BEARING PERFORMANCE ANALYSIS OF TAPERED END BEARING FRICTION PILE UNDER COMBINED TORQUE-VERTICAL LOADS

In order to investigate the bearing performance of tapered end bearing friction piles under the combined effect of torque T and vertical load V, the paper obtained separately the differential governing equations of pile vertical displacement and torsion angle under the action of vertical load and torque on pile top based on the energy method and the variational principle, in which the subsoil shear modulus was assumed to be non-zero at the ground surface and have a distribution form of power function with depth. The ultimate vertical load and torque of tapered end bearing friction pile were solved by MATLAB programming, and then the corresponding bearing capacity envelope diagram was obtained. Under T→V loading sequence, the influence of initial torque on the vertical bearing characteristics of tapered end bearing friction pile was analyzed by changing the initial torque value. The influence of parameters on tapered end bearing friction pile under combined T-V loads was analyzed. The results show that, compared with equal section pile, the ultimate vertical load and ultimate torque of tapered end bearing friction pile under pure compression and pure torsion are increased. Under T→V loading sequence, the bearing capacity envelope of tapered end bearing friction pile is expanded compared with the equal section pile. With the increase of the change rate of pile diameter, the bearing capacity envelope of tapered end bearing friction piles also expands outward. When the ratio of initial torque to ultimate torque exceeds a certain value, the ultimate vertical load of tapered end bearing friction pile begins to decrease significantly, and attention should be paid to T-V combination effect. For large-diameter long piles, it is necessary to pay attention to the effect of initial torque on the vertical bearing capacity of foundation piles. The vertical bearing capacity of single pile under T→V loading mode can’t be greatly improved simply by increasing the concrete grade.