Experimental Study On The Heat Preservation Layer Of Railway Subgrade In Seasonal Frost Regions

In seasonal frozen soil areas of China,with the change of climate and temperature,the railway subgrade will suffer from Frost heaving and thawing settlement disease,which seriously affected the stability of the subgrade structure and the driving safety of the train.In order to solve the adverse effects of subgrade freezing damage,relevant units and scholars carried out a large number of subgrade anti frost heave measures,among which the insulation method is the most widely studied.In view of the poor durability of commonly used subgrade insulation materials(EPS,PU,XPS,etc.),the foam concrete material commonly used in thermal insulation of building walls was studied,through the optimization of mix types and mix proportion design,the optimal mix proportion of different admixture system was obtained,and the performance of foam concrete with the best mix proportion of different admixture system was compared.Finally,the best performance of foam concrete was obtained;Combined with the measured data of subgrade temperature in the field test section,the COMSOL software is used to carry out numerical simulation analysis to verify the best performance of foam concrete insulation effect.The main research contents and results are as follows:(1)According to the basic experiment and the function of insulation board on the surface of the subgrade,the dry density of foam concrete is determined to be 1200kg·m~-33 and the water cement ratio is about 0.5.(2)In the fly ash cement foam concrete mixed with silty sand,the performance of the foamed concrete prepared according to the proportion of cement:fly ash and silty sand=4:5:1 is the best.(3)Based on the orthogonal test design method,the experimental performance of fly ash cement foam concrete mixed with ceramsite is studied.It is concluded that ceramsite foam concrete with ceramisite content 40%,15%fly ash instead of cement and water cement ratio 0.5 has the best performance.(4)The performance of foam concrete with the best mix proportion under two kinds of admixture system is compared and analyzed.It is concluded that the performance of foam concrete mixed with ceramsite is the best.(5)Based on the best performance of ceramsite foam concrete,the waterproofing measures are studied,and the result shows that the composite layered foam concrete has achieved good waterproof effect.(6)The temperature field numerical simulation of the best performance of the ceramsite foam concrete reinforced insulation subgrade under the condition of maximum frost depth is carried out.The results show that the ceramsite foam concrete has obvious thermal insulation effect on the subgrade,can alleviate the frost heave of subgrade.