东非黑棉土的膨胀特性及处治技术研究

发布时间：2019-03-25 13:55

【摘要】：近年来,我国工程建设集团在东非国家承担的公、铁路建设项目中,经常遇到当地黑棉土带来的工程问题。由于黑棉工具有较强的膨胀性,会使道路工程产生严重病害,因而不得不采用换填方案,增加了工程成本和土方量。对东非黑棉土的膨胀特性和处治技术进行深入研究,可以增加工程安全性、降低工程造价、提升环境效益。依托中资企业在东非地区的公、铁路工程项目,对东非黑棉土的概念、危害、分布以及地形地貌特征和气候特征等情况进行了详细地调研,并借助工程勘察资料和土工现场试验,对东非黑棉土的工程性质进行了初步地分析。对东非黑棉土原状土样的基本工程性质进行了试验和分析。依据土壤发生学的理论,对东非黑棉土所属土纲、黑色成因和主要膨胀性矿物来源等进行了研究。结果表明,东非黑棉土的黏粒含量高,液限和塑性指数高,自由膨胀率大,蒙脱石含量高,交换性阳离子数量大且以钙离子为主,CBR值很小。东非黑棉土属于典型的变性土,其中的蒙皂石族膨胀性矿物主要来源于中基性火山岩的原生和次生作用,其暗色主要来源于有机质的严重浸染和含铁蒙脱石。提出了改进的差分自由膨胀率指标和试验方法,阐述了其微观机理,进行了相关性分析并确定了膨胀势分级标准。在分子模拟软件中应用SPC/E位能模型、UFF力场、电荷平衡(QEq)算法和周期性边界等建立体系;应用Skipper,chang以及Chavez-Paez等人的怀俄明蒙脱石参数构建蒙脱石晶胞模型;采用Loewenstein规则处理蒙脱石中的类质同象问题。在此基础上,根据东非黑棉土和我国膨胀土的层间阳离子特征建立了三种蒙脱石构型。通过分子力学对蒙脱石超晶胞进行了结构优化,随后应用分子动力学模拟了在等温等压(NPT)系综下蒙脱石超晶胞分子运动的稳定状态,并通过径向分布函数(RDF)对层间阳离子的水化状态进行分析,进而分析了黑棉土的膨胀机理。由于蒙脱石矿物含量高且蒙脱石矿物层间的补偿性阳离子增强了主要阳离子的水化能力,导致了东非黑棉土的强膨胀性。应用不同掺量的石灰、火山灰以及石灰+火山灰对东非黑棉土进行了化学处治,并对处治土的工程性质进行了试验和分析。结果表明,相较于石灰或火山灰的独立处治技术,石灰和火山灰联合处治技术就可以取得更好的改性效果。3%石灰+15%火山灰的复配处治方案可以在降低工程造价的基础上满足《公路路基设计规范(JTGD30-2015)》的要求。结合计算机分子模拟研究、物相组成分析和工程性质试验的结果,提出了东非黑棉土改性的五大机理。
[Abstract]:In recent years, the engineering problems caused by the local black cotton soil are often encountered in the public and railway construction projects undertaken by China's Engineering Construction Group in East African countries. Because of the strong expansibility of the black cotton workers, the road engineering will cause serious diseases, so it is necessary to adopt the replacement scheme, which increases the engineering cost and earthwork quantity. An in-depth study on the expansion characteristics and treatment technology of the black cotton soil in East Africa can increase the safety of the project, reduce the cost of the project, and improve the environmental benefit. Relying on the public and railway projects of Chinese-funded enterprises in the East African region, the concept, harm, distribution, topography and climate characteristics of black cotton soil in East Africa were investigated in detail. With the aid of engineering investigation data and geotechnical field test, the engineering properties of black cotton soil in East Africa are analyzed. The basic engineering properties of undisturbed samples of black cotton soil in East Africa were tested and analyzed. According to the theory of soil genesis, the soil class, black origin and main expansive mineral sources of the black cotton soil in East Africa were studied. The results show that the clay content is high, the liquid limit and plasticity index is high, the free expansion rate is high, the content of montmorillonite is high, the quantity of exchangeable cations is large and Ca ~ (2 +) is dominant, and the CBR value is very small. The black cotton soil in East Africa belongs to the typical denatured soil, in which the expansive minerals of the Mongolian saponiferous group are mainly derived from the primary and secondary processes of the medium-basic volcanic rocks, and the dark color is mainly derived from the serious leaching of organic matter and the iron-bearing montmorillonite. The improved differential free expansion rate index and test method are put forward, the micro-mechanism is expounded, the correlation analysis is carried out, and the criterion of expansion potential classification is determined. In the molecular simulation software, SPC/E potential model, UFF force field, charge balance (QEq) algorithm and periodic boundary are used to establish the system, Skipper,chang and Chavez-Paez 's parameters of Wyoming montmorillonite are used to construct the cell model of montmorillonite. Loewenstein rule is used to deal with isomorphism in montmorillonite. On the basis of this, three montmorillonite configurations have been established according to the inter-layer cation characteristics of the black cotton soil in East Africa and the expansive soil in China. The structure of montmorillonite hyperfine cell was optimized by molecular mechanics. Then the molecular dynamics was used to simulate the stable state of the cell molecular movement of montmorillonite Shi Chao under isothermal and isobaric (NPT) system. The hydration state of interlayer cations was analyzed by radial distribution function (RDF), and then the swelling mechanism of black cotton soil was analyzed. Due to the high content of montmorillonite minerals and the compensatory cations between the layers of montmorillonite minerals, the hydration ability of the main cations is enhanced, which leads to the strong expansion of the black cotton soil in East Africa. In this paper, different amounts of lime, pozzolanic ash and lime pozzolanic ash were used to treat the black cotton soil in East Africa, and the engineering properties of the treated soil were tested and analyzed. The results show that compared with lime or pozzolanic ash, The combined treatment technology of lime and pozzolanic ash can obtain better modification effect, and the compound treatment scheme of 3% lime and 15% pozzolanic ash can meet the requirements of JTGD30-2015 (Design Code for Highway subgrade) on the basis of reducing the engineering cost. Based on the results of computer molecular simulation, phase composition analysis and engineering properties test, five mechanisms of modification of East African black cotton soil were put forward.
【学位授予单位】：东南大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：U416.1

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