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PRESIDENT GEORGE BUSH TURNPIKE

The SH 161 segment of the President George Bush Turnpike, or "the PGBT," is one of two PGBT segments constructed to date with EMC SQUARED® System subgrade treatment. The total construction value of the SH 161 (DNT-346) and SH 190 (DNT-323) projects was approximately $100 million. The SH-161 segment is located on the eastern side of Dallas-Fort Worth International Airport (DFW) in an area where swelling clays and sulfate-induced heave (attributable to the incompatibility of lime and other calcium based stabilizers such as cement and fly-ash) have long buckled and cracked highway pavements and building foundations. The swelling clay problems alone are so severe in this area that researchers have suggested that nothing less than a four foot depth of lime treatment would be necessary to counteract the differential movement below the stabilized layer which would be generated by changing moisture conditions and resulting soil volume changes.

In response to these problems, TxDOT Dallas District funded a laboratory study that was conducted at the Texas Transportation Institute (TTI). Soils were sampled for the research study from two area projects in 1996. These projects included the SH 161 segment of the PGBT project and a nearby addition to the Interstate 635 Freeway, (the Lyndon B. Johnson Freeway), known locally as "the LBJ." The TTI research study was completed in 1998. It reported that the EMC SQUARED System was superior to lime treatment for these problem soils and recommended its use on both the SH 161/PGBT segment and on the Interstate 635 project. The two projects were subsequently constructed with EMC SQUARED System subgrade treatments. Both of these projects also included portions of subgrade constructed with calcium based stabilizers, and they illustrate the findings of the TTI research study regarding sulfate-induced heave generated by the addition of calcium based stabilizers.

The President George Bush Turnpike is currently operating as a six lane tollway. While funded through TxDOT, the engineering, construction management, and operation of the tollway are under the direction of the North Texas Tollway Authority (NTTA). The thickness of NTTA's pavement structural section design for the SH-161 is impressive and necessary due to the serious nature of the local soil problems. A thirty-four inch thick treated subgrade supports a six inch thick base course constructed with hot mix asphalt, overlain by a thirteen inch thick continuously reinforced concrete pavement. The majority of the subgrade on this project was constructed with EMC SQUARED System treatments. A small area of subgrade was constructed with lime treatment. An additional area was treated with a lime-fly ash mixture (LFA), a combination of calcium based stabilizers thought to be slightly less reactive with sulfate bearing soils.

With nineteen inches of combined concrete and asphalt pavement structural section on the SH-161 segment of the PGBT, one might think that subgrade stabilization problems would be slow to surface. A project tour by NTTA, TxDOT and SSPCo personnel proved this is not necessarily true. While the main lanes built above subgrades constructed exclusively with EMC SQUARED System treatments were exhibiting no noticeable roughness or heave, this was not the case in areas where calcium based treatments were applied to the upper layer of the subgrade. The pavements above the lime-fly ash (LFA) treatment were exhibiting limited but noticeable roughness, which is not surprising given the calcium base of both lime and fly ash products. The pavement above the lime treated area has a prominent heave, or "roller coaster," as predicted by the TTI research study.

 

Soil Stabilization Products, Inc.
PO Box 2779
Merced, CA 95344

Toll Free: (800) 523-9992
Phone:     (209) 383-3296

Fax: (209) 383-7849

Email: INFO@SSPCO.COM

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