Underpinning a garden wall.

Hello. I had to dig a hole near a retaining wall as water was gathering and I needed a low spot to get a submersible pump in. It's done the job but the hole has got bigger due to the sides slumping. It's now starting to go under the walls foundations
I'd like to pour concrete in there but it's filling with water even though it hasn't rained for over a week.
Any ideas? It's on a small scale at the moment.

Pour the concrete in, it displaces the water.