Subgrade modification in Dallas 1

[geonet]

I've been asked to review a pavement submittal for a project in the Dallas/Ft. Worth area. The original design calls for 8-inches of continuously reinforced concrete pavement (rigid) on a base of 4-inches of Hot mix Asphaltic concrete (HMAC0. Below this the original design calls for 6-inches of lime treated subgrade, presumably for high swell soils. Because the section is very narrow (widening) and short (242linear feet) the contractor has proposed two alternative sections. The first involve replacing the lime treated subgrade with cellular concrete fill while keeping the base (HMAC) and pavement thickness the same. The second calls for increasing the pavement thickness to 13-inches and placing this section directly on "prepared" subgrade. I have requested and am awaiting the pavement design and geotech report however I have a basic question. Will a more rigid cellular concrete subbase allow more water infiltration than a lime treated subgrade therefore eliminating the benefit? Are there other pitfalls?

 

[dmoler]

Doesnt matter, since the lime treated subgrade or concrete fill will not prohibit the native clay below from being moisturized by cappilary action from the water below. From above, the HMAC and concrete pavement will stop the water. Is this the Eagle Ford formation? If so, be careful of lime treatment there due to sulfate reacting with the lime.

Trees are the big problem there if planted in the medians or shoulder, and they reach far horizontally. They send their roots into the clay and suck the moisture out, and the pavement gets torn up. I like the fact that they wont attack the concrete fill, while my experience in Dallas and Ft. Worth has been that they will attack the lime treated subgrade, especially if the lime leaches out.