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Thursday, March 20, 2014

The Science of Transportation: Sieve Analysis



You might think that highway construction is all about big machinery, heavy-duty vehicles, massive structures and materials by the ton – but it’s not.

Sure, those are important, but when it comes to building a road, science plays a strong role too. In fact, the work ADOT does off the project site and inside a lab is so significant that we are highlighting it here on the blog with a new series we’re calling, The Science of Transportation.

We’ll start today with a look into one of the methods used by ADOT to analyze soil samples.

The sieve analysis test, as you can see in the video above, is a way for technicians to create a profile of the sample’s size properties. That profile, in conjunction with other test results, is used to classify the soil – something that is useful for geotechnical engineers, road designers and construction crews.

This test is fairly straightforward.

First, the technician must prepare the sample by drying it and making sure there aren’t any clumps in the material. They weigh it at this point, too.

Next, the sample is screened through a series of sieves. The test starts with a very coarse sieve, and continues with sieves that get finer and finer. The ADOT technician records the weight of the material retained by each sieve.

You can see in the video that a (loud) mechanical shaker is used to move the material through the sieves.

When it gets down to the very, very fine material, technicians will need to split the sample, dry it, weigh it, wash and dry it again before continuing on to the next set of sieves. The screens on these sieves have very small openings that let only the smallest particles through.

Once all the material from the sample has been sieved, the sum of the individual weight of the material from each sieve is compared to the weight of the entire sample that was taken prior to sieving. If the difference between the two weights is more than 1 percent, the sample must be recombined and the sieving process would start all over again.

All of the information is recorded to provide a profile of the material’s size properties.  

So, why does ADOT (and other transportation agencies) go to such lengths just to determine the size of the soil particles?

Transportation Tech John Miller sums it up best in the video above…

“You need to know what type of material you’re building on,” says Miller adding that it could be a heavy clay or sand – two soils that behave differently from each other. “It’s very important to run this test.”

For more on the Soils and Aggregate group, visit the ADOT website. Be sure to stay tuned to the blog ... in the coming months, we'll be featuring more of the tests this group performs.
Posted by Angela DeWelles   |  Labels:  Geotech, Materials-Testing, Science-of-Transportation, Soil-and-Aggregate-Lab, Video
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