Short answers, pulled from the story.
Shaft sinking is the process of excavating a mine shaft from the top down, starting from the surface with no access to the bottom. It is used to reach underground ore bodies and create vertical passages for moving people, materials, ore, and ventilation air. It is considered one of the most difficult of all mining development methods.
The deepest continuous single-lift mine shaft in the world is the main shaft at South Deep Mine in South Africa, owned by Gold Fields Limited, reaching a depth of 2,991 meters. Along with its twin ventilation shafts, it took ten years to sink and equip.
Following the Hartley Colliery disaster, the United Kingdom made single-shaft mines illegal in 1862, requiring all underground mines to have a second means of egress. Many other mining jurisdictions around the world adopted the same rule.
Shaft sinkers are specialized mining contractors who excavate mine shafts. Today they are concentrated in Canada, Germany, China, and South Africa. The work has historically been among the most dangerous of all mining occupations.
Mass concrete is the primary lining material, poured in lifts of six meters as the shaft advances. Other materials used include shotcrete, brick, cast iron tubing, precast concrete segments, and in extreme cases composite liners, bitumen, and even squash balls depending on the geology.
Full-face shaft boring works like a vertical tunnel boring machine and represents a recent advance in mechanized shaft sinking. As of 2019, the method had shown promise but was not yet widespread in the industry.