Study On The Relationship Between Pore Structure And Physical And Mechanical Properties Of Foamed Lightweight Soil In Expressway Subgrade

In recent years,the roadbed demand of expressway construction is increasing rapidly,and the lack of roadbed filler is a problem urgently to be solved.As a new subgrade filler,foamed lightweight soil has attracted much attention due to its advantages of light weight,good compressive resistance and convenient construction,and has become an important option for the diversification of subgrade filler.Different from ordinary concrete,foamed lightweight soil has no aggregate inside and is filled with a lot of pores.The relationship between its pore structure and physical and mechanical properties needs further study.Therefore,in this paper,three kinds of density foamed light soil used in the Chengle highspeed expansion project of line G0512 are selected as the research object.Combined with a series of laboratory tests and mesoscopic numerical simulation,the relationship between the pore structure and physical and mechanical properties(permeability resistance and compressive strength)of the foamed light soil is systematically studied.The research contents and results are as follows:(1)X-CT(X-ray computed tomography)tests were carried out to quantitatively analyze the pore structure parameters of foam lightweight soil.The results showed that there were significant differences in the pore structure of foam lightweight soil with different densities.With the increase of density,the fractal dimension,surface void ratio,average pore size,and pore connectivity showed a decreasing trend,while the average wall thickness and pore shape factor showed an increasing trend.The pore size is an important factor affecting the pore shape factor and pore connectivity of foam lightweight soil,and the smaller the pore size,the larger the pore shape factor and the lower the pore connectivity.(2)Carry out impermeability test.A new type of steel structure pressure water tank was developed and the impermeability of light foamed soil was tested.The relationship between pore structure and impermeability of light foamed soil was discussed based on the X-CT test results.The results show that there are significant differences in the impermeability of foamed lightweight soils with different densities.The pore structure of foamed lightweight soil is closely related to its impermeability.The smaller the porosity and average pore diameter,the larger the average wall thickness,the lower the pore connectivity and the stronger the impermeability.(3)The relationship between pore structure and compressive strength of foamed lightweight soil was studied by combining experiment with mesoscopic numerical simulation.A mesoscopic numerical model of foamed light soil was established based on the X-CT test results,and the model parameters were calibrated according to the uniaxial compression test results.The quantitative relationship between the pore structure and compressive strength of foamed light soil was established by using the calibrated model.The results show that the calibrated mesoscopic numerical model can accurately evaluate the strength characteristics of the foamed light soil.The pore structure of light foamed soil is closely related to its compressive strength.The degree of influence of different pore structure parameters on compressive strength is in the following order: porosity > pore diameter >pore connectivity > pore shape factor.