济南浅层地基微观结构及分形特征研究
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摘要
天然沉积土的宏观力学特性与微观结构紧密相关,研究土体微观结构对深入揭示土的宏观力学特性具有重要意义。首先研究济南地区深度在50 m以内黄河冲积地层天然沉积土的物理力学参数分布特征,再采用场发射扫描电镜试验,分析各土层不同方向土样的微观结构特征,最后应用分形理论,研究各层土分形维数的演化规律及其与物理特性参数间的相关性。结果表明:第(7)层黄土是以粗粉粒为主体骨架的蜂窝状大孔隙结构,第(8)层粉质黏土是碎屑粉粒为骨架的蜂窝结构,第(9)、(10)和(11)层粉质黏土是以黏粒集合体为基本单元的薄层状絮凝结构。不同土层土体土粒和孔隙的分形行为明显,随着地基深度增大,土粒和孔隙的分布分维数均逐渐加大,形态分维数均逐渐减小,土粒的粒径变化比孔隙的孔径变化明显,而孔隙的形态变化比土粒复杂。土体的分维数与含水率、孔隙比、液塑限、黏聚力和内摩擦角之间存在较强的相关性。
The macroscopic characteristics of rock and soil are closely related to the microstructure. Therefore,study on the microstructure of soil to reveal the macroscopic mechanical properties of soil has extremely importance. Firstly,the distribution characteristics of physical and mechanical parameters of 50 m shallow natural sedimentary soils in Jinan area were studied and then microstructure of different soil layers in different directions were examined by FESEM tests. According to fractal theory,the microstructures of soil samples were quantitatively analyzed to explore the evolution law of fractal dimension and the relevance between basic physics parameters and fractal dimension. The results show that the 7thloess is a honeycomb-like large pore structure with coarse particles as the main skeleton; the microstructure of 8thsilty clay is a honeycomb-like pore structure with clastic particles as skeleton and the 9thto 11 thsilty clay is a thin layer of flocculation structure with the clay aggregate as the basic element. The fractal behavior of soil particles and pores is obvious. With the increase of the depth of shallow ground,the distribution fractal dimension of the particles and the pores gradually increases and the shape fractal dimension decreases. Compared with the pores,the change of diameter of particles is significant,but the pore shape is more complex than that of the particles. The soil fractal dimension has strong correlation with water content,pore ratio,liquid and plastic limit,cohesion and internal friction angle.
The macroscopic characteristics of rock and soil are closely related to the microstructure. Therefore,study on the microstructure of soil to reveal the macroscopic mechanical properties of soil has extremely importance. Firstly,the distribution characteristics of physical and mechanical parameters of 50 m shallow natural sedimentary soils in Jinan area were studied and then microstructure of different soil layers in different directions were examined by FESEM tests. According to fractal theory,the microstructures of soil samples were quantitatively analyzed to explore the evolution law of fractal dimension and the relevance between basic physics parameters and fractal dimension. The results show that the 7thloess is a honeycomb-like large pore structure with coarse particles as the main skeleton; the microstructure of 8thsilty clay is a honeycomb-like pore structure with clastic particles as skeleton and the 9thto 11 thsilty clay is a thin layer of flocculation structure with the clay aggregate as the basic element. The fractal behavior of soil particles and pores is obvious. With the increase of the depth of shallow ground,the distribution fractal dimension of the particles and the pores gradually increases and the shape fractal dimension decreases. Compared with the pores,the change of diameter of particles is significant,but the pore shape is more complex than that of the particles. The soil fractal dimension has strong correlation with water content,pore ratio,liquid and plastic limit,cohesion and internal friction angle.
引文
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[20] MIAO Tongjun,YANG Shanshan,LONG Zhangcai,et al.Fractal Analysis of Permeability of Dual-Porosity Media Embedded with Random Fractures[J]. International Journal of Heat and Mass Transfer,2015,88:814-821.
[21]党发宁,刘海伟,王学武,等.基于有效孔隙比的黏性土渗透系数经验公式研究[J].岩石力学与工程学报,2015,34(9):1909-1917.
[2]刘宏伟,刘文白,崔勇涛,等.固化吹填土的渗透性及其分形维数的定量研究[J].科学技术与工程,2017,17(13):60-65.
[3]周萃英.土体微观结构研究与土力学的发展方向:若干进展与思考[J].地球科学,2000(2):215-220.
[4] AHMED A. Compressive Strength and Microstructure of Soft Clay Soil Stabilized with Recycled Bassanite[J]. Applied Clay Science,2015,104:27-35.
[5] WU Zhilong,DENG Yongfeng,LIU Songyu,et al. Strength and Micro-Structure Evolution of Compacted Soils Modified by Admixtures of Cement and Metakaolin[J]. Applied Clay Science,2016,127-128:44-51.
[6]陈琳,喻文兵,杨成松,等.基于微观结构的青藏高原风积沙导热系数变化机理研究[J].冰川冻土,2014,36(5):1220-1226.
[7]石刚,支喜兰,马建秦,等.黄土的组分及微观结构特征与地基承载力[J].公路交通科技,2005,22(12):46-49.
[8]张先伟,孔令伟,王静.针对黏性土胶质联结特征的SEMEDS试验研究[J].岩土力学,2013,34(增刊2):195-203.
[9]徐日庆,邓祎文,徐波,等.基于SEM图像的软土三维孔隙率计算及影响因素分析[J].岩石力学与工程学报,2015,34(7):1497-1502.
[10]胡海军,蒋明镜,彭建兵,等.应力路径试验前后不同黄土的孔隙分形特征[J].岩土力学,2014,35(9):2479-2485.
[11]赵月平.膨胀土分类的分形插值评价方法[J].人民黄河,2015,37(6):91-94.
[12]刘松玉,张继文.土中孔隙分布的分形特征研究[J].东南大学学报,1997(3):129-132.
[13]吕海波,赵艳林,孔令伟,等.海相软土孔隙分布的分形特征及应用[J].桂林工学院学报,2006(1):50-53.
[14] LU Yang,LIU Sihong,WENG Liping,et al. Fractal Analysis of Cracking in a Clayey Soil Under Freeze-Thaw Cycles[J]. Engineering Geology,2016,208:93-99.
[15] XU Yongfu,CAO Ling. Fractal Representation for Effective Stress of Unsaturated Soils[J]. International Journal of Geomechanics,2014,15(6):98.
[16] ALFARO SOTO M A,CHANG H K,VAN GENUCHTEN M T. Fractal-Based Models for the Unsaturated Soil Hydraulic Functions[J]. Geoderma,2017,306:144-151.
[17]中华人民共和国水利部.土工试验方法标准:GB/T50123—1999[S].北京:中国标准出版社,1999:50-52.
[18]张季如,祝杰,黄丽,等.土壤微观结构定量分析的IPP图像技术研究[J].武汉理工大学学报,2008,30(4):80-83.
[19]陶高梁,张季如.表征孔隙及颗粒体积与尺度分布的两类岩土体分形模型[J].科学通报,2009,54(6):838-846.
[20] MIAO Tongjun,YANG Shanshan,LONG Zhangcai,et al.Fractal Analysis of Permeability of Dual-Porosity Media Embedded with Random Fractures[J]. International Journal of Heat and Mass Transfer,2015,88:814-821.
[21]党发宁,刘海伟,王学武,等.基于有效孔隙比的黏性土渗透系数经验公式研究[J].岩石力学与工程学报,2015,34(9):1909-1917.
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