Experimental Study On Bearing Capacity Of Pipe Piles Under Vertical Cyclic Loading And Simulation Of Particle Flow

Prefabricated pipe piles are more and more widely used due to their high construction speed,high quality,low environmental pollution and economical advantages.Pile foundation has been widely used in traffic engineering.During its service,it not only has to bear the dead load generated by the self-weight of the superstructure,but also bears the vertical cyclic load with obvious periodicity.The force is complicated.In this paper,the indoor large-scale vertical dynamic load tester and particle flow numerical simulation software developed by ourselves are used to study the dynamic response of pipe pile under different working conditions.The conclusions are as follows:(1)The test of single pile sinking in sand soil shows that with the increase of penetration depth,the penetration resistance of open pipe pile gradually increases,and the proportion of inner and outer frictional resistance increases gradually;during pile sinking,pile circumference The displacement of the ground surface decays rapidly with the increase of the distance from the pile.At the beginning of the pile,the height of the soil plug is the same as the penetration depth of the pile.With the increase of the penetration depth,the formation speed of the soil plug gradually decreases and tends to occlude.(2)The dynamic test of model single pile in sand soil shows that under the cyclic load ratio of 0.1 and 0.2,the surface displacement of the pile is rapidly attenuated with the distance from the pile,and the vibration amplitude and frequency are more Large,the surface displacement is larger;the pile top settlement is faster and slower first,and the total settlement increases with the cyclic load ratio,vibration amplitude and frequency;with the increase of the cycle period,the outer frictional force of the upper part of the pile is significantly reduced.The outer frictional resistance of the central part increased significantly,and the inner frictional resistance of the lower part of the pile body decreased,and gradually stabilized after 200 cycles.(3)The results of indoor static load test in sand indicate that the top load of the pile is mainly borne by the side friction at the beginning of loading.When the load reaches about 45% of the ultimate load,the pile end resistance gradually exerts,andthe ultimate bearing capacity of the open pipe pile is about closed.83% of the pipe pile.The numerical simulation of particle flow shows that the ultimate bearing capacity of the open pipe pile is about 85% of that of the closed pipe pile,which is similar to the conclusion obtained by the indoor static load test.(4)The simulation results of particle flow show that under dynamic load,the influence range of soil around the pile is about 5~8 times of the pile diameter;the vertical displacement of the pile mainly occurs at the beginning of the cycle,and the displacement continues with the cycle.The decrease and tend to be stable,the total settlement of the pile increases with the increase of the cyclic load ratio;with the increase of the cycle period,the outer frictional resistance of the upper part of the pile is obviously reduced,and the outer frictional resistance of the middle part is obviously increased and after 10 cycles.Gradually stable,there is no significant change in the internal frictional resistance of the pile.(5)The vertical dynamic load test results of single pile in clay show that under the cyclic load ratio of 0.5,the settlement speed of the pile is fast and then gradually stabilizes,and the total settlement increases with the increase of the load frequency.When loading the pile,the outer frictional resistance of the middle part is obviously reduced,the outer frictional resistance of the lower part is obviously increased,the inner frictional resistance of the lower part of the pile is obviously reduced,and it is gradually stable after 200 cycles.