Introduction

In today's agriculture markets, a number of existing & other more temporary warehouses are being turned into grain storages. In parallel with this is range of financing mechanisms now available to producers, processors & transporters of grain. To provide some level of comfort to financiers & audit houses, SigmaCubed has developed an audit process that establishes the suitability of storages to manage inherent risks in warehousing commodities. Additionally, quantities of stock-on-hand can be accurately determined to ensure balances on books meet with expectations in regard to the quantity of stock financed.

Vertical storages (Silos)

For silos, irrespective of construction material, the dimensions (Height, Diameter, Hopper Volumes etc.) are required and should be supplied by the storage owner or operator. If these dimensions are not known, access to the engineers working diagrams from construction may assist. Failing this, the dimensions need to be measured on-site at the time of stock take for each storage type. Even if the dimensions have been supplied, it is a good cross-check to re-measure some at the time of stock take.

The following points provide the basis for and some pointers as to what measurements need to be made.

• Firstly, access is needed to the site layout, getting an overview of the commodity layout in the respective stores on site. A photocopy of this will layout should be obtained and reference made to it prior to measuring each storage.
• Once a plan as to the order storages will be measured, access is needed to the top of the storage. There is a hatch at the top of each bin whether it is at the side or along the roof. For some older concrete silos, access is made internally up a ladder or, in some cases, a one-man lift. Note the following:
  • OH&S regulations will require the use of a harness.
  • Older stores may not have these safety instruments in-built.
• Drop a calibrated tape, fitted with a small sample bucket, from the access point & record the measurement to the grain. Note the following:
  • The grain configuration. THIS IS CRITICAL
  • When the tape is removed, check the sample bucket & note the commodity against the silo plan provided by the storage owner.
• There a number of potential configurations which will need to be accounted for to ensure accurate results are achieved. The most commonly seen scenarios are as follows, along with some points of note:

Horizontal storages – Sheds

At the highest level, sheds & bunkers are simply masses of grain which (generally) conform to known geometric shapes. This allows ready measurement & calculation of the volume(s) contained therein. With sheds, the grain mass can be readily broken down into 3-dimensional arrangements of known (measured) widths, lengths, & heights. Similar to silos, the storage owner/operator should have these dimensions to hand or the engineers' working plans too. Save for this, the storage can be measured on-site at the time of stock take. To assist, when the shed needs to be measured on-site, the following points may be of use.

Storages with little/no product segregation:

• The minimum number of bays across the shed's width should be 4.
  1. Side wall to Roof Reference Point at ¼ of the shed's breadth.
  2. Catwalk, immediately above the grain's tripping point. This will be the high point of the grain bulk.
  3. Roof Reference Point at ¾ breadth to side wall.
• Ideally, the number of bays should be 6
  • Same reference points for 4 bays but additionally includes the points immediately either side of the peak
  • This accounts for where most significant change in the grain's slope occurs.
  • The bay widths & lengths should be measured & recorded.
  • The heights to the reference points from the floor or points of known height should also be measured & recorded.
  • See below for example.
• Once the shed has been gridded & heights to the reference points checked or determined the measurement can begin.
  1. The best way to measure the storage is with a team of 3 surveyors, one on each wall & one on the catwalk.
  2. Moving along the storage length, the measurements will be the displacement between the grain surface & the reference points at each grid point. Ideally, the catwalk surveyor should be the recorder. Once a measurement is announced, the recorder should repeat this value back to the surveyor for confirmation.
  3. Repeat this process moving along the shed's length.
  4. An example of a raw data recording sheet is provided below for reference.
• Once the measurement is complete, determining the total grain volume can proceed. First, calculate the volume of each bay and then sum them all to give the total. (n.b. bay volume is the bay area (bay width × bay length) × arithmetic mean height of the four bay ordinates.)

For storages with product segregation:

• Measure & record the width & depth of each bay using a calibrated tape or laser distance gauge.
  1. Ascertain the simplest form for the product in each bay. (See examples below)
  2. Make the minimum number of measurements to describe the shape being assessed.
  3. The formulae to calculate the volume of the mass are provided in each example.
  4. Multiply the calculated volume by the density (test weight) of the product to estimate the actual mass.

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Horizontal storages – Bunkers

The use of and the technology behind successful storage of grain in bunkers has progressed markedly in a relatively short period of time. Now grain can be stored in the open under tarpaulin covers both safely & professionally. The volumetric assessment of bunkers, whilst similar to that of grain in a shed, has the obvious problem in the lack of reference points against which to make & compare measurements.

There are a number of ways to determine the heights of the grain at each reference point.

1. Total Station Approach with mapping software.
   • A total station or TST (total station theodolite) is an electronic/optical instrument used in modern surveying and building construction. The total station is an electronic theodolite (transit) integrated with an electronic distance measurement (EDM) to read slope distances from the instrument to a particular point, and an on-board computer to collect data and perform advanced coordinate based calculations.
   • Robotic total stations allow the operator to control the instrument from a distance via remote control. This eliminates the need for an assistant staff member as the operator holds the reflector and controls the total station from the observed point.
   • With this approach, the storage does need to be gridded as the station does the mapping electronically.
   • Advantages of this approach is the precision achieved in the measurements.
   • Disadvantages of this approach are the need for highly trained operators and with the capital cost of the equipment utilised the daily rates for surveyors is very high.
2. Hand-held lasers with mapping software.
   • Similar to total station with a lower manday rates given the less expensive instrumentation.
   • Provides topographical 3D survey & highly accurate volumetric assessment.
   • Can be performed safely with a single operator.
   • SigmaCubed offers this service at highly competitive rates.
3. Calibrated Angle finders to allow trigonometric calculation of heights.