Experimental Study On Triaxial Compression Test Of Saline Frozen Silty Sand

As the basis of the permafrost engineering construction, frozen soil mechanics’s development process depends on the needs of the development of the national economy in cold regions:the exploitation of useful mineral resources,developing transportation,construction of civil and industrial buildings and other aspects of the building. In cold regions’ engineering design, construction,late operation and maintenance, the strength and deformation characteristics of frozen soil provide important theoretical basis to the practical application of these projects. Mechanical properties of frozen soli are affected by internal factors such as moisture, bubbles, particle size, salt content, organic matter content and external conditions such as temperature, strain rate, confining pressure,stress and strain history. Study of the mechanical properties of frozen soil is divided into two categories:experimental and theoretical study. The former mainly on the strength and deformation behavior of frozen soil body under different experimental conditions; The latter is based on elastic-plastic theory and creep theory to establish constitutive models which have a reasonable reflection of the mechanical behavior of frozen soil body. However, due to the complexity of permafrost and the diversity of the nature of external conditions, we need to conduct a further study for mechanical properties of frozen soil.The first of this thesis was conducting a constant strain controlled loading rate triaxial compression tests at a confining pressure range of 0.3MPa～18MPa at a temperature of-2℃,-4 ℃,-6℃ for the natural state of salinity soil, the salt washed soil and the configured salt washed soil with different soil containing sodium salt content (0.5%,1.5%,2.5%) of frozen silty sand.We obtained the test curve was strain softening style,and was divided into linear stage,plastic stage and softening stage,at the same time through the analysis of strength results,we obtained that as the confining pressure increasing,the trixial compressive strength was first increasing the decreasing;As the temperature decreasing, the strength was increasing, and they showed a linear relationship in a double logarithmic coordinates; As sodium content increasing, the strength was first decreasing then increasing.Then this thesis was conducting a constant strain controlled loading rate triaxial compression tests at a confining pressure range of 0.3MPa～18MPa at a temperature of-2 ℃ for frozen silty mixed with 1% of nano silicon dioxide content.we obtained its test curve was strain softening style, and we can take advantage of the modified Duncan-Chang hyperbolic model fit well with the stress-strain curve; With respect to undoped nano silicon dioxide frozen silty sand, its strength have a significant growth; And through differentiating for modified Duncan-Chang hyperbolic model, we obtained the variation of initial modulus with the confining pressure can be divided into three stages.Finally, according to the test results of the above, using the predecessors’ research results and the least square method, Through the analysis of variation of strength of natural saline frozen silty sand and frozen silty sand configured different salt content,we obtained a exponential strength criterion and a parabola strength criterion, and it can predict its intensity very well.