Quantifying Moisture Sensitivity of a Soil During Compaction

[ih8xc]

I'm looking for a method to quantify the sensitivity of a soil to changes in moisture content during compaction. Where I work a wide variety of soil types are used for bulk filling, but predominantly they are clean granular soils or they are silt to sandy silt tills. During the wet season we have problems reaching compaction with the silts due to high moisture and the inability to dry it out. Since most of our clients, and some of the contractors, are clueless when it comes to the environmental constraints of using these types of materials from borrow sites as bulk fill, I would like to be able to apply a moisture sensitivity value to our structural fill criteria. This way there is a very clearly defined requirement or warning with regards to the use of this material.

My initial thought was to determine the rate of change of the slope of the proctor curve. Basically, apply a 3rd order polynomial trendline to the data, derive to find slope, derive again to find rate of change of slope, and calculate a value at the optimum moisture content. Alternatively, I could determine the portion of the proctor curve above the compaction criteria (95 or 98%) and determine the moisture content range of that portion of the curve (say 9%, 6 below and 3 above optimum).

I'm wondering if there is a standard way of doing this, or if others have found an effective way to quantify the moisture sensitivity.

 

[fattdad]

an upside down V or an upside down U.

do folks actually know which soil in the field belongs to which proctor curve from the lab (i.e., how often are one-point compaction tests run on soils from the field and how often do folks prepare a project specific family of curves (so tired of the Ohio version. . . )?

enjoy your journey.

f-d

ípapß gordo ainÆt no madre flaca!

 

[ih8xc]

Not really sure what you mean by upside-down V or U. We don't do single point proctors; all have a minimum of 4 points and we typically repeat every 1000 m[sup]3[/sup] or so.

 

[Ron]

ih8xc...don't try to complicate the issue. Look at the Proctor curve and the slope on either side of optimum. If steep and within about 2% of optimum on either side when you draw a horizontal line through the curve at the minimum acceptable compaction (usually 95% or above), the material is fairly moisture sensitive.

You should run a new Proctor when you notice or suspect a material change.

 

[darthsoilsguy2]

Not sure about advanced math, but if one specifies import fills to meet USCS classes usually specified and all on-site structural fill materials to have a minimum ASTM D698 Max Dry Density of 95 PCF, it weeds out a lot of the violent offenders.

 

[JMackNH]

I've worked on projects where there is not only a compaction specification (95%), but also a moisture specification. This is typically +/- 2% of the optimum moisture. It is very helpful when placing siltier material, which can sometimes give you passing compaction results, but is pumping, weaving or showing other signs of instability. The +/- value could be customized to the individual Proctor curves, as well.

 

[Aduliat]

ihxc, I think you are over-complicating it. As far us you are talking about the same dirt, check your moisture (+/-2%) and your compaction. If it is beyond OMC+2%, you are obviously going to have difficulty to compact it. So, you do not want to create a new equation to check moisture sensitivity.