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Lime Treatment of Road Subgrade Saves Time and Money on Large Project in Contra Costa County
Windemere, a community located in the Dougherty Valley of San Ramon, includes 6,300 new homes on 2,900 acres. In addition, the community includes two schools, a commercial center and other public facilities.

The new roads being constructed at Windemere are representative of the first time Contra Costa County has seen lime treatment of roadbeds utilized on such a grand scale. Griffin Soil, along with their client, convinced Contra Costa County and the City of San Ramon that lime treatment would be the best approach to treat the expansive soils on the property, and would vastly improve the overall quality and longevity of the new roads. Additional benefits included a decrease in necessary grading activity and reduction in the development’s impact on the adjacent community.

The team had to overcome the misconceptions at the County and City that lime treatment was only appropriate and useful in wet conditions, and that lime treatment of structural road sections would not be as effective as the traditional approach of importing vast amounts of baserock to achieve the desired pavement section for designed traffic index.

Since the magnitude of the treatment would be unlike any the county had seen before, several concerns needed to be addressed before all approvals were obtained. Working with Griffin Soil, a plan was presented that addressed issues of quality, cost, and schedule control. Griffin’s history of handling projects of this scale, combined with an extensive demonstration of their state-of-the-art equipment, convinced the County of Contra Costa that lime treatment as performed by Griffin Soil would ensure that consistency and quality control objectives were met.

The first order of business was to determine the optimum product and mix design for the native soils. The dominant soil type in the Dougherty Valley consists of highly expansive clay. This type of material is well suited for a quicklime treatment. Samples were taken of the subgrade material for R-Value testing. It was determined that the optimum mix design for the material would be 4 percent High Calcium quicklime. Results of the R-Value testing indicated values of up to 85 from the original untreated material of 5. These results are typical of lime treatment on clayey soils.

The resulting roadbed is not only more stable and durable than would have been possible with traditional treatment, but the added benefits of lime treatment are significant, and include:

- The use of only 1,500 truckloads of imported rock as opposed to the 6,000 truckloads that would have been necessary with traditional road construction.

- A time savings of about 30% in the completion of the roads.

- Reduced wear and tear during the construction process on existing roads leading into the project - ultimately saving money and time for public works departments and residents.

- Environmental benefits that include a reduction in the need to further deplete quarries, and less air pollution due to reduction in trucking requirements.

- Reduction in the amount of grading required at the site, due to enhancement of the strength of the existing soil.

- Reduction in the amount of shrink/swell of the subgrade material, which had caused the failure of several streets adjacent to the development.