800.632.BARR www.barr.com

open-pit slope stability

pit-wall stability analysis for open-pit mining

Designing the steepest pit-wall angle that is consistant with safety and stability will obtain the best economic result from a mining project.

Barr Engineering Co. has more than 40 geotechnical en-gineers and scientists. We assist our clients by providing expertise in final pit-wall design, highwall and spoil slope design for coal mines, waste dump design, wall control blasting design, performance monitoring, and forensic engineering. Pit-slope engineering requires an under-standing of subsurface conditions, the load and defor-mation characteristics of soil and rocks, and the effect of structural features such as faults and joints. Our engineers utilize experience, knowledge, representative and reliable data, and appropriate analysis tools and techniques.

slope stabilityRecognizing the characteristics and development of unstable slopes, and understanding the mechanisms through which they fail, is essential. We perform stability evaluations to address the final pit-wall slope require-ments for soil and rock slopes under static and seismic conditions. Our engineers analyze overall angles, inter-ramp angles, safety bench intervals, safety bench widths, and final wall-blasting techniques. Our experience with slope stability projects include:

• final pit-wall design

• stable highwall design

• spoil-pile and waste-dump design

• resolution of specific stability problems

• wall-control blasting design

• seismic hazard analyses

geotechnical modelingAssessments of open-pit slope stability projects require various forms of computer modeling, which aids in the efficient evaluation of multiple scenarios. Effective model-ing depends on a well-developed understanding of mate-rial properties based on field data, material-parameter data, and knowledge of the program. Barr has experience with multiple geotechnical engineering modeling pro-grams, including:

• FLAC-2D and FLAC-3D

• SWEDGE

• DIPS

• GeoStudio

• Plaxis

• UDEC, 3DEC, and PFC

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instrumentationField observations and monitoring are essential to mining projects because they provide the means by which the engineer can design a project to be safe and efficient. Deep open pits in certain locations can experience sig-nificant deformations, and monitoring and instrumenta-tion are essential to safe and effective operation. Barr’s instrumentation experience includes:

• automated robotic total stations

• piezometers (includ-ing vibrating wire) and monitoring wells

• inclinometers (traver-sing and in-place)

• remote monitoring• tilt sensors and extensometers

groundwater and seepageGroundwater and seepage are factors in many open-pit projects. Seepage is a major safety issue that, if left un-checked, may result in slope failure by a variety of mecha-nisms. Open-pit mines often require ex-pit pumping to keep water away from the pit walls and ensure a safe and efficient mine. The lack of proper seepage investigation and monitoring can result in a lack of pit-wall stability. We have extensive experience in assessing, modeling, and mitigating groundwater and seepage problems.

final pit-wall study for confidential clientA team of Barr geotechnical engineers performed con-ceptual final pit-wall studies for two iron mines in northern Minnesota. The studies involved field reconnaissance, a review of all available data, kinematic and limit equilib-rium analysis, estimation of stable-slope configurations, final wall-blasting procedures, and an assessment of the data gaps and deliverables needed to achieve a final de-sign. Barr submitted a report of the findings that provided estimates of the overall slope angles, inter-ramp angles, safety bench intervals and widths, and final wall-blast designs.

surface coal mine slope-stability projectsBarr performs numerous slope-stability studies for surface coal mines. Often, these studies are completed to sup-port ground control plans that mines are required to submit. Studies include conducting field work to obtain overburden core for testing; supervising soil laboratory testing; and analyzing laboratory testing results, highwall stability, and spoil pile or waste dump stability. Barr super-vises the installation of vibrating wire piezometers and inclinometers and analyzes the data. We also develop active highwall presplitting designs as part of cast blast-ing programs. Projects have included locations in North Dakota, Wyoming, Texas, Montana, and Canada.

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investigative drilling programsAlacer Gold is expanding its mine in east-central Turkey, a region prone to earthquakes and characterized by rock formations of widely varying strength with significant jointing and faulting. To design stable mine pit slopes for the pit expansion, Barr developed an investigative drilling program that provided accurate geological data and used com-puter models to determine safety factors for numerous potential pit-slope designs. Alacer Gold worked closely with Barr to develop the mine slopes, including the require-ments for blasting and monitoring the mine for the feasibility study.