The State of Indiana was
expanding the Wabash Valley Correctional Institute over
an area of abondoned coal mines. The depth to the roof of
the mine was 300 feet. The mine was completely flooded,
the water table only 15 feet below the surface.
Significant engineering work had been performed to
delineate the mine and remaining supports. The work
involved the utilization of mine maps, core drilling and
ground penetrating radar. Three weak areas were
discovered where the existing pillar spacing created a
potential for subsidence at the surface.
It was decided
to stabilize the mine by drilling into the mine and
creating barriers with a lower slump grout at natural
openings. The voids would then be completely filled with
a high slump infill grout.
The schedule for performing the work was very tight.
Funding of the job was contingent on phases being
complete on a compacted schedule. The State of Indiana
wanted the building contractor to be able to use the
entire construction season for surface construction. This
required the subsidence contractor to work multiple
shifts to mantain the schedule.
The Judy
Company, Inc. was issued a contract for
just over $1.6 million to complete the subsidence
remediation. The contract allowed 90 days for completion
of the project and included a $15,000 bonus for early
completion. By working multiple shifts, just over 60
calendar days were needed for substantial completion.
Venture Drilling (Talequah, OK) was issued a
subcontract for the drilling. Using an air rotary system,
31,102 lf of drilling was performed. A Drilltech D-40-K
was modified by installing two hydraulic pipe racks
holding 300+ feet of pipe. A 3" pipe was then fitted
to the bottom of the hole for grout injection.
A continuous
mix grout plant was mobilized to produce
the majority of the fill. Conventional concrete pumps
were used to place the grout. A magnetic flow meter with
a strip chart recorded monitored flow and pressure during
placement. The mine was significantly more rubbelized
than anticipated and mixed designs were modified to
maximize penetration. The grout mix utilized high
percentages of Class "C" flyash and local river
sand. When the job was finally complete, over 9,000 cu. yds. of fill had been placed.
Continuous Mix Grout Plant-Supplies
Material at a Steady Rate.
Injection Pipe Withdrawn as Void Was
Filled
