弱膨胀土在浸水膨胀过程中的微观结构变化特征
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摘要
为探究膨胀约束条件对膨胀土水化稳定后微观结构的影响,对河南一处膨胀土开展了不同荷载下室内一维膨胀变形试验,并采用真空冷冻干燥法对初始和膨胀稳定后的土样脱湿,然后进行扫描电镜试验和压汞试验,测定土样微观结构类型和孔隙分布的情况。扫描电镜试验结果表明:重塑膨胀土呈紊流结构,颗粒排布没有明显的方向性;在允许体积膨胀的条件下,颗粒中的伊蒙混层羽翼状边缘被充分水化,边缘更为光滑,粒间连接也变弱,土体从紊流结构逐渐过渡为粒状堆叠结构。压汞试验结果表明:不同荷载下土样的孔径分布曲线均为三峰曲线,土中的孔隙按照等效孔径大小可以分为大孔隙、小孔隙、微孔隙和超微孔隙。与初始土样相比,恒体积膨胀条件下,土样中的小孔隙被压缩成微孔隙。在上覆荷载为0 kPa和50 kPa的侧限膨胀条件下,由于上覆荷载小于土的膨胀力,土颗粒能够推开其旁边的颗粒,所以土中各类型孔隙的体积含量均增多。
One-dimensional swelling tests under different load conditions were conducted to obtain the evolution of Nanyang expansive soil's microstructure. Samples with initial state and samples swelling under different conditions were freezing-dried to get prepared for Scanning Electron Microscope(SEM) tests and Mercury Intrusion Porosimetry(MIP) test. Then the modification in microstructures and pore size distribution were analyzed. SEM tests show that soil-particle arrangement has no obvious directionality. Samples with initial compacted state and swelling under constant volume are in turbulent flow structures, while samples swelling under 0 or 50 kPa surcharge are of granular structures after reaching steady state. MIP test shows that the pore size distribution curves of samples under different swelling conditions are of three peaks. Pores in soils can be classified into macro-pore, fine-pore, micro-pore and ultra-micro-pore. Compared with initial states, fine-pores in samples swelling under constant volume are compressed into micro-pore. The volumes of all kinds of pores in samples swelling under 0 or 50 kPa surcharge loads all increase as the surcharge loads are larger than the expansive force. In this situation, soil particles can push each other away.
One-dimensional swelling tests under different load conditions were conducted to obtain the evolution of Nanyang expansive soil's microstructure. Samples with initial state and samples swelling under different conditions were freezing-dried to get prepared for Scanning Electron Microscope(SEM) tests and Mercury Intrusion Porosimetry(MIP) test. Then the modification in microstructures and pore size distribution were analyzed. SEM tests show that soil-particle arrangement has no obvious directionality. Samples with initial compacted state and swelling under constant volume are in turbulent flow structures, while samples swelling under 0 or 50 kPa surcharge are of granular structures after reaching steady state. MIP test shows that the pore size distribution curves of samples under different swelling conditions are of three peaks. Pores in soils can be classified into macro-pore, fine-pore, micro-pore and ultra-micro-pore. Compared with initial states, fine-pores in samples swelling under constant volume are compressed into micro-pore. The volumes of all kinds of pores in samples swelling under 0 or 50 kPa surcharge loads all increase as the surcharge loads are larger than the expansive force. In this situation, soil particles can push each other away.
引文
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[12] WASHBURN E W. Note on a Method of Determining the Distribution of Pore Sizes in a Porous Material[J]. Proceedings of the National Academy of Sciences, 1921, 7(4): 115-116.
[13] ZHANG L M, LI X. Microporosity Structure of Coarse Granular Soils[J]. Journal of Geotechnical and Geoenvironmental Engineering, 2010, 136(10): 1425-1436.
[14] 邹维列,陈轮,谢鹏,等. 重塑膨胀土非线性强度特性及一维固结浸水膨胀应力-应变关系[J]. 岩土力学,2012,33(增2):59-64.
[15] 谭罗荣,孔令伟.膨胀土膨胀特性的变化规律研究[J]. 岩土力学,2004,25(10):1555-1559.
[16] 丁振洲,郑颖人,李利晟. 膨胀力变化规律试验研究[J]. 岩土力学,2007,28(7):1328-1332.
[17] 卢子威,张文慧,王晶晶. 重塑膨胀土膨胀力室内试验研究[J]. 河北工程大学学报(自然科学版),2015,32(3):47-50.
[2] 谭罗荣,张梅英,邵梧敏,等.灾害性膨胀土的微结构特征及其工程性质[J].岩土工程学报,1994,16(2):48-57.
[3] 马晓宁,王选仓,孙进玲,等.陇南地区膨胀土微观结构与膨胀性[J]. 南水北调与水利科技,2016,14(3):111-114,149.
[4] PEDARLA A, PUPPALA A, HOYOS L R.Swelling Behavior of Expansive Clays Incorporating Mineralogy and Pore Size Distribution via SWCC[C]//Advances in Unsaturated Soils: Proceedings of the 1st Pan-American Conference on Unsaturated Soils, PanAmUNSAT 2013. Cartagena de Indias, Colombia, February 20-22, 2013: 305-308.
[5] 胡冉,陈益峰,周创兵.基于孔隙分布的变形土土水特征曲线模型[J].岩土工程学报,2013,35(8):1451-1462.
[6] 陈宇龙. 云南膨胀土的微观结构特征[J]. 岩土工程学报,2013, 35(增1): 334-339.
[7] CUI Y J, LOISEAU C, DELAGE P. Microstructure Changes of a Confined Swelling Soil Due to Suction Controlled Hydration[C]//Proceedings of the 3rd International Conference on Unsaturated Soils (UNSAT 2002), Recife, Brazil. March 10-12, 2002: 593-598.
[8] 张先伟, 孔令伟, 郭爱国, 等. 基于SEM和MIP试验结构性黏土压缩过程中微观孔隙的变化规律[J]. 岩石力学与工程学报,2012,31(2):406-412.
[9] LIN B, CERATO A B. Applications of SEM and ESEM in Microstructural Investigation of Shale-Weathered Expansive Soils along Swelling-Shrinkage Cycles[J]. Engineering Geology, 2014, 177:66-74.
[10] 陈宝,朱嵘,常防震.不同压应力作用下黏土体积变形的微观特征[J].岩土力学,2011,32(增1):95-99,369.
[11] ZHANG J, SCHERER G W. Comparison of Methods for Arresting Hydration of Cement[J]. Cement & Concrete Research, 2011, 41(10):1024-1036.
[12] WASHBURN E W. Note on a Method of Determining the Distribution of Pore Sizes in a Porous Material[J]. Proceedings of the National Academy of Sciences, 1921, 7(4): 115-116.
[13] ZHANG L M, LI X. Microporosity Structure of Coarse Granular Soils[J]. Journal of Geotechnical and Geoenvironmental Engineering, 2010, 136(10): 1425-1436.
[14] 邹维列,陈轮,谢鹏,等. 重塑膨胀土非线性强度特性及一维固结浸水膨胀应力-应变关系[J]. 岩土力学,2012,33(增2):59-64.
[15] 谭罗荣,孔令伟.膨胀土膨胀特性的变化规律研究[J]. 岩土力学,2004,25(10):1555-1559.
[16] 丁振洲,郑颖人,李利晟. 膨胀力变化规律试验研究[J]. 岩土力学,2007,28(7):1328-1332.
[17] 卢子威,张文慧,王晶晶. 重塑膨胀土膨胀力室内试验研究[J]. 河北工程大学学报(自然科学版),2015,32(3):47-50.