Agapito Associates Inc.

Oxbow Mining—Somerset, Colorado, USA

kgreathouse — Wed, 24 Aug 2011 19:47:11 +0000

Elk Creek Geotechnical Program

Agapito Associates, Inc. (AAI) has been involved in long-term geotechnical investigation and design at the Oxbow Mining, LLC, Elk Creek Mine, dating back to the pre-development phase. Services provided by AAI include horizontal stress measurement, numerical modeling of seam interaction, rock mechanics testing, and mine-wide roof and floor characterization. Future mining involves increased cover depth, and one of the primary areas of work is in developing pillar design strategies appropriate for the increased cover. Recently, AAI designed and installed an extensive geotechnical instrumentation system for characterizing ground response to longwall abutment loading, including pillar loading, entry convergence, and roof deflection. The resulting data was used to calibrate numerical modeling inputs to observed ground response. Modeling and other design approaches were then used to develop a range of pillar design strategies for Oxbow in support of mine planning.

Ridges Basin Dam—Durango, Colorado, USA

kgreathouse — Mon, 22 Aug 2011 20:15:31 +0000

Weeminuche Construction Authority

After detailed design of cable trenches and final instrument specifications included as part of the instrument procurement process, AAI mobilized a field crew to the Ridges Basin Dam sight in June of 2005 to drill the boreholes and install the first piezometers and the inclinometer into the foundation rock at the bottom of the dam excavation. Over the next 2 years, AAI installed 27 fiber-optic piezometer transducers and 21 vibrating-wire piezometer transducers plus 3 vibrating-wire weir gage level transducers. An inclinometer casing and 4 survey instrument piers were also installed at the dam. Over 48,000 feet of fiber-optic and vibrating-wire cable was installed in trenches and pulled through the conduit into the Control House where AAI installed the data acquisition hardware. Instrumentation and data acquisition hardware installation was completed in September of 2007.

SD-1500 at Ridges Basin Dam

C-b Tract, Off-gas Shaft—Piceance Creek Basin, Colorado

kgreathouse — Mon, 22 Aug 2011 19:47:25 +0000

Occidental Oil Shale

This project involved a proposed in-situ retort oil shale mine located in Piceance Creek Basin, Rio Blanco County, Colorado. The scope of work included: (1) prepare a mine layout and operations plan, (2) evaluate the existing facilities and develop plans and estimates for modifications to support the new mining plan, (3) develop design engineering, cost estimate and schedule of new 1800-ft-deep off-gas (high temperature gas) shaft, (4) review condition of existing shafts, shaft liners, and hoisting equipment and facili-ties, (5) design new mine and MIS support facilities, and (6) prepare a capital and operating cost estimate for mining and retort development.

The mine layout was developed to utilize the existing shafts and shaft stations, minimize development costs while main-taining essential safety functions. Seventeen retorts and room-and-pillar areas were considered for supplementary oil shale production. The modified in-situ process required a dedicated off-gas exhaust shaft involving selection of construction methods, design, and a cost estimate.

Of the existing facilities, shaft liners needed some upgrade, stations required remedial attention, water handling in the shafts required installation of new control measures, and hoisting systems needed some refurbishment. Loading pocket facilities required completion, provision made for shaft bottom clean-out, and the headframe loadout modified.

The design of the new mine and MIS support facilities incorporated mining sequencing, ground support, mining equipment selection, materials handling, ventilation, and underground services. The capital cost estimate, prepared from design drawings, included a detailed scope of work and engineering estimate for Year 1 of the project. An operating cost estimate for the mine was also prepared following similar procedures. A spreadsheet-based cost model was used to facilitate mining cost calculations.

Yucca Mountain Project—Nevada, USA

kgreathouse — Mon, 22 Aug 2011 19:40:05 +0000

Sandia National Laboratories

AAI was contracted to Sandia National Laboratories to provide geotechnical, analytical, and field services to the Yucca Mountain site characterization studies in the early- to mid-1990s. AAI established an office in Las Vegas, Nevada, to support the project with up to ten engineers, scientists, and geologists. Modeling studies ranged from drift stability under thermal and seismic loads to regional stress changes and fault activation studies. A drift design methodology using both analytical and empirical methods was developed. Two three-dimensional stress analysis tasks are detailed below.

The three-dimensional boundary-element program, BEST3D, was used to understand the stress distribution along the intersection of the main tunnel and waste emplacement drift. The stress results were used to predict the rock mass failure over the drift wall using Mohr-Coulomb strength parameters.

Analysis of the thermally induced stress changes along the shaft axis were required for input to the shaft liner design. AAI completed this task at QA Level 1 using the STRES3D code. Each panel was modeled as rectangular and horizontal, each with differing elevations and time of waste emplacement. The thermally induced strain and stress changes along the axis of the shaft at the breakout rooms and Exploratory Studies Facility were evaluated. This model was again used to evaluate stress changes at specific drift locations using the same emplacement geometry and emplacement scheme.

AAI participated in the preparation of a shaft liner design guide for the proposed exploratory shafts at Yucca Mountain. A computer program (SHAFT), developed by AAI based on an original solution for stresses and displacements around a circular shaft, was employed to consider in-situ, thermal, and seismically-induced stresses in the shaft liner. Fiber-reinforced concrete and various forms of reinforcing were investigated to minimize problems with liner cracking.

Other projects included tunnel mapping and installation of rock instrumentation during construction of the Exploratory Studies Facilities.

Oil Sands Cavity Mining Geomechanical Assessment—Alberta, Canada

kgreathouse — Mon, 22 Aug 2011 16:43:01 +0000

Confidential Energy Client

Agapito Associates, Inc. (AAI) completed a geotechnical evaluation of cavity stability, inter-cavity pillar sizing, and subsidence potential for a proprietary, concept-level borehole hydraulic mining method developed for extracting bitumen-rich oil sands in the Athabasca oil sand deposit in northern Alberta, Canada.

Numerical modeling was conducted using FLAC to simulate cavity response during the mining sequence. The model simulated the complex non-linear and pore-pressure dependent behavior of the oil sands. Under low cavity pressures, cavity stability was shown to be controlled by mechanical degradation of the oil sands caused by gas exsolution.

Surface and subsurface subsidence caused by pillar convergence and overburden movement was modeled over a wide range of mining depths. Alternative mining geometries and the use of backfill were evaluated for optimizing the mining process, minimizing subsidence, and maximizing resource extraction.

GasTech, Inc.—Powder River Basin, WY

kgreathouse — Mon, 22 Aug 2011 15:50:43 +0000

Underground Coal Gasification Cavern Subsidence

GasTech, Inc. (GasTech) is in the process of permitting a series of underground coal gasification (UCG) wells as part of a pilot project in the deep coals of the Powder River Basin (PRB), Wyoming. GasTech commissioned Agapito Associates, Inc. (AAI) to analyze the long-term behavior of UCG caverns after completion of the pilot project. The analysis provided estimates of surface and aquifer displacements, and stability assessments of the pillar between rows of caverns.

Numerical analysis was performed to account for extraction-induced stress changes and the non-elastic behavior of the weaker coal seams. Five types of input were considered in the analysis: cavern geometry, stratigraphy, rock properties, in-situ stress, and groundwater pressure. The main coal-producing seams were represented in the model, including the target Upper Wyodak coal bed which is about 60 feet thick at a depth of about 1,000 feet below ground. In-situ stresses were based on nearby hydrofracture measurements. Modeling was performed using FLAC3D.

Geotechnical issues addressed include estimated height of roof collapse above the UCG caverns, estimated disturbance of aquifers, and the potential for surface subsidence. Recommendations were developed for well spacing to optimize resource recovery given limitations on subsidence.

Kemmerer Mine—Wyoming

kgreathouse — Fri, 11 Mar 2011 22:45:54 +0000

Chevron Mining, Inc.

Highwall Slope Stability

AAI has investigated various aspects of highwall stability at several pits at the Kemmerer Mine, including large-scale slope failure, wedge analysis, and most recently, rockfall risk assessment. Alternative catch bench and berm designs were evaluated using the statistical CRSP program and numerical UDEC models. Both programs were calibrated using on-site experimental measurements.

Highwall Mining Evaluation

A comprehensive evaluation was completed of the geotechnical and operational issues related to conducting highwall mining in three different pits. The combination of multiple thick, steeply dipping seams and variable topography resulted in a challenging optimization study balancing recovery, practicality (cost), and safety. Candidate mining configurations involved varying the opening inclination and mining height (multiple passes) and using multiple lifts. Several empirical design techniques were employed in addition to a number of numerical models to develop pillar design charts for the optimum opening configuration. The weakening effect of the highwall mining openings on overall slope stability was also analyzed.

Concentric Energy—Wickenburg, AZ

kgreathouse — Mon, 28 Feb 2011 22:21:15 +0000

Uranium Resource Estimate 43-101

Agapito Associates, Inc. (AAI) was engaged by Concentric Energy Corporation to complete the original independent NI 43-101 Technical Report and resource estimate for the Anderson Mine uranium and vanadium property located near the town of Wickenburg, Yavapai County, in west-central Arizona, USA. Mineralization occurs in the sequence of Miocene-age lacustrine (lake-bed) sediments which unconformably overlie andesitic volcanics. The uranium-vanadium resource was defined by 1,393 vertical exploration drill holes, including 1,320 downhole gamma surveys and a total of 5,596 chemical assays, completed by Minerals Exploration Company of Union 76 Minerals, a subsidiary of Unocal Corporation, and Urangesellschaft U.S.A., Inc. in the 1970s.

AAI coded a Visual Basic program based on the classic U.S. Atomic Energy Commission GAMLOG algorithm to convert natural gamma radiation counts taken from historical logs to equivalent radiometric grades of uranium oxide (U3O8), with adjustments for hole characteristics and disequilibrium. Composite grades and thickness were determined for multiple radiometric beds in each drill hole and applied to a computer block model to estimate the grade and quantity of mineralization. Historical measurements were validated by confirmation drilling overseen by AAI’s NI 43-101 Qualified Persons in 2006.

The 43-101 Technical Report was submitted for the first time to the Toronto Stock Exchange in 2010 following Global Uranium Corporation’s acquisition of the project.

Billie Mine—Death Valley, California, USA

kgreathouse — Wed, 02 Feb 2011 23:01:08 +0000

American Borate Company

The Billie Mine utilized long-hole stoping with backfilling to extract borate. This mining method resulted in the creation of tall, narrow pillars which were critical to the stability of the mine. AAI was involved in the development of the mine plan and identification of the optimum pillar width. Pillar widths were selected by conducting computer simulations of stress analyses of the mine structure for different candidate pillar geometries. These analyses incorporated the effects of confining pressure, applied by the backfill, on pillar strength. Upon implementation of the mine design, an extensive geotechnical instrumentation program was used to evaluate the mine design and monitor overall stability.

Recent work following a 5-year mothballing of the mine has included monitoring or rehabilitation efforts, assessment of alternate ramp options, introduction of high-extraction mining using cemented fill, review and updating of mine ventilation system, monitoring of mine planning, and assessing mining-induced subsidence.

The mine ceased production in 2005 and AAI has provided guidance in mine closure.

Chemical Lime Company—Ripplemeade, Virginia, USA

kgreathouse — Wed, 02 Feb 2011 22:00:53 +0000

Instrumentation Installation

The field work at the Kimballton Mine in Ripplemeade, Virginia, includes NX sample coring of the roof and floor of the 15E level of the mine, USBM-method overcore stress measurements, and installation of Geokon mupltiple-position borehole extensometers (MPBXs). An NX sample core hole was drilled through the ore zone and into the footwall to a total depth of 137.8 feet. Another NX sample core hole was drilled into the roof of the mine to a depth of 11.4 feet. The core from both core holes was logged by CMC and the core was transported back to Grand Junction, Colorado, for sample selection and strength testing.

The first stress-measurement hole was drilled vertically down into the floor to a depth of 43.8 feet. Five USBM-method overcore stress measurements were successful in this hole. The second stress measurement hole was drilled horizontally to a depth of 49.8 feet. Six overcore runs were attempted and all were successful. Two Geokon two-anchor MPBXs were installed into pillars on the 12E level to monitor pillar separation in the horizontal plane.