Volumetric surveys

DTM

Surveying loose material properly is not just a case of wandering around on top of it pressing the button from time to time. The type of material and its physical properties need to be considered. Is the surface loose but then compacted at a few centimetres depth? Is it likely to form voids within the body?. Is there a record of the shape of the ground on which it has been placed and might the material have compressed into that surface? The unit value of the material is also a factor, as this will determine how accurately the survey needs to be conducted. For high value material, it may be worth shaping up the stockheaps, prior to survey, to create a regular surface which will make accurate measurement easier.

One aspect often neglected is when to measure. There may not always be a choice; often it is a case of "here is the material". However, if the material is being dug out and stored, then there is the option of measuring the hole dug or the heap made. It is normally quicker and cheaper to measure the heap BUT the hole dug represents the actual amount of material, whereas the heap may not be well compacted and have many air voids. Thus the heap volume can be up to ten percent greater than the hole it came from: for an unscrupulous earthworks contractor, this is a nice bonus.

Heaps do settle, of course, especially if they were not well compacted when first built. It can be expected that a heap which has stood for some years untouched, apart from the rain washing material off, will have less volume than when first placed. The washed off material, together with spillage which occured when the material was first placed may have a significant value, as may any material placed as a base to level the ground before the heap was first built. This "carpet" material may need to be recorded separately as the value will probably be lower (the material is likely to have some contamination and may need treatment if it is to be used).