Background

The Teck / Corona / Laramide Thunder Lake West property is part of the historic Thunder Lake Gold Deposit, which is located near Dryden, Ontario.

Following the original completion of mining at the site, run of mine rock waste was used for backfilling the portal at the Thunder Lake West property. The portal was a 4 x4.5 m opening, located just below grade.

By 2003, most of the waste rock had sloughed down the mine decline. The failure of this back-filled rock was most likely due to insufficient plug length down the decline and water flooding of the workings to the portal back.

TBT Engineering’s Role

TBT Engineering was retained to inspect the exposed portal and design a new portal closure plug, consistent with Province of Ontario Regulations which would also allow the site to be reopened at some time in the future. Tasks associated with this project included:

• Assembly and review of available existing data
• Site inspection and survey
• Confirmation of design criteria
• Discussions with local Ontario MNDM staff
• Preparation of design drawings and specifications
• Preparation of construction drawings and specifications
• Submission of as built drawings

Result (Project Methodology)

The new design encompassed the use of pre-cast concrete blocks and geo-grid to form a wall, complete with side and top seals. All precast concrete was prepared by a Dryden concrete supplier and trucked to the site. All concrete for the foundation, side and top seals was prepared at the Dryden Plant and trucked to the site as well.

The Portal Plug was constructed with drainage pipes through the plug to equalize water pressure on both sides. The pipes were surrounded with coarse drain gravel and wrapped with non-woven geotextile. The concrete blocks where provided with lateral support that consisted of geo-grid and compacted Granular B material, as opposed to reinforced earthing.
TBT Engineering worked with Layfield Plastics of Edmonton, AB and Alston Associates of Markham, ON to supply a design for the geotextile anchoring system for the pre-cast concrete block plug.

Quality Control Procedures

TBT Engineering’s construction inspector was present to ensure the design specifications were followed and to carry out compaction tests of the granular material during the construction of the plug in 2005 / 2006.