Beginners Guide to Room and Pillar Mining | An Underground Miner

Sometimes the old ways are best.

Despite incredible advances in technology enabling a new era of surface mining, room and pillar remains one of the most popular underground mining methods today.

While incredibly complicated and (like all underground operations) fraught with risk, this technique is still effective and is in widespread use.

Our guide covers all you need to know about these historic and breathtakingly elegant mining systems.

Among the oldest mining methods, this technique has been used since medieval times in Europe.

It's an effective way to mine horizontal strips of ore, making it ideal for sedimentary, flat-lying deposits that form in layers.

A room and pillar mine features a vertical shaft leading down to the productive area.

The productive area is where most mining activity takes place because it's where the valuable ore deposits are.

The shaft is used for material handling and extraction.

This area consists of a series of rooms.

Today, they're typically laid out in grid formation, as this is the best way of stabilizing the overburden.

The overburden, or overlying strata, is the mass of rock and other material left standing above the productive mining area.

The collapse of this area would be disastrous, so miners must leave some support in place to prevent the underground mine from caving in.

This is where the pillars come in.

Large pillars are left standing in each room to provide support in mined-out areas.

The distribution of these pillars (and the rooms) should ideally be even, but this is made much harder because ore deposits don't form in neat grids.

Therefore, determining which parts of the operation should be left as walls, where pillars should be located, and which areas should remain open as rooms require careful exploration before work begins.

Productivity and how cost-effective the mine is depends on establishing a regular pattern that allows the best access to valuable ore deposits.

While this is one of the oldest underground mining techniques, the method is constantly being refined to improve yield and safety.

Here's a step-by-step guide to how a room and pillar mine is developed.

First, a deposit must be identified and determined as suitable for this technique.

Coal, iron, and uranium are among the most common materials extracted using this method.

Salt and gypsum mines also frequently follow this design, and it's sometimes used for oil shale.

The system suits hard rock deposits better than other popular techniques like cut-and-fill mining.

Ownership is allocated when exploration begins.

This ensures that the owner takes responsibility for the full exploration procedure - while coal seams (or otherwise) may have already been identified, exploration is costly and should be handled by the project owner.

Exploration should determine how productive the area is but should also determine whether this is the best system and whether materials can be mined safely.

As noted, these mines are best designed in a grid formation using square pillars to prevent cave-ins.

If the ore can't be productively mined while establishing a secure roof, other methods, such as block caving, may be preferred for hard-rock mines.

A short review on the surficial impacts of underground mining - Scientific Figure on ResearchGate. Available from: https://www.researchgate.net/figure/Room-and-pillar-method-in-underground-mining-Hamrin-1980_fig2_229044874 [accessed 24 Jan, 2023]

The mine will be planned far in advance of excavation.

The region's rock mechanics must be thoroughly understood before a coal mine or otherwise is established, and the ideal pattern for open spaces and pillars should be determined.

Rooms should be as even in size and shape as possible while maximizing extraction.

Uneven rooms have several drawbacks in coal mines, such as:

There are two types of support in a coal mine developed using this method - barrier pillars and panel pillars.

Barriers are much wider and sturdier and typically flank smaller panels.

They're known as barriers because their role is to prevent a complete cave-in if a panel subsides.

Once the mine has been designed and approved as safe, productive operations can begin.

Material is typically removed via a vertical shaft away from the productive area and out of the mine.

The traditional method was to blast deposits and consistently remove material from the productive area.

However, continuous miner operations involve constantly grinding away rock and ore and removing it much faster.

This reduces the risk of an overly large pile developing in the productive area, which may hinder operations.

One drawback of this technique is that yield depends on an equable distribution of ore.

However, improved exploration techniques and innovative equipment from brands like Komatsu, Caterpillar, and Atlas Copco have made it easier to plan large-scale room and pillar mines with a cost-effective yield.

Once the deposit has been fully mined, perhaps the most common option is "retreat mining."

This method has been criticized in recent years because it's extremely risky both to workers and local geology.

This technique involves strategically removing the remaining pillars, causing the roof to collapse and the productive area to be filled in by the overburden.

Destroying pillars while inside the mine is obviously incredibly dangerous.

Remote destruction can minimize the risk to personnel and equipment but can still have harmful consequences.

When the overburden collapses, the surface becomes much less stable.

It may become unsuitable for building, and local habitats may also be threatened.

An alternative to retreat is to continue maintaining the area or to repurpose it.

Maintenance is expensive and requires long-lasting commitment.

Many old room and pillar mines have been out of service for over a century and are in a state of disrepair, risking collapse.

In the US, historic mining states like West Virginia face increasing risks from poorly maintained mines.

Other regions have come up with some elegant solutions, for example, reinforcing the area and repurposing the underground area as storage or commercial space.

Room and pillar mining is used across the US and in many parts of the world.

While much of its early development was in Europe, it's rarely used there today.

It's perhaps most common in coal mining regions.

Coal is relatively easy to extract while using this method, and it's still sometimes considered preferable to more modern techniques like sublevel caving for a consistently productive coal mine.

As the method involves less overburden excavation than strip mining, the room and pillar technique is often preferred for deeper operations, especially in the coal industry.

CC Image by Dennis Jarvis via Flickr.

As with virtually all mines, the predominant risk is that the overburden collapses.

This risk is mitigated by well-distributed pillars that bear the overburden's weight equally.

Another hazard is airflow management.

Uneven room shapes and sizes make it harder to distribute air around the mining space, making it a hazardous environment for workers.

The other major risk comes with retreat and/or poor maintenance.

It's increasingly important for companies and local authorities to work together to develop a plan for what happens to room and pillar mines once they cease to be productive.

The engineering that goes into designing pillar size, shape, and dispersal today is incredibly precise.

It's staggering that this has been an effective mining technique for centuries - old-fashioned mines of this style were incredibly risky places to work.

This elegant, ingenious method is still considered the most effective technique for many mining operations today.

Learn about more mining methods and stay up-to-date by checking out our blog!

This article was written by An Underground Miner