I’ve written before about construction work and quality assurance/quality control. When we do material testing for construction (whether it is earthwork, rock, aggregate, concrete, geosynthetics or whatever), we usually “sample” a small portion of material that is involved in the overall work. For example, when using a nuclear density meter, the test only involves about as much soil as you could fit in a coffee can (is a coffee can even still a good reference for a volume?)
So, how do we extrapolate this coffee can sized sample out to represent an area the size of a Walmart store? If we have enough of these data points, can we apply the method of kriging? Wait, what’s kriging? According to Wikipedia (https://en.wikipedia.org/wiki/Kriging), “kriging is a method of interpolation for which the interpolated values are modeled by a Gaussian process governed by prior covariances. Under suitable assumptions on the priors, kriging gives the best linear unbiased prediction of the intermediate values”. Okay, that doesn’t help. Kriging techniques are used by people who estimate the amount of mineral reserves in ore bodies. Kriging isn’t just a method of averaging. Kriging is a interpolation technique that takes into consideration the distance and the degree of variation between known data points (ref: https://www.sciencedirect.com/topics/earth-and-planetary-sciences/kriging). Well, that sounds awesome! Surely, that would be a useful tool?
Nope! We have something even better! What is it? Observation! Yup, pure and simple observation. But Bryan, how is observation better than math and science? Kriging is used for everything from real estate appraisal to astronomy. It must be the way to go! Nope. It’s our eyes and intellect that win out. How? Well, we have to watch. We watch and see whether the area tested has received the same treatment as the area that it is to represent. How many times did the compactor drive over this area? Was it the same throughout? How about the water truck and all the other vehicles? Is the material consistent over this entire area? Is the area being tested consistent enough that the test is truly representative? We can really know this best through observation.
The eyes and the mind are sometimes the most powerful engineering tools we have. Next time you’re on a construction project, go outside and observe!