INUNDATION

INUNDATION

Sudden inrush/influx of huge amount of water in mine working.

REASONS of inundation in opencast working

•Heavy rainfall

•Presence of aquifers, ground water table above the workings .

•Sudden inrush of water form catchment area

•Absence of water garland around the working

•Quarry made in HFL zone

•Quarry connected to old waterlogged working

•Heaving of floor of the working due to excessive underground water pressure.

•Inadequate pumping capacity

PREVENTION OF INUNDATION IN OPENCAST WORKING

•Surface Run off should be prevented from entering the excavation.

•Drainage slopes should be maintained at every bench & sump should be made at the

      lower points

•Preparation of garland drain around the quarry.

•Construction of Embankment against the river /mullah  flowing near the working.

•Adequate pumping capacity.

•Adequate monsoon preparation.

•Dumping area of the working should be on the higher ground.

•Use of borehole pumps in case of ground beneath the working charge with

       high pressure water.

•A  careful assessment of danger of inundation from surface water should be made before onset of the monsoon

•& adequate precaution from danger of inundation should be laid down & implemented

•Effectiveness of the precaution laid should be checked regularly  & by surprise inspection.

•Fixation of danger mark of water level, effectiveness of signaling & communication system should be made regularly.

•Standing orders for withdrawal of person in case of apprehended danger  should be famed & enforced.

•All concerned should be made familiar with the standing orders.

•MOCK REHEARSALS SHOULD BE MADE ONCE IN EVERY MONTH DURING MONSOON SEASON.

•During  heavy rain ,the manager of the mine or the senior most official present  should go round the surface to check the vulnerable points & effectiveness of the safety.

•The area safety officer  should made close liaison with the mine officials.

•Specific precaution to observed in the mine should be prominently displayed in the office of the manager.

Capacity of the sump should be adequate.

•Capacity of the pump should be adequate. Arrangement should be made for the measurement of water level in the sump.

•During monsoon pump should be adequately manned for operation and maintenance staff

126. Danger from surface water

 (1) [(a)] Where any mine or part thereof is so situated that

there is any danger of inrush of surface water into the mine or part, adequate protection against such inrush shall be provided and maintained.[Whether such protection is adequate or not can be determined by the Chief Inspector or whose decision shall be final.]

[(b) Except with the permission of the Chief Inspector in writing and subject to such

conditions as he may specify therein and subject to the provisions of clause (a), every

entrance into a mine shall be so designed, constructed, and maintained that its lowest point

(which means the point at which a body of rising water on surface can enter the mine) shall

be not less than 1.5 metres above the highest flood level at that point].

2) No workings shall be made in any mine vertically below –

(a) any part of any river, canal, lake, tank or other surface reservoir; or

(b) any spot lying within a horizontal distance of 15 metres from either bank of a river or

canal or from the boundary of a lake, tank or other surface reservoir;

except with the permission in writing of the Chief Inspector and subject to such conditions as he may specify therein.

(3) Every application for permission under sub-regulation (2) shall be accompanied by two copies of a plan and section showing the existing position of the workings of the mine,

 the proposed layout of workings,

the depth of the surface, the position and

depth of any goaves in every seam in the neighborhood,

all faults, dikes and other geological disturbances and such

other particulars as may affect the safety of the mine or of the persons employed therein.

Explanation. – Where sand or alluvium are lying in the course of a river, canal, lake, tank or

reservoir, the depth from the surface shall be reckoned from the surface of hard ground

underlying such sand or alluvium.

[(4) All workings made under sub-regulation (2) shall be clearly demarcated belowground.

(5)(a) A competent person shall, once at least in every 14 days during the rainy season and

once at least in every 30 days during other periods of the year, examine every protective

measure provided under sub-regulation(1), whether in use or not, for their stability. A report of every such examination shall be recorded in a bound paged book kept for the purpose, and shall be signed and dated by the person making he examination and countersigned by the manager.

(b) The protective measure and workings aforesaid shall also inspected, once at least in

every quarter by the manager personally.]

Monsoon preparation

Garland drain & diversion channels around open cast working should be inspected, cleaned and modified & size of the drain should be adequate so that water do not overflow during heavy rain.

Embankment against river & nullah should be examined for the stability.

Capacity of the sump should be adequate.

Capacity of the pump should be adequate.

Arrangement should be made for the measurement of water level in the sump.

During monsoon pump should be adequately manned for operation and maintenance staffs.

Spares parts of pumps ,pipe ranges &electrical equipment should be kept in stock. Pump house should be provided with effective communication system.

Arrangement should be made for record of rainfall. Quantity of water pumped out ,variation in water level in sump shall be made.

•1.Manager shall made standing orders  for immediate action to be taken to guard against danger of inundation. The standing order shall indicate HFL of the area, THE WARNING LEVEL and WITHDAWAL LEVEL for the equipment and men.

     2.A plan shall be mad to show the position of the working places, vulnerable equipment, sumps & pumps installed with RL

     3.Arrangement for quick withdrawal of  the equipment shall be made.

Drainage of overburden dumps shall be checked.

During heavy rains frequent patrolling by the mine officials .

EMBANKMENT

Embankment constructed against a jore or nullah to protect the mine from flood water.

DESIGN & CONSTRUCTION

Height-As per law ht. of the embankment shall be above 1.5 m above the H.F.L.. This is minimum ht. But ht. should be decided by considering

•Time required for the withdrawal of person from the mine.(extent of working, dip of the working, means of transportation, means of communication etc.)

•Rate of rise of water level

So considering all factor of safety it advisable to keep ht. of the embankment 3 mt. above the HFL.

Minimum width at top-

For simple earthen embankment the thumb rule is

Width=ht. of the embankment

Width of the base= 3 times the ht. of the embankment.

SIDE SLOPE

On upstream side may be 1 in 5 , on the other side it may be steep as 1 in 2.

 SIDE PROTECTION

The side facing water is to be protected against wave action by stone pitching.

Arrangement to be made for growing vegetation on other slope, which may also be provided with berms and arrangement for drainage for rain water to allow flow along definite designed water channels. Toe protection and provision of toe drains ,vertical chimeny drain etc , may be provided.

LENGTH

Length of embankment should be such that to contain the water against features to be protected.

Type of material and design of foundation-

Clay-  lime-Unstable

Mine overburden material dozed by dozer often have low compaction , void spaces .

Foundation to be designed as per bearing strength of the ground.

SLUICE GATES

Provided with regular passage at appropriate level with one way sluice gates for pumping out water from mine side to nullah, jores.

Care of construction-

•Supervised by competent engineers.

•The fill has to be brought in stages and compacting to 50mm.

•Most impervious soils are located in the center and most coarser and more previous material towards the slope.