I am trying to model an irregular shape of excavation in underground rock.

My problem is simple. I can't mesh my model.

When hit Mesh->Part-> OK to mesh the part, Abaqus shows an error, which I've never had before. (please refer a figure below)

The error is "mesh generation failed due to a problem in the propagation of mesh seeds"

Can anyone shows how to resolve this issue?

I attach a python script. Please run it and take a look at my model. Thank you. 

Here is my approach.

1. create a quarter model with a rectangular shape of excavation 

2. do radial pattern to create 3 more instances to get a full model

3. set local seeds along the excavation for a mesh refinement

4. generate mesh (the error comes up here)

I use "Geometry Diagnostics" to check any geometry or topology issue, nothing has found.