Hide or delete a single division line in a radial chart

Hello everyone

I made an MS Excel program to calculate forces in reinforced concrete tunnels.

I have made radial charts to graph the values of moment, axial force and shear force.

I modified the scale of the charts to 15000 max and -15000 minimum and the greater unit to 15000 so I don't have that many radial division lines.
By doing this, I can make the line that represents "zero" be a single line; however, MS Excel will still plot an outside radial division line representing the 15000 value.

I have tried making "zero" to be the greater unit in the chart scale but Excel says the number has to be greater than zero.

I would like just the zero radial line to appear, because it would represent the tunnel itself. And I would like to have the outer division line to be white or if possible to not show at all, so it would be hidden in the chart.

I tried drawing a white donut shape to hide the outer line but whenever I change the tunnel diameter in my excel program, the chart changes and the donut shape would have to be redrawn again.


Here is one of the charts:

Tunnel moments.jpg

Could someone here have any ideas on how to hide the outer division line? Can it be done?

Thank you