Pavement Subgrade Mitigation

[colzy]

Hi,
I am seeking a second opinion of a geotechnical professional. We have to reconstruct the pavement of a parking lot (1.75 acre) the parking will have stalls and driveways for trucks use. We were told the subgrade consists of stiff to hard High Plastic clay with moisture content varying between 23 to 36 percent and an R-Value of 5. My questions are:
1) I know engineers would like the subgrade compacted to 95 percent but this is stiff to hard clay, can we go without compacting the subgrade or maybe compact the finish subgrade surface to 90 percent?
2) how's handling High Plastic Clay during excavation? and is it cheap to excavate and replace with aggregate base?
Thanks for your imput.

 

[emmgjld]

colzy
I think I have some info for your problem. First,some questions:
is the R Value from a Hveem Stabilometer Test? assuming Yes then,
do you have Swell values from the Hveem Test for each individual sample?
is the R Value = 5 or is it actually <5?
was the swell considered critical to arriving at the R Value?
what is the value of gravel equivalent section, from the plotting of Stabilometer gravel vs swell gravel?

 

[JML4TCM]

The R-value needs to be determined for the saturated sample, especially for a clay material. The properties of the clay will be very different depending on moisture content. Many times the subgrade soil is only evaluated at the in-situ moisture content at the time of evaluation. The problem with this is it does not account for seasonal variations in the moisture content. All soil subgrades will become saturated during sometime in the life of the pavement and that will typically be the critical condition for the pavement.