Study On Shear Mechanism Characteristics Of The Soil-structure Interface Under High Pressure And Thawing Conditions

With more and more projects in frozen soil area,it is urgent to study the mechanism of freeze-thaw action.Engineering disasters caused by freeze-thaw cycles will cause structural damage to the soil-structure interface,which is mainly reflected in the influence on the mechanical properties of the soil-structure interface.In this paper,freezing conditions,including freezing boundary conditions（temperature and confining pressure at freezing boundary）,temperature gradient and freezing direction,are summarized in the study of freezing and thawing mechanism.Frozen wall in artificial freezing method in the study is thought to be in a state of freezing conditions-high pressure and thawing.Based on the theory of composite material mesoscopic strength material with frozen soil parameter,the discrete element method is used to simulate the high pressure and thawing state soils-structure interface shear test to explore the specimen in the process of shearing macro mechanical response and microstructure evolution.In addition,to explore the influence of different freezing conditions（normal pressure,freezing gradient and freezing direction）on the dynamic mechanical properties of soil-structure contact surface,systematic laboratory tests were carried out,and the following results were obtained:（1）Based on the meso-mechanical view of composite materials and the classical mixed law idea,the elastic constant of frozen soil material was deduced.To consider the influence of the degree of thawing of frozen soil,the damage concept was introduced,and the damage factor was used to characterize the temperature decrease of the elastic constant of frozen soil caused by temperature.To consider the pressure-thawing effect of frozen soil under high pressure,the thawing point of frozen soil under high pressure was modified.The mechanical parameters of frozen material are determined as the parameters used in the numerical simulation model.（2）It is revealed that the macroscopic mechanical response of soil-structure interface under normal thawing state simulated by discrete element:（1）The peak shear strength and residual shear strength of the contact surface increase with the increase of normal stress,and have different changing trends under the influence of different thawing temperatures.The shape of shear stress-displacement curve is also significantly affected by thawing temperature.（2）The influence of structural surface roughness is obvious.According to the growth trend of the stress-strain curve,when the morphology scale H₀ is small,it is similar.When the peak stress transitions to the residual value,the transition is relatively gentle,and the difference between the peak and the residual value is small,while the difference between the peak and the residual value is larger when H₀is large.（3）The dynamic evolution of the microstructure in the discrete element simulation interface shear test is studied and revealed:（1）The positive correlation between the normal stress and particle displacement,coordination number and crack area in the simulated sample was carried out by using a semi-empirical piecewise formula with higher accuracy.When the shear force of the contact surface increases,the displacement of the particle shear direction also increases in the same time.When the pressure is high,the area with small coordination number becomes smaller and is distributed in the left and right corners of the shear box.When the normal pressure is high,cracks will be formed through the whole sample.（2）The effect of the roughness of the structural surface lies in the role of the rough bulge to"bite"the nearby particles and then drive some particles to move.The larger the rough bulge part of the structural plane,the smaller the coordination number between the particles and the structural plane.When the shear displacement is carried out,the particles near the rough bulge will passively move to the shear direction,and the coordination number becomes smaller.（4）The dynamic shear test results reveal that the dynamic mechanical properties of soil-structure interface are affected by different freezing conditions:the normal pressure has a significant effect on the dynamic response curve,backbone curve and dynamic shear strength;The direction of freezing has a certain influence on the variation of hysteretic cycle motion.With a smaller freezing gradient,the curve of horizontal freezing condition also shows three stages of change,and the faster the stress hardening rate of the backbone curve is.The papers include 42 figures,8 tables and 131 references.