Experimental Research On The Shear Creep Behaviors Of Warm Permafrost-concrete Interface

In recent years,with the continuous development of the western development and the strategy of revitalizing the northeast of China,a large number of engineering projects have been constructed in cold regions;and the construction and operation of buildings(structures)have destroyed the hydro-thermal balance of the natural frozen soil,which caused secondary disasters in the project.As the main foundation form in permafrost area,pile foundation is widely used because of its less disturbance to the project in cold area and good bearing capacity.With the development of engineering construction and operation to more refined and high standardization,in order to reduce the degradation of bearing capacity of pile foundation in the process of using and ensure the stability of line foundation in frozen soil area,the research on long-term bearing capacity of pile foundation has become the focus of attention.For this reason,this paper studies the shear creep characteristics of the frozen soil-concrete interface,selects two types of fine-grained soil and discusses the creep characteristics of the interface with different soil(frozen silt and frozen silty clay),different moisture content(22% and 25%)and different roughness(0,0.039,0.059 and 0.098mm)under the condition of-1? test temperature and normal stress of 150 kPa.According to the results of the contact creep curve,the creep curve of the step loading is ladder like,with the same shear failure characteristics.With the increase of shear stress and creep time,the shear creep displacement of the specimen increases gradually,which shows the characteristics of viscous failure.When the shear displacement increases to a certain value,the contact surface of the specimen suddenly fails.When the horizontal shear stress is low,the displacement has attenuation characteristics,and the creep displacement tends to a constant value with the increase of time;when the horizontal shear load is further increased,the creep curve shows non attenuation characteristics,and with the accumulation of time,the contact surface has shear failure.In addition,the shear displacement of the interface is smaller than that of the interface.Under the same loading condition,the long-term creep strength of frozen silty clay concrete interface is lower than that of frozen silty clay concrete interface,and the shear creep displacement is larger.The frozen soil concrete interface has obvious creep deformation characteristics.During the shear creep test of the interface,the frozen soil first deforms instantaneously under the shear load,and then creep.In addition,through the comparative test of two groups of creep under the same load and the constant creep under the constant load,it is found that the final stability trend is basically the same.When stable creep is achieved,the time for constant creep to reach stable creep is long and the shear displacement is small.It can be concluded that the loading time of the step loading test in this paper can better reflect the trend of the decaying creep under the action of the decaying creep load.According to the analysis of the corresponding stress-strain isochronous curve,when the shear stress is low,the stress-strain curve is approximately a straight line,and the strain in the same time creep stage is relatively intensive,and the deformation displacement is small;when the shear stress is high,the stress-strain curve shows the curve characteristics of gradually decreasing slope and correspondingly increasing deformation displacement.In addition,the stress-strain isochronous curves of the two kinds of soils are all in the form of broken lines,which shows that the shear creep of the frozen silt concrete contact surface and the frozen silty clay concrete contact surface has nonlinear characteristics;with the increase of creep time,the isochronous curve continuously inclines to the shear displacement axis,and shows that the nonlinear characteristics increase with the increase of time.When the water content of the sample increases from 22% to 25%,the unfrozen water content of the sample also increases correspondingly.The formation of water film between the contact surfaces leads to the increase of the lubrication effect of the contact surfaces and the weakening of the friction effect between the contact surfaces,which makes the shear creep strength of the contact surfaces decrease with the increase of the water content.With the increase of the moisture content of the specimen,the cumulative time of creep failure of the contact surface decreases gradually,and the shear stress decreases accordingly.In addition,compared with the creep characteristics of frozen silty clay concrete interface,with the increase of water content,the creep of frozen silty clay concrete interface has stronger rheology and plasticity,and the water content of the sample has more obvious influence on the characteristics of frozen silty clay concrete interface.In addition,the long-term creep strength of interface shows a decreasing trend with the increase of the sample moisture content.The long-term strength of shear creep on the interface increases with the increasing of roughness,meanwhile,the shear displacement corresponding to the shear creep also shows a tendency of increasing with the increase of the roughness on the interface.When the contact surface roughness of the frozen silt concrete samples with 22% water content is 0mm,0.039 mm,0.059 mm and 0.098 mm respectively,the long-term shear creep strength of the contact surface is 110.4kPa,147.9kPa,166.65 kPa and 204.15 kPa respectively,the contact surface roughness increases from 0 mm to 0.098 mm,and the shear creep strength increases by 85%.The results show that the long-term shear creep strength increases significantly with the increase of contact surface roughness.