Study On Compression Characteristics Of Frozen Soil

The compressibility of soil is a classical subject in geotechnical engineering.Generally speaking,settlement happens in foundation soil under surcharge loads,and gradually becomes stable along with time.However,when the compressibility of the soil does not meet the requirements,the soil settlement will continue even after a long period of time,which will affect the stability of the building.For frozen soils,the modulus is high under relatively low temperatures,and there is generally no obvious compressibility in industrial and civil infrastructures and is usually not considered.However,as the temperature rises the modulus of frozen soils decreases,and the mechanical properties of warm frozen soils are similar to those of unfrozen soils.With global warming,temperature of frozen soil rises in permafrost regions.The compressibility of frozen soils must be taken into consideration when the deformation of highway and high-speed railway is strictly controlled in permafrost regions.First of all,this paper introduces the state of the art of the compressibility of the unfrozen soil and frozen soil,as well as basic methods for studying soil compressibility.In order to investigate the influence of temperature on the compressibility of frozen soil,a test program for frozen soil was made in light of the test method of unfrozen soil.Then extensive study on the compression characteristics of frozen soil was carried out.In this study,the frozen saturated ISO standard sand,a frozen saturated silty sand and a frozen saturated clay were taken as study objects,and step load tests under different temperatures were carried out using a self-developed confined compression apparatus for frozen soils.Tests were conducted at the loads of 1,2,3,5,10MPa and under temperatures of-0.5,-1.0,-2.0,-3.0,-5.0oC.The e-?_z and e-lg?_z curves were obtained based on experimental data,and then the coefficient of compressibility and the compressibility index were analyzed.The main findings are as follows:(1)The coefficient of compressibility and the compressibility index of the unfrozen soil and frozen soil under different temperatures were compared and analyzed.Changing tendencies of the two parameters along with temperature were then discussed for the soils from room temperature to negative temperatures up to-5oC.(2)It is found that the compression curve of all the three kinds of frozen soil samples are similar to that of the samples under room temperature.For warm frozen samples,the compressibility is considerable.The compressibility of frozen soil is closely related to temperature,and the coefficient of compressibility increases with temperature in the form of exponential function.(3)It is found that the generally recognized empirical formula can be used to fit modulus,and the relationship between the formula parameters and temperature were established.This study may provide sound theoretical basis for deformation control engineering constructions in permafrost regions.