Studies Of The Effects Of Toe Debris On The Vertical Bearing Behavior Of Friction Piles And End Bearing Piles

Toe debris is easily appeared during bored piles construction,which causes negative effects on the vertical bearing behavior of bored piles.Toe debris has negative effects on the development of end resistance and side resistance.The research on the development of side resistance is relatively short,which is incapable to cognize the effects of toe debris on the vertical bearing behavior of friction piles and end bearing piles.In order to study the working behavior of piles with toe debris,using finite element analysis software ABAQUS,bored piles in sand were taken as examples,changing the thickness,mechanical parameters of toe debris,and aspect ratio of piles to research load-settlement curves,vertical ultimate bearing capacity curves with the parameters of toe debris,settlement of piles with the parameters of toe debris,and shaft resistance with the parameters of toe debris.The results show that when the thickness of toe debris is within 100 mm,the loss rate of ultimate bearing capacity is about 4.5%-5%,the thickness of toe debris has large effects on side resistance;at the same thickness of toe debris,the ultimate bearing capacity improves with the increment of the compression modulus of toe debris(the compression modulus of toe debris is smaller than half of the compression modulus of pile side soil),and side resistance increases greatly.Poisson's ratio,the angle of internal friction,and cohesive forces of toe debris have finite effects on the vertical bearing capacity.When the relative displacement of the pile-soil interface is big,the larger values of Poisson's ratio,the angle of internal friction,and cohesive forces promote shaft resistance.With the increment of the aspect ratio,load-settlement curves of normal piles develop from slow type to steep drop type,the slopes of the load-settlement curves of piles with toe debris get steeper,and the curves of the load-settlement curves of piles with toe debris get closer to the normal piles,toe debris has smaller effects on the vertical bearing capacity,the loss rate of ultimate bearing capacity is below 5%.For end bearing piles with good supporting layer in sand,changing the thickness,mechanical parameters of toe debris,and aspect ratio of piles to research load-settlement curves,ultimate bearing capacity of piles curves with the parameters of toe debris,settlement of piles with the parameters of toe debris,and axial force with the parameters of toe debris.The results show that the appearance of toe debris lead to great loss of vertical bearing capacity,the load-settlement curves develop from sloe type to steep drop type,the vertical bearing conditions develop from friction end bearing piles to end bearing friction piles.With the increment of the depth of toe debris,the vertical bearing conditions tend to be like friction piles.With the increment of the compression modulus of toe debris,the load-settlement curves of piles with toe debris develop from steep drop type to slow type,the vertical bearing capacity improve a little,and the settlement of piles decreases greatly.Poisson's ratio,the angle of internal friction,and cohesive forces of toe debris have finite effects on the vertical bearing capacity.With the increment of the aspect ratio,the effects of toe debris on the vertical bearing capacity get bigger,the loss rate of ultimate bearing capacity improves,as for normal piles,the proportion of loads shared by end resistance gets bigger,and for detect piles with toe debris,the proportion of loads shared by end resistance almost remains the same.