Is a Sieve Analysis Accurate?

If you regularly use Cone Penetration Testing on the job, you probably already know that there are a number of alternative soil testing methods out there. Some of the more common procedures include the Standard Penetration Test, which has been covered before in this blog, and the sieve analysis, also known as the gradation test.

Most commonly used in civil engineering, this basic soil testing method is used to assess the particle size distribution of soil and other granular material. 

But is sieve analysis accurate?

As is the case with Standard Penetration Testing, sieve analysis can provide accurate results, but only in the right conditions or scenarios. In fact, sieve analysis can achieve optimal accuracy only if certain conditions are met.

First off, sieve analysis needs a proper representative example of soil from the building site, meaning particles must be mixed well within the testing sample. The sample must also be of the right size, so it does not overload the sieve and skew the results.

In terms of equipment, sieve analysis requires:

• Test sieves that conform to relevant standards
• Reliable sieve shaker and analytical balance
• Error-free evaluation and documentation
• Proper cleaning and care of equipment, especially sieves

When these conditions are met, it is possible to get accurate and consistent results from sieve analysis, but only with coarse materials larger than #100 mesh. When it comes to finer materials smaller than #100 mesh, sieve analysis becomes less accurate.

The reason for this is the mechanical energy used to move particles through the dry sieve can compromise particle size. Fortunately, this can be offset somewhat with wet sieve analysis as long as the testing particles aren’t changed by the addition of water. Sieve testing is also less accurate for non-spherical particles as they may have trouble fitting through the mesh.

In other words, if you already know that you’re dealing with materials suited to sieve analysis, it is a fairly quick, easy, and cost-effective test to use.

However, it’s rare that you’ll already know what kind of soil you’ll be dealing with going into a new build site. This makes relying solely on sieve analysis an impractical course of action.

Fortunately, advanced soil testing methods that share none of the restrictions of sieve analysis, like Cone Penetration Testing, are readily available.