贵阳红黏土介-微观结构对力学特性影响试验研究
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摘要
为阐明贵阳红黏土宏观力学强度与变形特性的介-微观机理,同时考虑不同围压、不同干密度下贵阳重塑红黏土宏观力学特性之间的差异,通过不固结不排水三轴剪切试验、N2吸附测试及电镜扫描(SEM)测试,研究了原状和重塑土样因颗粒形态、孔隙结构与分布等不同所产生的宏观力学特性之间的差异。试验结果表明:不固结不排水三轴剪切试验条件下贵阳红黏土原状样应力-应变曲线表现出具有驼峰状的应变软化特性;重塑样则呈现出明显的应变硬化现象。随着干密度的增加,一定围压下重塑样强度曲线硬化现象加强;随围压增加,强度不断增强。原状和重塑土样氮气吸附-脱附等温曲线均表现出明显的Ⅳ型、H3滞后环,曲线整体均呈反"S"型。不过,在平均孔径、比表面积、总孔容积等指标上有差异,反映出原状样孔隙主要由中大孔构成,含部分微小孔;经重塑后大孔和微孔有所减少,介孔呈增多趋势。扫描电镜(SEM)下原状样较重塑样介-微观结构更加复杂,介-微观结构形态参数更加优化,表现出明显的原生结构、更强的力学强度。
In order to explicate the macroscopic mechanical strength and meso-microscopic mechanism of deformation characteristics of Guiyang red clay and simultaneously consider the differences among the macroscopic mechanical properties of Guiyang red clay under different confining pressures and different dry densities,the differences among the macroscopic mechanical properties caused by different particle patterns,different pore structures and different distributions of the undisturbed and remolded Guiyang red clay are studied herein through the relevant unconsolidated-undrained triaxial shear test and N2 adsorption and electron micro-scope( SEM) testing. The experiment result shows that the strain-stress curve of the undisturbed sample of Guiyang red clay exhibits a hump-shaped strain softening characteristics under the condition of unconsolidated-undrained triaxial shear test,while the remolded sample presents obvious strain hardening phenomenon. Along with the increase of dry density,the hardening phenomenon of the strength curve of the remolded sample under certain confining pressure is enhanced,while the strength continuously increases along with the increase of confining pressure. The nitrogen sorption-desorption isotherm curves of both the undisturbed and remolded samples show obvious type IV and type H3 hysteresis loops,of which both the curves exhibit inversed S types.However,differences are there among the indexes of the mean pore size,specific surface area,total pore volume,etc.,which reflects that the pore of the undisturbed sample mainly consists of mid-large pores with a part of micro-pores. After remolding,the large and micro-pores decrease to some extent and the meso-pore shows an increasing trend. Under the scanning electron microscope( SEM),the meso-microstructure of the undisturbed sample is more complicated than that of the remolded one,while the parameters of the meso-microstructural pattern are more optimal and present obvious primary structure and stronger mechanical strength.
In order to explicate the macroscopic mechanical strength and meso-microscopic mechanism of deformation characteristics of Guiyang red clay and simultaneously consider the differences among the macroscopic mechanical properties of Guiyang red clay under different confining pressures and different dry densities,the differences among the macroscopic mechanical properties caused by different particle patterns,different pore structures and different distributions of the undisturbed and remolded Guiyang red clay are studied herein through the relevant unconsolidated-undrained triaxial shear test and N2 adsorption and electron micro-scope( SEM) testing. The experiment result shows that the strain-stress curve of the undisturbed sample of Guiyang red clay exhibits a hump-shaped strain softening characteristics under the condition of unconsolidated-undrained triaxial shear test,while the remolded sample presents obvious strain hardening phenomenon. Along with the increase of dry density,the hardening phenomenon of the strength curve of the remolded sample under certain confining pressure is enhanced,while the strength continuously increases along with the increase of confining pressure. The nitrogen sorption-desorption isotherm curves of both the undisturbed and remolded samples show obvious type IV and type H3 hysteresis loops,of which both the curves exhibit inversed S types.However,differences are there among the indexes of the mean pore size,specific surface area,total pore volume,etc.,which reflects that the pore of the undisturbed sample mainly consists of mid-large pores with a part of micro-pores. After remolding,the large and micro-pores decrease to some extent and the meso-pore shows an increasing trend. Under the scanning electron microscope( SEM),the meso-microstructure of the undisturbed sample is more complicated than that of the remolded one,while the parameters of the meso-microstructural pattern are more optimal and present obvious primary structure and stronger mechanical strength.
引文
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[15] LIN Q,YAN J,ZHOU J,et al. Microstructure study on intactclay behavior subjected to cyclic principal stress rotation[J]. Proce-dia Engineering,2016,143:991-998.
[2] YUAN J,HE Y,LIU J. Construction ofweak expansive red clay on Dongxin Ex-pressway in Hunan Province,China[J].Journal of Performance of Constructed Fa-cilities,2016,30(1):C4015001.
[3] ROMERO E,SIMMS P H. Microstructure investigation in unsatu-rated soils:a review with special attention to contribution of mercuryintrusion porosimetry and environmental scanning electron microscopy[J]. Geotechnical&Geological Engineering,2008,26(6):705-727.
[4] YOU Z,LAI Y,ZHANG M,et al. Quantitative analysis for theeffect of microstructure on the mechanical strength of frozen silty claywith different contents of sodium sulfate[J]. Environmental EarthSciences,2017,76(4):143.
[5]徐永福.非饱和膨胀土的结构模型和力学性质的研究[J].岩石力学与工程学报,1998,17(5):610.
[6]胡瑞林,官国琳,李向全,等.黄土湿陷性的微结构效应[J].工程地质学报,1999,7(2):65-71.
[7]施斌,姜洪涛.粘性土的微观结构分析技术研究[J].岩石力学与工程学报,2001,20(6):864-870.
[8]廖义玲,余培厚.红粘土的微结构及其概化模型[J].工程地质学报,1994,2(1):27-37.
[9]周远忠,刘新荣,张梁,等.红粘土微观结构模型及其工程力学效应分析[J].地下空间与工程学报,2012,8(4):726-731,835.
[10]李景阳,朱立军,梁风,等.碳酸盐岩残积红粘土微观结构的扫描电镜研究[J].中国岩溶,2002,21(4):2-7.
[11] TANG Y,SUN K,ZHANG X,et al. Microstructure changes ofred clay during its loss and leakage in the karst rocky desertificationarea[J]. Environmental Earth Sciences,2016,75(6):537.
[12]南京水利科学研究院.土工试验规程:SL 237—1999[S].北京:中国水利水电出版社,1999.
[13]陈超,夏扬,石莹,等.微硅粉的微观结构分析[J].商品混凝土,2016(7):39-42.
[14]何余生,李忠,奚红霞,等.气固吸附等温线的研究进展[J].离子交换与吸附,2004,20(4):376-384.
[15] LIN Q,YAN J,ZHOU J,et al. Microstructure study on intactclay behavior subjected to cyclic principal stress rotation[J]. Proce-dia Engineering,2016,143:991-998.