Hi thanks for your question. My name isXXXXX can assist with this.
If his land is causing damage to yours, as appears to be the case, then you should be able to insist that he remove it or that you will issue proceedings based on the law of nuisance.
You can ask the Court for either force him to remove the soil, or alternatively, grant an order permitting you to do so and preventing him from stopping you.
This is similar to the case of Leaky -v- National Trust, where the court held as a matter of legal principle that one landowner should prevent a state of affairs on his own land that causes damage to his neighbouring land: http://www.e-lawresources.co.uk/cases/Leakey-v-National-Trust.php
I see you've gone offline - when you're back, I'll gladly continue this chat with you.