A residential
neighborhood was constructed over the #7
coal seam in Rock Springs, WY. Significant subsidence
events had occurred in the approximate 100 feet of
overburden causing damages to structures, streets, and
utilities.
In June of 1989, Stan Barnard of the State of Wyoming,
Department of Environmental Quality issued a $2.6 million
contract to The Judy Company, Inc. to stabilize
approximately 190 residences.
Working in
a residential environment posed many new challenges.
Rubbelized
zones were encountered as much as 35 feet
higher than the original 6 foot coal seam. The technical
approach consisted of consolidating the rubble in a
controlled manner to effect 8 inch diameter columns to
support the overlying sandstone. A controlled grout was
required because of the various conditions of the rubble,
which ranged from tightly compacted to voids as much as
two feet.
To
construct the columns a 6 inch diameter bore hole was
drilled through the rubble. An inflatable packer with 5
inches of contact was set in a suitable location as
determined by an electric log. An 8 inch slump cement/flyash grout was pumped through a 2 inch line to
the hole as much as 700 ft from the plant. The grout had
initial set characteristics of 30 minutes, necessitating
on site mixing. The custom manufactured plant was able to
mix and dispense 25 cy/hr. To control the migration of
the grout, a thixotropic admixture was injected as needed
at the wellhead.
At completion
of the project approximately 900 holes for 94,800 LF of
drilling was performed and 18,100 CY of grout was placed.
Patrick Carr managed and supervised construction for The
Judy Company. Kenneth Wilbur was the project engineer for Johnson-Fermeilia Co., the consulting engineers.
Portable Drill Used in Confined
Areas
