| 酸性环境干湿循环条件下膨胀土的膨胀特性及微观作用分析 |
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| 引用本文： | 常锦,杨和平,肖杰,刘雄,毛瑞,陈冠一. 酸性环境干湿循环条件下膨胀土的膨胀特性及微观作用分析[J]. 中国公路学报, 2019, 32(3): 34-43. DOI: 10.19721/j.cnki.1001-7372.2019.03.004 |
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| 作者姓名： | 常锦 杨和平 肖杰 刘雄 毛瑞 陈冠一 |
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| 作者单位： | 1. 长沙理工大学 交通运输工程学院, 湖南 长沙 410114;2. 长沙理工大学 道路灾变防治及交通安全教育部工程研究中心, 湖南 长沙 410114;3. 苏交科集团股份有限公司, 江苏 南京 210019;4. 台州市交通勘察设计院, 浙江 台州 318001 |
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| 基金项目： | 国家自然科学基金项目（51608053）；湖南省自然科学基金项目（2017JJ3335）；湖南省研究生科研创新项目（CX2017B458） |
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| 摘 要： | 弄清酸雨及干湿循环共同作用下膨胀土的膨胀性能及其微结构与矿物成分的变化,对研究酸雨区膨胀土的基本性质劣化及工程问题意义重大。为此,以广西酸雨重灾区百色原状膨胀土为对象,模拟酸雨(pH=3,5,7)与干湿循环(n=1,2,3,4)两者共同作用的环境,开展了无、有荷膨胀率试验,并采用扫描电镜(SEM)、压汞仪(MIP)和X射线衍射仪(XRD)分析了该环境下试样的微结构及矿物成分的演变规律。研究结果表明:酸性环境使试样的膨胀率增大,溶液的pH值越小,膨胀率越大;随干湿循环作用次数的增加,不同溶液环境下试样的膨胀率均先增大后趋于稳定,且2次作用后的增幅最大;经酸性环境与干湿循环共同作用试样的膨胀率增大更多,溶液pH值为3和5,经2次干湿循环后其膨胀率比pH值为7的分别增长了24.7%和7.9%;上覆压力能明显抑制试样膨胀率的增长,设定测试压力越大,该值下降越显著。酸性环境与干湿循环共同作用下膨胀率增大的机理可通过微观结构分析作出解释:酸性环境作用下膨胀土中游离SiO_2,Al_2O_3,K_2O,MgO,CaO等胶结物出现不同程度的溶蚀和淋滤,削弱了叠聚体结构间的联结作用,使面面叠聚结构的排列趋于分散,微孔隙体积及数目不断增大,同时遭受干湿循环作用后,土中微孔隙加速发育,土颗粒与溶液水间化学反应更剧烈,致使其膨胀变形进一步增大。因此,酸雨重灾区的膨胀土工程建设,必须考虑酸性环境与干湿循环共同作用造成的膨胀土基本性质劣化的不利影响。
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| 关 键 词： | 道路工程 膨胀土 酸性环境干湿循环 膨胀性能 微结构 |
| 收稿时间： | 2018-06-07 |
Swelling Characteristics and Microscopical Analysis of Expansive Soil Under Dry-wet Cycles in Acid Environment |
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| CHANG Jin,YANG He-ping,XIAO Jie,LIU Xiong,MAO Rui,CHEN Guan-yi. Swelling Characteristics and Microscopical Analysis of Expansive Soil Under Dry-wet Cycles in Acid Environment[J]. China Journal of Highway and Transport, 2019, 32(3): 34-43. DOI: 10.19721/j.cnki.1001-7372.2019.03.004 |
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| Authors: | CHANG Jin YANG He-ping XIAO Jie LIU Xiong MAO Rui CHEN Guan-yi |
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| Affiliation: | 1. School of Traffic and Transportation Engineering, Changsha University of Science & Technology, Changsha 410114, Hunan, China;2. Engineering Research Center of Catastrophic Prophylaxis and Treatment of Road & Traffic Safety of Ministry of Education, Changsha University of Science & Technology, Changsha 410114, Hunan, China;3. Sujiao Group Co., Ltd., Nanjing 210019, Jiangsu, China;4. Taizhou Traffic Survey and Design Institute, Taizhou 318001, Zhejiang, China |
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| Abstract: | The expansion properties of expansive soils and their microstructure and mineral composition are significantly affected by the combined effects of acid rain and dry-wet cycles. It is, therefore, of utmost importance to study the deterioration of their basic properties and subsequent engineering problems in areas of acid rain. For this purpose, Baise expansive soil from the heavy acid rain area of Guangxi was selected as the target sample. The coupled effects of acid rain (pH=3, 5, 7) and dry-wet cycle (n=1, 2, 3, 4) on expansion properties of expansive soil were studied based on the load-free and loaded expansion rate tests. The evolution of the microstructure and mineral composition of the samples under the combined effects of acid rain and dry-wet cycles was analyzed using scanning electron microscopy (SEM), mercury porosimetry (MIP), and X-ray diffraction (XRD). The results show that the acid environment increases the swelling deformation of expansive soil, which is, in turn, inversely proportional to the pH value of the solution. With an increase in the dry-wet cycle times, regardless of the solution environment, the sample expansion rate first increases and is then almost stable. The largest increase occurs after two dry-wet cycles. Following the combined effects of acid environment and dry-wet cycle, the expansion rate of the sample increases more substantially. When the solution pH value decreases from 7 to 5 and 3, the sample expansion rate increases by 24.7% and 7.9%, respectively. Vertical pressure can significantly inhibit the growth in expansion rate of the sample; the greater the stress, the more significant the decrease in the expansion rate. The mechanism of increase in expansion under the combined effects of acid environment and dry-wet cycle can be explained by microstructural analysis. Under an acid environment, free colloidal minerals, such as SiO2, Al2O3,K2O, MgO, and CaO, present in expansive soil show different degrees of erosion and leaching. The erosion of colloidal minerals weakens the strength of the structural connection between the stacking structures and disperses the face-to-face stacked structures, resulting in continuous increase of the size and number of micro-voids. Moreover, the additional effect of dry-wet cycle promotes the chemical reaction between soil particles and water in the solution, resulting in further increase of micro-pores and soil swelling deformation. During engineering construction using expansive soil in the heavy acid rain area, the adverse effects of acid environment and dry-wet cycle on the deterioration of the basic properties of expansive soil should therefore be considered. |
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| Keywords: | road engineering expansive soil dry-wet cycles in acid environment swelling characteristic microstructure |
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