What is the correct tool/method for digging out existing concrete holes for fence posts

Question

My garden needs a new fence as well as two new fence posts. There is an existing concrete base along the boundary which is already securing three posts and has holes where two posts snapped in the wind at the base.

One of the holes is intact with all four sides:

The other hole appears to have one of its sides broken, you can't see it from the following picture, but there's no sign of it when poking into the ground at the base:

My question is two fold:

1. What tool/method should I use to dig out the old debris/wood from the snapped fence post? It's obviously a tight space and I suspect I need to work smarter not harder.

2. For the hole that has one side of the concrete missing - what could I do to sure up the hold? Should it be relatively easy to lay more concrete around it? Or is there some other method of securing it I haven't thought of?

Answer 1

I doubt you can get the broken off posts out and new 4x4 posts in with the holes intact. In one case on this site the poster had clean holes and put in steel posts which are smaller enough in diameter than the original wood posts that they could be inserted plumb into the existing retaining wall.

If your concrete is relatively weak, you might be able to break down the concrete on the two "outer" sides flanking each post using manual tools, such as a heavy steel concrete breaker bar or a heavy mattock with pick on one end. An alternative is an electric jackhammer which you can rent.