CONSTRUCTION OF a cut-off wall to prevent leakage has just started on the Hodges Village dam at Worchester near Massachusettes, US. The dam, built in 1959 by the US Army Corps of Engineers, is the only of the 35 built in New England by the Corps without a water resistant core.
The dam was designed to store water in a dry bed reservoir in times of flooding, but during extreme flooding in 1968, 1987 and 1993, water has seeped through it.
At the request of the Corps, Bauer of America, a subsidiary of German foundation specialist and equipment manufacturer Bauer Spezialtiefbau, has just started construction of a new cut-off wall.
Main work is to build a 23,200m2 vertical concrete cut-off wall through the main dam and an adjacent dyke. This 800mm thick and up to 45m deep structure will be socketed a minimum of 1.5m into the underlying bedrock, a fine grained mica schist with strength of up to 127N/mm2.
Excavation of the overlying granular and cohesive soil is being carried out with a Bauer BC30 diaphragm wall cutter under bentonite slurry. A GB50 hydraulic grab unit is used to remove material, which is then separated from the slurry using two desanding plants. The harder schist is being removed with a BC30 hard rock cutter.
Bauer is also building access roads, removing the top of the dam embankment, building the working platform and guide walls, removing and reinstating the random fill and drainage blanket and restoring the area. The reservoir will be kept in service throughout the contract period, which is expected to finish in July 1999.