 |
 |
 | |
    |
|
ENVIRONMENTAL CONSTRUCTION AND REMEDIATION Shallow Soil Mixing The site for a new county jail was situated on a former railroad yard on the banks of the Monongahela River in Pittsburgh, Pennsylvania. The site was surrounded by the city's major transportation arteries. Site investigations indicated the presence of hydrocarbon contamination from former underground storage tanks and railroad refueling activities.
Total petroleum hydrocarbon concentrations (TPH) with concentrations up to 11,000 ppm, were discovered up to 25 ft deep. Site soils were extremely variable and consisted of river bottom alluvia, slag, cinders and fill.
Removal of soils at shallow depths was feasible on part of the site, but much of the contamination was adjacent to Interstate I-376, one of the main highways through Pittsburgh. A gravity retaining wall, formed by grouting with microfine cement, was specified to hold the Interstate in place and solidify contaminants while the bulk of the soils were removed and replaced.
Due to the variability of the soils, the importance of retaining the Interstate and the higher cost of grouting, Geo-Con was able to present a value engineering proposal to replace the grouting with a soil mixing alternative. A three-row shallow soil mixed (SSM) wall was constructed, which provided a 25 ft wide gravity retaining wall. In areas beneath the bridge, jet grouting was used to complete the retaining wall.
Working under a tight schedule, Geo-Con completed the retaining wall and soil treatment in about two weeks. The removal and disposal of approximately 25,000 cy of contaminated material next to the wall began after only one week of curing. Soil-cement unconfined compressive strengths generally exceeded 500 psi in 7 days with some results as high as 1000 psi in one month.
The SSM provided a gravity retaining wall and waste treatment in a cost-effective manner. SSM reduced the project schedule and the cost of the work.
|
 |
