PIT DESIGN

PIT DESIGN

HEIGHT AND WIDTH OF BENCHES IN OPENCAST MINE

1.In Alluvial, soil, morum, gravel, clay, debris ( soft over burden), the sides shall be sloped at an angle

Of safety not exceeding 45 degree from the horizontal or at an angle Regional inspector permit.

Kept benched at ht. not exceeding 1.5 m and width shall not be less than ht.

2. In coal sides shall be sloped at an angle of safet not exceeding 45 degree from the horizontal or the sides shall be kept benched not exceeding 3 mtr. In ht..

IN MECHANISED MINE

1.A.Ht.of bench shall not exceed the maximum reach of m/c used for digging, excavation and removal.

 incase of uniformly soft rock the regional inspector may permit the extension of the ht. up to 3 mt. above the digging ht. of the m/c.

B. Width of any bench shall not be less than

§Width of any m/c plying on the bench plus 2 mtr.

      Or

§If the dumper is plying on the bench 3 times the width of the dumper.

      Or

 §Twice the  plan length of excavators like shovel and twice the length of body of m/c like dragline  whichever is more.

Provided that where dragline  used the width of any bench below in coal /overburden at the finishing stage  shall not be less than 3 mtrs.

or

§the ht. of the bench whichever is more.

§Safety precaution – when persons are employed within 5m of the working face adequate precaution shall be taken to ensure their safety by dressing .

HAUL ROADS

Haul road is life line in the operation of any opencast mine.

Parameters for good haul road;

vShall be to provide one way traffic. Where it is not practical  width  shall  not  be less than 3 times the width of any m/c plying on the road.

vCorners and bends shall be such that it shall provide clear  view for a distance  of not less than 30mtr. along the road.

vwhere it is not practicable  there should be separate  two  roads for up and down traffic.

vAt curves super elevation shall be provided according to speed of the vehicle.

vNo road shall have gradient less than 1 in 16 at any place.

vRamp over small stretches shall have gradient up to 1 in 10.

vWhere any road exist above the level surrounding area , it shall have a strong parapet walls or embankments not less than 1 mtr  ht.

v Road signs shall be provided at every turning points for the guidance of the drivers.

vAt every curve , parapet walls or vertical posts Zebra lines shall be provided

vThe portion of surface haul road in mine premises where there is heavy traffic of men and machines should have separate lane properly fenced off from the haul road for pedestrians and two wheelers.

vStandard traffic signs shall be displayed at conspicuous places alog the haul road.

v road surfaces shall be maintened smooth and of sufficient strength.

vLoaded trucks and dumper shall not reverse on gradient.

vA berm at least half the diameter of the wheel of the largest dumper plying or one meter whichever is greater and of adequate width provided at the edge of the spoil or coal dump.

Small vehicle shall not be allowed on the haul roads.separate road shall be provided at

For the small vehicle. Only authorized vehicle shall be allowed

With raised red flag in the daytime and redlight in the night.

The flag  or light shall be visible for the dumper operator from a distance

Of at least  30m.

Stander of illumination-Roadways and footpath from bench to bench – minimum standard of illumination 3 Lux horizontal.

Factors  responsible for slope failure

vSlope angle

vGeo mechanical properties of slope materials.

vPresence and orientation of faults and other discontinues.

vPresence of water.

vDepth of the pit.

vEffect of blasting.

vPresence of u.g. working.

vPresence of fire

vPresence of week bed in the OB

vUndercutting or toe cutting

v PROBLEMS ACCOCIATED WITH HIGHWALL

1.Because of jointing , slabbing  etc. probability associated with

Slope failure increases.

2.It will require deep hole blasting with heavy amount of explosives.

Which will produce vibration, fly rocks, boulders air blast etc.

3.Because of slope failure or boulder falling from the top ,severe damages of machineries

And serious accident to persons.

4.Supervision is difficult.

5.Water pressure in the joint responsibility for more frequent slope failure.

6. Problem of floor sliding due to presence of aquifers.

Precaution-

1.Angle of slope of the bench should be equal or less than angle of repose of the bench rock. For dragline bench angle of slope of the high wall benches varies from 70-80 deg.

2.Face should form an angle with the main cleats, fractures etc.

3.Bench dose remain for long time, quick rate of advance.

4.Controlled blasting should be practiced..

5.Highly charged water bearing strata should be dewatered by putting boreholes with pumps.

6.Weak plane in the strata should be cement groued.

7.Bench ht. should not be more than required.

8.Design and review shall be done by experts from  CMRI,CMPDIL  etc.

9.Undercutting and toe cutting should be avoided.

EFFECTIVE        DRAINAGE

1.The quarry should provided with effective garland drains.

2. The benches  should have effective toe drains.

3.Stablity may be improved by effective drainage of the slope . Horizontal holes are drilled in to the slope face for effective drainage  & to reduce water pressure. Holes are drilled at angle of 5 degree will facilitate free flow of water. Holes may be 10-15 deep at intervals of 5m or less. A pipe inserted in to the hole to prevent caving. The pipe should be perforated.

SPOIL BANK

1.Slope of spoil bank face shall be determined by the natural angle of repose of the material, but shall not in no case exceed 37.5 degree from the horizontal.

2.The spoil bank face shall not be retained by artificial means at an angle in excess of natural angle of repose. Any spoil bank exceeding 30m in ht. , should be benched so that no bench exceed 30m ht. and general slope does not exceed I1 vertiacal to 1.5 horizontal.

3.Incase of working by dragline ,where the inclination of  the bed rock does not exceed 5 deg. From the horizontal, the ht of overburden dump shall not exceed 60m.A bench of 10- 15m wide in overburden overburden shall be maintained between these dumps and final dump created by the dragline. If the inclination of the bed rock exceeds 5 deg., the ht. of the forebank shall be suitably planned.

3.The toe of the spoil bank shall not allowed to reach a railway or other public works or other public roads or building or other permanent structure not belonging to the owner of the mine closer than a distance equal to the vertical ht. of the face.

4. A suitable fence shall be erected between any roadway or public works or road or building or structures and toe of the active spoil bank at a distance of not less than ht of the spoil bank.

5.No persons shall be permitted to approach near the toe of  an active spoil bank.

6. The manager shall appoint the sufficient no. of competent persons to supervise dumping operation.

7. The manager shall formulate Dumping rules which shall specf

y a.The provision of system of drainage

b.System of inspection

c.Maximum ht. of the bench. The ht of the shall not exceed 60m .

8.