Dr Roozbeh

1. For thick retaining walls/secant walls/diaphragm walls ( thickness greater than 3 ft ) , modeling the wall as a linear soil element seems more logical than a beam element.
2. I modeled a secant pile wall with an equivalent X-section of 1 ft x 3.5 ft. once as a beam element with interface and once as a elastic soil element.
3. The results were significantly different. 
Trying to figure out why and the interface comes to mind first. Using the linear elastic model, I cannot find a way of modeling the interface.
Any thoughts ?
Thank you

I'm not sure why you need to use prefer to solid elements. I have never done it myself so I really can't give you a clear answer. I always use beam element because figuring out the proper properties and also applying the spacing in solid element is not easy.

Dr Roozbeh

The main reason is the thickness of the walls and its effect on the soils and adjacent footings behind it during lateral deflection. I am currently studying a problem where there is a property wall around 3 ft behind the wall ( 3.5 ft thick). If I model the beam at the center of the wall, the distance between it and the other wall will be 4.75 ft as opposed to 3 which could make a difference.

Not sure if it will make much of a difference but knowing the soil behind the wall will settle for a distance behind the wall under lateral deflection, thought of checking if the results differ.

Thank you