LOZANO
Civil/Environmental
- Feb 11, 2008
- 3
Does anybody have experience with a 95 modified compaction?
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95 modified compaction.
- Thread starter LOZANO
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civilperson
Structural
Yes, a common spec for subgrade in runways and taxiways.
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- #3
You can get 95% compaction with any soil, really as the 100% is based on the material you are using. So you are comparing apples and apples - not your soil to another type of soil.
Just read an interesting article from some comparisons done on Texas soil in that 100% modified proctor was found to be equal to or better than 100% relative density (as determined by the relevant ASTM specs for min and max density). Mainly on SP soils, though.
Just read an interesting article from some comparisons done on Texas soil in that 100% modified proctor was found to be equal to or better than 100% relative density (as determined by the relevant ASTM specs for min and max density). Mainly on SP soils, though.
for silty soils here, 95% standard is easy for the most part @+3/-5% opt moisture...some crappy silts need +/-1or2% opt moisture. for 95% mod, it's about the same as trying to get 98% standard at +/-1or2% opt moisture...98% mod is on the order of 100+% standard at opt moisture. the soils here vary so much, i rarely see more than 98% standard spec'd except on DOT projects where it's 100% standard. i understand that other parts of the country have different "typical" specs due to the local soil types/conditions.
even at 98% standard here, i've seen the subgrade look like hell under a loaded tandem axle because the upper 6" or so shear and blow out all to heck under the tire loads....the last really bad project like this i can remember had a CBR=3 (the "heavy duty" section had 6" GAB and 3" AC...wasn't my spec and i'm sure the pavements are already torn up due to construction traffic).
even at 98% standard here, i've seen the subgrade look like hell under a loaded tandem axle because the upper 6" or so shear and blow out all to heck under the tire loads....the last really bad project like this i can remember had a CBR=3 (the "heavy duty" section had 6" GAB and 3" AC...wasn't my spec and i'm sure the pavements are already torn up due to construction traffic).
dirtscience
Geotechnical
Lozano, you can get 95% on ANY soil (even topsoil if someone is misguided enough to test it). But, like some of the posts suggest, this isn’t the whole story. Not even close. It doesn’t address soil STABILITY (rutting, etc.), an ‘adequate subgrade’, etc.
As some of the prior posts suggest, a Proctor test is first performed on the soil in question. During that test, the soil is compacted and (to simplify things) two main pieces of info are generated: 1) max. dry density, 2) the moisture content that the soil has to be at in order to attain this max. dry density (usually a range).
The contractor now has to compact the soil to 95% of the max. dry density; i.e. 95% of the Modified Proctor number. If the soil is too wet or too dry, you're out of luck and will have to either wet the soil down, or dry it out prior to compaction.
As some of the prior posts suggest, a Proctor test is first performed on the soil in question. During that test, the soil is compacted and (to simplify things) two main pieces of info are generated: 1) max. dry density, 2) the moisture content that the soil has to be at in order to attain this max. dry density (usually a range).
The contractor now has to compact the soil to 95% of the max. dry density; i.e. 95% of the Modified Proctor number. If the soil is too wet or too dry, you're out of luck and will have to either wet the soil down, or dry it out prior to compaction.
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Lozano: Obviously, yes, it would require some additional effort - perhaps one or more likely 2 additional passes and, depending on the material (i.e. sensitivity to moisture content - peak of curve), somewhat more attention to the placement moisture content.
yes. it makes perfect sense given that it takes less effort to get 80% compaction (sort of like driving a nail...one blow gets you a little ways in, two blows gets you farther...947 blows is probabably a lot of wasted energy). the more effort you put in (up to a certain point), the more beaten-together-hard the soil should be. if it's too wet or too dry of the optimum moisture, it won't get as hard. some materials require a few other "special" construction measures due to the inherent properties but i'll show restraint and not get side tracked too much farther.
the proctor is more or less a measure of the compaction effort put in to the material (via a standardized test). and based on how well the materials is compacted somewhere near "optimum" material conditions, other engineering properties can be extrapolated.
yes, i realize i'm long winded and get on a roll and off the question sometimes but discussing and understanding soils is a slippery slope...a seemingly simple question leads to answers that need additinoal discussion about other relative thing. soils are by far the most complicated "animal" i've dealt with and i'm still learning something new every single day i'm at work. okay okay..i'm making myself stop now.
the proctor is more or less a measure of the compaction effort put in to the material (via a standardized test). and based on how well the materials is compacted somewhere near "optimum" material conditions, other engineering properties can be extrapolated.
yes, i realize i'm long winded and get on a roll and off the question sometimes but discussing and understanding soils is a slippery slope...a seemingly simple question leads to answers that need additinoal discussion about other relative thing. soils are by far the most complicated "animal" i've dealt with and i'm still learning something new every single day i'm at work. okay okay..i'm making myself stop now.
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