Experiment And Numerical Simulation Of Anti-freezing Effect Of Improved Soil Subgrade In Seasonal Frozen Area

With the rapid development of China’s transportation system,more than half of the roads are built in the cold regions of China.The huge quantities mean that a large amount of earth and stone materials are needed.In order to meet the requirements of subgrade filling quantity and stability,new materials need to be added to the road subgrade.Oil shale is rich in reserves in China,and its industrial waste is huge and difficult to deal with.Based on the principle of sustainable development,it is used as a raw material for subgrade filling and combined with road engineering,and applied in seasonal frozen soil areas in China,which can protect the environment and maintain the stability of subgrade at low temperature.In this paper,two kinds of waste materials,oil shale waste residue and fly ash,are mixed into silty clay to obtain a new type of subgrade improved soil.The causes and protection methods of subgrade diseases in seasonal frozen areas are analyzed.A series of experimental studies are carried out on the thermal parameters of the improved soil with different mix proportions and its frost resistance as subgrade filler.Combined with the water-heat coupling effect of frozen soil subgrade,the practical application of the improved soil is numerically simulated.Specific test contents are as follows:(1)Under the condition of meeting the requirements of subgrade strength,five proportions of oil shale waste residue and fly ash improved soil are selected,and the specific values of specific thermal conductivity and specific heat capacity of the improved soil are obtained through experiments,as well as the changes of thermal parameters under the conditions of freezing and multiple freeze-thaw cycles.(2)On the basis of theoretical analysis of water-heat coupling of seasonal frozen soil subgrade,the causes of road diseases are studied,which can be used to analyze the changes of liquid water migration,different mix proportions.In order to reduce the influence of permafrost in cold region and seasonal frozen soil in seasonal frozen region on road subgrade,the change trend of water,ice,temperature,stress and strain of subgrade improved soil fill under freezing condition is depicted,and the influence of water heat coupling comprehensive action of subgrade improved soil under freezing condition on deep soil is studied,and the numerical model calculation basis is provided.(3)The indoor freezing test was carried out on the improved soil with the best mechanical properties and the improved soil with the best thermal insulation properties,and the data of temperature,moisture,stress and strain in the soil were collected and compared with the indoor freezing test data of silty clay.The test results show that the improved soil with the best thermal insulation performance can make the deep layer of subgrade enter negative temperature for a longer time,the temperature of each part of the soil inside is higher,the freezing depth is shallower,and the situation of water migration and stress concentration is less.(4)Combined with the seasonal frozen soil area water-heat coupling mathematical model and COMSOL Multiphysics software,the mathematical module of COMSOL is redeveloped.The modified soil with the best thermal insulation performance is used as the subgrade thermal insulation layer for numerical simulation,and the long-term water migration,ice-water phase transition and temperature distribution are predicted.Combined with the numerical simulation results,the beneficial effects of oil shale waste residue-fly ash modified soil as the subgrade thermal insulation layer are analyzed.