tubbing
A lining of timber or metal around a mineshaft, which is watertight, used to safely penetrate quicksand, water, etc. It can be made of various materials, such as wood, concrete, or cast iron.
tubbing: watertight shaft lining for unstable ground
Tubbing is a cylindrical lining installed inside a mineshaft to create a watertight barrier when sinking through water, quicksand, clay, or other unstable strata. The tubbing itself bears the weight of overlying material and resists the pressure of water and unconsolidated soil, allowing miners to work safely in the shaft below. Without it, water would flood the shaft or loose material would collapse inward, making deeper mining impossible.
Traditional tubbing used timber staves, fitted like barrel rings and bound with iron hoops, typically 12 to 18 inches wide. This timber lining was often driven downward as excavation progressed, sinking under its own weight or with help from ballast. Cast iron tubbing became common in the nineteenth century, offering superior durability and watertightness. Modern shafts sometimes use reinforced concrete rings or steel plate sections bolted together. The choice depends on shaft diameter, depth, water pressure, and expected service life.
Installation and operation
Tubbing is installed in segments as the shaft is sunk deeper. Once the shaft reaches a certain depth, the next section is lowered into place and sealed or sealed to the section above it. For timber tubbing, caulking with oakum and lead or pitch ensures watertight joints. Cast iron tubbing sections are often seated on a concrete or timber collar and caulked or sealed with lead wool forced into the joint with a caulking tool. As the shaft sinks further, weight and hydrostatic pressure press the tubbing firmly into the ground, which helps create the seal.
Failures in tubbing occur when joints open due to uneven settling, when material deteriorates after decades of service, or when the lining develops cracks from ground movement. Water seepage indicates joint failure and must be addressed quickly to prevent shaft flooding. Inspection requires entry into the shaft and close examination of all joints, a hazardous operation performed only by trained personnel.
The term derives from the resemblance to a tub or barrel. Mining engineers distinguish tubbing from lagging, which is temporary timber bracing driven close together without caulking; tubbing is permanent, watertight, and integral to shaft stability. Tubbing remains essential in any deep shaft sinking operation in wet or unstable ground, and many historic mine shafts continue to rely on nineteenth-century iron or timber tubbing to remain dewatered and safe.