There are many ways error can be introduced when calculating product stockpile volumes at a quarry or mine site. Even so, the amount of error can be reduced by:

• applying proper stockpile management techniques,
• ensuring adequate ground control placement, surrounding and within the stockpile floor area both before surveying and before stock placement,
• undertaking high-quality aerial surveys of the stockpile floor, and
• applying appropriate volumetric calculation methodologies.

The simplest and most effective way to reconcile a stockpile volume is to build it on a horizontal floor. Each stockpile should be constructed discretely, open on all sides with a clearly defined toe. It should be free of vegetation growth both on its surface and overhanging its position. Although this is not always possible to achieve, it should be considered the gold standard for stock management.

When stock is stored in a bin area, the floor should be made from a hard material. The bin should have solid and straight vertical walls. This enables machinery to recover as much material as possible from along the inside edge of the bin.  Moreover, the boundary is unambiguous when defining the limits for the volume calculation.

Floors on which stockpiles are constructed should be as planar as possible.  Volumes calculated from consistently oriented floors reconcile far better than floors with an undulating or complex form. Get ground control markings installed in floors before placement. Also, undertake benchmark surveying to have a known base across the floor. The base will change over time.

Have operators plane the stock floor in preparation of receiving stock. This leads to greater recovery of product when later retrieved. It also avoids contamination across the contact zone between floor and stockpile.

Furthermore, make sure the stockpile is discrete and doesn’t come into contact with other loose materials around its limit. This avoids cross-contamination with adjacent products or non-stock material. If adjacent piles join, they will typically grow at different rates. This can develop a wide zone of cross contamination along the boundary. 

Techniques are available for determining volumes in conjoined stockpiles. This also applies to stockpiles that abut a bund wall. Nevertheless, they typically are at best approximations of the actual retrievable amount located on the ground. 

Avoid placing tyres or blocks directly into the pile upon which product description plates are then installed. They introduce error into volume calculations if not appropriately edited out or accounted for.

Sweeping the toe up of a stockpile before surveying provides greater opportunity to clearly define the floor and stockpile interface. This is especially crucial for smaller PSD (particle size distribution) materials. These materials achieve a lower angle of repose more quickly than coarser PSD material. Sand and dust sized materials can easily spread out away from the main stockpile area. This spreading results in lost recovery and increases the floor height. Consider applying a colored gradient map over the stockpile area when defining stock boundaries. This technique ensures that the stockpile toe can be clearly discerned from the surrounding floor.

Placing ground leveled control pads in the stockpile floor area provides observable references for QAQC. These references are useful when undertaking survey reconciliation. They are also beneficial during operational activities. Stock loss into floors is common as product material spreads during placement and retrieval. The true base of a pile is often not fully retrieved. Over time, incremental material gains occur on the floor. These gains should be regularly graded out, thereby recovering this lost material.

To obtain the most precise volume for stock on ground surveys are required before and post stock placement. When floors are planar and stockpiles are discrete from other features, the pre-placement survey is no longer necessary. Nonetheless, for conjoined materials, dual surveys are needed. Without them, material is often cookie cut in the intermix area. This error introduces inaccuracies into reporting. The amount of error can be highly variable and dependent upon whether one or both parts are active. Assignment of reference surfaces in the volume calculation are an established method of dealing with more complex volume calculations.

Another matter requires regular maintenance. This is particularly true for materials stored for a longer period. It involves keeping their surface free of vegetation. Road base and dust stocks are more likely to have vegetation grow on their surface. This occurs when they are stored for some time. Keeping stockpiles free of vegetation prevents the introduction of contamination of organic material into the stockpile. It also reduces over reporting error in volume calculations.

A considered traffic management plan should be integrated into the placement of materials within the stock area. This approach can reap benefits for stock volume reconciliation.

Remember that reconciliation of tonnage for stock volumes encompasses more than just the factors influencing volume. Extra factors like bulk density and moisture content will come into play.

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