In the spring of 1996, a landslide in Rockland, Maine sent
two homes and 300 feet of bluff into the ocean. The clay that made up the bluff
sheared into blocks, losing 90% of its strength as it collapsed. The city of
Rockland was worried that more homes, along with the city's water and sewer
lines on the Samoset Road would fall into the ocean as well, so preventing
further movement of the slope was crucial.
The engineering firm of Gerber-Jacques Whitford was hired to
stabilize the area. Construction work to buttress the Samoset Road at the top of
the landslide area would be difficult because of the soft clay, so special
precautions had to be taken. It was determined that heavy fill would be used at
the bottom of the slide first, followed by a lighter fill at the top. Riprap at
the base of the slide would prevent erosion of the fill material, and base
layers of geotextiles, sand, and gravel would provide the support necessary for
the work to be completed.
Shot rock, with a density of 145lb/ft3 was used as a heavy
fill at the base of the slide area. For a lighter-weight fill, cement kiln dust,
from the nearby Dragon Products facility was used. Nearly ten thousand cubic
yards of the 95-lb/ft3 material was donated from the Thomaston cement plant.
The use of the CKD did have its downsides. The fine material
caused some dust problems and compaction was difficult. Extra effort was
necessary to work with the CKD, and this resulted in higher costs than
traditional fill. Dragon gave Rockland the cement kiln dust at no cost though,
and the project served as a demonstration of a beneficial use of the waste
material.
Information courtesy of Dick Reynolds and the City of Rockland.
