Experimental Study On Mechanical Properties Of Guiyang Red Clay Under Different Stress Paths

In this paper,the red clay of the foundation pit of Huaxi Interchange Expressway Project in Guiyang City,Guizhou Province is chosen as the research object.Combined with the soil characteristics and stress characteristics of the foundation pit and slope of red clay foundation pit and slope,the stress path,water content and drainage mode are considered.The mechanical properties of Guizhou red clay under different conditions were studied in laboratory by means of soil structure integrity(undisturbed or disturbed red clay),consolidation mode and so on.For the first time,the concept of unloading ratio is introduced to study the relationship between unloading ratio and deformation and failure of red clay under excavation.At the same time,from the point of view of soil mechanics,the structural changes of red clay under different stress paths and water content under external loads are studied quantitatively by using the concept of structural parameters for the first time.The relationship between macro-variability and mesostructural parameters is discussed.The main conclusions are as follows:(1)Macro-mechanical characteristics of red clay under different stress paths: Under different stress paths,whether undisturbed red clay or remolded red clay,the stress-strain relationship and pore water pressure characteristics are very sensitive to the stress path.On the whole,the intact undamaged red clay is more sensitive to the stress path than the remolded red clay whose structure has been destroyed.At the same time,different moisture content,consolidation mode and initial consolidation confining pressure have different effects on the mechanical properties of red clay under each stress path.(2)The relationship between unloading ratio and deformation of red clay under excavation unloading: the unloading ratio-strain relationship of undisturbed and remolded laterally unloaded red clay in Guiyang is studied for the first time by referring to the concepts of unloading ratio R and initial unloading ratio R0,and the relationship between unloading ratio and deformation is studied for the first time by introducing the concepts of unloading ratio R and initial unloading ratio R0.It is found that the unloading deformation of laterally unloaded red clay is not immediately shown,but is obvious at a certain unloading ratio.The unloading deformation of laterally unloaded red clay can be divided into slow deformation stage and deformation failure stage,and the unloading deformation of laterally unloaded red clay can be divided into slow deformation stage and deformation failure stage.The unloading ratio between the two stages has an obvious inflection point.The stress path,consolidation mode,final value of consolidation confining pressure and moisture content have obvious influence on the relationship between unloading ratio and strain,and the initial unloading ratio R0 value is different under different conditions,and the stress path,consolidation mode,final value of consolidation confining pressure and moisture content have obvious influence on the relationship between unloading ratio and strain.The initial unloading ratio can be used to quantitatively analyze the deformation and failure of red clay.The initial unloading ratio is closely related to the stability and deformation failure of red clay.(3)The relationship between micro-structural parameters and macro-deformation: the relationship between structural change characteristics and corresponding mechanical behavior of Guiyang red clay was studied.It is found that the structural parameters of stress ratio,which can be quantificationally expressed by dynamic change,are suitable for describing the structural and mechanical behavior of red clay,and it can be connected with the mechanical behavior of red clay under external load.It has certain sensitivity,rationality and regularity under different conditions.