I feel like I have been having discussions about Stabilization quite a bit lately. I decided to write this post because I just started reviewing a model that has actually modeled the Stabilization and I wanted to see what everyone thought about that.
First off, after reading the Specs, I have come to the conclusion that the pay item for Stabilization is more for a process than a material. I do understand that there is some material that gets mixed in with the Embankment, but that seems to be somewhat incidental. Most of the material is covered under the Embankment pay item, which is why that is a CY item. Then the Stabilization is the process of mixing, compacting, and grading that Embankment, which is why that is a SY item. My concern is that by modeling the stabilization, you are eliminating that area from the Earthwork Cut/Fill Volumes, which would reduce your Embankment quantity.
I came to this conclusion from reading Specs 160-3.1: "Prior to the beginning of stabilizing operations, construct the area to be stabilized to an elevation such that, upon completion of stabilizing operations, the completed stabilized subgrade will conform to the lines and grades shown in the Plans. Prior to spreading any additive stabilizing material, bring the surface of the roadbed to a plane approximately parallel to the plane of the finished graded surface shown in the Plans."
Also, simply from the fact that we have never modeled Stabilization in the past and it has always been a 2D plan quantity.
What does everyone think?
Zach,
Some FDOT Criteria and standards show a 2D section representation of stabilization. This can lead one to believe that it should be modeled, and contractors may have to add approved material. However, because it is a SY quantity and the objective is to compact various materials to specific density prior to building the roadbed or finished subgrade, only the plan limits need to be derived from the model. Thus, a volume is not necessary. Only use the limits determined from the roadbed Base limits of your corridor model. All additional material and re-work of the insitu soils is included in the SY cost for stabilization.
Vern
Thanks Vern. The only thing I would add is that most of the time the stabilization area is slightly larger than the limits of the base. Typically, stabilization would extend under curb to 4" behind the curb. Or in flush shoulder situations, it would extend to the edge of the unpaved shoulder.
I usually just end up drawing a 2D shape for the stabilization and attaching the appropriate item type to it so the Takeoff Manager will pick it up.
Zachary Billings, P.E.
Senior Roadway Engineer (Licensed in FL and MI)
CONSOR Engineers, LLC
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