This is a question we get pretty frequently from our clients in Calgary. A lot of our clients don’t know what is meant by 98% compaction, just that they need the geotechnical technician with a nuclear gauge to tell them they’re at 98%.
This explanation is true for other levels of compaction as well, so questions like “what is 95% compaction” are answered in just the same way.
98% Compaction is Just A Percentage
Setting up a typical scenario is a good way to explain this. Imagine you’ve just packed a lift, and the technician is testing the soil. He hammers the pin, fiddles around on his nuclear gauge, then tells you that the soil is at 95% compaction.
What just happened? What did the machine do?
All the gauge did was compare the density of the soil that was just packed to a maximum density the technician entered into the gauge before the test. It’s telling the geotechnical tester that the soil that was just tested is at 95% of the theoretical maximum density the soil can reasonably achieve.
How Does Factor Determine the Maximum Theoretical Density?
The maximum density used in nuclear gauges for compaction testing is determined in our geotechnical laboratory, using a Proctor lab test, usually just called a “Proctor” when discussing compaction onsite. The Proctor is the maximum density for the soil at its optimum moisture content.
The Proctor test is a simple test. It consists of simply ramming three layers of soil into a cylinder with equal numbers of blows each layer. This is done on 4 different cylinders at different moisture contents, which are then dried and weighed.
After each of the four samples are weighed, the one with the highest density is the Proctor density. (we actually graph the points and determine the maximum density using a best fit line, but this explanation is close enough)
The Proctor test is critical to perform in advance of field testing, otherwise, field results are essentially meaningless as there is nothing for the technician to compare his results to.
What Is The Difference Between 95% Compaction and 98% Compaction?
You probably already know what the difference is after we’ve gone through it above, but here’s another way to look at it, just in case we did a bad job of explaining.
95% compaction is just 95% of the Proctor density, whereas 98% compaction is 98% of the Proctor density.
If the Proctor density is 100 (let’s ignore units here), and the percent compaction is 95, that means that the soil that was just packed has a density of 95. 95/100 = 95% = 95% compaction! Same for 98%. 98/100 = 98% = 98% compaction.
Conclusion
I hope this article helped you with understanding what 98% compaction refers to. If you need geotechnical soil testing in Calgary or its surrounding areas, please contact us and we’ll be happy to help.
