Experimental Study On Interaction Between Frozen Soil And Pile Group Foundation

Since the great cooperation initiative of "the Belt and the Road" has been put forward,a large number of construction projects in cold regions have been put on the agender.And the pile foundation has many advantages,such as good bearing characteristics and construction of convenience.It has been widely applied in cold regions construction projects.Therefore,it is of great significance to study the mechanisms of frost heave and thaw between frozen soil and pile group foundation.Many scholars have carried out experiments and theoretical research,and obtained a lot of valuable results.This paper adopts GWD-150 high-low temperature alternating test machine,5G102 linear displacement sensor,BX120-3AA resistance strain gauge,DH3818-2 static strain tester and temperature-control water supply system to simulate the conditions of unidirectional freezing and thawing of soil in nature,and studies the interactions between frozen soil and pile group during frost heaving and thawing.The influences of major factors such as freezing temperature,melting temperature and pile space on some key variables in the pile-soil system during the process of frost heaving and thawing of remolded silty clay were investigated.The main research results are as follows:(1)Frost heave model experiments were carried out to study the temperature field of frozen soil samples with the same moisture content,the displacement of the top of piles and the side friction of piles at different depths under freezing temperatures of-10?,-15?and-20 ? and pile spacing S=2d,3d and 5d,.The test results show that the soil temperature around the pile develops a gradual change trend during the unidirectional freezing process,which is influenced by freezing temperature.The curve of soil temperature around the pile can be divided into three stages:the stage ?-rapid cooling stage,the stage ?-slow transition stage and the stage ?-temperature stabilization stage.The frozen front moves down slowly with the extension of freezing time.The lower the freezing temperature is,the faster the temperature decreases in stage I,and the deeper the frozen front position is.The development of uplift displacement on pile group foundation can be divided into three stages:stage?-rapid growth,stage ?-stable growth and stage ?-stabilization stage.The lower the freezing temperature is,the larger the uplift displacement is,and the uplift displacement of corner pile is obviously larger than that of central pile.At different freezing temperatures,the side friction of piles at the same location develops similarly.Along the pile body,the positive and negative friction changes alternately,and the force on the pile body is basically balanced.The lower the freezing temperature is,the greater the average lateral friction of the central pile and the corner pile are.At the same freezing temperature,the maximum absolute value of lateral friction of corner pile is larger than that of central pile,and the location of the maximum value is different.Under the same conditions,the temperature development of soil samples with different depths is less affected by the spacing of piles,while the uplift displacement at the top of piles and the lateral friction of piles at different locations are more affected by the spacing of piles.With the increase of pile group spacing,the top displacement of piles at different positions increases,the difference between the top displacement of central pile and corner pile decreases,and the lateral friction resistance of piles at different positions also increases.The difference between the lateral modulus resistance of corner pile and central pile also decreases.The central pile shows obvious pile group effect(2)In the thawing settlement model experiments,the soil sample is frozen at-20? for a period of time,and then is respectively heated to 10?,15? and 20 ?.The temperature field of the soil sample,the settlement of piles at different locations and side friction are measured under the condition of pile spacing S=2d,3d and 5d.The test results show that the development of temperature of soil samples at different depths is basically similar and has obvious time effect.It can be divided into three stages:stage ?-slow cooling stage,stage ?-heating stage and stage ?-temperature stability stage.The development of settlement of piles at different locations can be roughly divided into three stages:stage ?-pile stability stage,stage ?-rapid settlement stage and stage ?-slow settlement stage.Compared with stage ?,the slope of temperature change in stage ? decreases obviously,and the settlements of piles tend to be slow.The higher the melting temperature,the longer the duration of the second stage,the more complete the thawing settlement of frozen soil and the larger the final settlement of piles.When the distance between piles is fixed,the higher the melting temperature is,the greater the side friction resistance of the pile body is,and the side friction resistance of the central pile is smaller than that of the angular pile.When the melting temperature is fixed,with the increase of the distance between piles,the side friction resistance of the pile body at different positions increases,and the difference decreases.