Experimental Study On Deformation Characteristics Of Compacted Loess Under Alternate Action Of Dry-wet And Freeze-thaw Cycles

China is one of the countries with the most widespread loess distribution in the world.Loess exists in large areas in northwestern and northern China.These areas are also seasonally frozen soil areas.The roadbeds and slopes in the area are closely related to loess.Soil engineering is inevitably degraded by the dry-wet-freeze-thaw cycle,resulting in complex deformations.In severe cases,it will induce engineering diseases such as uneven settlement and slope instability,which will seriously threaten the safety and stability of related projects.A comprehensive study was carried out on the deformation characteristics of compacted loess under the action of dry-wet-freeze-thaw cycles.Based on the Jihe Expressway Project in Shanxi Province,this paper aimed at the engineering problem of the periodic uplift and settlement of the loess subgrade over time.The site compacted loess was sampled and the relevant indoor test research was carried out.The main results obtained are as follows:(1)An experimental study on the soil-water characteristic curve of unsaturated compacted loess was carried out.Combined with axis translation technology,filter paper method and saturated salt solution method,the soil-water characteristic curve of compacted loess is measured,and the soil-water characteristic curve in the full suction range under different dry densities is obtained,revealing the net average stress,temperature and dry density The law of influence of other factors on the water-holding characteristics of compacted loess.(2)Based on the fully automatic consolidation instrument,conventional compression tests and collapsibility tests were carried out on the compacted loess that has experienced different numbers of dry and wet cycles,and the number of dry and wet cycles,initial water content,and initial compaction The influence law of compression characteristic and collapsibility characteristic.(3)Based on the triple temperature-controlled unsaturated soil triaxial instrument,the compacted loess dry-wet cycle test,three-dimensional freeze-thaw cycle test and dry-wet-freeze-thaw cycle test were carried out to control the suction under different dry densities,and the porosity and volume of the loess sample were obtained.The evolution law of strain with the number of cycles,and the influence mechanism of different cycle conditions on the deformation of compacted loess is analyzed.The influence of the number of dry and wet cycles and the number of freeze-thaw cycles on the volume deformation of the loess sample in the coupling process was explored,and a multiple linear regression model of compacted loess considering different cycles was established.(4)The distribution characteristics of the pores in the compacted loess were grasped by the mercury porosimeter test.Using scanning electron microscopy(SEM),qualitatively describe the effects of initial compaction,the number of dry and wet cycles,and the number of freeze-thaw cycles on the microstructure of loess samples,and use the microstructure characteristics to explain the macroscopic laws to achieve macroscopic deformation characteristics and Combination of microstructure characteristics.