Any help would be appreciated. 

Due to years of erosion due to wave action, 8 of the 10 posts holding up  my dock require “shoring up”.  The posts that are deepest in the water are still touching concrete but has been undermined, the center 3 posts have about 3 sides of mortar still touching the post but it is questionable if the posts are sitting on solid ground.  And finally, the center back post was on dry land evidently, when it was built, but has now been undermined/eroded by the wave action and is not acting as a post anymore.  It is hanging in the air about one foot above ground now.

The land is fairly steep, maybe 20-30 degrees.  the front posts (4) are approx 10 feet to bottom of decking, center posts are about 7 feet, and the back center post is only about 3 feet due to its location on the shore. In winter, all posts are dry, in summer the front and middle posts are in water and the back posts get only wave action.

The soil has lots of shale, and is otherwise red clay (Alabama)  The water level will come up 12 feet in a couple of months.

Any tips on how to remortar correctly would be appreciated.  I though of just building small forms around existing posts and pouring more mortar, will this work??

Thanks in advance.

Sawdog