Analysis Of Mechanical Properties And Influencing Factors Of Coastal Artificial Frozen Soil

With the continuous development and utilization of underground space in Fuzhou,the scale of subway is expanding day by day.Artificial ground freezing method has been widely used in the construction of subway connecting passage in water-rich areas.The freezing curtain in the connecting channel is under the combined action of compression and folding,or transverse bending.The section may have a compression and folding stress zone,which is easy to produce unpredictable brittle failure and cause engineering accidents.In this paper,combined with the situation of Fuzhou coastal soft soil layer,two typical soils of Metro Line 4were selected for indoor test,and the characteristics of compressive strength of coastal artificial frozen soil were studied.The main research results are as follows :(1)This paper improves the function of the testing machine based on the existing universal testing machine compression fixture device.The testing machine can carry out indoor tests of uniaxial compression,uniaxial creep and three-point flexural mechanical properties;It can also arbitrarily set and control the temperature of the chamber of the cured specimen to complete the mechanical test at different temperatures;It is also possible to study the deformation characteristics of frozen soil by changing the loading rate and strain rate.(2)Through the test of uniaxial compressive strength characteristics of coastal frozen soil,the relationship between uniaxial strength and the main influencing factors(temperature and moisture content)was obtained by considering four factors: temperature,moisture content,salt content and loading rate.The test shows that under different soil types,the compressive strength is inversely proportional to the temperature and proportional to the moisture content.The enhancement rate of silty clay was positively correlated with temperature.The rate of increase in compressive strength of silty soil was negatively correlated with temperature.The growth rate of compressive strength of both soils was positively correlated with the moisture content.(3)By carrying out the three-point flexural strength test of coastal artificial frozen soil,the influence of temperature and water content on the flexural strength is mainly considered.It is concluded that the temperature is inversely proportional to the three-point flexural strength and the elastic modulus.The moisture content is proportional to the three-point flexural strength and the elastic modulus.As the temperature decreases from-5°C to-15°C,the change rate of flexural strength of silty clay increases gradually,while the change rate of flexural strength of muddy soil decreases gradually.(4)Based on the test results of uniaxial compressive strength and three-point flexural strength of frozen soil,the comprehensive comparative analysis of compressive strength and flexural strength from four aspects of sensitivity,failure mode,temperature and water content shows that the compressive strength test of frozen soil is shear failure,and the flexural strength test is tensile failure.During the process of decreasing from-5 °C to-15 °C,the folding pressure ratio shows an increasing trend as a whole.In the process of increasing water content,the ratio of folding pressure also shows a growing trend.(5)Based on the ANSYS finite element software,the finite element model was established based on the flexural strength test results.Through the numerical simulation of the frozen soil beam,the calculation results were analyzed and compared with the experimental results.