September 19, 2017

Forestalling disaster

Slope failure

 At any given time, it is safe for open-pit mines to regard the risk of slope failure as high at all times. Thus, effective structured slope monitoring systems should be adopted as part of slope management. As the saying goes: “You can’t manage what you don’t know”, right information is point of the departure.   

It is easy to nonchalantly dismiss the significance of structured slope monitoring, not until one encounters harrowing statistics of rock fall accidents. Precisely, the severity of the problem on an African mine can be mirrored from an observation that South Africa’s Department of Mineral Resources made about the situation in the country which states: “The majority of accidents occurring at mines are a result of rockfalls, either seismically or gravitationally induced.” If that is not a crisis, then what it is?

Mariska de Lange, 3D Laser Mapping, a specialist from 3D Mapping in a paper she presented at the Geomatics Indaba early in 2015 Africa, The importance of structured slope monitoring in the mining industry, provides the background information which suggests that the occurrence of an accident on an open-pit mine is a matter of when and not if at all times.

Lamentably, with reference to the situation in South Africa, she notes: “Over the last few years the fatality rate pertaining to rockfall and rock burst-related accidents has reached a plateau and no real or meaningful improvement has been attained.” To say the least, this alarming fact implies that open pit mine is catastrophe-prone.

It’s a fallacy to claim that slope failure occurs without a warning, according to de Lange.  There is a scientific explanation behind each failure. In fact, more often than not, rockfalls could be or should be regarded as a harbinger of a larger slope failure. Slope failure may also be precipitated by environmental factor.  Ultimately, the buck stops with mines themselves.

Obligatory exercise

Fortunately, mines cannot do as they wish. Legislation obliges them to prioritise the working conditions of their employees. In South Africa, the Mine Health and Safety Act (MHSA): The MHSA, 1996 (Act No. 29 of 1996), provides for the protection of the health and safety of employees and other persons affected by the South African mining industry. If this is too general, then Section two of the Act is more explicit about the significance of mines taking bold action. It stresses that they should be equipped with effective systems to ensure safety. Thus, dealing with slope movement is a very critical safety aspect which mines have to deal with.

Monitoring in slope management

However, you can only manage what you know very well. Hence, de Lange underlines the importance of incorporating monitoring in slope management. She points out that, through slope monitoring a mine can detect potential unstable ground and assess the performance of slope design.

Through monitoring correct measures can be put into place to prevent major slope failures whose consequences can be too ghastly to contemplate. de Lange’s argument is that by gathering accurate data, risks can be mitigated, saving lives, loss of expensive capital equipment and (who knows even preventing the premature closure of a mine).

Moreover, structured monitoring can be an integral part of the slope design process, specifically ascertaining whether the behaviour of the designed structure is good and right.

Not an exact science

Empirical evidence indicates that accidents have still occurred in open-pit mines where supposedly “fail-safe” monitoring systems were applied. That’s why it has to be noted that slope monitoring is as effective as the quality of the systems utilised. This is the fact mines have consider.

It has to be acknowledged that there are no clear cut solutions for slope monitoring in open pit mines. All the more what makes a time-consuming exercise is that a number of objectives must be met, as de Lange points out. The main ones she cites are safety operational systems to protect personnel and equipment, provide vital geotechnical information, assessing the performance of the implemented slope design and determine the pattern of rock behaviour.

Effective solution?

Even a tried and tested product can underperform when not used properly, sometimes.  However, says holistic approach to slope monitoring would entail the use of right deformation monitoring in addition to geotechnical and surveying applications such as characterising rockfall, three dimensional (3D) rock mass structure and delineating features.

Monitoring made easy

Thankfully, increasingly used by mine surveyors and geotechnical engineers, slope monitoring software fills the gap. It identifies significant movement and report any potential areas of slope failure. In essence, it has eliminated guess work and costly defective estimations from slope monitoring.

A matter of urgency

While reading from statistics they might be a high probability of slope failure in South Africa, the situation in other African countries could be worse. What heightens the risk is that no information is available to measure the scale of slope failure disaster exposure. This makes structured slope monitoring a relevant intervention.

 

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