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秸秆纤维改良黏土作为填埋场衬垫防渗材料的可行性研究

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针对垃圾填埋场运行过程中压实黏土衬垫开裂破坏失效中的关键科学问 题,试图采用农作物秸秆纤维改良传统压实黏土衬垫,以提高衬垫系统的抗开 裂特性以及承载能力。为评价秸秆纤维改良黏土作为填埋场衬垫材料的可行性, 开展秸秆纤维改良黏土开裂试验研究,研究连续失水干燥与干湿循环作用下改 良黏土的开裂规律,提出秸秆纤维黏土混合料的最佳配合比。通过室内土工试 验,研究不同秸秆纤维掺量的压实黏土以及酸碱化学溶液腐蚀的改良黏土的强 度与变形特性。开展酸碱化学溶液腐蚀下秸秆纤维改良黏土的微观结构试验研 究,分析了化学溶液腐蚀条件下改良黏土的微观形貌、孔隙结构以及物质相比 的演化规律。基于流体运动方程、溶质对流弥散方程、力平衡方程以及相关边 界条件,建立反映渗流-应力-溶质耦合作用下填埋场衬垫变形的数学模型,并采 用此模型仿真分析了衬垫的变形破坏规律以及污染物运移扩散趋势。基于以上 研究,得出如下主要结论, (1)干湿循环作用对压实黏土开裂影响显著,随干湿循环次数的增多,开 裂愈发明显;秸秆纤维改良黏土具有较好的抗开裂特性,随纤维掺量的增加, 开裂因子(CIF)出现了先增大后减小的趋势,且当纤维掺量为 0.3%时,CIF 仅为 0.00813; (2)纤维掺量为 0.3%的改良黏土承载能力较高,无侧限抗压强度达到 459.15kPa、抗剪强度指标 c、φ 为 80.97kPa、21.06°、渗透系数为 5.0×10 -8 cm/s、 压缩系数 α 和压缩指数 Cc 达到最小值分别为 0.18 MPa -1 和 0.065 MPa -1 ,压缩模 量 Es 值为 9.356 MPa。酸碱化学溶液对秸秆纤维改良黏土强度特性影响显著, 其无侧限抗压强度、抗剪强度明显下降,且酸性化学溶液腐蚀强度高于碱性化 学溶液。 (3)酸碱化学溶液对黏土微观结构具有较大影响。腐蚀后压实黏土表面愈 发粗糙、平整度下降,沟壑明显,比表面积增大;孔径增大,二次孔、中孔增 多,颗粒排列由片堆结构演化至点-点排列结构。黏土中的有机质成分在酸碱化 学溶液作用下出现腐蚀分解现象,且酸性腐蚀程度远大于碱性条件。 (4)基于秸秆纤维改良黏土衬垫变形与污染物运移数值仿真计算结果可 知,在填埋场运行 50 天后,改良黏土衬垫层变形基本达到稳定状态,其应变为 2.84%。衬垫层内作用点的变形量是呈轴对称变化,在衬垫层左右边界处其变形II 量为最大值。改良黏土中各点的浓度随时间的增加而增大,且污染物浓度随衬 垫层深度的增加而减小。在 600 天时,渗滤液污染物已穿透衬垫层。污染物浓 度的变化是呈轴对称变化,在衬垫层轴线处污染点的浓度为峰值。 关键词,垃圾填埋场,衬垫系统,秸秆纤维,改良黏土,干燥开裂III ABSTRACT Crop straw fiber was used in the compacted clay liner to improve the resistance characteristics of the carrying capacity of the liner system, in order to aiming at the key scientific issue of compacted clay liner cracking failure in landfill running. For evaluating the feasibility of straw fiber modified clay as landfill liner materials, compacted clay cracking test was carried out. The laws of modified clay cracking in wetting-drying cycles were researched, and the best mix proportion of crop straw fibers. The strength and deformation of different straw fiber content and acid-base chemical solution corrosion of compacted clay was researched by indoor soil test. The microscopic morphology and pore structure of acid-base chemical solution corrosion straw fiber compacted clay was analyzed by microstructure experiment. The law of liner deformation and failure and transport tendency of contaminant spread was numerical simulated under seepage - stress - solute coupling. Based on the results: (1) Wetting-drying cycles had significant effect on the cracking of compacted clay, with the increase of the number of the cycles, the cracks became increasingly apparent. The straw fiber improved clay has better resistance characteristics to cracking, and CIF first increased and then decreased. When the fiber content was 0.3%, CIF was 0.00813. (2) The carrying capacity was the best when the fiber content was 0.3%. The unconfined compressive strength was 459.15kPa, and c was 80.97kPa and φ was 21.06°. The permeability coefficient was 5.0×10 -8 cm/s, and α was 0.18MPa -1 , and the minimum Cc was 0.065MPa -1 . Es was 9.356 MPa. Acid-base chemical solution the straw fiber improvement clay had significant affect to strength characteristics. (3) Acid - base chemical solution had a large impact on the microstructure of compacted clay. Clay surface roughening, flatness decreased significantly and ravines, and the specific surface area increased. Pore size, the second hole and the hole increased, the particle arrangement by the evolution of a sheet pile structure toIV the point-point arrangement structure. Composition of organic matter decomposition corrosion under the action of acid-base chemical solution, and the acidic corrosion a much greater extent than alkaline conditions. (4) Based on the results of numerical simulation as deformation and contaminant transport of landfill liner with straw fiber modified clay, After 50 days of landfill running modified clay liner deformation reached steady state, the strain was 2.84%. The point of landfill liner on deformation is a axisymmetric variation, its deformation is maximum around the left and right border of landfill liner layer .Each point of landfill liner layer on the modified clay concentration increased with the increase of the time ,and the pollutant concentration decreased with the increase of depth of the cushion layer .In 600 days, leachate pollutants crossed through liner laye. Pollutant concentration change is axisymmetric, concentration of pollution was peak value on the axis of liner layer. Key words: Landfill; liner system; straw fiber; modified clay; crackingV 目 录 第 1 章 绪论 ............................................ 1 1.1 研究背景及意义 ..................................................................................... 1 1.2 国内外研究现状 ..................................................................................... 3 1.3 主要研究内容及技术路线...................................................................... 7 1.3.1 研究内容 ................................................................................................. 7 1.3.2 技术路线及报告的结构安排 .................................................................. 8 第 2 章 秸秆纤维改良黏土的开裂特性...................... 10 2.1 引言 ....................................................................................................... 10 2.2 改良黏土的开裂试验 ........................................................................... 10 2.2.1 试样材料 ............................................................................................... 10 2.2.2 试验方法 ............................................................................................... 11 2.3 试验结果与讨论 ................................................................................... 12 2.3.1 连续干燥失水作用下改良黏土的开裂 ................................................ 12 2.3.2 干湿循环作用下改良黏土的开裂 ........................................................ 18 2.4 本章小结 ............................................................................................... 25 第 3 章 秸秆纤维改良黏土的强度与变形特性................ 27 3.1 引言 ....................................................................................................... 27 3.2 试样材料与方法 ................................................................................... 28 3.3 试验结果与讨论 ................................................................................... 28 3.3.1 改良黏土强度与变形 ........................................................................... 28 3.3.2 酸碱腐蚀作用下改良黏土强度与变形特性 ........................................ 34 3.4 本章小结 ............................................................................................... 39VI 第 4 章 酸碱腐蚀秸秆纤维改良黏土的微观结构特性 .......... 42 4.1 引言 ....................................................................................................... 42 4.2 试验材料与方法 ................................................................................... 43 4.3 试验结果与分析 ................................................................................... 43 4.3.1 SEM 微观形貌 ........................................................................................ 43 4.3.2 微观孔隙结构 ....................................................................................... 47 4.3.3 TG-DTA 分析........................................................................................ 52 4.4 本章小结 ............................................................................................... 55 第 5 章 秸秆纤维改良黏土衬垫变形的数值仿真计算 .......... 57 5.1 引言 ....................................................................................................... 57 5.2 秸秆纤维改良黏土变形的数学模型 .................................................... 58 5.2.1 数学模型 ............................................................................................... 58 5.2.2 边界条件 ............................................................................................... 59 5.2.3 数值模拟与分析 ................................................................................... 60 5.3 本章小结 ............................................................................................... 65 第 6 章 结论与展望 ..................................... 66 6.1 主要结论 ............................................................................................... 66 6.2 展望 ....................................................................................................... 68