II think you would like to know the extend seismic forces from the pile..if i am correct then you have to choose correct mesh size to capture the changes in stress condition due to earthquake. Also, it depends on the magnitude of seismic forces and the point in which it is acting from the pile. so, you go with trial analysis by varying mesh size and see whether the mesh is capable of capturing the changes in stress conditions due to seismic forces..ok all the best..

Hi Dagnaw Wudu

There are 2 criteria when establishing the boundaries (lateral and depth):

1) the ground response near the end of the lateral boundaries should be essentially the same as the free-field response without any structures

2) all response parameters should not change within some tolerance (say 5%) if you put the boundaries much further to the sides and bottom.

If you use transmitting / non-reflecting boundary conditions the overall size of the model decreases, but you need to properly define these boundaries.

Good luck,

Stoyan

First I would like to say thank you all of you for your valuable insights and advice.

Dear , Juneid Bakr (PhD.),From your explanation I have impressed with the term "Sensitivity Analysis" to determine the lateral stretch and vertical depth of our numerical model.But,Here I have two questions:

1)Which control parameters are very sensitive for boundary (Box) effects in "Dynamic"numerical model.

2)How can perform this analysis with typical example (if possible).

I thank you very much! Dr.Junied Bakr

I think that using 25 times the pile diameter in both directions is a good practice and 1.5 to 2 pile length for the mesh depth, as recommended by Randolph (1978) in his Ph.D. thesis. It is better make sure that FLAC3D has some sort of transmitting (absorbing or silent) side boundaries to avoid the incident wave reflection into the soil domain from the side boundaries. One more thing, kindly make sure that FLAC3D has porous media formulation that will be active during the seismic action to account for the generation and dissipation of pore water pressure during and after applying the seismic event and to model the liquefaction that may take place in some cases.

Thank you so much! Dr. Tarek Nageeb Salem