Experimental Study On Seismic Performance Of PHC Pipe Pile In Soft Soil Area

As a reliable pile type of prefabricated pile,prestressed concrete pipe pile has lots of advantages,such as,high bearing capacity of a single pile,reliable quality,energy saving and environmental protection,construction speed,as well as good economic benefits and so on,widely used in the engineering construction.After the underconstruction residential building collapsed events in Shanghai Lotus,the problem of the prestressed concrete pipe pile gradually aroused attention of the domestic engineering sector.Some areas have done a corresponding restriction on the application of the prestressed concrete pipe pile in different soil layer in order to ensure the safety of prestressed concrete pipe pile under horizontal seismic load.However,design and calculation theory is not very mature,due to special engineering properties of prestressed concrete pipe pile and the complexity of aseismic mechanism of prestressed concrete pipe pile foundation.So,it is necessary to study mechanism of the prestressed concrete pipe pile under earthquake load systematically and deeply.Study of its seismic performance is of much important significance.Firstly,in view of the high brittleness of prestressed concrete pipe pile,compound reinforced concrete pipe pile is made by collocating non prestressed reinforcement additionally and full scale in-situ tests are carried out.The test loading program is made through research of the "building foundation design code" and "building seismic test method" on the loading system.The loading process and failure mode of the prestressed concrete pipe pile are recorded and analyzed in detail.Research shows that the damage form of prestressed concrete pipe pile under horizontal load is flexural failure,rather than shear failure.Secondly,loading behavior of the prestressed concrete pipe pile under horizontal cyclic load is studied systematically,revealing the law of stiffness degradation,energy dissipation capacity and the accumulation of plastic deformation of the soil around pile,discussing the failure mechanism and the loading mechanism of the reinforcement of the composite reinforced concrete pipe pile.Pile deformation curvature is calculated using the measured horizontal displacement of pile.Distribution of bending moment of pile can be reflected by deformation curvature of pile and good effect has been obtained.The study result shows that the displacement ductility coefficient of composite reinforced concrete pipe pile is larger than that of conventional pipe pile and ductility can be improved.At the same time,there is an optimal ratio of non prestressed reinforcement.The test results shows that the ductility of composite reinforced concrete pipe pile is optimal when the ratio of non prestressed reinforcement is 0.75%,that is,the optimal ratio of non prestressed reinforcement is 0.75% in this case.The reinforcement stress of the pipe pile distributes in the range of 5.5m(11D)along the pile shaft concentratedly and the rest is almost zero.Lastly,feasibility of reciprocating loading system is verified,through the comparison of the test results of the reciprocating loading and the unidirectional loading.Referring to the formula for the characteristic value of the horizontal bearing capacity of single pile in the codes,calculation formula of horizontal ultimate load of a single pile of composite reinforced concrete pipe pile is proposed,and calculation formula of the characteristic value of horizontal bearing capacity of single pile under the allowable crack of the pile is proposed.