I have pit sinkers among my ancestors and there are some other things you might want to look at.
They may have been involved in associated industries. My pit sinking ancestors started off as lead miners, worked as colliery managers as well as pit sinkers, ran brickworks (they needed a lot of bricks for the shafts) and also sunk shafts for railway tunnels.
They sometimes formed new partnerships for new contracts. I found records of the dissolution of one of the partnerships in the London Gazette that you can search online. Sinking one pit could go on for a couple of years or more, especially if it was a deep pit and they had problems. I've managed to find one or two newspaper reports.
Also it might be worth checking engineers' associations. I found one of my ancestors in the records of The Chesterfield and Derbyshire Institute of Mining Civil and Mechanical Engineers (records at Chesterfield Library). No doubt other parts of the country had similar associations.
Regards,
Peter