DRIVAGE OF ROADS IN COAL AND STONE

DRIVAGE OF ROADS IN COAL AND STONE

After a shaft reaches about 2 m below the coal seam to be worked or below the particular horizon or level in a metalliferous mine, the formation of roads is carried out according to a worked out plan. Where a shaft touches a coal seam, essential roads in coal are driven to reach the limits of shaft pilllar for ventilation, transport, drainage, stowing and distribution of electric/compressed air power. Beyond the shaft pillar the drivage of roads and extraction of coal depends upon the method of work to be adopted to win the coal.

Whenever any work is being done in a mine the following points should be borne in mind as they are the cardinal points for any mining activity, safety dominating all other considerations.

1. Safety and mining regulations.

2. Support of roof and sides and surface features.

3. Ventilation.

4. Drainage.

5. Transport.

Needless to emphasise, economics must always be kept in mind when considering any of the cardinal points stated above.

Drivage of roadways in coal in a mine so that their network reaches a predetermined boundary is known asDevelopment of the mine. The boundary may be the lease boundary of the mine, a fault plane, a dyke or any other artificial boundary.

In a metalliferous mine, a producing underground mine requires a carefully planned network of shafts, drifts -and raises. The preparation of this network is known as development.

Development of a mine by a method of working known as the bord and pillar method—the normal method of working in this country—consists of driving a series of narrow roads, separated by blocks of solid coal, parallel to one another and connecting them by similar set of narrow parallel roadways driven nearly at right angles to the first set. Fig 7.1 shows the plan of a general scheme of developing a mine by bord and pillar where the entrance is by inclines.

Definitions

The terms used in coal mining practice are given below:

A seam is assumed to be thin if normal thickness is less than 1.5 m; moderate if between 1.5 m and 4.5 m; thick if between 4.5 m and 9.0 m and very thick if beyond 9 m.

The stratum is referred to as flat if general inclination does not exceed 5° to the horizontal; inclined if it is between 5° and 18°; steep if it is between 18" and 40° and very steep if inclination is beyond 40°.

The workings are assumed as shallow if their average depth is below 200 m; moderately deep if between 200 m and 450 m and deep if beyond 450 m.

The gassiness of a coal seam is laid down by a circular of the D.G.M.S. in 1967 and the mines are divided into three categories of gassiness as shown in the table below:

                      

Gassiness degree	% of inflammable gas in general body or air	rate of emission of gas m3te of coal raised
I	below 0.1 and	below 1
II	above 0.1 and/or	1-10
III		above 10

A road in a coal seam proper is called a gallery.

A road which is driven along the dip of the seam is called a dip gallery and sometimes only a dip. A road driven along the strike of a seam is called a level gallery or simply a level. A dip gallery may be along the true dip of the seam or along an apparent dip. A level gallery may not be truly along the strike of the seam but may be slightly rising in bye, i.e. towards the working face, for considerations of haulage and drainage.

A roadway in stone connecting two or more coal seams is called a drift.  It is sometimes referred to as stone gallery if only one of the ends of the road is in coal and the other is a blind end.

A solid block of coal surrounded on all sides (or nearly all sides) by galleries is known as pillar. It forms the natural support of the roof in a mine.

Where the galleries in a seam are generally along the dip-rise and strike forming square or rectangular pillars, a gallery which cuts across the pillars, due to its drivage along an apparent dip, is called a crosscut, such crosscuts are sometimes required for facility of ventilation, drainage, and haulage or stowing.

A gallery in the process of being driven is called a heading. The moving front of any working place or the in bye end of any gallery, roadway or drift is called a face. A face in coal is also called a working place or simply a working.

When a set of dip or rise headings is driven, one of the headings is called a main dip or main rise respectively and the other headings on either side are known as companion dips or companion rises. The main dip or rise usually carries haulage arrangement and sometimes auxiliary fans. The main dip is equipped with face pump in addition.

A district is an area in a mine having a number of working places. The word "Section" is also sometimes used to denote a district, e.g. north section, west section, etc. But the use of the term section is not recommended where a seam is being worked in two or more sections like top section, bottom section, etc. The term panel is also sometimes used to denote a district which is separated from other districts by an artificial barrier of brick walls or by a natural barrier of coal.

Cover is the vertical depth of a place in the mine from surface.

Metal mining terminology

The terms used in metal mining practice are as follows (Fig 7.2.);

Level — A level roadway in the ore body or vein which follows the strike. In metal mines a level is rarely in a straight line (unlike in coal mines).

Cross cut— A level tunnel or roadway which leads from the shaft or level and passes through the country rock in order to cut across the lode at an angle to the strike.

Drive or drift— A horizontal tunnel or roadway parallel lo strike of the lode or vein but it can be located in the country rock either on the footwall side of the lode or on the hang wall side. It is called a footwall drive in the former case and hang wall drive in the latter case. The term level is sometimes used for drive, but the distinction should be noted.

Cross drifts or Cross drive — It is a horizontal underground roadway driven within the ore-body between the hanging wall and the footwall. It is usually at right angles to the dive or drift.

A reef drive is in the vein itself or partly in the reef and partly in the wall rock, usually the footwall.

Level interval — The vertical distance between two adjacent main levels, main horizons or main drives.

Sub level or intermediate level- a level or drive situated between the main levels or main drives.

Raise — A connection between two levels in an ore body driven in an upward direction. Raises intended for passing ore from an upper level to lower one under its own weight are called ore chutes. Short ore chutes intended for drawing broken ore from the blocks are called Draw holes.

Ore pass — An ore pass is a vertical or steeply inclined underground passageway for downward movement of ore by gravity. This term is not used in coal mining.

Draw point — A spot on the floor from where gravity fed ore of a higher level is loaded into tubs or mine cars.

Winze — A dipping connection in the ore body joining two levels. A raise or winze is located mostly near the footwall of the ore body.

Plat or station — It is the excavation adjoining the shaft at each of the different levels where men and materials are removed or delivered.

Stope — An area from where ore (and in some cases, a little country rock in the hang wall and footwall) has been extracted and the hang wall allowed to cave or supported by filling of some material like sand, mill tailings, blocks of granite, etc.

Stoping — Extraction of ore from a block or pillar formed during development. As a rule sloping is started on each side of a raise-winze connection.

 

Fig, 7.2

1. Auxiliary shaft. 2, Main shaft, 3. Staple pit, 4. Sump  5. Raise  6. Short ore chute or draw hole.

7. Cross cut. 8, Drift along strike of ore body. 9. Cross drift

In metal mining terminology development of a mine menus formation of a network of shafts, drifts and raises, in the early stages of mine work, with a view to

(a) prospect the orebody from underground for more details,

(b) arrange for drainage, ventilation and transport,

(c) divide the mine area into convenient sections for future working, and

(d) enable the mine planners to decide upon the methods of stoping.