Caliche Use for Road Aggregate

[wijgeng]

Hi,

Does anyone have any experience on using Caliche for a road base material? Our contractor is proposing the use of this material, but we (as the owners of the project) are not familiar with it.

The project is in the pan handle of Texas and our company is based out of Minneapolis, MN. We are building a wind farm and our contractor plans to use Caliche for the access road base material. We typically use crushed limestone for our aggregate in MN and none of our engineers have any first hand experience with Caliche.

There are two primary functions our roads must meet. First, we have to deliver tower components which are very heavy (e.g., 170,000 lbs) as well as accommodate concrete trucks (approximately 30 trucks per foundation and the access roads could have 4 or 5 foundations on each road). The second phase will consist of fairly light maintenance truck traffic (maybe an F350 style truck) and the roads are expected to last for 20 years with light maintenance. As I mentioned, our roads in the upper Midwest have been built with crushed limestone and they perform very well (we cement stabilize or use geo-grid on the access road subgrade to provide additional strength for deliveries and concrete trucks). Does anyone have experience using caliche? Is there anything we should know about this material before allowing our contractor to move forward with its use? From what I've heard, it seems that this material loses strength when wet? How much rain will affect the road and how long does it take for the road strength to return?

Thanks!

 

[EireChch]

I am not familar with the material but a quick google search found the following paragraph within the following link from the FHWA website.

https://www.fhwa.dot.gov/engineering/geotech/pubs/05037/01.cfm

Throughout the history of pavement design, special problems have been encountered in relation to pavement support. These include expansive soils, frost susceptible materials, caliche, karst topography, pumping soils and highly fluctuating groundwater conditions. The solution to these problems is often to remove and replace these materials, often at great expense to the project. Today there are a number of alternate techniques available to resolve these issues, as discussed in Chapter 7.

I also found this paragraph from the following link:

http://d2dtl5nnlpfr0r.cloudfront.net/tti.tamu.edu/documents/0-4358-1.pdf

The Caliche appears to be the worst performing base; it has the lowest in-place modulusand highest dielectric value. In many areas of the state, designers use 70 to 80 ksi for Class 1 bases when placed on stabilized layers; however, the average value for the caliche is in the 40 to 50 ksi range.


Seems like it is used regularly as a subbase but I would be hesitant based on the limited search.

 

[oldestguy]

I'd call the highway commissioner for the county and ask for their opinion. Otherwise, the Materials Section of the state DOT.

 

[cvg]

we have a lot of caliche in Arizona. it is not used for road base. Depending on the degree of cementation, it may or may not be moisture sensitive. We generally do not construct a subbase.

 

[cvg]

suggest meeting the following minimum physical properties

well graded, from no. 30 to 1 inch maximum
crushed, not rounded or sub-rounded material
no more than 12% fines
PI less than 5
Los Angeles abrasion, 500 revolutions, no more than 40% loss
R-value of 70 minimum

 

[dik]

cvg:
In this environment, I would restrict the fines to approx. 8%... 12% may be prone to frost heave susceptibility... maybe not an issue in Texas.

Dik

 

[Terratek]

"Caliche" is a colloquial term, especially when used by a contractor, to be avoided in professional design unless you can find a specification that defines it. Always be wary of the contractor suggestion.

One could presume the subgrade materials given the location, but you didn't state them, so it's impossible for you to get an informed answer. Are you a geotechnical engineer, or have one on staff you are helping? If you are a structural engineer, as indicated by your tag, how comfortable are you with designing pavement subgrade, let alone out of state?

The best course of action would be to retain a professional geotechnical engineer with local experience. There is s DOT spec that will get you what you need, but at the risk of sounding harsh, if you or your team can't figure out which one it should be, you probably shouldn't be designing the subgrade.

If it's "no big deal" because it's "just a dirt road", then an engineer should not be required.

 

[Okiryu]

You will need to check for durability and results may not be so good. That's why it is not normally used as road base/subase materials as cvg noted. Check your state's DOT requirements for durability of base courses.