Soil pipe

[fizzypop100]

The ground is permanently wet where the pipe meets the ground and had no rain for weeks

I would guess that the cover on the side is either cracked or needs tightening because it is leaking.

But it could be the joint above is leaking. I would dry it thoughly with kitchen roll paper and then wrap some more around and flush the toilet a few times and then look at the paper to see if you can establish where the leak is.

You say soil pipe, but mention rain. Is that a soil pipe carrying waste from your bath/wc,/sink, or is it taking away rainwater from your roof and guttering?
Or both? Both is not ideal.
Where does it go below ground level? Is it backed up maybe? Is the a inspection cover you can lift and check if it's running clear?
Unless it is blocked or some cracks around the fitting, then it shouldn't be leaking. Remedy is to either unblock or change/repair the fitting.

Since there is an access point for rodding, this suggests to me that there is a historic problem that may need attention.