Study on mechanical properties and microstructure of improved saline soil subgrade filler

The harm of saline soil to infrastructure engineering is manifested in its collapsibility after immersion and corrosion of underground structure. The influence on engineering construction mainly depends on the physical properties, content, salinity and natural environment. To clarify the interrelation between the microstructure and mechanical properties of saline soils in cold region after improvement, the pile numbers K602+800, K603+832, K636+187, K642+997 on the highway from Qarhan to Golmud in the Qarhan Salt Lake District of the Qinghai-Tibet Plateau were selected for the mixed saline soil of chloride and sulfate SW-HC47(fine sand high chlorine saline soil), CL-HC17(silty viscous high chlorine saline soil), GF-HC37(breccia high chlorine saline soil), SF-HC38(fine sand high chlorine saline soil) was used as a research soil sample, and cement was added to improve it. Firstly, unconfined compression strength(UCS) was carried out for the improved saline soil with different proportions of cement (6%, 8%, 10%, 12%), and the optimal incorporation amount was clarified. Secondly, the improved specimen was scanned by electron microscopy, the interval estimation method was used to select the optimal magnification. Thirdly, Using the pore system and fracture system identification software Particles (Pores) and Cracks Analysis System(PCAS) and professional image processing software Image Pro-Plus, the microscopic analysis of porosity, average from factor and other parameters before and after soil improvement was carried out, The interrelation between the microscopic parameters and the UCS improved soil is determined by the gray correlation analysis. Finally, combining the tests and analyzing the influence of curing agent materials on the improvement effect of saline soil from a microscopic perspective.The results indicates: ①The optimal magnification of different soil samples is different. The optimal magnification of SW-HC47 and SF-HC38 was 400 times. The optimal magnification of soil samples CL-HC17 and GF-HC37 is 200 times. ②With the increase of the number of curing days from 7 days to 28 days, the proportion of large pores in the four improved soil samples decreased significantly. The porosity, average from factor and fractal dimension of the four cement improved soil samples decreased with the increase of curing days. The Probability entropy varies less. ③Individual micro-parameters affect the UCS to different extents.