Common Support Types used in Mining Engineering Tunnels

From the earliest days of mining until the middle of the 20th Century timber was the standard supporting medium due to its abundant availability and attractive strength and load-deformation characteristics. Traditionally, timber has been employed extensively for support in coal mines even at shallow depths as roof support is required owing to the weakness of the rocks associated with the Coal Measures. in hard rock mines, however, this has not always been the case as the stronger rock types often provide safe, self-supporting tunnels particularly in shallow depth conditions.
The load-deformation characteristics of wood make it a suitable material for mine support purposes as even in the post-failure state it retains the ability to support a load even at high values of strain.
An early use of timber for support of mining tunnels was the herringbone system and appears to have led to development of the steel arch support. The use of timber required considerable craftsmanship and time and effort to perform the support operations. Large amounts of timber were required in broken ground conditions and even then such support tended to be less than satisfactory in view of the significant voids which were inevitably left. The use of the rolled steel joist significantly contributed to reducing the time and effort, in addition to skill, involved in erecting mine roadway supports. There was also a significant improvement in safety as a result of the adoption of steel mining supports as opposed to timber for use in mining tunnels and roadways. Undoubtedly, steel supports were better suited to the significant deformation characteristics of coal mining tunnels and roadways than was that of timber. The superior strength and durability properties of steel supports in addition to ease of construction were over-riding factors when compared to wood for support purposes.
Wood is rarely used as a main form of tunnel support in the majority of modern mines in developed countries. Standing steel sets and rockbolts are the most commonly applied forms of support in such mining excavations. Concrete and shotcrete supported tunnels have a relatively limited application but they tend to be used in special situations rather than as a general tunnel lining technique. There are some exceptions, however, and one example is that of deep level main tunnels used for developing mining districts in the Campine Coalfield, Belgium. These tunnels have been supported by concrete segmental types and given significant stability and durability advantages. This form of support has also found application in the coal mining industries of other countries where long life (>50 years) tunnels are required.