SELECTION OF LEVEL INTERVALS

2.3 THE FACTORS CONSIDERED FOR SELECTION OF LEVEL INTERVALS.

LEVEL INTERVAL

·         Level is a road way driven parallel to strike

·         Vertical distance between two levels called level interval

·         Distance between two levels measured along the plane of ore body called length of back or simply back

·

PURPOSE OF LEVELS

·         

1.         Passing adequate ventilation
2. ·         Obtain more production
3. ·         For access in to stoping area
4. ·         For inspection
5. ·         To reduce number of supports
6. ·         For easy extraction
7. ·         For sampling of ore

SIZE OF LEVELS

Size of level should be such that it should provide ample space for

1.  Movement of machinery

2.  Passing ventilation with least rubbing surface

3.  Without congestion

4.  Width generally 3 – 4.8m

5. Height 1.2 – 3m

6. If mechanization desired the dimensions are 4.3mx3m

7. Maximum width of level permitted by law 4.8m

8. Maximum height of level permitted by law 3m

FACTORS AFFECTING LEVEL INTERVALS

1. ·         Nature of deposit
2. ·         Degree and extent of exploration
3. ·         Thickness of deposit
4. ·         Dip
5. ·         Regularity and stability of ore and walls
6. ·         Cost of transportation
7. ·         Driving cost
8. ·         Characteristics of strata
9. ·         Cost of drivage
10. ·         Extension of deposit
11. ·         Geological disturbances

Nature of deposit:

Regular deposit :level interval is more

Irregular deposit: shorter the level interval

Degree and extent of exploration

Ore with erratic values : shorter level intervals

Uniform values of ore : more level interval

Thickness:

Thicker deposits :shorter level intervals

Thin deposits      : longer level interval

Dip

Flat deposits: shorter level interval

Slightly inclined deposits: shorter level interval

Steep deposits :longer level interval

Regularity and stability of ore and walls

Ore and walls are rigid and stable: longer level interval

Weak unstable: shorter level intervals

Cost of transportation

Increasing distance between levels : more transportation costs

Shorter level intervals :less cost

Driving costs

Longer level intervals: less number of levels,winzes and cross cuts

Shorter level intervals; more winzes,raises cross cuts

Characteristics of strata

Strong strata :longer intervals

Weak strata: lesser intervals

Cost of drivage

Greater level interval :more cost of drivage

Extension of deposit

Extension on dip side :longer level interval

Extension along strike :shorter level interval

Geological disturbances

Restricts the level intervals

Method of stoping

Open stopes : less level interval

Filled stopes: more level intervals