Study On Mechanical Properties And Freezing Law Of Hefei Weak Expansive Soil Under Low Temperature

The artificial freezing method uses artificial refrigeration technology to temporarily change the properties of the rock and soil to achieve the purpose of strengthening the soil.It is widely used in modern civil engineering construction such as deep well construction,mine excavation,and subway tunnels.The damage caused by phenomena such as frost heave and thaw settlement to roadbeds,bridges and culverts,foundation pits and other projects cannot be ignored.Therefore,the study of the mechanical properties and freezing laws of frozen soil will help to make more reasonable use of artificial freezing methods.This paper takes the weak expansive soil in western Hefei as the research object,and studies its mechanical properties and freezing laws.First,the basic physical indexes of weakly expansive soil are measured through three sets of basic geophysical tests,namely,limit water content test,free expansion rate test,and freezing temperature test.The test results of the measured liquid-plastic limit,freezing temperature,and expansion coefficient of the soil samples were compared with the specifications,and the results showed that the test soil samples were weakly expansive soils.Secondly,the soil is subjected to uniaxial compressive strength tests and uniaxial compression creep tests with a water content of 24%and temperatures of-5?,-10?,-15? and-20?.The test results show that:in terms of uniaxial compressive strength,the compressive strength gradually increases as the temperature decreases.In terms of uniaxial compression creep,when the stress is loaded at 0.3 and 0.5,the creep is mainly manifested as attenuation creep,that is,the attenuation stage and the stable stage,and with the increase of stress at the same temperature,the deformation value of the stable creep stage gradually increase.At 0.7 stress loading,the creep at temperatures of-10? and-15? mainly manifests as non-attenuating creep,that is,attenuation phase,stable phase and acceleration phase.Based on this,the functional relationship equation between the compressive strength and temperature is established,which reflects the change law of the compressive strength of frozen soil with temperature.By introducing the generalized Kelvin creep model and Nishihara creep model and considering the influence of temperature on the creep deformation,the creep deformation of the frozen weakly expansive soil is predicted,and the model parameters are optimized and identified based on the simulated annealing algorithm and particle swarm algorithm,The results show that the generalized Kelvin creep model and Nishihara creep model can better reflect the creep deformation law of frozen weakly expansive soils,but at 0.7,there are some errors in the process of describing the accelerated creep stage,but they can predict creep The overall trend of deformation.Finally,the frost heave test was carried out on the weak expansive soil.The bottom-up one-way freezing test without water supplementation was mainly carried out on the Hefei weak expansive soil.The initial moisture content,cold end temperature and compaction degree of the soil were analyzed.The following conclusions are obtained:when the degree of compaction is different,the temperature of the soil after unidirectional freezing and stability gradually decreases with the increase of the degree of compaction,and the greater the degree of compaction,the greater the amount of frost heave.When the temperature of the cold source and the degree of compaction of the soil are the same,the initial moisture content of the sample has a weak effect on the stable temperature in the test.When the soil moisture content and degree of compaction are the same,the frost heave of the soil gradually increases with the decrease of the cold source temperature.The freezing depth of the sample shows a trend of rapid development first and then slow development and finally stabilizes,and the closer to the cold end,the first freezing.The data and analysis obtained from the experimental research in this paper provide a certain theoretical basis for the rational use of artificial freezing in areas with weakly expansive soils.Figure[48]Table[5]Reference[66]...