Analysis Of The Mechanical Behavior Of Conical Piles In Cold Regions Under Freeze-thaw Cycle

Freeze-thaw cycles of soil in cold regions will cause the uplift of piles,which affects the stability and serviceability of pile foundation.Conical piles have the effect of anti-uplift.However,its mechanical behavior and pile-soil interaction mechanism are not clear,which limits its wide application in practical engineering.In order to explore the mechanical behavior of conical piles under freeze-thaw cycle,an orthogonal test study on the shear strength and tensile strength of the silt-concrete interface under freezing action was performed.Based on the experimental results,an interaction model was proposed for the conical pile-soil contact surface,which is applied to the numerical simulation on the conical pile-soil interaction under freeze-thaw cycle action.The mechanical characteristics of pile-soil contact surface and anti-uplift mechanism of conical pile were obtained.The main research contents and results are as follows:(1)According to the silt-concrete interface under freezing action,orthogonal direct shear and tensile tests were carried out under the various conditions of moisture content,temperature and dry density.The test results show that the order of the influencing factors on shear and tensile strength is: moisture content > temperature > dry density,in which the moisture content and temperature have a significant effect,but the dry density has no significant effect.The interface shear and tensile strength test are the best under the condition of low temperature,high water content and low dry density.(2)Under freezing action,the interface shear strength increases with the rise of the moisture content and the absolute value of the temperature and its growth rate is affected by the normal pressure.With the rise of normal pressure,the effect of moisture content on the interface shear strength decreases gradually,while the effect of temperature can still be promoted.There is interaction between moisture and temperature.Based on the experimental results,an explanation is given for the formation and failure mechanism of the freezing strength of the pile-soil interface.(3)In the test moisture content range,the freezing tensile strength of the contact surface is positively correlated with the absolute value of temperature,and it increases linearly with the increase of moisture content.There is interaction between moisture and temperature.With the decrease of temperature,there is a critical negative temperature where interface frozen tensile strength changed from rapid growth to slow growth.Under the same conditions,the shear strength of the contact surface is significantly smaller than the tensile strength,and there is an exponential relationship between the shear strength and the tensile strength.(4)Based on the test results,the interaction model of conical pile-soil interface is put forward and verified.The numerical model of anti-uplift conical pile under the action of freeze-thaw cycle is established by ABAQUS.It is found that the conical pile has a good effect of anti-uplift.The cumulative freeze-thaw displacement of pile is negatively related to the cone angle and positively related to the number of freeze-thaw cycles.When the cone angle is increased to 9 °,the accumulated amount of freeze-thaw can be basically eliminated.At the same time,the mechanical behavior of the conical pile is analyzed,and an explanation is given for the mechanical mechanism of the anti-uplift performance of the conical pile.(5)The mechanical mechanism of the anti-uplift effect of conical pile is: the structural characteristics of the conical pile make the pile subject to tensile stress component,which reduces or even eliminates the normal compressive stress of the frozen soil on the pile,so as to restrain the frost heaving force on the pile,and finally achieve the anti-uplift purpose.In the process of pile-soil interaction,the cone angle is inversely proportional to the normal compressive stress on the pile body.Therefore,the larger the cone angle is,the better the anti-uplift effect of the conical pile is.