Comparative Study On The Performance Of Shear Creep Of Undisturbed And Remolded Q₂ Loess From Jingyang

Loess is a widely distributed quaternary sediments with typical structure.Its mechanical properties of the loess are determined by the macroscopic and microscopic factors.The strength loess is affected the water content and dry density.The structure of loess is influenced by its mineral composition,particle size distribution and pore distribution.Therefore,it is of great significance to study the mechanical properties of loess from macroscopic and microscopic aspects.Focusing on rheological properties and structure,the strength and structure of loess are studied by macroscopic mechanical tests and micro quantitative analysis based on Jingyang Q2 loess.The main research results are as follows:(1)To overcome the shortcomings of the existing shear test instrument,the improved pure shear creep instrument is put forward and used for the pure shear test and the pure shear creep test of original loess and remolded loess in Jingyang Q2.Results show that the utillity of the instrument can effectively avoid multiplicity in back calculation.Pure shear test and pure shear creep test can directly be carried out in the ring knife,while pure shear creep parameters can be obtained quickly and accurately.(2)The variation of the strength of the original and remolded loess with the water content and dry density was studied.The results show that brittle failure occur in both original and remolded loess in the pure shear test.The slope of the stress-strain curve increases with the decrease of the water content in both original and remolded loess before the shear displacement reaches 1mm,which indicates that the damage mode of the soil sample has changed.(3)The variation of rheological properties of the original and remolded loess with the water content and dry density were studied.The results show that the strain-time curves are different under different pure shear stress conditions.When the shear stress value is smaller than the critical value of soil samples,the loess deformation is attenuation,and reaches the steady-state quickly.When the pure shear stress value is higher than the critical value,the creep deformation of the loess increases gradually.When loess is under high stress,accelerated creep stage will occur,and specimen will be destroyed quickly.(4)Based on Burgers model,the pure shear creep model of loess is established.The calculation results of pure shear creep model were compared with the results of pure shear creep test,which shown that the constitutive model can better reflect the creep test of loess.(5)The distribution of mineral composition,particle size composition and pore distribution in the original and remolded loess of Jingyang Q2 are studied in this paper.It is found that the quartz mineral content in remolded loess is almost the same as that in original loess.To some extent,the particle size distribution of the quartz indicates the strength of loess.Carbonate minerals may easily influenced by outer-environment,which may affect the strength of loess.It is found that the porosity in original and remolded loess is relatively high.The original structure of loess is damaged in the process of remolding,while large pores are more likely to be changed.Therefore,under the same initial condition,the mechanical properties of original loess are better than remolded loess.In conclusion,the effect of loess structure on the mechanical properties can be quantitatively evaluated by mineral composition and pore distribution.