What is Soft-Foot?
Soft-Foot can be compared to a washing machine that has one leg shorter than the other three. This unevenness and lack of contact with the floor will cause the washing machine to rock. That can also happen with all rotating equipment and may result in machine failure if not corrected. 
What’s causing Soft-Foot?

Several factors may cause a Soft-Foot. Maybe the underlying foundation is warped, bent, uneven, or damaged. The same may be true for the machine foot. The gap between the foot and the foundation may already be filled with compressed/bent or otherwise damaged shims. This condition may distort the machine’s frame as the foot is drawn down to the base by the foundation bolt’s tension. In our business, we call this a squishy foot. But also consider environmental factors like dirt and debris, which may have worked their way in-between. A more complex Soft-Foot is caused by forces external to the machine, like stress-induced forces created during any stage of the alignment process. What’s more likely is that you will find a combination of the above causing a Soft-Foot:

The most common Soft-Foot situations are:

Parallel Soft-Foot; when the machine foot does not have contact with the foundation and creates an in-between gap.  

Angular Soft-Foot;  when the machine foot makes contact with the foundation on one side only, it bends, resulting in an intermediate angle.

To prevent Soft-Foot, you’ll need something to fill the gap, 
the space between the 
foundation and machine foot.  
We call this a chock.