Renewing Rock Mechanics Programs For Evaporite Ground Control

Renewing rock mechanics programs article for Potash Works magazine.



A valuable article in PostashWorks 2014 magazine contributed by SRK

Renewing Rock Mechanics Programs for Evaporite Ground Control
Author: Tim Coleman

Although the mining of potash dates back to the 1300s, it was first established on a large scale in Germany in the late 19th century.  Forty-five years ago, a few mines started production outside of Eastern Europe and used mining plans based on conventional room and pillar mining techniques. Counter-intuitively, the combination of strong pillars and small rooms led to recurring excavation back failures of a type more commonly associated with conventional soft rock mining environments. To solve the resulting safety and productivity problems, each new potash operation established comprehensive rock mechanics programs. These programs focused on the time-dependent creep deformation of the evaporites, as measured in the laboratory and underground.

The stress control/relief mining methods and extraction ratios established during this period of intense study have barely changed in four and a half decades. Slight revisions to accommodate mining equipment improvements have achieved small increases in extraction ratios. However, as reserves have been extracted and mine depths and production rates have increased, so too have induced stresses escalated. As a result, the poor back conditions encountered in the 1970s are presenting challenges to current potash and salt mining operations.

Production rooms and panels are generally not impacted by the long term creep deformation of the evaporite orebody, because these excavations are mined and completed in a few months. Permanent mine infrastructure and development entries are, however, impacted by long-term, mining-induced stress redistribution. In time, the increased loading on the infrastructure causes excavation damage and failure.

Many of the theories upon which potash mining is based assume continuous, homogeneous deposits. However, in reality potash deposits are complex entities. They comprise beds of evaporites and conventional sedimentary rocks with contrasting characteristics, for example carnallite, salt horses, clay bands and leach zones. These variations can be highly significant as they can substantially affect excavation performance, disrupting production and impairing the safety of underground personnel.

With the resurfacing of challenges encountered during the early days of potash mining, successful methodologies from that time need to be reviewed. The safe extraction of conventional salt and potash deposits around the world depends on the resumption of comprehensive rock mechanics programs and the development of associated expertise. A wealth of experience has been gained in other aspects of mining such as stress management, ground reinforcement and support, instrumentation, software analytical tools, and ground control monitoring. Considerable benefits could be achieved by applying this knowledge to the salt and potash mining industry.

About SRK Consulting

SRK Consulting is an independent, international consulting practice that provides focused advice and solutions to clients, mainly from earth and water resource industries. For mining projects, SRK offers services from exploration through feasibility, mine planning, and production to mine closure. Please see www.srk.com for more information.

Contacts:
Tim Coleman, Principal Consultant, Mining and Rock Mechanics, SRK Consulting (Vancouver), T: +1-604-681-4196, F: +1-604-687-5532, E: tcoleman@srk.com
Mark Liskowich, Principal Consultant, SRK Consulting (Saskatoon), T: +1-306-955-4799, F: +1-306-955-4750, E: mliskowich@srk.com

 

 

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