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What is Hydrometer Analysis Testing?

By December 6, 2023No Comments3 min read

Hydrometer analysis testing is one of the services offered by Encorus’ civil testing group. This procedure measures the particle-size distribution of fine-grained soils to ensure the integrity of subject materials.  Particle size is important in determining whether a soil is suitable for a particular application Particle size influences numerous soil characteristics, including permeability, compatibility, drainage, erosion resistance, and shear strength.

How do you perform hydrometer analysis testing?

Hydrometer analysis testing begins with obtaining a sample of soil material from the construction site or subject area. The soil sample is passed through a sieve to ensure that it is the appropriate size for the test. This material is placed into a cylindrical container along with a fluid mixture to suspend the particles within the container. The mixture is then agitated using  an agitation machine and the tipping method, which involves placing a rubber stopper in the opening of the cylinder to prevent any leaks, and then turning the entire cylinder upside down and then back for a period of time.

After the sample mixture has been agitated, it is placed on a flat, stationary surface so that the contained material can be measured using a hydrometer. The hydrometer measures the position of the soil particles within the fluid suspension at a specific time. Hydrometer measurements should be taken and recorded at 1, 2, 4, 15, 30, 60, 240, and 1440 minutes.

The readings from the hydrometer are plotted to create a gradation curve, which sorts the particles by size in both time and position as they settle to the bottom of the container. According to Stokes’ Law, larger particles will fall through a fluid faster than smaller particles. Calculations are performed based on the gradation curve and other factors to determine the particle size distribution of the sample soil material.

The resulting particle size distribution calculation can be used to help determine other engineering properties at the construction site, such as hydraulic conductivity, compressibility, and shear strength.

Who performs hydrometer analysis testing, and where?

Hydrometer analysis testing is typically performed by geotechnical engineers, soil scientists or technicians in laboratories that specialize in soil testing. These professionals have the expertise and equipment required to accurately perform these tests and interpret the results. Once soil samples are collected from the site, the testing is usually performed in a laboratory setting rather than on-site because it involves precise measurements and controlled conditions.  In some cases, specific laboratory standards or quality control certifications may be required to perform hydrometer analysis testing.

What situations is hydrometer analysis testing used in?

Since hydrometer analysis testing is commonly used in numerous applications related to soil mechanics, geotechnical engineering, and construction, the are many situations where it is valuable. A few of these include foundation design, road and pavement design, land-use planning, and earthwork in construction. In these situations, if hydrometer analysis testing is not performed, or not done properly, it can lead to problems such as compliance issues, inefficient drainage, foundation design issues, and poor construction quality.