Structural Characteristics Of Loess And Its Effect On Soil Shear Strength

Loess is a kind of special granular material,and its structure and physical-mechanical properties are closely related.In the development of loess research from macro,microscomic and micro to multi-scale comprehensive research,the role of structure in the study of loess strength characteristics has received more and more attention and discussed deeply.Starting from the structure,especially the change of micro-structure,revealing the nature and macro-deformation mechanism of loess is the main direction to study the shear deformation and failure of loess at present.Therefore,it is of great scientific significance to carry out structural research and explore the relationship between structural research and shear strength of soil,and it can also provide some theoretical guidance for engineering practice.Taking the Q3 loess in Yan'an as the research object,this paper analyzed the relationship between loess structure and its deformation and failure characteristics under different water content,and discussed the corresponding change characteristics of micro-particle morphology and micro-structure in the process of Loess shear deformation.The main results are as follows:(1)The particle morphology,contact relationship and pore distribution of undisturbed loess and remolded loess were analyzed by means of scanning electron microscopy and mercury intrusion porosimetry test.Based on previous research results and mercury intrusion porosimetry results,the Loess pore can be divided into four types:macropore(d?16?m),medium-pore(4?m-16?m),finepore(0.04?m-4?m)and micropore(d?0.04?m).(2)Triaxial consolidated undrained shear tests with different water content were carried out,and the variation of shear strength with water content was analyzed.The results show that the shear strength has a quadratic non-linear negative correlation with water content:(?1-?3)f=A?2-B?+C?The internal friction angle of loess has a power function relationship with water content:c=A?B,and the internal friction angle has a good linear relationship with water content:?=k?+b?(3)The undisturbed loess and remolded loess show different yield characteristics.The structural yield stress decreases with the increase of confining pressure,which can strengthen the structural yield stress of soil.Under the same conditions,the structural yield stress of undisturbed and remolded loess has obvious difference,and the relationship between structural yield stress and water content is non-linear:?(?1-?3)=-A?2-B?+C?(4)During the process of loess shear failure,the micro-structure characteristics change obviously,the soil structure tends to be compact,the particle edges and corners disappear in a rounded shape,the contact between support and cementation gradually becomes mosaic contact,and the pore in the soil appears the phenomenon of "one changes to the other".