Experimental Study On The Anti-heave Property Of Pile Foundation In Seasonal Frost Regions

It is common to occur the upward freezing pulling damage to the pile foundation in seasonal frozen soil area.Based on the key project of science and technology research and development program of China railway corporation’’the roadbed frost heaving and thawing prevention and control technology(2011G026-A) of the Harbin-Qiqihar Passenger Dedicated Line’’, we analyze the reason of upward freezing pulling phenomenon of the pile foundation through market investigation, combined with high and low temperature alternating free-thaw cycling test box, and design antifreeze-pulling performance test apparatus with our own, processing cone angle 0°、5°、7°、9°、11°with aluminum alloy and wood material as the pile body and doing the indoor geotechnical experiment to test the basic physical and mechanical parameters of soil. And then we simulate the phenomenon of the freeing pulling and thawing of the pile foundation in seasonal freezing soil regions with each sample experiencing three times of freeze-thaw cycle, analyze the rule of the change of internal temperature and the pile foundation. When the experiment is finished, we still test the moisture content of the sample to reveal the law of moisture migration in the process of freezing and thawing cycle,so as to provide reference for the design of the pile foundation in seasonal freezing soil regions,The main research content and research achievements include.(1)Through the actual test, the autonomous-invented apparatus can meet the test requirements.(2)During the process of the freezing and thawing cycle, the internal temperature of the sample shows the cosine shape change, and the soil’s melting rate is greater than the freezing rate. Through the isotherm diagram, we obtain the changing curves of soil freezing depth with time.Changes of soil displacement distribution is the “step” downward, with the thawing settlement of soil displacement greater than the freezing-pulling displacement. The upper water content of the sample is significantly greater than the lower moisture content.(3)Thefreezing-pulling displacement of the pile foundation has close relationship with the pile cone angle and the pile density. The freezing-pulling displacement the pile foundation is inversely proportional to the pile cone angle, with the greater of the cone angel, the smaller of the of the displacement of the freezing-pulling, therefore the more stable of the pile body and the optimal cone angle can overcome the tangential freezing-pulling force;the freezing-pulling displacement the pile foundation is inversely proportional to the pile density, with the greater of the density, the smaller of the freezing-pulling displacement, and only when the tangential freezing-pulling force is greater than the weight of the pile body, the pile foundation will be displacement.(4)The freezing-pulling displacement of the pile foundation has largely connected with water content of the soil and times of the freezing-thawing cycles. The freezing-pulling displacement of the pile foundation is proportional to the the water content, with the greater the water content, the larger the freezing-pulling displacement; the freezing-pulling displacement of the pile foundation is gradually becoming more stable with the increase of the times of the free-thaw cycles.(5)We conclude the relationship of the freezing-pulling displacement of the pile foundation with the pile cone angle, density, water content of the soil and times of the freeze-thaw cycle according to test data.