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SIMM Structural inspection and maintenance management of mining structures

By Spencer Erling,
Education Director, SAISC

BACKGROUND AND LEGAL REQUIREMENTS
Engineers should be aware of the legal requirement contained in the Occupational Health and Safety Act 1993 and subsequent amendment GNR.1010 of 18 July 2003: Construction Regulations, 2003 which states in Chapter 9’s subclauses:

“(4) Any owner of a structure shall ensure that inspections of that structure upon completion are carried out periodically by competent persons in order to render the structure safe for continued use: Provided that the inspections are carried out at least once every six months for the first two years and thereafter yearly and records of such inspections are kept and made available to an inspector upon request.

(5) Any owner of a structure shall ensure that the structure upon completion is maintained in such a manner that the structure remains safe for continued use and such maintenance records shall be kept and made available to an inspector upon request.”

The Mine Health and Safety Act and Regulations (Act 29/1996) covers regulations regarding appointment of managers to inspect mining structures. At the first SMMH Conference in 2009 Peter Gage presented a paper on a spreadsheet based methodology for doing such inspections.

THE SIMM METHOD
The SIMM method takes these concepts a lot further and categorises various degrees of deterioration and their ‘structural’ importance. In Anglo American’s and other Mining companies’ who have adopted this technology, reporting methods and methods to ensure safety critical items are attended to are also covered.

This article will concentrate on the inspection and risk assesment as to the degree of degradation and its implication for structural safety (as envisaged by construction regulations).

WHAT ARE THE FUNCTIONAL REQUIREMENTS?
Functional requirements are split into six main groupings:
1. Safety
a. Any collapse has potential for serious injury or death
b. Hand railing and flooring prevent falls
c. Barriers to keep people away from vehicles                                                   

2. Strength
a. To prevent collapse
3. Stiffness
a. To limit deflections
b. To provide confidence (i.e. eliminate perceptions of whippy structures that might otherwise be strong enough for its purpose)
c. Enable equipment functionality

4. Vibration
a. To prevent vibration related injury
b. To prevent fatigue damage and failure                                                                                                                                              c. To enable equipment to function properly

5. Liquid retention and containing materials
a. Primary requirements for tanks
b. Bunds to contain spills
c. Storage, separation and movement of minerals

6. Other
a. Fire barriers
b. River crossings
c. Storm water culverts

PREPARING FOR A SIMM INSPECTION
Section 5 of SIMM goes into the preparation that may be necessary to enable the inspector to properly and safely carry out his duties and covers aspects such as:
1. Risk assessment to cover
a. The tasks
b. Access (safe working at heights or in confined spaces)
c. Tools

2. Safety induction and training of inspection personnel

3. Time and personnel allocations for
a. Shut down requirements
b. Knowledgable personnel to accompany the structural engineer who may be a visitor
c. Effect of any NDT inspection that may be required

4. Access, lighting and visibility
a. What cannot be seen cannot be inspected
b. Clear up the site/structure of dirt and spillage
c. Is inspection of bins and silos required from the inside and outside and how can this be achieved without emptying the whole system?

CHAPTER 6 OF SIMM PROVES TO BE THE NUB OF THE ISSUE – CONDITION CATEGORY REQUIREMENTS
a. Quantify deterioration adequately and avoid vague descriptions
b. Give consistency in reporting for accurate communication
c. Definitive descriptions should be simple to remember and to use
i. Too few categories leads to loss of defintion.
ii. Too many categories are difficult to remember and create complexity in the ‘what to do decisions’.
SIMM uses the following guidelines as shown in Table 1: The interpretation of the numbering system is easy:
1 & 2 means everything is still good and everyone is happy
3 & 4 means it is time to plan, budget and to do something
5 & 6 means we are out of time, find the money, do it now!

HOW TO REPAIR IT?
First prize would be a repair and weld procedure etc. drawn up by a qualified person. But only too often the urgency of the repair just does not provide for such niceties.

SIMM gives a few very basic repair guidelines that almost any trained boilermaker can safely carry out (see figure 1).

You will notice that no attempt is made to cut out the deteriaration, which could of course lead to collapse but rather to ‘strengthen from outside’ to unsafe areas.

Patches welded on from the outside being the order of the day.

SIMM CHAPTER 9 – WHAT KIND OF CONDITIONS CAN LEAD TO DETERIORATION?
1. Corrosion of steel and reinforcing
a. Various examples of steel corrosion were shown from a good condition (0) to appaling condition (5) in steelwork
b. The phenomenon of rusting reinforcing steel inside concrete that upon expansion and exfoliation causes spalling of concrete. Once again photos supported the descriptions.                                                                                 

2. Cracking examples (once again extensive photos of examples were shown to illustrate the six conditions)
a. Fatigue (cyclical loaing) cracking
b. Shrinkage of concrete during curing (this also applies to timber drying out)
c. Bursting as described under 1b above
d. Impact damage

3. Structural damage caused by
a. Falling objetcs
b. Vehicle impact
c. Pressure from groud or foundation movements

4. Wear of steel or concrete
a. From flow of materials
b. In chutes and hoppers
c. Around feed and discharge points of silos and bins
d. Elbows in pipes

5. Connections in steel and timber
a. Loosening of bolts due to
i. Vibration
ii. Poor original installation and/or tightening

6. Rotting and biological attack of timber
a. Drying out
b. Termites
c. Other boring insects
d. Burrowing animals

7. Chemical attack in concrete
a. Chlorides and salts attacking the mortar bonding
b. Exposes the aggregate causing loosening
c. Penetration of oxygen and other gasses follow
d. Corrosion of the reinforcing results

8. Last but definitely not least – Modifications
and cut-outs
Inappropriate modifications, cut-outs for
…pipe access or other purpose
…has a great potential to reduce the strength of structures
…often found in steel structures.

Change is easy… Management of change is not. This is critical to the life of our structures.

IN CONCLUSION
Just the extent of inspection required in deteriorating structures can be large. This makes the process difficult and often quite tedious and laborious.

The SIMM method has created a systematic approach by the the standardisation of degrees of deterioration associated with the different causes of deterioration. The result is that items requiring urgent attention can and are identified so remedial steps can be put into place quickly.

This does not reduce the effort that is required to do this important job properly. It certainly does take the ‘hit and miss’ out of the process, eliminates broad sweeping statements that have lead to drama in the past.