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Block Caving Projects

Climax Molybdenum Company, Henderson Mine Abutment Load Monitoring Instrumentation Program, Empire, Colorado, USA
   The Henderson Mine is a block caving operation located in Empire, Colorado.  AAI installed borehole pressure cells (BPCs) and borehole extensometers, trained Henderson personnel in reading the instrumentation, and conducted overcoring stress determinations in the 7210 Production Level.  Mechanical properties tests for measuring the unconfined compressive strength (UCS) and elastic properties (elastic modulus, E, and Poisson's ratio) were conducted on core from the borehole extensometer holes.  The geotechnical data produced by this instrumentation and overcoring project provides valuable information for warning of potential hazards and optimizing future mine design.

   A Microsoft Access database was developed to streamline instrument data entry and storage, automatically present graphical and numerical results, automatically generate reports, and issue threshold warnings for rod and borehole extensometers, and BPCs.

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.

   AAI performed a ventilation survey, network modeling, and ventilation technology transfer for this dewatered and reopened block caving molybdenum mine. A new ventilation borehole was sized to accommodate conversion from gravity draw to diesel equipment.

• Mining Engineering

• Ventilation Engineering

• Highwall Mining

• Blasting & Explosives Eng.

• Solution Mining

• Rock Mechanics

• Rock Testing

• Stress Measurements

• Forensic Engineering

• Geology & Drilling Management

Project Summaries - Mineral

• Base Metals

• Coal

• Fertilizer Minerals

• Gold

• Limestone

• Oil Shale

• Trona

• Other

Project Summaries - Capability

• Backfill

• Directional Drilling

• Forensics

• Geologic Studies

• Longwall

• Mine Reclamation

• Overcoring Stress Determinations

• Resource/Reserve Evaluation

• Slope Stability

• Solution Mining

• Subsidence

Abstracts

• Coal

• Hard Rock Mining

• Industrial Minerals

• Oil Shale

• Nuclear Waste

• Numerical Modeling

• Slope Stability

• Tunnels & Tunneling

• Ventilation