III. Read the text and do the tasks following it. The main classification of methods of working coal-seams is as follows: (1) Board and pillar; (2) Longwall advancing; (3) Longwall retreating; (4)

The main classification of methods of working coal-seams is as follows: (1) Board and pillar; (2) Longwall advancing; (3) Longwall retreating; (4) Semi-longwall; (5) Horizon mining.   

Hard and fast rules¹ distinguishing between these various methods cannot be laid down in some cases as so many modi­fications and combinations of the methods exist at various collieries working under different conditions. The general principles underlying² the three chief systems may be brief­ly outlined as follows:

Board and pillar mining, variously called "room and pillar", "pillar and stall", "post and bank" and "stoop and room", consists of driving "boards", "stalls" or "rooms" to split up the area to be worked, so as to leave "pillars" or "stoops", which may or may not be extracted at a later date.  

Under normal workings by this method, no packing is employed. Thus pillars when extracted are generally "retreat­ed", that is the pillars farthest away from the shafts are then taken out before those nearer the shafts.

Longwall advancing working consists of long faces or "wide places" from which all the coal is removed for a given working section and the necessary roads are made through the goaf where formerly coal lay. The roof near the working face is supported by props, bars and chocks, and by packs built up of material which falls from the roof, or may be imported.

Packs may be such as to support only the roadways left for the further extractions of the mineral and for ventilation pur­poses, when the system is referred to as³ "caving". They may also be built at varying intervals, i.e., "strip packing", or the void of goaf may be packed solid, i.e. "solid packing".

Longwall retreating working consists of first driving road­ways through the solid coal at such intervals as may be nec­essary for the extraction of the coal in a later operation, and of such lengths as may reach either the boundaryof the area of coal to be worked, or an arbitrary boundary. The blocks of coal thus formed are then worked on the longwall principle, but the direction of advance of working is from the boundary towards the shafts.

Notes

1. Hard and fast rules—твердо установленные правила (критерий)

2. principles underlying — принципы, которые легли в ос­нову

3. the system is referred to as — система называется

IV. Comprehension Check.

Find the following words and word combinations in the text:

Очистной забой, карьер, камерно-столбовая система, система сплошного забоя прямым ходом, система сплошного забоя обратным ходом, бутовая полоса, верхняк, стойка, целик, шахтный ствол.

Answer the following questions orally:

1. What is the main classification of modern methods of working coal-seams?

2. What is a pillar?

3. Are the pillars extracted?

4. What is referred to as packing?

5. By what means is the roof near the working face supported?

Answer the following questions in written form:

1. What does the board and pillar method consist of?

2. What are the general principles of longwall advancing work­ing?

3. What does longwall retreating working consist of?

V. Discuss the following with your groupmates.

What are the advantages and disadvantages of modern methods of coal mining? Is the work of a miner safer now (comparing with early days)?

 

COAL CUTTING

I. First thoughts. In what way was coal mined in early days?

II. Study the words. Make sure you know them. Practice the pronunciation.

Drill, heading, hand-operated, explosive, power supply, shape, dimension, blasting, hewer, undercut, middlecut, overcut, fireclay, handshear, holing, sprag, shot-hole, cleavage, shaft, arm, cutting teeth, groove, core, supersede, cutter loader.