干湿循环下滑带土强度特性与微观结构试验研究
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摘要
库区水位周期性波动,巨大的水位变幅使库岸滑坡滑带土处于干湿循环变化之中,而干湿循环作用影响土体的强度特性。基于此,以三峡库区某典型库岸滑坡滑带土体作为研究对象,对经历不同干湿循环次数的土样进行环剪试验、扫描电子显微镜(SEM)试验和核磁共振(NMR)试验,分析干湿循环作用下滑带土强度特性和微观结构变化规律,并初步探讨干湿循环对滑带土强度影响的微观机制。试验结果表明:干湿循环作用下,滑带土残余强度的劣化特性十分明显,且前3次干湿循环导致土体强度衰减幅度较大,之后衰减趋势减弱,土体强度逐渐趋于稳定,同时,黏聚力的劣化效应大于内摩擦角;随干湿循环次数的增加,以叠聚状、凝块状为主的团粒逐渐分散、解体,颗粒间连接由面-面接触逐渐向面-边、面-角接触演化,表现为土体内孔隙数量增多,土颗粒形态变化,粒间距离增加,微小孔隙逐渐向大孔隙演变;干湿循环作用下,滑带土内亲水性黏土矿物吸水膨胀、失水收缩而引发土颗粒、孔隙及胶结物等微结构变化是导致滑带土残余强度劣化的内在原因。
Large hydro-fluctuation and periodical water level changes in the reservoir have caused the slip zone soil of the banks to experience drying-wetting cycles, which has a great influence on strength characteristics of soil. In this paper, a series of drying-wetting cycle tests on the slip zone soil from an ancient landslide is carried out. The soil samples after different runs of drying-wetting tests are then used to conduct the ring shear tests, scanning electron microscope(SEM) tests and nuclear magnetic resonance(NMR) tests. The results of these tests can be used to analyze the changes of soil microstructure and strength properties during drying-wetting cycles, and to investigate the microscopic mechanism of changes in strength properties. The research indicates that the deterioration of the residual strength of soil is obvious in drying-wetting cycles. The first three drying-wetting cycles result in a larger attenuation of soil strength, then the decay trend weakens and the soil strength gradually stabilizes. At the same time, the deterioration effect of cohesion is greater than the internal friction angle. Besides, the results also show that the clump-like aggregates are gradually disintegrated with the increase of drying-wetting cycles, and the way of connection of soil particles changes from plane-plane to plane-edge and plane-angle. Meanwhile, under the drying-wetting cycles, the number of pores in the soil increases, the morphology of the soil changes, the distance between the grains increases, and the small pores gradually change to the large pores in soil. The pore and cement microstructure changes of soil particles caused by clay mineral swelling and shrinkage are the causes of deterioration of the residual strength of slip soil under the drying-wetting cycles.
Large hydro-fluctuation and periodical water level changes in the reservoir have caused the slip zone soil of the banks to experience drying-wetting cycles, which has a great influence on strength characteristics of soil. In this paper, a series of drying-wetting cycle tests on the slip zone soil from an ancient landslide is carried out. The soil samples after different runs of drying-wetting tests are then used to conduct the ring shear tests, scanning electron microscope(SEM) tests and nuclear magnetic resonance(NMR) tests. The results of these tests can be used to analyze the changes of soil microstructure and strength properties during drying-wetting cycles, and to investigate the microscopic mechanism of changes in strength properties. The research indicates that the deterioration of the residual strength of soil is obvious in drying-wetting cycles. The first three drying-wetting cycles result in a larger attenuation of soil strength, then the decay trend weakens and the soil strength gradually stabilizes. At the same time, the deterioration effect of cohesion is greater than the internal friction angle. Besides, the results also show that the clump-like aggregates are gradually disintegrated with the increase of drying-wetting cycles, and the way of connection of soil particles changes from plane-plane to plane-edge and plane-angle. Meanwhile, under the drying-wetting cycles, the number of pores in the soil increases, the morphology of the soil changes, the distance between the grains increases, and the small pores gradually change to the large pores in soil. The pore and cement microstructure changes of soil particles caused by clay mineral swelling and shrinkage are the causes of deterioration of the residual strength of slip soil under the drying-wetting cycles.
引文
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[14]韦秉旭,刘斌,欧阳运清,等.干湿循环作用对膨胀土结构性的影响及其导致的强度变化[J].工业建筑,2015,45(8):99-103.WEI Bing-xu,LIU Bin,OUYANG Yun-qing,et al.The effect of drying-wetting cycles on expansive soil structure and its induced variations in strength[J].Industrial Construction,2015,45(8):99-103.
[15]张英,邴慧,杨成松.基于SEM和MIP的冻融循环对粉质黏土强度影响机制研究[J].岩石力学与工程学报,2015,34(增刊1):3597-3603.ZHANG Ying,BING Hui,YANG Cheng-song.Influences of freeze-thaw cycles on mechanical properties of silty clay based on SEM and MIP test[J].Chinese Journal of Rock Mechanics and Engineering,2015,34(Suppl.1):3597-3603.
[2]邓华锋,李建林,朱敏,等.饱水-风干循环作用下砂岩强度劣化规律试验研究[J].岩土力学,2012,33(11):3306-3312.DENG Hua-feng,LI Jian-lin,ZHU Min,et al.Experimental research on strength deterioration rules of sandstone under“saturation-air dry”circulation function[J].Rock and Soil Mechanics,2012,33(11):3306-3312.
[3]曹玲,罗先启.三峡库区千将坪滑坡滑带土干-湿循环条件下强度特性试验研究[J].岩土力学,2007,28(增刊1):93-97.CAO Ling,LUO Xian-qi.Experimental study of dry-wet circulation of Qianjiangping landslide’s unsaturated soil[J].Rock and Soil Mechanics,2007,28(Suppl.1):93-97.
[4]梁和成,单慧媚.天然饱水-失水对三峡库岸边坡土体的影响研究[J].岩土力学,2014,35(7):1837-1848.LIANG He-cheng,SHAN Hui-mei.Effect of natural water-saturation and water-loss on bank-slope soil in Three Gorges reservoir[J].Rock and Soil Mechanics,2014,35(7):1837-1848.
[5]姚志华,陈正汉,朱元青,等.膨胀土在湿干循环和三轴浸水过程中细观结构变化的试验研究[J].岩土工程学报,2010,32(1):68-76.YAO Zhi-hua,CHEN Zheng-han,ZHU Yuan-qing,et al.Meso-structural change of remolded expansive soils during wetting-drying cycles and triaxial soaking tests[J].Chinese Journal of Geotechnical Engineering,2010,32(1):68-76.
[6]李江,许强,胡泽铭,等.川东红层原状滑带土饱水软化试验研究[J].岩石力学与工程学报,2015(增刊2):4333-4342.LI Jiang,XU Qiang,HU Ze-ming,et al.Experimental research on softening of undisturbed saturated slip soil in eastern of Sichuan province red bed[J].Chinese Journal of Rock Mechanics and Engineering,2015(Suppl.2):4333-4342.
[7]黄斌,傅旭东,谭凡,等.含水率对滑带土强度及变形影响试验研究[J].岩土力学,2012,33(9):57-62.HUANG Bin,FU Xu-dong,TAN Fan,et al.Experimental study of relationship between water content and strength or deformation of slip soil[J].Rock and Soil Mechanics,2012,33(9):57-62.
[8]李维树,邬爱清,丁秀丽,等.三峡库区滑带土抗剪强度参数的影响因素研究[J].岩土力学,2006,27(1):56-60.LI Wei-shu,WU Ai-qing,DING Xiu-li,et al.Study on influencing factors of shear strength parameters of slide zone clay in Three Gorges Reservoir area[J].Rock and Soil Mechanics,2006,27(1):56-60.
[9]中华人民共和国行业标准编写组.SL237-1999土工试验规程[S].北京:中国水利水电出版社,1999.The Professional Standards Compilation Group of People’s Republic of China.SL237-1999 Specification of soil test[S].Beijing:China Water Power Press,1999.
[10]王顺,项伟,崔德山,等.不同环剪方式下滑带土残余强度试验研究[J].岩土力学,2012,33(10):2967-2972.WANG Shun,XIANG Wei,CUI De-shan,et al.Study of residual strength of slide zone soil under different ring-shear tests[J].Rock and Soil Mechanics,2012,33(10):2967-2972.
[11]吴迪,简文彬,徐超.残积土抗剪强度的环剪试验研究[J].岩土力学,2011,32(7):2045-2050.WU Di,JIAN Wen-bin,XU Chao.Research on shear strength of residual soils by ring shear tests[J].Rock and Soil Mechanics,2011,32(7):2045-2050.
[12]邓华锋,肖瑶,方景成,等.干湿循环作用下岸坡消落带土体抗剪强度劣化规律及其对岸坡稳定性影响研究[J].岩土力学,2017,38(9):1-10.DENG Hua-feng,XIAO Yao,FANG Jing-cheng,et al.Shear strength degradation regularity of hydro-fluctuation belt soil of bank slope in drying-wetting cycle and its influence on the bank slope[J].Rock and Soil Mechanics,2017,38(9):1-10.
[13]董金玉,赵志强,杨继红,等.干湿循环作用下滑带土的变形演化和强度参数弱化试验研究[J].四川大学学报(工程科学版),2016,48(增刊2):1-7.DONG Jin-yu,ZHAO Zhi-qiang,YANG Ji-hong,et al.Research on the deformation evolution and the strength weakening of slip soil under wetting-drying cycle[J].Journal of Sichuan University(Engineering Science Edition),2016,48(Suppl.2):1-7.
[14]韦秉旭,刘斌,欧阳运清,等.干湿循环作用对膨胀土结构性的影响及其导致的强度变化[J].工业建筑,2015,45(8):99-103.WEI Bing-xu,LIU Bin,OUYANG Yun-qing,et al.The effect of drying-wetting cycles on expansive soil structure and its induced variations in strength[J].Industrial Construction,2015,45(8):99-103.
[15]张英,邴慧,杨成松.基于SEM和MIP的冻融循环对粉质黏土强度影响机制研究[J].岩石力学与工程学报,2015,34(增刊1):3597-3603.ZHANG Ying,BING Hui,YANG Cheng-song.Influences of freeze-thaw cycles on mechanical properties of silty clay based on SEM and MIP test[J].Chinese Journal of Rock Mechanics and Engineering,2015,34(Suppl.1):3597-3603.