Annual Report,2009 - Directorate General of Mines Safety

DGMS Annual Report, 2009
anchored or fixed shall be of good construction, suitable material, adequate strength
and free from visible defect and shall be properly maintained.
Head gear frame are generally not maintained for serviceability. Some of the members
are removed for the convenience making structure unstable. Initial defects of
fabrications of bolts, rivets are enlarged. Improper coating for protection of structure
leads to corrosion of steel and reduction of properties due to environmental effects.
Mishandling of structure leads also to deterioration of structure.
Durability and serviceability of head gear depends on constant watch on structure and
audit for its stability. Material properties changed during service life need to be
checked and identified.
Following important factors are to be carried out from time to time verified with the
original.
Check to be carried out:-
1. Study the change in static and dynamic loads.
2. Evaluate change in configuration of head gear. Forces in members are to
checked and a diagram to be drawn to ensure resultant failing inside back leg.
3. Joints of members are to be checked (rivets, welds, bolts)
4. Strengths of material must be ascertained by taking samples.
5. Deflection and physical movement in all direction and vibration should be
measured by applying 50%, 100%, 120% loads. Deformation of frame,
buckling of each individual members in joint are need to be checked.
Cracks/defects shall be carefully checked.
6. Plastic stage of sections used should be checked by observing change in colour
and ductility of section.
7. Ultra sound pulse velocity (N.D.T.) should be done to assess the strength
cracks or defects in concrete. Concrete core may also be taken to assess the
compression strength of concrete by N.D.T. Cover meter test or hammer tests
may be carried out to assess the damage.
Rehabilitation of Head gear
After full condition assessment and structural audit of the head gear frame for all
points mentioned above scheme of rehabilitation and bringing back to original
condition shall be prepared. Scheme of retrofitting and rehabilitation will vary from
mine to mine. Broadly classified items rehabilitation are mentioned below :-
1) Retrofitting of members to maintain original stable configuration of structure.
2) Bringing back to original properties of materials and section by adding
additional structure member.
3) Replacement of bolts, welds, rivets and correcting the perfect alignment of
member.
4) For unstable head gear frame, deflection, physical movement is corrected.
5) Apply low diffusivity coating like epoxy to whole structure surface.
6) Grout, shotcrete, inject or jacket polymer concrete to strengthen the foundation
of head gear frame and fill up the cracks in the concrete.
The structural audit of head gear shall be carried out once in five year. I am sure
that in the interest of safety, all mining Companies shall take immediate action to
implement the above recommendations.
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