Modified Proctor compaction test 1

[Junkwisch]

Hi, this is my first year doing engineering site characteristic. I would like to ask a few questions in regard to modified proctor compaction test result.

For example, I have two test results.
12% @ 100lb/ft^3
and
15% @ 110lb/ft^3

What is the meaning of these numbers?

I assume that 100lb or 110lb/ft^3 are corresponding to the energy of the hammer. Is that correct?

Furthermore, what are the numbers 12% and 15% represent?
Is it the moisture content?

Best Regards
Junkwisch

 

[BigH]

Please read ASTM D688 and D1557 (or its D1556) - The test gives you an "optimum water content" (OMC) and a maximum dry density (MDD). Can also read Monahan 'Construction of Fills".

 

[Ron]

BigH is correct. Get a copy of ASTM D698 (Standard Proctor) and ASTM D1557 (Modified Proctor) and read them. The Proctor method, commonly used, was developed by R.R. Proctor in 1933.

The two values in each example you gave are the following:

12% @ 100 pcf ..... (Generally is written as 100pcf at 12%).....the 100 pcf is the maximum dry density as determined by the laboratory test. Since you asked about the modified Proctor, we'll presume that those values you gave are from a laboratory test using the modified Proctor method (ASTM D1557). The 12% is the optimum moisture content. These are determined from the peak of the laboratory curve.

These numbers are developed through the laboratory test. For most tests, 4 specimens of the same soil are compacted in volumetric molds with a known/calibrated volume. The test procedure starts with a dry soil and the only variable throughout the test sequence is to vary the moisture content of each specimen. As an example, moisture is added to the dry soil to start with a moisture content of around 8 to 10 percent. For the modified Proctor, the specimen is compacted in 5 layers with 25 blows of a 10 lb rammer in each layer. This defines the input compaction energy to the specimen. Each specimen is compacted the same way, only varying the moisture content as noted. The next specimen then has moisture added before compacting in an increment of about 1.5 to 2 percent, so this specimen might have a moisture content of, say, 10 to 12 percent. The same procedure is used through the 4 specimens.

For ease of comparison, we use the dry unit weight of the soil, not the wet unit weight in plotting our results. From these results a plot can be developed of dry unit weight in pcf vs. moisture content in percent. This results in the "Proctor Curve" as we typically know it.

The laboratory test (Proctor) is then used as the basis of comparison to field density tests or in-place density tests done at the site to determine the percent compaction for specification compliance. As an example, suppose your field density test shows that you have an in-place wet density of 103.6 pcf and a moisture content of 10.7 percent. The dry density of the soil in place is 103.6 /(1+moisture content) or 103.6/(1+0.107)=93.6 pcf. If you compare this to your example of 100 pcf @ 12%, then you have an in-place compaction of 93.6 or 94 percent.....just under a typical 95% compaction requirement. This tells you that you need to compact more.

We could go on and on about this concept. I am attaching a short summary of "How to Use a Proctor Curve". This is similar to the same concept found in the textbook "Principles and Practices of Commercial Construction", 9th Edition, Pearson Publishing.

 

[oldestguy]

The two poster members above are well experienced advisers and their advice is great. I would add that if you would explain more what your work position is and the type of supervision you have, we may be able to help more. Is this a student project? In other words, you may need a whole lot more help than reading how a test procedure is done and why. Is English your major language? The more we know about your situation, the better we can help.

 

[BigH]

The one item missing on my friend Ron's write-up (and graph) is the zero air voids curve (ZAV). None of the points of the test can lie on the right side of this curve AND in the field testing, no result can either. If it does, something is wrong. Hard to get field people to check even if you tell them time and time again.

 

[Ron]

BigH...agree completely! I spend at least one complete lecture on how to calculate the ZAV curve and how it is used in the lab and field.

 

[fattdad]

we don't know from the OP whether these are wet densities or dry densities. In light of the general nature of the OP, I'd hate to suggest s/he's looking at dry density.

The ZAV and the LOO are two items that deserve more attention then they're given!

f-d

ípapß gordo ainÆt no madre flaca!

 

[BigH]

Graph

 

[BigH]

Table

 

[oldestguy]

A lot can be learned by searching on Google for "U-tube Proctor Test". There are many videos there, including some for some on-line courses apparently.