Piqua, OH: Deep Soil Mixed Cutoff Wall, Lockington Dam
Geo-Con constructed a DSM cutoff wall in an existing earthen embankment of the Lockington Dam in Piqua, Ohio. After the catastrophic flood of 1913 in Dayton, a series of flood prevention dams were built over a number of years, including the Lockington Dam. The dam was constructed of hydraulic fill with a puddled low permeability core, with a crest length of 4500 ft and an average height of 70 ft. The core was placed to within 20 feet of the crest, corresponding to the spillway elevation.
New regulations and calculations of maximum flood conditions indicated loss of freeboard and possible dam overtopping in the extreme case. It was, therefore, decided to extend the existing cutoff to the dam crest.
The bid package presented two alternates: A conventional cement-bentonite slurry wall with HDPE liner or an Auger Mixed Soil-Cement wall. The HDPE liner was stipulated, as there were concerns regarding wall desiccation given that the wall would only be in service during peak flood conditions. The soil mix alternate proved to be the more cost-effective solution. In addition, laboratory tests indicated that the soil-cement material proved highly resistant to desiccation.
The wall was formed using Geo-Con's DSM rig, mounted on a Manitowoc 4100 crane down to a depth of 20 ft. The soil-cement slurry used was remote pumped (up to a distance of 2500 feet) to the rig and produced a wall with an average strength of 60 psi at 28 days and a permeability of 1x10-6 cm/sec. Construction took place through the severe winter of 1992-1993 with a peak production of 7000 sf per shift. In all, 67,000 sf of DSM cutoff was installed.