Excavating around a canary palm

[newtotrees]

I have a reasonably large canary palm/Phoenix Canariensis in my garden (about 20ft tall, planted 10 years ago in London) but I am planning to excavate around it to build a patio. I’ve attached a picture of the palm.

The excavation would be about 4 or 5ft below the level of the bed containing the palm, to the left of the palm (where the path is) and the front (toward that crumbling wall in the bottom right of the picture, which is crumbling due to being ancient and there being an old tree stump right against it).

How close do you think I could get the edge of the retaining wall to the palm without huge risks to the retaining wall from roots? Ideally, I would like the retaining wall to be to the right of where the path is, but is that far too close to the tree?

I’m not really sure how much bigger the tree will get in the climate here, but hopefully not much bigger!

Thanks for any advice!!

 

[Raintree]

In my opinion when you are up against a situation dealing with a tree's root system and the tree has obviously out grown it's location. It's best to remove the tree. That being said, palms being monocots don't have invasive roots nor do they have buttress support roots. One can excavate fairly close to the palm trunk without causing significant negative impact on the trees health.
In your situation the two main concerns are. Soil volume to maintain a tree of that size and stability of the plant.