Marcin Kasprazak, 26, attacked Michelina Lewandowska with a Taser at their home after becoming bored of his relationship with her but wanting to keep hold of their young son.
With the help of teenage friend Patryk Borys he bound and gagged her with parcel tape and after around six hours put her into the box which was driven to woodland near Huddersfield and buried in a shallow grave.
Terrified Miss Lewandowska, 27, only managed to escape by using her engagement ring to cut herself free from the box and clawing her way back to the surface.
Kasprazak of Penistone Road, Huddersfield, was found guilty by a jury last month by a jury of her attempted murder.
He admitted kidnap and possessing the prohibited Taser.
Sentencing him at Leeds Crown Court yesterday the Recorder of Leeds, Judge Peter Collier QC said “being buried alive must be one of the most dreadful ways to die that anyone can imagine.”
After stunning Miss Lewandowska with the Taser and keeping her prisoner for around six hours Kasprazak had driven her in the box to Woodsome Road where it was carried up a steep verge into deserted woodland.
“There you covered the box with earth, leaves and branches and tree roots – whatever you could find.
“You placed a heavy branch over the top of the buried box.
“It was your intention that should not be found and it was your intention that she would die there.
“The death you intended would have been long and slow.
“It is mind-numbingly awful to imagine the sort of death you intended her to die.”
“Fortunately she escaped, her raw determination to survive for the sake of your son is undoubtedly what saved her.
The judge said she first managed to wriggle her hands out of the bindings then to remove her engagement ring which she had kept despite Kasprazak having ended their engagement, using it to cut the bindings on her legs.
Then from her cramped position she tore at the small grab holes on either side of the box enlarging a gap until she could push her way out and seek help.
Meanwhile Kasprazak had taken her bank card and used it at supermarket to withdraw £500 from her account before he was later arrested at Borys’s home.
Judge Collier said Miss Lewandowska “is suffering and will continue to suffer significant psychological harm. I am satisfied that these events will unsettle any prospect of stability for her for years to come.”
Borys, 18 of Rashcliffe Hill Road, Huddersfield was sent to a young offender institution for four and a half years after he admitted kidnap.
The judge said he accepted his role was subordinate but he had made no attempt to question or intervene in Kazprazak’s actions.
Kasprazak claimed to the jury he used the taser after becoming angry about Miss Lewandowska’s treatment of their son and that when he took the box to the woodland only intended to frighten her so she would leave Huddersfield and not take the boy.
She described after the trial still suffering nightmares “that Marcin will come back to find me and kill me.”
“During my time inside my shallow grave where I was buried alive, I feared that my life was at an end and I was going to die.”
“I prayed to God to help me to survive so that I could look after my young son. The thought of him gave the strength to fight my way out of the box and save myself.”
“For many years I loved Marcin Kasprazak very much, but after his horrific attack upon me my feelings towards him have turned to hatred.”
“I really hope that no one will ever experience what I went through on that day in May at the hands of a man whom I loved and trusted.”