**2. Mechanized underground coal mining**

#### **2.1 Longwall system**

In India, the first mechanized longwall mining was implemented in Moonidh in 1978. Longwall mining is a new era in underground coal mining across the globe. This method can be adopted even in weak roof strata conditions with the help of an armoured face conveyor (AFC). Gassy seams are also easier to work on as there are few roadways, and ventilation presents a little problem. Longwall mining can be operated in two ways: longwall advancing and longwall retreating.

#### *Underground Coal Mining Methods and Their Impact on Safety DOI: http://dx.doi.org/10.5772/intechopen.109083*

Proper scientific exploration is the critical key to the success of longwall mining. It should preferably be implemented in coal seams that are free from geological disturbances and dirt bands. The unforeseen encounter of such dirt band or geological disturbance hampers the underground production and, results in the idle time of machinery and, increases the chances of spontaneous combustion, may even result in substantial human and economic losses.

In a longwall advancing system, a rigid cycle of operations is to be followed. Faults or other geological disturbances cannot be proved in advance. For some distances behind the working face, the roadways are on moving ground. In such conditions, the uninterrupted working of roadway belt conveyors is more challenging to ensure.

When the boundary is reached, the salvage of all support materials and the removal of all machinery must be expedited if serious losses are to be avoided. The gate roads are maintained in solids and, therefore, they are well supported. In advancing the gate roads, as the boundary is reached, the longest length of conveyors, haulage tracks, etc., are required, but in retreating, these lengths go on decreasing, thus reducing the transport cost accordingly.

Packing goaf may be avoided completely, But if there are contiguous seams, packing may be required. The labor required for unproductive work of packing can be reduced. Hence, the number of productive shifts can be increased. There is no leakage of air, so ventilation is less affected [19–22]. The schematic diagram of longwall mining is shown in **Figure 3***.*
