Determination of Stockpile Volumes

Landair Surveys, ERIC BIRZULIS discusses how to determine the volume of stockpiles

MANY quarries request surveys at six monthly intervals to determine the volume of stockpiles. They request this information for auditing, stockpile management or valuation purposes.

Auditors can use the surveyed volume of the stockpiles to compare the tonnage of material going over the weighbridge compared to the tonnage of material being output from the plant. The tonnage of material being output may be determined using a conveyor belt scale or a weight belt feeder.

The difference between the tonnages shown at the weighbridge and the plant should be contained in the stockpiles. From the surveyed stockpile volumes, a tonnage may be calculated using the specific gravity of the material.

There are two methods that Landair Surveys uses to determine stockpile volumes; ground survey or aerial survey. The advantages and disadvantages of each method will be discussed below.

Ground Survey

Surveyors use special GPS receivers to measure the location and levels of the tops and toes of stockpiles and any other changes in grades. This data is recorded electronically to an accuracy of +/-20 millimeters and downloaded directly into survey software at the office. A 3D model of the stockpile is then prepared using the soft ware and a volume is determined. Ground surveying is possible in any weather conditions and at short notice, is more accurate than aerial surveying. Generally results are also available sooner. If there are many stockpiles to measure then the ground survey is time consuming.

Aerial Survey

Using an airplane, Landair Surveys take vertical overlapping photographs of the stockpiles. These overlapping photos are then brought into photogrammetric software and then 3D models of the stockpiles are prepared and volumes determined. Aerial surveying allows a snapshot of all a quarries stockpiles at a single instant and is an efficient method for stockpile measurement when there are many stockpiles or the quarry is remote.

Obtaining the best results

Both ground and aerial surveying produce the best results when the stockpiles are smooth. This is because fewer points are required to be measured and it is easier to prepare a 3D model of smooth surfaces.

It is also important to consider the ground surface that the stockpiles sit on. Obviously neither ground nor aerial surveying can measure the ground underneath a stockpile.

A smooth ground surface will allow accurate volume determination whereas if the ground beneath the stockpile is irregular or sits partly on a bench or against an irregular wall, surveyors will need to use a best estimate of what the ground is doing under the stockpile.

Landair Surveys has been performing a wide range of surveys for quarries since 1974 including volume surveys, royalty surveys, marking work authority and extraction limit boundaries, title re-establishments, subdivisions, borehole surveys, quarry mapping, quarry aerial photographs and feature and level surveys. Surveyors have undertaken the CMPA Work Safely training and hold Red Cards.

If you would like to find out more about the surveying services that we offer or have any questions please contact Erik Birzulis on 03 9887 2888 or erik@landair.com.au

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