In the ever-evolving world of computing, the increasing availability of 64-bit processing computers has exciting consequences for HCItasca software. Namely, the increased amount of addressable memory will allow the creation of dramatically larger numerical models. We are pleased to announce that the upcoming release of FLAC3D will provide 64-bit capability, the first of our codes to do so. Please see the Software section below for more information.

—Roger Hart, Director of Software Services

 

Intensifying Dewatering to Increase Rock Stability in Highwalls

Improvement to Existing Dewatering Practices
HCI currently is involved in a series of projects at South African and Botswana diamond mines where we are attempting to "intensify" the current pit dewatering. Residual passive inflow (i.e., the flow into the pits despite active dewatering efforts to date) and high seepage faces in the highwalls can decrease the safety factor, especially when there are kimberlite "shells" in the highwalls. Intensifying the dewatering has at least two components:

1) Maintaining maximum achievable drawdowns by installing new dewatering boreholes of higher hydraulic efficiency (first figure below), and

2) Installing sub-horizontal drainholes into the more permeable hydrogeologic units in the highwalls to reduce the seepage face (second figure).

Potential Effect of Hydraulically More Efficient Dewatering Wells on Seepage Faces and Ground-Water Levels

Numerical ground-water flow simulations were conducted using MINEDW and MODFLOW-SURFACT to evaluate the potential effects of these two proposed dewatering efforts. The models predict that intensifying the dewatering could reduce the heights of seepage faces in the sandstones by as much as 40 to 50% relative to current conditions (figure below).

Potential Effect of Hydraulically More Efficient Dewatering Wells and Horizontal Drainholes on Seepage Faces and Ground-Water Levels

Future Dewatering Investigations
Increasing depths of mines requires dewatering of deep geologic features such as fractured metamorphic basement rocks and basal sandstones with bulk hydraulic conductivities of less than 0.3 m/day. Furthermore, high-temperature ground water (in the range of 42 to 46º C) and the presence of gas in the deep ground-water system, together with targeted drawdowns of 450 to 500m, pose challenges to the design and operation of dewatering systems. Three-dimensional flow modeling using MINEDW with a collapsing finite-element mesh that simulates changes in pit configurations over time will be used to help plan the dewatering.

 

Update Alert:
Current Versions
updated since
August 24, 2006:






Upcoming Release
FLAC3D 3.1, scheduled for release this December, offers substantial performance enhancements and more with the following new features.

• Availability on 64-bit platforms (all X-64 architecture excluding IA-64 (Itanium)); the current 2GB limit on model size is no longer a barrier to building large and/or complex models
• Efficient parallel processing executes jobs in nearly half the time it took with previous releases (a measured speed increase of 1.8 on two-processor machines)
• Nodal Mixed Discretization (NMD) offers a plasticity simulation solution for tetrahedral meshes that avoids the computational complexity and cost associated with higher order tetrahedral elements as implemented in ABAQUS, ANSYS, and others. Users should note that this feature has not been fully validated.
• Local octree mesh refinement in the 3DShop option offers a means to concentrate zones in areas of interest while maintaining a reasonable total zone count
• Built-in training option with each new license (more below)
• New embedded liner structural element
• Menu accessible HTML-help file containing the contents of the Command Reference, FISH Reference, and Examples volumes from the full FLAC3D Manual is provided in addition to the standard printed and PDF copies

Detailed information on these and other features is available on the FLAC3D 3.1 Pre-release page on our web site.

Note on Availability
With FLAC3D Version 3.1 targeted for release on December 1st, the following changes have been adopted for sale and distribution of the code:

• For new purchases — As of October 15 we will no longer sell Version. 3.0. Between October 15 and the code release, clients that purchase Version 3.1 will receive Version 3.0 at the time of purchase as well as access to the pre-release of Version 3.1. Purchasers will receive Version 3.1 automatically once it is officially released.
• For current Version 3.0 users — Current users have until November 15th to pre-purchase at a 35% discounted rate over the price of upgrading after release.

 

New Staff
HCItasca is pleased to announce the addition of three individuals to its international engineering staff. Steve Axen is a professional engineer with a background in geological engineering who has joined HCI in Denver, Narayan R. Mamidi is a geomechanics engineer who brings his experience in rock engineering and ground control to Itasca Consulting Canada Inc., and Alfred Mudau is a geotechnical technician who has signed on with Itasca Africa. Welcome to Steve, Narayan, and Alfred.

 

Preliminary Announcement
HCItasca will host an international FLAC/DEM conference in Minneapolis in the spring of 2008. Past HCItasca-sponsored symposia have focused on individual 2D/3D code pairs (e.g., FLAC and FLAC3D). This conference will consider topics germane to all the HCItasca codes and, as such, promises to be a wide-ranging and in-depth look at the state of numerical modeling in geomechanics. Look in this section in the December issue for the initial call for papers and information to follow.

 

Spring Training Courses
HCItasca's annual round of introductory training courses are scheduled from the first week of April 2007 through the beginning of May. The course schedules, curriculae outlines, registration forms, and more are available now.

New Built-In Training Option for FLAC3D
Purchasers of new licenses of FLAC3D Version 3.1 — to be released in December 2006 — will receive free admission to the regular three day introductory course on FLAC3D that is offered each Spring. Training is offered at the offices of Itasca Consulting Group, Inc. in Minneapolis. The training is completely optional. Please note this offer is not valid for upgrades or additional keys on an existing license. The dates for the next training course are April 9-11, 2007.
No discount will be applied to purchasers of new licenses who will not participate to the free training course.

 

The adjacent image shows the draw of material at a caving mine. The vertical section illustrates the drawdown of waste (magenta) relative to underlying rock (blue, cyan, green, orange and purple). The influence of the cave boundary in producing lateral rilling is seen on the right side of the section. Isolated draw can also be observed in the center drawpoints, resulting in rapid drawdown of waste material. This plot was created by Andre van As of Rio Tinto using Itasca's industry-sponsored code REBOP. Mr. van As' work with REBOP has been used to analyze material drawdown, waste entry and recovery at a number of existing and proposed block cave operations.

 

Publications since August 20, 2006:

Brummer, R. K., C. P. O'Connor and A. Turichshev. (2006) "Comprehensive Geomechanical Design of a Large Underground Observatory at 6800 Ft," in Golden Rocks 2006 — 50 Years of Rock Mechanics, Colorado School of Mines, June 2006 (Proceedings of the 41st U.S. Rock Mechanics Symposium). Paper No. 06-1162. D. P. Yale et al., Eds. ARMA.

Kwon, J. Tutumluer, E., Konietzky, H., Keip, M.-A. "Investigation of geogrid base reinforcement mechanisms considering residual stress and confinement effects" in Proc. 8th Int. Conference on Geosynthetics, Yokohama, Japan, 18.-22.10.2006, p. 993-996. J. Kuwano & J. Kosedi, Eds. Millpress, Rotterdam, 2006.

Watson, A. D., C. D. Martin, D. P. Moore, T.W.G. Stewart and L. J. Lorig. (2006) "Integration of Geology, Monitoring and Modelling to Assess Rock Slide Risk," Felsbau, 24(3), 50-58.

Tucker, M., S. S. Kanchibotla and M. Ruest. (2006) "Modelling Coal Loss in Open-Pit Blasting Using PFC2D," in FRAGBLAST – 8 (8th International Symposia on Rock Fragmentation by Blasting, Santiago, Chile, May 2006), pp. 109-113. Santiago: Editec.