I've a wall in tension that should be in compression.

As shown in the screenshot below I've a symmetric model where the excavation is conducted in 2 steps, removing half of the bench on the left & installing the wall then excavating the right half & constructing the right hand wall.

The wall on the left behaves as expected, with the wall going into axial compression however the wall on the right strangely goes into tension. 

This is clearly as a result of the 2-step excavation as both walls go into axial compression when you clear the bench in one go & construct the walls at the same time.

Any idea as to why the model is behaving in this way?

Thanks