| Accurately grasping the mechanical characteristics of frozen soil is important to the construction and operation and maintenance of engineering in cold regions.Because of the difference of soil quality,external environment and the complexity of frozen soil mechanical properties,different scholars adopt different methods to select the elastic index of frozen soil and to determine its constitutive model.In order to further study these mechanical properties of frozen loess and to explore the rationality of its determination method,a series of conventional triaxial loading tests were carried out on frozen loess in Inner Mongolia Helin areas.The mechanical characteristics of frozen loess,such as deformation,strength and elastic index,were studied.The main research contents and conclusions are as follows:(1)A series of compression tests of frozen Helin loess under different temperatures and confining pressures were carried out,and the stress-strain curves and volume-strain curves of frozen loess under different conditions were obtained.The test results show that the stress-strain curve of frozen loess is strain hardening,and the corresponding volume strain always shrinks first and then expands with the increase of axial strain.(2)Two different methods were used to determine the elastic modulus of frozen Helin loess.It was found that the initial tangent modulus E0 and secant modulus E0.5 increased with the decrease of temperature,and E0 fluctuated more with the change of temperature.The variation of initial tangent modulus E0 and secant modulus E0.5 with confining pressure can be roughly divided into two stages.In the low confining pressure stage,E0 and E0.5 increase with confining pressure.When confining pressure increases to a certain value,E0 and E0.5 decrease with the further increase of confining pressure.In this process,the relationship between E0 and confining pressure shows greater discreteness.(3)Poisson’s ratio of frozen Helin loess was determined by two different methods.It was found that under different confining pressures,bothμ0 andμ0.5 decreased with the decrease of temperature,and the linear relationship betweenμ0.5 and temperature was stronger.At different temperatures,the values ofμ0 andμ0.5 first increase and then decrease with the increase of confining pressure,and because the frozen loess samples are ice-saturated,the Poisson ratios determined by these two methods are relatively small.(4)The analysis results show that the strength of frozen Helin loess first increases with the increase of confining pressure,and when confining pressure increases to a certain value,the strength of frozen loess decreases with the further increase of confining pressure;the strength and yield limit of frozen loess increase with the decrease of temperature,and have a linear positive correlation with the absolute value of temperature.In order to describe the non-linear decrease of frozen loess under confining pressure,the cohesion and internal friction angle of frozen loess are analyzed based on Mohr strength criterion and envelope theorem.It is found that the cohesion of frozen loess increases with confining pressure,while the internal friction angle decreases with confining pressure.(5)Study the complex deformation characteristics and construct the elastic-plastic constitutive model of frozen Helin loess.In view of the difficulty of accurately describing the complex deformation of frozen loess in the existing constitutive models,the hardening law is determined directly from the experimental data.The yield surface of frozen loess is determined by the plastic isoline.The elastic-plastic constitutive model of frozen loess considering the influence of temperature is constructed by the correlation flow rule,and the elastic-plastic constitutive model is verified. |
