|
Our
Expertise . . . |
Base Metal Projects
-
Compania Minera Santa Barbara,
Inc., El Mochito, Honduras
-
Copper Range Company, White
Pine, Michigan, USA
-
Crandon Mining Company,
Wisconsin, USA
-
Glenn Springs Holdings, Inc., Ducktown, Tennessee,
USA
-
Molycorp, Inc., Questa, New Mexico
-
Savage Zinc, Inc.,
Gordonsville, Tennessee, USA
Compania Minera Santa Barbara, Inc., Sublevel VCR with Hydraulic Backfill,
El Mochito, Honduras
 Ventilation Engineering--AAI provided design support to mine
operations at Breakwater's El Mochito Mine to modify the ventilation system
to improve existing ventilation and support expansion of the underground
facilities. Extensive underground workings have resulted in large
leakage and poor performance of the existing system. Field pressure
and volume surveys were performed to characterize resistance of the major
intake and exhaust airways and establish leakage of the system.
Computer network models were generated and calibrated with the survey data.
Network modeling using the MTU code was performed to specify the number and
size of new ventilation boreholes and develop specifications for fan
performance. Secondary distribution of the air to new working areas
was also planned using network simulation. Computer analysis of mine
psychrometric conditions in production slots was performed to establish air
volumes and air conditioning required to maintain acceptable face working
conditions.
Mining
Engineering--Sublevel opening stoping with cemented backfill is used
to extract high-grade zinc ore from the San Juan orebody at El Mochito.
Mining of the central portion of the orebody was largely complete, leaving
recovery operations located in the final lift of the hanging wall, in sill
pillars between production levels, and at the base of the orebody which was
offset into abutment zones created by mining overhead. Rock mechanics
analyses were used to sequence stope extraction on the upper levels where
existing large cave zones and shortfalls in backfill placed portions of the
ore at high risk. New stope development layouts were designed for
lower levels where abutment stresses were causing rock failure.
Development extraction ratios were reduced to ensure stable access during
stope production. Computer modeling was used to estimate abutment
loads due to overhead mining. These loads were then used in modeling
mining extraction to back-analyze stress levels causing rock failure to
develop estimates of rock design strength.
New ore reserves identified by
underground drilling required development of mining plans for extrapolation
of the existing open stope technology to depths up to 4500 ft. AAI
personnel designed geotechnical programs and trained site personnel in
collection of geotechnical data during resource drilling of the potential
new ore zones. Rock quality data from the San Juan orebody was
generated and used for comparative, empirical design in the new ore zones.
Copper Range Company, White Pine Mine, White Mine, Michigan, USA
The White Pine Mine is an extensive room-and-pillar copper mining
operation. Ground conditions vary widely throughout the mine due to changes
in geologic structure, depth of cover, and the magnitude uniformity and
orientation of in situ stresses. AAI has successfully completed numerous
projects at White Pine including:
-
In
situ stress determinations.
-
Mechanical property tests and numerical modeling analyses to evaluate the
effects of the orientation and magnitude of in situ stresses and
mining-induced stress concentrations on mining operations.
-
Recommendations regarding pillar and opening dimensions and orientation.
-
Numerical modeling analyses for a proposed pillar rubblization and solution
mining plan identifying areas of high stress concentrations which can result
in potentially difficult ground conditions and pillar failure.
-
Ventilation/fire simulations to assess the effects of diesel fuel fires on
the mine environment and ventilation systems.
|
|
|
Crandon Mining Company, Crandon Project,
Wisconsin, USA
AAI has provided rock
mechanics consulting services for mine design of the zinc massive sulfides
at the Crandon Project since 1992. Stable dimensions for blasthole open
stopes with delayed backfill were projected based on rock mass quality data
developed from core evaluations. Geotechnical data were evaluated for three
specific locations within the orebody to assess variability in conditions.
Empirical stope design criteria were used to estimate the stable dimensions.
Analysis of stresses around open stopes was performed using 3D
boundary-element and FLAC3D modeling. Pillar loading in primary and
secondary extraction was evaluated using 3D modeling of the three initial
mining areas. Impacts of the apparent orientations of existing joint sets on
stope surfaces were evaluated using probabilistic key block modeling in 3D.
Hydrologic impacts due to mining next to the planned crown pillar were
evaluated to provide assurance that surface groundwater aquifers would not
be adversely impacted. Cut-and-fill methods were recommended beneath the
crown pillar to assure long-term isolation of the glacial aquifer. A plan
for managing groundwater inflow was presented.
Glenn Springs Holdings, Inc., TDR Monitoring at the Copperhill Mining
District, Ducktown, Tennessee, USA
The Copperhill Mining District in southeastern Tennessee had been
mined by open stope methods from the turn of the century into the 1970s. The
stopes were mined close enough to the surface that several dramatic collapse
subsidence features had developed. AAI assessed the relative risk of
subsidence, and delineated various levels of potential for collapse. AAI
designed a TDR monitoring program based on this subsidence evaluation. The
crown pillars overlying open stopes were drilled into from the surface to
confirm the depths to the openings. The drill holes were then plugged with a
borehole friction plug that was modified by AAI to function as the delivery
system for the TDR cable and the grout tremie system. This was important to
assure that the TDR cable was not damaged by drill steel entering the drill
hole. AAI also designed high-pressure end caps for TDR cables to assure that
groundwater intrusion to the cable dielectric was prevented. Groundwater
intrusion turns TDR cables into effective piezometers, but destroys their
function as deformation measuring instruments. AAI is currently providing
technical review of the TDR data.
Molycorp,
Inc., Questa Mine Subsidence Monitoring and Analysis, Questa, New Mexico,
USA
AAI completed a comprehensive subsidence study for the Questa block
caving molybdenum mine for Molycorp, Inc. in support of the Mine
Closure/Closeout Plan ultimately submitted to the New Mexico Energy,
Minerals and Natural Resources Department-Mining and Mineral Division and
the New Mexico Environmental Department. The study comprised investigation
of historical block caving subsidence at the Questa Mine and elsewhere,
instrumentation and monitoring of subsidence over a new block cave at
Questa, core drilling, laboratory core testing, field mapping, geotechnical
characterization, and, ultimately, predictive modeling of future subsidence
associated with the long-term mine plan. AAI developed and implemented a
program for monitoring cave development and subsidence using downhole time
domain reflectometry (TDR) cables. Field mapping and ground monitoring data
were applied to empirical and phenomenological models for estimating the
magnitude and duration of subsidence, the long-term post-mining surface
topography, subsidence-related impacts, and safe timing for mine closure
reclamation activities. Numerical modeling included three types of computer
codes: influence function, continuum, and discontinuum codes. A highly
realistic simulation of subsidence and the complex mechanisms of caving was
possible using the leading-edge, three-dimensional Particle Flow Code code.
Findings of the study facilitated mine closure and reclamation planning.
Molycorp, Inc., Questa Mine, Questa, New Mexico, USA
Molybdenum ore is mined by block caving methods at Molycorp’s
Questa Mine. AAI has provided geotechnical consulting services to the mine
since 1979. Development of a new orebody, the D Orebody, began in 1999 at
twice the depth of previous mining. AAI was called upon for the design and
evaluation of ground support on the Grizzly and Haulage Levels beneath the
planned cave. Three-dimensional numerical analysis of stress conditions was
conducted for critical stages of the cave evolution. The three-dimensional
geometry of the cave was modeled over the planned course of mining. The
local three-dimensional geologic structure was explicitly defined in the
model to assess the damage potential of transient abutment stresses in
different rock types.
Proposed ground support options, subjected to critical stress conditions in
different rock types, were evaluated with a subsequent three-dimensional
model comprising the complex geometry of the ore transfer raises connecting
the Undercut, Haulage, and Grizzly Levels. Cast concrete and steel liners
were explicitly represented in the model with shell-type elements to capture
the liner-ground interaction. Liner stresses were induced by plastic
deformation of the surrounding yielding rock. Analytical results revealed
probable damage zones and design weaknesses associated with the various
liner options. From the analytical results, underground observations, and
experience at the mine, Molycorp personnel were provided with a performance
ranking of the proposed support options and recommendations for improved
design.
Savage Zinc, Inc., Gordonsville/Elmwood and
Cumberland Mines, Gordonsville, Tennessee, USA
For this highly complex, 100-year-old, random room-and-pillar base
metal mine, AAI performed a detailed ventilation survey, prepared network
models, and transferred network modeling technology to the mine operation.
The primary objectives of this project were to reduce operating costs
associated with power for the ten underground booster fans.
|
|
AGAPITO
ASSOCIATES, INC.