NOT firm & unyielding Finish Base 1

[Dirtcop24]

I'm currently on a project that has a subgrade issue that was not addressed and covered with Base. Six inches of Recycled Class II Base was moisture conditioned and compacted. The density results over the pumping areas were allegedly 95%+. However in my experience, it's sometimes possible to obtain passing tests and still have a pumping grade. I suggested that we proof roll it with a loaded water truck. And guess what, it was badly deflecting. This is to be an ally with heavy traffic. The structural section is six inches of Base and ten inches of 560C 3250 psi concrete (no steel). Should the concrete be placed over this pumping area without stabilizing it?? It should be noted, we are not pumping this concrete and loaded concrete trucks will be driving over this grade the day of the pour making it much worse. I suggested hogging out some of the base and increasing the concrete section to 12+ inches. Any thoughts would greatly be appreciated. Thank you

 

[LittleWheels]

Laying concrete slab pavement over a soft subgrade is just asking for significant problems down the line, probably quite quickly.

 

[SlideRuleEra]

1) Should the concrete be placed over this pumping area without stabilizing it??

2) This is to be an ally with heavy traffic. The structural section is six inches of base and ten inches of... concrete (no steel).
I suggested hogging out some of the base and increasing the concrete section to 12+ inches.

1) No.

2) Throwing (Owner's) money at the problem by increasing concrete thickness 2+ inches will solve nothing. If "time is of the essence", look into making the base much thicker than 6" (say, 18"+) and backfill with material suitable for wet conditions (crushed stone). This will still be expensive, but should solve the problem... when existing conditions are difficult, proper solutions are not "cheap".

 

[TigerGuy]

Have you considered a grid in the subgrade? Pumping subgrades can be chased to great depth without finding stable conditions. A geogrid can help strengthen the upper layers to help bridge the soft areas.

 

[Dirtcop24]

Thanks for the quick responses. Geogrid was suggested at the beginning of the project. And unfortunately the Consultant dropped the ball and allowed the Base to be placed. I neglected to mention that the majority of the Finish Base is good. The pumping is isolated to an area 24'x 60' in a 3000' long area. Removing the Base and installing geogrid is the way to go. Obviously proceeding without addressing the deflecting area is never a viable option. And good point about throwing owners money at the problem! Thank you