Maximum soil compaction.
Maximum soil compaction.
(OP)
I just have recieved a report of soil compaction test performed on a project I am working on. Two test report relative compaction of 106 and 111 percent. The geotechnical engineering firm used a Standard proctor to find the maximum dry density. The test were taken in sp soils with optimum moisture of 9.7 percent. The inplace moisture content was 4 percent. I feel that the numbers may be wrong, or a different proctor needs to be used. I seem to remember from my geotech classes( my memory may be a little fuzzy) that the maximum field density could only be 104.5 to 105 percent of laboratory desity. Should i be concerned. These test are under the building pad and in fill material used to correct poor soils.





RE: Maximum soil compaction.
I would question the 9.7% optimum in an SP material. That doesn't fit either. For a Standard Proctor, the optimum moisture in an SP material is typically higher than for the same material under a Modified Proctor.
The Standard Proctor shouldn't have been used here. Even if specified by an ill-informed Civil Engineer or Architect, the testing laboratory/Geotechnical Engineer should have questioned it.
RE: Maximum soil compaction.
I have looked back at other test results and several 105% test results were reported.
RE: Maximum soil compaction.
Around a compaction curve for a material, there are three zones which are likely to cause failure of the compacted material. Too wet (i.e. bottom right of the compaction graph) and a cohesive soil can suffer long-term settlemt due to consolidation of the material and a loss of water. Too dry and this can result in overcompaction leading to swelling (cohesive soils with very low air voids, upper left hand corner of graph), or too much air causing collapse failure due to inundation of water (bottom left of curve. It sounds very likely that the wrong compactive effort was used to identify the maximum dry density, as you have achieved a 'relatively' high compaction at completly the wrong moisture. If when you re-test the material (with an increased compactive effort), please be sure to assess the previous results in light of the possibility of collapse failure.
I would also suggest that you detemine the particle density (specific gravity in old money), and calcualte the air voids of the previous tests and plot the air void line on the compaction curves.
Geotechnical fill, using cohesive soils, for under a building should be between 100% of the standard proctor to 100% of the modified proctor with 0 to 5% air voids, based on current guidance in the UK.
RE: Maximum soil compaction.
You have a condition that might cause the value to go a bit higher, simply because you have standard proctor in a clean fine sand (SP). With good compactive effort (vibratory compaction at or near optimum moisture), you can get good compaction. Again, the moisture contents look out of whack. You are right to question these results.
RE: Maximum soil compaction.
RE: Maximum soil compaction.
Eris Uygar
RE: Maximum soil compaction.
D = (1-Pc)Df + 0.9 PcDc
where:
D = adjusted max density (Mg/m³)
Pc = proportion by weight of coarse particles removed
Df = max dry density of the fine material
Dc = particle density of the removed coarse material (Mg/m³)
I have used this in the past, and wrote my dissertation on this subject when I did my Degree in Civil Engineering.
However, it still comes back to the actual moisture content of the material determined in-situ, what will be the effect on the placed and compacted material if it becomes inundated?
RE: Maximum soil compaction.
Eris Uygar
RE: Maximum soil compaction.
Also be sure the person doing the insitu testing is doing it correctly. for nukes that means scraping and leveling the base and driving the pin.
Good Luck
RE: Maximum soil compaction.
The other possible scenario is that if a large boulder is near the gauge, you would also get lower moisture and higher dry density.