February 2006

Above: typical 0.3m thick shotcrete barricade; Below: FLAC3D model of predicted failure mechanismPaste Barricade Technical Study

Barricade failure is a core geotechnical risk that is an inherent feature of any open stoping mining method that employs paste fill. Design of paste fill barricades throughout the mining industry currently relies upon simplified analytical solutions that are severely limited in their representation of geometry, material properties, and the wall-barricade interface. Revell Resources and Itasca Consulting Group, Inc. have initiated a collaborative study to develop a design methodology that better represents barricade construction and the paste filling process. Currently, five of the major paste fill operations in Australia are participating in the study. Three-dimensional numerical modeling is used to improve on analytical solutions by explicitly modeling paste fill barricades.

Stage 1 of the project (currently underway) consists of a review of the current analytical design techniques for paste fill barricades and development of a more advanced technique of three-dimensional numerical modeling of barricade geometry, material properties, and the loading conditions applied by a paste fill mass. Stage 2 of the study will consist of obtaining in situ measurements of the barricade response to a measured load. These data will then be used to back-analyze the numerical modeling results. The outcome will be an updated set of design guidelines that will improve understanding of the imposed loads and failure mechanisms of paste fill barricades, allowing mine operators to balance strength and safety against cost and practicality.

A Word on Specification of Reference Axes for In Situ Stress Tensors

Separate projects conducted by Itasca engineers during 2005 have highlighted inconsistencies between the reference axes that are used to specify the in situ state of stress and different mine coordinate systems.

The reference axes adopted by the in situ stress measurement community are a right-handed coordinate system with X (north), Y (east) and Z (vertical down). However, mine grids are often expressed as X (eastings), Y (northings) and Z (vertical up), which is also a right-handed coordinate system. Simply stating that a right-handed coordinate system applies does not specify the orientation of the reference axes, as there is no universally accepted standard coordinate system that is used throughout the mining industry. Without specific definition of the orientation of the reference axes, a cartesian stress tensor is meaningless.

If the in situ state of stress is expressed in terms of three field principal stress magnitudes and the dip and bearing of each principal stress, the problem goes away.

PFC2D and PFC3D Version 4.0 are available now as pre-releases. The capabilities to be developed for version 4.0, along with information about what is currently implemented in the pre-release, are described here.

Sign up Now!
Registration deadlines for the spring introductory code training courses are approaching. Registration for the courses is closed one month prior to the start of the class. The first of the approaching deadlines is for the FLAC course, which will be held April 3-5. Information is available online on course schedules, registration information, and more...

Update Alert:

Current Versions
updated since
Nov. 15, 2005:

Geo-Congress 2006
Roger Hart and Zorica Radakovik-Guzina of Itasca Consulting Group, Inc. will be attending the Geo-Congress 2006: Geotechnical Engineering in the Information Age conference in Atlanta, GA, February 26 - March 1, 2006. Roger is the co-author of a paper entitled "Modeling of Landfill Stability with Barrier Walls: A Practical Example Using Limit Equilibrium and Numerical Methods" that will be presented at the 10:00am "Numerical Modeling" session on Wednesday March 1. In addition, Itasca will have a booth in the exhibitor hall. If you are planning to attend the conference, please stop by the booth to say hello.

SME 2006
Personnel from the HCItasca offices Hydrologic Consultants Inc. and Itasca Consulting Group, Inc. will also be exhibiting at the 2006 SME Annual Meeting and Exhibit, March 26-29 in St. Louis. The meeting is one of the mining industry's largest in North America. HCItasca offices have been represented at past meetings in Salt Lake City and in Denver. We look forward to getting in touch with colleagues, friends, and associates at this year's meeting.

John Mahoney of HCI will be one of the co-instructors of a short course entitled "Introduction to Applied Environmental Geochemistry and Geochemical Modeling" to be offered May 1 to 5, 2006, at the University of Alberta in Edmonton, Canada. The course is designed for geo-science professionals, geologists, soil scientists, and hydrogeologists. The course will examine the geochemical principles that are essential to cost effective management of groundwater and waste management problems. Complete details (schedule, outline, registration, and more) are available in the course brochure or online.

Publications since November 15, 2005:

Shimizu, Y. (2005) "A Fixed Coarse-Grid Thermal-Fluid Scheme and a Heat Conduction Scheme in the Distinct Element Method," in Computational Methods in Multiphase Flow III (Multiphase Flow 2005). Third International Conference (Portland, Maine, October-November 2005), pp. 241-250, A. A. Mammoli and C. A. Brebbia, Eds. Boston: WIT Press.

   ©2006 HCItasca, Inc.

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