trumpeting

Trumpeting is a narrow channel or cavity that forms between the brick lining of a mine shaft and the surrounding rock or concrete collar. Water and fine material migrate through this space, typically following gravity downward, gradually enlarging the void. The term describes both the physical channel itself and the problem it represents: a pathway for water ingress and material loss that weakens the structural integrity of the shaft.

The condition develops most often in older shafts or those with inadequate grouting behind the lining. During shaft sinking or renovation, the brick or stone lining is supposed to be backed solidly with grout or mortar, but incomplete filling leaves voids. These voids become pathways where percolating groundwater and fine particles migrate behind the lining, eroding the backing material and enlarging the space. The process is typically slow but relentless, particularly in wet mines or where hydraulic pressure is high.

Trumpeting differs from more general spalling or deterioration because it is specific to the boundary between lining and surrounding material. The damage is hidden from surface inspection; it becomes evident only when water seeps through at unexpected points, when lining shifts or settles unevenly, or when a formal survey detects voids during shaft maintenance. The name itself suggests the trumpet-like shape the channel can assume as it widens.

In operating shafts, trumpeting poses real risks. Water flow can accelerate, carrying away supporting material and creating zones of unstable ground above or below the lining. In extreme cases, section of lining can collapse inward or outward. The condition is particularly serious in shafts that carry men, materials, or ventilation, where sudden failure has severe consequences.

Detection relies on visual inspection from inside the shaft, water ingress patterns, or more recently, ultrasonic or ground-penetrating radar methods that can identify voids behind the lining without breaking it. Repair typically involves grouting under pressure through small holes drilled into the lining, forcing new grout into the void to stabilize the backing and seal the pathway for water. Preventing trumpeting in new work requires thorough grouting behind all lining, proper drainage, and regular monitoring of any early seepage.