重金属侵入下岩土的力学特性及固化机理研究

发布时间：2018-01-21 14:36

本文关键词： 岩土重金属迁移特性土工试验质量比固化性能体变特性本构关系　出处：《中南大学》2014年博士论文　论文类型：学位论文

【摘要】：重金属污染岩土在我国广泛分布,尤其在有色矿产资源大省的广西、云南等地。岩土体被重金属元素污染后,颗粒间的胶体被溶蚀、胶结强度被破坏而改变了土体的内部结构,导致岩土体的孔隙比、压缩性增大,抗剪强度降低、承载力下降等性质的变化。目前对重金属污染岩土的工程性质、固化机理、防治措施的研究成果较少,在工程建设中大多将其作为一般土处理或不处理,导致污染岩土路基、边坡、建筑地基等开裂、垮塌工程事故的发生。因此研究污染岩土的工程特性、本构关系、固化机理及防治措施,对评价与治理重金属污染岩土地(路)基、边坡,以及合理利用重金属污染土体资源具有重要意义。本文首先调查了广西重金属污染岩土的分布情况,统计了污染岩土的基础数据,确定了广西污染土的背景值的大小、相关变异系数,并以此划分了重金属污染岩土的分布范围。建立了污染迁移试验模型对重金属元素(镉)Cd、(铅)Pb、(锌)Zn迁移特性进行了研究,采用偏最小二乘法(PLS)对各元素迁移能力进行了线性回归分析,确定了三种元素迁移能力、自净能力的大小关系。研究结果表明：(镉)Cd、(铅)Pb的迁移特性较强,不受土体自净能力的影响,(锌)Zn的迁移特性受土体自净能力的影响较大,迁移特性最弱。通过三轴试验、压缩试验和直剪试验对重金属污染土进行了研究,在100、200、300KPa围压条件下,对5种重金属含量不同的污染土试样：一般土、污染土(重金属元素质量比分别为：1%、2%、3%、4%)进行三轴对比试验。试验结果表明：污染土的强度随着重金属元素的含量的增加显著降低,围压增大对重金属含量低的污染土的强度的影响不显著,质量比小于1%时,峰值强度降低10%-15%,质量比大于3%时,峰值强度降低40%-50%；直剪试验结果表明：质量比小于1%的污染土抗剪强度-垂直压力曲线基本平行,垂直压力与抗剪强度成正比,抗剪强度降低幅度为5%-10%,质量比大于3%的污染土抗剪强度-垂直压力曲线表现为不规则,抗剪强度降低45%-55%左右；压缩试验结果表明,污染土与一般土的压缩量差别较大,质量比超过3%以上时对压缩性的影响尤为显著。根据三轴试验结果与Mastsuoka-Nakai准则建立了污染土的本构关系,经验证该模型在描述污染土的应力-应变关系方面更符合实际。探讨了有机物固化下的重金属污染土力学性能与体变特性,在低、相对中高围压条件下,对原状污染土与添加固化剂的污染土试样进行了三轴固结排水剪切对比试验,绘制了两种污染土试样的力学体变特性曲线。采用修正剑桥模型形式作为压缩屈服面与Pietruszczak和Stolle所提出的屈服函数作为剪切屈服面建立一个适用于污染土的双屈服面弹塑性本构模型,将试验结果作为计算参数对模型进行了验证。该模型克服了单曲面模型的不能模拟土体体变临界状态的缺陷,较为合理地反映了污染土的体变过程。结果表明：添加有机物固化剂显著提高了重金属污染土的强度,有效改善了重金属污染土在低围压作用条件下体胀、中高围压作用下体缩的力学特性；双屈服面应变软化弹塑性本构模型的拟合结果与试验结果较为吻合,表明该模型在描述重金属污染土体变特性方面具有一定的优越性。分析了不同试验条件下重金属污染岩石的性能变化,根据试验结果探讨了重金属含量对岩石风化速度、力学性能的影响,以及重金属元素对岩石水化、水解作用影响的机理；同时根据重金属元素的侵入性能、延伸性能大小关系,建立了污染岩石侵入面损伤的三维组合本构模型,并对模型拟合结果与试验结果进行了对比。结果表明：重金属元素导致双电层厚度增大,扩散层的斥力发生改变,水化膨胀应力增大,导致了岩石裂隙面的扩张、延伸,强度降低,重金属元素水解常数形成新的M-OH,促进岩石水解作用的发生；重金属污染物质量比与岩石风化关系呈多项式型关系,曲线呈抛物线型；侵入面损伤三维组合本构模型拟合结果与试验结果具有较好
[Abstract]:Heavy metal contaminated rock and soil is widely distributed in China , especially in Guangxi , Yunnan and so on in the large province of nonferrous metals . After heavy metal elements are contaminated , the colloid in the particles is eroded , and the strength of cementation is destroyed to change the internal structure of soil mass , which leads to the occurrence of cracking and collapse of soil and soil subgrade , slope , building foundation and so on . In this paper , the distribution of heavy metal contaminated soil in Guangxi was investigated . Based on the statistics of the basic data of polluted soil , the paper studied the background value of polluted soil in Guangxi , and determined the distribution scope of heavy metal contaminated soil . The results showed that the migration characteristics of Cd , Pb and Zn were determined by using partial least square method ( PLS ) . The results showed that the migration characteristics of Cd and Pb were not affected by the self - cleaning ability of soil . The results show that the strength of the polluted soil decreases by 10 % -15 % and the mass ratio is more than 3 % . The results show that the strength of the polluted soil decreases by 10 % -15 % and the mass ratio is more than 3 % . The mechanical properties and rheological properties of heavy metal contaminated soil under the solidification of organic matter were discussed . The mechanical properties of the polluted soil samples were verified by using the yield function of the modified Cambridge model as the compressive yield surface and the additive curing agent . The results show that the addition of the organic curing agent significantly improves the strength of the heavy metal contaminated soil and effectively improves the mechanical properties of the heavy metal polluted soil under the condition of low confining pressure . The fitting result of the double yield surface strain softening elastic - plastic constitutive model is more consistent with the experimental results , which indicates that the model has certain advantages in describing the soil deformation characteristics of heavy metals . The effects of heavy metal contents on the weathering speed and mechanical properties of rocks and the effects of heavy metal elements on the hydration and hydrolysis of rocks are discussed . The results show that the heavy metal elements cause the double layer thickness to increase , the repulsive force of the diffusion layer is changed , and the hydrolysis constant of heavy metal elements increases , which leads to the formation of new M - OH , which promotes the rock hydrolysis .

【学位授予单位】：中南大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TU43;X53

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