For existing project pile with unexposed pile head

it is difficult to use the regular lowstrain method to detect depth of the pile bottom.Parallel seismic（PS）method

however

has shown a great potential.PS method can be conducted by exciting the pile side vertically

obliquely

or horizontally.A three dimension（3D）finite element（FE）model was developed to model the procedures of the PS testing by use of lateral knock on the pile side surface vertically

obliquely at an angle of 45°

and horizontally

respectively.The travel time of first arrival ware at different depths were red and segmental linear fitting were carried out.The results show that by knock on the pile side surface vertically or obliquely at an angle of 45°

the testing is based on one dimensional P wave signal of the pile

whereas by knock on the pile side surface horizontally

the testing is based on flexural wave signal of the pile.As flexural wave velocity of the pile is close to the P wave velocity of the saturated soil

it is difficult to identify the initial pile bottom depth by the intersection of the two fitting lines.Vertical or oblique knock on the pile side is more suitable.