Triaxial Compressive Strength And Defotmation Mechanism Of Frozen Sand

With the increasing of engineering activities in frozen soil region,the research on mechanical properties of frozen soil under complex stress has become an important topic in geotechnical engineering in cold region.Compared with conventional thawed soil,because of the presence of ice,the mechanical properties of frozen soil are not only related to the composition and water content of soil particles,but also to the test conditions such as temperature,strain rate and confining pressure,showing strong temperature sensitivity and rheology.Many researchers on the basis of a large number of frozen soil test,according to temperature,confining pressure and strain rate under the condition of three factors affecting the frozen soil mechanics properties change research has made some achievements,however,since the test of the researchers are frozen soil type and the difference of test conditions,but under different influencing factors,the mechanics properties of permafrost change is basically summarized all kinds of test results.This paper summarizes the research conclusions of different researchers,coMPares and analyzes the differences of test conditions and conclusions of different researchers,and provides a theoretical basis for the research on strength and deformation of frozen sand soil under different conditions.Papers in frozen soil as the research object,through to the temperature was-2 ℃,-5 ℃,confining pressure is 0.5 MPa,2 MPa,the strain rate is 0.006 mm/min,0.012mm/min,0.125 mm/min,1.25 mm/min under the condition of triaxial shear test,analyzes the strength of frozen soil under different test conditions and parameters change trend of modulus,and under different strain rate change trend are analyzed in fitting.Finally,the discrete element particle flow software is used to reproduce the triaxial test of frozen sand under different conditions,and the changes of the strength and modulus in the triaxial test under different conditions are reflected by the changes of the mesoscopic parameters of the parallel bond model parameters in the discrete element.The main conclusions of the study are as follows:(1)Temperature,confining pressure and strain rate all affect the stress-strain curve of the triaxial test of frozen sand.The confining pressure has an effect on the shape of the stress-strain curve: when the confining pressure is 0.5MPa,the stress-strain curve has a peak value and shows a strain hardening trend.When the confining pressure is 2 MPa,no peak occurs,and the stress-strain curve is strain softening.The influence of temperature is mainly reflected in the srength of frozen soil.Under the same confining pressure,the peak strength of stress-strain curve at-5 ℃ is greater than that at-2 ℃.Under the same temperature and confining pressure,the larger the strain rate,the greater the peak strength of the frozen sand.Meanwhile,the larger the strain rate,the smaller the peak strength with the corresponding strain.(2)the peak stress intensity of frozen sand will decline with the increase of time,and the strength will increase with the increase of strain rate.The relationship between peak strength and strain rate can be expressed as a power function,and the exponent of the power function is a test parameter related to temperature and confining pressure.(3)the peak strength of deviatoric stress can be expressed as a power function of strain rate,and the parameters of the power function are related to temperature and surrounding rock.Under the same confining pressure,with the decrease of temperature,the curve of increasing the peak deviatoric stress intensity under different strain rates is almost parallel,indicating that the effect of strain rate on the peak deviatoric stress intensity is less than that of temperature.(4)the parallel bonding model in discrete element can be used to simulate the mechanical behavior of the triaxial test of frozen sand.When the temperature decreases,the ice cementation in the frozen sand increases,the cohesion between the particles increases,and the bonding strength in the model also increases.The influence of confining pressure is mainly reflected in the stiffness of simulation parameters.As the confining pressure increases,the stiffness coefficient set by simulation also increases.By measuring the dip Angle of shear zone after particle movement,it is found that the strain rate has little influence on the dip Angle of shear zone,while the decrease of temperature will increase the dip Angle of shear zone,and the increase of confining pressure will decrease the dip Angle of shear zone.