*2.4.3 Nevid method*

Neels Joubert and David Posthma developed this extraction method, so it is named NEVID after them. In this method, the snooks are predesigned in such a way as to ensure that the roof to let down in a controlled and safe manner, that is, adequate strength (width to height ratio) is maintained. For every three rows, a stooper pillar was left in addition to snooks formed. It was found that sometimes the snooks created failed unexpectedly due to inadequate strength. The primary purpose of the stopper

**Figure 8.**

*Nevid method (a) pillar extraction sequence, and (b) pillar extraction sequence layout for a complete panel [38].*

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

pillar is to take an additional load off the pillars, which are extracted while they are spaced far enough apart to crush as required, mainly when the goaf hangs [38–40].

The main reason for the immediate successful results of this method is that compared to the previous mining methods in South Africa, the cut's length was reduced and maintained appropriately to pillar size. All the lifts were driven into the pillar at an angle of 45 degrees. Another aspect of the method's success was all the lifts in the extraction sequence were marked with the help of survey pegs and direction lines. In 2001, this method adopted panel zoning, which is a process of identifying the hazards based on geological information with the help of geological mapping to zone a panel during the development phase into low-to-high-risk zones [38]. The schematic manner of extraction to be followed in the Nevid method is shown in **Figure 8***.*

#### *2.4.4 Yield pillar method*

The yield pillar method is one of the oldest extraction methods employed in underground coal mining. The main principle of the yield pillar method is to design the size of remnant pillars in such a way that they will fail in a slow and controlled manner. Thus, the method involves leaving pillars in the back area in a systematic way so that they yield over a period of time. The remnant pillars, which are allowed to yield, are designed in such a way that their width-to-height ratios are greater than five. Slices are made into pillars in a systematic and sequenced way. Along with a remnant pillar for yielding, this method allows leaving snook. The extraction of snook is highly dependent on local strata behavior, and experiences gained [41–43]. The schematic manner of extraction in the yield pillar technique is shown in **Figure 9***.*

Although yield pillar behavior is conceptually simple, in-mine implementation is often difficult. These difficulties arise, in part, from-

**Figure 9.** *Yield pillar method.*


Advantages, disadvantages, and present status of various mining methods are shown in **Table 1**.
