Carved in Stone


September 1, 2011

U is for Undergrounder

Underground mining offers an attractive alternative for those who can adapt to conditions of underground life.

By Bill Langer

Undergrounder –– Noun (1) ape-like troglodytes who live in darkness underground and surface only at night; a.k.a. Morlock; observed by the Time Traveller in the year 802,701 AD (H.G.Wells, The Time Machine, 1895). (2) A person who extracts crushed stone from an underground mine (W.H.Langer, Aggregates Manager, Aug 2011).

A while back, I once again read The Time Machine. The story, basically, is a narrative told by a person referred to as the Time Traveller who had returned from his trip into the future. About halfway through the book, the Time Traveller described what he concluded was an underground labyrinth.

“Beneath my feet, then, the earth must be tunnelled (sic) enormously… The presence of ventilating-shafts and wells along the hill slopes — everywhere, in fact, except along the river valley — showed how universal were its ramifications. …I began to suspect their true import.”

My mind drifted away from the book. The true import about underground aggregate mines is that they exist. In fact, during 2007, there were 86 active underground mines in the United States that collectively produced 68.6 million metric tons of crushed stone; more than 5 percent of the annual U.S. crushed stone production.

Many underground aggregate mines are extensions of surface quarries into the walls of open-pit quarries, but some consist of inclined haulways driven into quarry floors. Some are completely independent of existing quarries.

Most underground aggregate mining uses the “room-and-pillar” mining technique that involves the removal of rock from “rooms” while leaving an array of rock “pillars” to support the overlying roof. Rooms are generally 45 to 50 feet wide and, in some instances, as high as 50 feet.

Equipment used in underground aggregate mines includes horizontal drill jumbos and downhole track drills; scaling rigs (to remove loose rocks from the ribs and roof of the mine); roof-bolting equipment (to secure the roof of the mine); ventilation fans (to provide fresh air for workers and remove exhaust fumes from machinery); as well as loading and hauling equipment.

Depending on conditions, underground mining of aggregate is about 50 to 60 percent more expensive than extracting aggregate from surface quarries with similar rock properties. Even so, it may be more economical to mine underground than to strip excessively thick overburden or import aggregate from distant locations.

Even where high-quality rock is present, the not-in-my-backyard (NIMBY) syndrome or incompatible land uses near a quarry may prevent an operator from acquiring new land or even expanding from a surface quarry onto land already owned. Underground mining may be favored where these conditions exist.

There are significant advantages to underground aggregate mining. Working conditions are not affected by rain, snow, wind, or outside temperature — mine air temperatures hover around 50 to 65 degrees F throughout the year. The workers have stable employment, stockpiles do not need to be large, rock does not freeze, and responses to unexpected demands of material are possible at any time. Neighbors are isolated from the ‘nuisances’ of mining.

Frequently, the space created by underground mining can prove more profitable than the rock removed. Spent underground aggregate mines have been turned into state-of-the-art business parks with millions of square feet of commercial and industrial space used as warehousing, laboratories, manufacturing facilities, food storage, records, and data storage…the list goes on and on.

As the Time Traveller observed…

“[I]n the end…the [undergrounders] would become as well adapted to the conditions of underground life, and as happy in their way, as the Upperworld people were to theirs.”

Bill Langer is a geologist with the Mineral Resources Team of the U.S. Geological Survey and can be reached at 303-236-1249 or via e-mail at

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