The Nuclear Density Gauge

When building structures and roads the soil must be compacted to an appropriate level.  One tool that is commonly used to determine how well the soil has been compacted is the nuclear density gage.  The nuclear density gauge is one of the top picks for many of the firms that do geotechnical work because it is a machine that can deliver fast and accurate results.

Aside from the nuclear density gauge, there are a few other methods of measuring the soil’s level of compaction, some of which would be a balloon test as well as a sand cone test.  On most job sites the nuclear density gauge is used because of its simplicity and speed at which results may be obtain.  While using a nuclear density gauge results can be recorded in minutes and reported to the contractor at the job site.   In comparison, the sand cone and balloon tests can take up to a day to calculate the results.

http://www.naturalbuildingblog.com/proctor-soil-compaction-test/

 Before any of these tests may be used, one must first sample the soil and conduct a proctor test on it.  A proctor test is hitting the soil with a hammer multiple times at different water contents.  The varying soils at different water contents are then dried and weighed.  From this data a curve is constructed to find the maximum compaction of the soil.  The maximum compaction found in the lab is then compared to the compaction results that the nuclear density gauge found in the field to determine the relative compaction percentage.  This comparison informs the contractor if they need to add more water or if they need to take the water out of the soil to compact the soil to the required compaction percentage. 

http://www.fhwa.dot.gov/engineering/geotech/pubs/05037/08.cfm

The nuclear gauge is a very simple machine to use.  However, it does use radiation to obtain its results and should be handled with extreme care.  Due to the radiation that is used in this machine, one must go through a training to become certified to use the nuclear density gauge.  The two main sources of radiation that the nuclear density gauge uses are cesium-137 and americium-241.  Before using the nuclear density gauge one must calibrate it daily to the correct setting to ensure that it is working properly before going out to the job site.  The first step of using the nuclear density gauge to measure the compaction of the soil is to prepare a hole by using a hammer and a spike or just simply a slide hammer.  After the hole has been made, you can simply slide the rod on the nuclear density gauge into the hole exposing the cesium-137 into the soil.  After the machine is started the cesium-137 sends out waves of gamma radiation that are then collected by the detectors on the bottom of the gauge.  The americium-241 is used to find the moisture by calculating the dry density and wet density.  The gauge then calculates and displays relevant values such as the dry density of the soil, wet density of the soil, compaction of the soil, and the amount of water in the soil.

https://rmcmed.com/2012/08/31/radiation/

To get an idea of how much radiation a gauge produces, individuals operating the gauge are required to wear a badge that detects the radiation.  The maximum radiation that one person can have in a given year is 5000mREM.  Upon completion of my job, I submitted badge and testing showed that I had less than 50mREM in 6 months.  This shows that if the nuclear density gauge is used properly it is a very safe machine.

Like any machine there are good and bad things about the nuclear density gauge.  The best thing about the nuclear density gauge is the speed at which it works.  If the proctor has already been finished back in the lab the soil compaction results can be calculated in under a minute.  It is also very easy to use once trained properly on the dangers of the radiation.  However, it is rather heavy, being around 40lbs, and the extensive training that is required to handle this device may turn some people away.  Also, this machine will not work during the rain do to the americium-241.  Another downside of this gauge is the overall cost.  The machine is expensive and all the paperwork that is required for it is also quite expensive.    Overall, I would highly recommend this machine to anyone in the field since its pros outweigh its cons.  On a scale of one to five I would give the nuclear density gauge a four.

For more information please look at the following link.
http://www.apnga.com/i_gauge_basics.html