Lime Modification in the Limelight
May 1, 2009
Standing water and deep ruts were causing major delays at Sugar Grove’s Municipal Drive site before Mt. Carmel was contracted to stabilize the soil.
The village officials in Sugar Grove, Illinois, had a problem. Their project to build a new road—Municipal Drive—about 40 miles west of Chicago was facing wet, weak and unstable soil conditions. Determined to stay on schedule so pavement construction could resume, everyone involved in the project gathered for a meeting on site in early November 2008.
The meeting included representatives from the village, the consulting firm (Engineering Enterprises Inc.), the asphalt paving contractor (Geneva Construction) and the Illinois Department of Transportation (IDOT). Two options were discussed for stabilizing the subgrade: undercutting and lime modification. Although undercutting and backfilling is a common approach to dealing with poor subgrade soils, the total undercut area on this project would have been fairly large—18,975 square yards. It was estimated that undercutting 12 inches and backfilling the area with coarse aggregate would cost more than $300,000.
After the subgrade soil and lime kiln dust were mixed, Mt. Carmel shaped the area to rough grade with a motor grader.
But with the exception of Geneva, no one else on the project had much experience with Mt. Carmel or lime modification. Some questioned the effectiveness of this method and worried the process would be too dusty. However, Geneva convinced the group to hire Mt. Carmel based on the predicted cost savings.
Mt. Carmel arrived on site with its equipment and personnel on a cold Monday morning in mid-November. The subgrade was rutting with moisture contents ranging as high as 30–35%. On the south end of Municipal Drive, the fat clay was rutting under light truck traffic and almost 2 feet of fill was needed to achieve subgrade elevation. On the north end of the extension, the soil was much siltier and extremely unstable. “In this part of Illinois, soil types change constantly,” says Jim Pape, Mt. Carmel superintendent. “I was not surprised to see the sandy, silty area right next to the heavy clay soil—that’s just the way it is up here. Special measures have to be taken because all soil types react differently with lime, water, mixing and compaction. Careful attention to detail is the key to quality.”
A vibratory padfoot roller initially compacted the lime-modified soil.
Using this process, the soil gained strength immediately because of the reaction between the LKD, water and soil. By 10:00 a.m. the south end of Municipal Drive had been treated and compacted and was ready for the excavation contractor, J&S Construction, to begin placing the next lift of fill soil to bring the area to elevation. J&S finished placing the second lift of fill on the south end by mid-afternoon. The loaded scrapers and tractors caused no damage to the treated subgrade, which had been rutting under light truck traffic just hours before.
A smooth drum roller performed final compaction and sealing.
Mt. Carmel also invited personnel from IDOT to come and view the process on this project. Even with the cold temperature and the wind gusting to 25 mph, several took the opportunity to see the soil stabilization process and equipment in action. What stood out the most to them was that the process was nearly dust free. Mt. Carmel builds its spreader trucks in-house, and the two trucks used on this site were selected because of their dust-minimizing design. The back of each truck was equipped with a patented dust collection system that constantly captured fugitive dust emitted during spreading, and then recycled it back into the spreader’s hopper.
After Mt. Carmel finished treating the soil, J&S Construction placed the next lift of fill soil on the south end of Municipal Drive.
According to all involved on the project, the use of lime modification was a success. The village of Sugar Grove and IDOT realized a significant cost savings on this project—estimated to be $220,000. Additionally, there was no need to remove and waste poor soil; it was treated in place and turned into a stable working platform capable of passing a proof roll in a matter of hours.
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