【作者】 刘伟；

【导师】 谈云志； 付伟；

【作者基本信息】 三峡大学 ， 建筑与土木工程（专业学位）， 2019， 硕士

【摘要】 填筑用红黏土的改良,主要通过添加石灰、水泥等碱性材料来实现,但由于在现场拌和时,石灰和水泥等碱性稳定材料很难均匀拌和入填筑材料内部,只能附着在土团的表面,导致改良效果不甚理想。同时,室内试验采用的填筑用土,根据各规范要求严格限制了土粒尺寸,致使稳定材料在室内试验研究与实际的工程应用中表现出一定的性能差异。并且在长期服役过程中,红黏土呈弱酸性的特点易与碱性改良材料发生互损效应,使其耐久性劣化,对工程项目造成经济损失。因此,论文寻找了一种新的碱性激发材料(偏高岭土)来增强石灰稳定红黏土的耐久性。结合石灰改良红黏土在路基填筑中的应用,开展以下主要试验探究:(1)通过偏高岭土协同石灰稳定红黏土的强度试验,探究了其强度演化规律,并得出了偏高岭土最优质量掺入比。(2)通过对应最优偏高岭土掺入比下,不同团粒红黏土混合试样的力学试验,研究了不同团粒对稳定红黏土的力学性能的影响。(3)模拟改良红黏土的干湿循环作用,以无侧限抗压强度结合微观试验为判据,研究了稳定红黏土的耐久性。得到如下结论:1)以偏高岭土和石灰作为红黏土的增效材料,通过开展无侧限抗压强度试验,研究了改良红黏土的强度与增效材料的掺量关系,以及养护龄期内的强度演化规律。结果表明:掺入偏高岭土后,最大团粒尺寸不超过0.5mm和5mm的红黏土分别在28d和60d以前强度快速增长,生成大量胶结物联结土体内部团粒和填充团粒间孔隙,起到填充和支撑效应,有效增强了土体结构,提升了土体强度。偏高岭土的掺量与强度提升非线性关系,当偏高岭土过量后强度提升系数出现下降。2)通过将红黏土分别过5mm、2mm、1mm、0.5mm筛,获得最大团粒尺寸不同的红黏土,进而开展了不同最大团粒尺寸改良红黏土的力学性能(剪切强度试验、收缩性试验和压缩性试验)研究。试验发现,随着团粒尺寸的增大,试样混合物级配趋于不良,掺入的偏高岭土和石灰附着在红黏土团聚体间,使得形成的胶结物并未改变试样骨架尺寸,造成粘聚力增加,而内摩擦角变化不大;与相同团粒的石灰土相比,MK-L红黏土能有效抑制石灰土的收缩,其中团粒尺寸越大,线缩率降幅越大;MKL红黏土的在1mm、2mm和5mm时压缩量在早期相近,受团粒尺寸的影响较小,形成的骨架相似。养护后,石灰土和MK-L红黏土压缩量受团粒尺寸影响均较小,火山灰反应进一步减弱了团粒尺寸对骨架的影响。据此,若将MK-L红黏土应用于实际工程中,能有效避免团粒差异性引起的骨架效应。3)开展了MK-L红黏土的耐久性研究,以红黏土、石灰土和MK-L红黏土为研究对象,分别将试样进行0、3、7、12和18次干湿循环后,测试无侧限抗压强度和孔隙分布(MIP)。所得结果如下:MK-L红黏土强度损失率整体低于石灰土;并且随着干湿循环次数的增加,石灰土的强度损失率有进一步增大的趋势,且分布在1～100μm的孔隙明显增多,而MK-L红黏土的强度损失率变化较小,大孔隙基本不变化。说明偏高岭土与石灰作用形成的胶结物能有效抵抗干湿作用引起的土体胀缩,从而增强土体的耐久性。该研究可以为当前石灰改良红黏土存在的缺点提供新的解决思路,也可为实际工程的应用提供参考建议,具有重要的理论意义和实际工程应用价值。更多还原

【Abstract】 Currently,Lateritic soils for filling works are mainly improved by adding alkaline materials such as lime and cement.However,it is difficult to break up the soil mass under natural conditions to uniformly sized aggregates,especially when mixing with lime,cement,etc.on site.Thereby making it difficult for the stabilizers to uniformly mix and permeate the core layers of the soil particles;instead,it adheres to the surface of the soil.However,the soil used in the laboratories strictly limits the particle size of the soil according to the requirements of various specifications,resulting in a certain performance difference between the laboratory material and field conditions.In the long-term service process,the weakly acidic Lateritic soil can easily interact with a stabilizer,which deteriorates its durability and causes economic losses to the project.Therefore,the paper sought a new pozzolanic material(metakaolin)to enhance the durability of lime stabilized laterite.Combined with the application of lime-treated Lateritic soils in roadbed fills,the main experimental investigations were as follows:(1)using the compressive strength test of metakaolin and lime stabilized laterite to study the strength development of the soil and the optimal blending ratio of metakaolin.(2)The mechanical tests of different soil particle size laterite mixed samples were carried out by the corresponding optimum metakaolin incorporation ratio,and the effects of different soil particle sizes on the mechanical properties of treated Lateritic soils were studied.(3)Simulating the dry-wet cycle of stabilized laterite,and analyzing the unconfined compressive strength combined with the microscopic test.The main conclusions are as follows:1)Using metakaolin and lime as the synergistic materials for laterite,the unconfined compressive strength tests were carried out to study the relationship among the strength of the treated Lateritic soil,the amount of stabilizers,and the strength development during the curing period.The results show that: after the addition of metakaolin,the Lateritic soil with 0.5mm and 5mm maximum aggregates sizes increases rapidly at 28 d and 60 d respectively,and a large amount of cementitious compounds was formed between aggregates and filled the inter-granular pores.The filling effect effectively enhanced the internal structure of the soil strength.The addition of metakaolin had a nonlinear relationship with strength and when the metakaolin was in excess,the strength increases coefficient decreased.2)By sieving the Lateritic soil through 5mm,2mm,1mm,0.5mm sieves respectively,laterite with the largest aggregate size was obtained,and then the mechanical properties(Shear strength test,Shrinkage test,Compressibility test)of soil with different maximum aggregate sizes were carried out.It was found that as the particle size increases,the sample mixture was poorly graded,and the incorporated metakaolin and lime(MK-L)tended to adhere to the laterite aggregates,thus the formed cementitious material did not change the skeleton size of the sample.Therefore,the internal friction angle was not increased,yet the cohesive force was increased;MK-L treated Lateritic soil can effectively inhibit the shrinkage behavior.Clearly,the compression of MK-L Lateritic soil at 1mm,2mm,and 5mm was similar during the early curing stage and was less affected by the size of the aggregate,thereby forming a similar skeleton.After curing,the difference in the compression amount of MK-L Lateritic soil with different particles decreased,and the pozzolanic reactions further weakened the influence of the size of aggregates on the skeleton matrix.After the limetreated soil was cured,the amount of compression was close to the change in the size of the particles.Accordingly,when MK-L treated Lateritic soil is used in the field,the structural effect caused by the difference in aggregate sizes can be effectively avoided.3)The durability study of untreated,lime-treated,and MK-L treated Lateritic soil were carried out.The samples were subjected to 0,3,7,12 and 18 dry and wet cycles respectively.Thereafter,unconfined compressive strength tests and MIP tests were performed.The results show that: the strength loss rate of lime treated soil after incorporation with metakaolin is lower than that of lime treated soil,and the intensity of the rate of loss for lime-treated soil varies greatly with an increase in the number of dry and wet cycles,and was distributed in 1～100μm pore sizes range.The pores were significantly increased,and the change in MK-L Lateritic soil pore structure was small.It shows that the formation of a network structure by metakaolin and lime can effectively resist the swelling and shrinkage of the soil caused by drying and wetting actions,thus enhancing the durability of laterite.This study can provide a new solution to the shortcomings of lime-improved red clay at present,and also provide reference suggestions for practical engineering application.It has important theoretical significance and practical engineering application value.更多还原