫描电镜（SEM）分析结果表明,已成功制出了潮湿土样水硬性加固所需的纳米材料。同时,研究发现,氢氧化钙在650 ℃下用马弗炉煅烧1.5 h后,可得到直径约50 nm、长度约200 nm的针状二次生石灰;这种二次生石灰经水消化后,会成为粒径在200～300 nm左右、大小十分均匀的扁平椭圆状纳米氢氧化钙颗粒;氧化钙在密封陈化一段时间后,也可使氢氧化钙的粒径达到纳米级。土样加固试验的结果显示,纳米石灰的乙醇分散液的渗透性优于分析纯氢氧化钙,钙基水硬性加固剂对潮湿土样的加固效果较为明显,有望成为一种适合于潮湿环境土遗址加固的新型材料。     

石棉纤维粉煤灰水泥加固软土试验研究

为研究石棉纤维加固软土的效果和机理,改善水泥土的脆性破坏特点,提出将石棉纤维的物理加筋作用与水泥、粉煤灰的化学加固作用相结合,通过对不同纤维掺量(0%~9%)的石棉纤维粉煤水泥复合土进行直剪试验、无侧限抗压强度试验、劈裂试验、扫描电镜试验,进而对石棉纤维加筋水泥土的强度性质和影响机理进行探讨。研究表明,石棉纤维配合水泥与粉煤灰能显著提高软土的强度和稳定性,改善水泥土的破坏形式。水泥粉煤灰配比一定时,石棉纤维增强水泥复合土各强度指标值存在最优掺量,纤维添加量在3%~6%之间,石棉纤维的加筋效果在水泥土中能得到很好的发挥,超过最优掺量则会降低复合土的强度值。     

新型固化材料在软土地区的应用探索

土加固技术经过近100年的发展,应用范围广泛,近20年来也出现了许多新型的加固材料。针对上海软土地基特点,通过对室内试验进行分析、室外原位搅拌桩施工、钻探取芯及芯样试验,分析了软土固化专用水泥这一新型固化材料的适用性,并提出一些相应的应用建议,以促进上海这类软土地基加固土技术的进一步应用发展。     

有机质含量对水泥土强度影响的室内定量研究

采用对盐城泻湖相软土掺入不同含量的有机质作为试料土,进行了大量的水泥加固室内试验。对试验结果进行了分析,提出了不同有机质含量软土水泥加固后的室内无侧限抗压强度的预测公式,同时建立了不同有机质含量的试料土经水泥加固后的室内强度比与有机质含量之间的定量关系,该定量关系式可以有效地对有机质含量在5.5 %～17.5 %的水泥加固后的无侧限抗压强度进行定量的预测。     

固化盐渍土核磁共振微观特征

采用核磁共振技术,对不同配比的水玻璃、石灰+粉煤灰及石灰+粉煤灰+水玻璃的固化盐渍土的微观特征进行检测,结合无侧限抗压强度试验,分析了各固化方案的盐渍土固化效果,讨论了强度成因的微观特征机制。结果表明,不同固化土的孔隙特征有较大差异。石灰+粉煤灰固化盐渍土大孔隙减少;石灰+粉煤灰+水玻璃固化盐渍土孔隙总体积减少,但同时有大孔隙生成;水玻璃固化盐渍土孔隙总体增多,但随水玻璃浓度增大,孔隙体积有所减小。石灰+粉煤灰+水玻璃固化盐渍土抗压强度远大于其他固化方案,但是其孔隙结构并不是最优,说明颗粒间的胶结情况对固化效果的影响远大于孔隙特征。     

Effect of lime and fly ash on swell,consolidation and shear strength characteristics of expansive clays: a comparative study

Expansive soils swell on absorbing water and shrink on evaporation thereof. Because of this alternate swelling and shrinkage, civil engineering structures founded in them are severely damaged. For counteracting the problems of expansive soils, different innovative techniques were suggested. Stabilization of expansive clays with various additives has also met with considerable success. This paper presents, by comparison, the effect of lime and fly ash on free swell index (FSI), swell potential, swelling pressure, coefficient of consolidation, compression index, secondary consolidation characteristics and shear strength. Lime content (weight of lime/weight of dry soil) was varied as 0%, 2%, 4%?and 6%?and fly ash content (weight of fly ash/weight of dry soil) as 0%, 10%?and 20%. A fly ash content of 20%?showed significant reduction in swell potential, swelling pressure, compression index and secondary consolidation characteristics and resulted in increase in maximum dry density and shear strength. Swell potential and swelling pressure decreased with increase in lime content also. Further, consolidation characteristics improved. Compaction characteristics and unconfined compression strength improved at 4%?lime and reduced at 6%?lime.     

Effect of the combination of lime and natural pozzolana on the compaction and strength of soft clayey soils: a preliminary study

Soft soil stabilization has been practised for quite some time by mixing additives, such as cement, lime and fly ash to the soil to increase its strength. However, there is a lack of investigations on the use of natural pozzolana alone or combined with lime for ground improvement applications. An experimental programme was undertaken to study the effect of using lime, natural pozzolana or a combination of both on the geotechnical characteristics of soft soils. Lime or natural pozzolana was added to soft soils at ranges of 0?C10% and 0?C20%, respectively. In addition, combinations of lime?Cnatural pozzolana were added to soft soils at the same ranges. Test specimens were subjected to compaction tests, shear tests and unconfined compression tests. Specimens were cured for 1, 7, 28 and 90?days, after which they were tested for unconfined compression tests. Based on the favourable results obtained, it can be concluded that the soft soils can be successfully stabilized by the combined action of lime and natural pozzolana. Since natural pozzolana is much cheaper than lime, the addition of natural pozzolana in lime?Csoil mix may particularly become attractive and can result in cost reduction of construction.     

Development of synthetic soil mixture for experimental shaking table tests on building frames resting on soft soils

In this study, a synthetic soil mixture has been developed and proposed for experimental soil-structure interaction shaking table tests on building frames with shallow foundations resting on soft soil deposits. The proposed mix provides adequate undrained shear strength to mobilise the required shallow foundation bearing capacity underneath the structural model while meeting both criteria of dynamic similarity between the model and the prototype to model soft soils in shaking table tests. To find the most appropriate mixture, different mixes with different proportions of mix components were examined in the soils laboratory. Performing bender element tests, the shear wave velocity of the soil specimens was acquired at different cure ages and the results were examined and compared. Based on the test results, a synthetic clay mixture consisting of kaolinite clay, bentonite, fly ash, lime and water has been proposed for experimental shaking table tests.     

Coupled consolidation model for negative skin friction on piles in clay layers

Expansive soils swell on absorbing water and shrink on evaporation thereof. Because of this alternate swelling and shrinkage, civil engineering structures founded in them are severely damaged. For counteracting the problems of expansive soils, different innovative techniques were suggested. Stabilization of expansive clays with various additives has also met with considerable success. This paper presents, by comparison, the effect of lime and fly ash on free swell index (FSI), swell potential, swelling pressure, coefficient of consolidation, compression index, secondary consolidation characteristics and shear strength. Lime content was varied as 0%, 2%, 4%?and 6%?and fly ash content as 0%, 10%?and 20%. A fly ash content of 20%?showed significant reduction in swell potential, swelling pressure, compression index and secondary consolidation characteristics and resulted in increase in maximum dry density and shear strength. Swell potential and swelling pressure decreased with increase in lime content also. Further, consolidation characteristics improved. Compaction characteristics and unconfined compression strength improved at 4%?lime and reduced at 6%?lime.     

Deformation Modulus of Fly Ash Modified with Lime and Gypsum

Deformation modulus of fly ash is one of the most important mechanical properties generally used in different design problems and also as an input parameter to sophisticated numerical techniques employed to assess the response of different structures resting on fly ash fill or embankment made of fly ash. Deformation modulus is usually expressed in terms of compressive strength. This paper presents the deformation modulus of fly ash modified with lime alone or in combination with gypsum at different strain levels. The values of deformation modulus obtained from both unconfined compression test and unconsolidated undrained triaxial test results are presented herein. The specimens for unconfined compression test and for undrained triaxial tests were cured up to 90 and 28 days, respectively. The effects of addition of lime (4–10%) and gypsum (0.5 and 1.0%) on the deformation modulus of class F fly ash are highlighted. With addition of lime and gypsum, the class F fly ash achieved the deformation modulus in the range of 190 MPa in UCS test and up to 300 MPa in triaxial test specimens tested under all round pressure of 0.4 MPa. Based on the present test results empirical relationships are developed to estimate deformation modulus of modified fly ash from unconfined compressive strength and relationships between initial tangent modulus and secant modulus at different strain levels are also developed.     

水泥–粉煤灰–煤渣–吹填粉细砂混合料强度试验

针对大型堆填场基层结构工程,本着就地取材节约成本的原则,利用吹填砂作为骨料,添加粉煤灰、煤渣和水泥,采用正交试验方法,编制正交设计表,配制不同比例的混合料进行无侧限抗压强度试验。采用方差对不同龄期的混合料抗压强度进行分析,并对混合料加固机理进行研究,给出了混合料最佳质量配比,即水泥20%,粉煤灰15%,煤渣10%,此时混合料的强度最大;其水泥掺量对混合料强度起着关键作用,随着龄期的增长粉煤灰与煤渣对混合料强度影响程度逐渐增强,不过煤渣对混合料初期强度影响不及粉煤灰。      

California Bearing Ratio and Brazilian Tensile Strength of Mine Overburden–Fly Ash–Lime Mixtures for Mine Haul Road Construction

The production and utilization of coal is based on well-proven and widely used technologies. Fly ash, a coal combustion byproduct, has potential to produce a composite material with controlled and superior properties. The major challenges with the production of fly ash are in its huge land coverage, adverse impact on environment etc. It puts pressure on the available land particularly in a densely populated country like India. In India the ash utilization percentage has not been very encouraging in spite of many attempts. Stabilization of fly ash is one of the methods to transfer the waste material into a safe construction material. This investigation is a step in that direction. This paper presents the results of an investigation on compressive strength and bearing ratio characteristics of surface coal mine overburden material and fly ash mixes stabilized with lime for coal mine haul road construction. Tests were performed with different percentages of lime (2, 3, 6 and 9%). The effects of lime content and curing period on the bearing ratio and tensile strength characteristics of the stabilized overburden and fly ash mixes are highlighted. Unconfined compressive strength test results cured for 7, 28 and 56 days are presented to develop correlation between different tensile strengths and unconfined compressive strength. Empirical models are developed to estimate bearing ratio and tensile strength of mine overburden–fly ash–quick lime mixtures from unconfined compressive strength test results.