Authors: Sandve, L; Forkheim, E; Slater, M; Bonin, G

Open access courtesy of:


Cite As:
Sandve, L, Forkheim, E, Slater, M & Bonin, G 2023, 'Mitigation of an open shaft at a legacy mine site in British Columbia, Canada using polyurethane foam', in B Abbasi, J Parshley, A Fourie & M Tibbett (eds), Mine Closure 2023: Proceedings of the 16th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth,

Download citation as:   ris   bibtex   endnote   text   Zotero

Legacy underground mining sites may include the presence of unsecured openings to surface, such as shafts, vent raises, and portals that pose a risk to public and animal safety. This paper presents a case study of the design methodology and use of a polyurethane foam (PUF) plug for the mitigation of an open shaft at a legacy mine site in British Columbia, Canada. Common methods of securing openings to surface include the design and construction of concrete caps or plugs, installation of steel grates, and/or placement of backfill. The method chosen depends on the remediation objectives, desired lifespan, and project setting. Openings in remote locations may require special considerations to optimise cost and reduce impacts on the environment due to the increased difficulty in transporting equipment and materials to the project site. The shaft that is the subject of this paper had previously been backfilled several times with rockfill by the site Owner, but the backfill had either migrated and/or settled over time, eventually resulting in an expression of surface subsidence. The shaft location is within steep terrain and only accessible from an unsanctioned foot and bike trail which limits access with mobile equipment. The use of PUF was advantageous in this situation due to its portability and ability to be hand-mixed and hand-poured into the opening, reducing the need to transport equipment to the project site which would have impacted the surrounding forest terrain. The PUF plug was constructed to prevent further subsidence and seal off access to the shaft to provide a long-term mitigative solution. The plug was required to have sufficient density, strength, and thickness to resist anticipated natural loads, and was designed to incorporate cementitious grout and backfill layers to provide ultraviolet (UV) and fire protection, respectively. An inspection port was also included in the design to facilitate long-term performance monitoring. Technical specifications and a work methodology for mitigating the open shaft with PUF were developed to meet the design basis. A quality assurance program consisting of on-site observations and monitoring of site conditions, as well as sampling of the PUF material for third-party density and strength testing was also carried out. A post-construction monitoring program will be implemented beginning in summer 2023, following snow melt, and will consist of visual monitoring at surface and at depth through the installed inspection port.

Keywords: mitigation, shaft, polyurethane foam, backfill, remote, opening to surface

Agisoft LLC 2021, Agisoft Metashape Professional, version 1.7.3, computer software, Agisoft LLC, St. Petersburg,
ASTM International 2016, Standard Test Method for Compressive Properties of Rigid Cellular Plastics (ASTM D1621-16), ASTM International, West Conshohocken.
ASTM International 2017, Standard Test Method for Tensile and Tensile Adhesion Properties of Rigid Cellular Plastics (ASTM D1621-16), ASTM International, West Conshohocken.
ASTM International 2020a, Standard Test Method for Apparent Density of Rigid Cellular Plastics (ASTM D1623-17), ASTM International, West Conshohocken.
ASTM International 2020b, Standard Test Method for Shear Properties of Sandwich Core Materials (ASTM C273/C273M-20), ASTM International, West Conshohocken.
Burghardt, JE 1994, ‘Polyurethane Foam Applications in the Closure of Abandoned Mine Openings’, National Park Service Geologic Resources Division, viewed 10 August 2021,
Charney, FA, Matheson, GM, Sieben, AK 1992, Design Procedures for Rigid Polyurethane Foam Mine Closures, U.S. Bureau of Mines, United States Department of the Interior, Denver, CO.
Government of British Columbia 2021, Health, Safety and Reclamation Code for Mines in British Columbia, Canada.
Lang, B 1999, ‘Permanent sealing of tunnels to retain tailings or acid rock drainage’, Proceedings of the 1999 International Mine, Water and Environment Congress, Sevilla, pp. 647-655.
Miller, EF, Hidber, K, Van Arem, M, Skurski, M, Murphy, RB & Chaplin, J 2019, ‘Mining reclamation 101: acquisition to reclamation - former Johnny Mountain Mine case study’, British Columbia Mine Reclamation Symposium, .
Munoz, D, Anderson, C, Lombardi, V, Gehrig, G, Katzer, J, Peterson, N & Vair, M 1999, ‘Polyurethane Foam Closures of Abandoned Mine Shafts – Colorado School of Mines Senior Design Project’, Proceedings of the 22nd Annual NAAMLP Conference, Steamboat Springs.
Nikl, J, Simzer, J, Kennard, D & Slater, M 2023, ‘Development of a Site-Specific, Relative Hazard Prioritization Tool at a Legacy Mine District in British Columbia’, paper presented at the 16th International Conference on Mine Closure, Australian Centre for Geomechanics, Reno, 2-5 October.
Priscu, C, Aldea, C-M, Wong, WK, Dunham, D & Lumley, B 2010, ‘Minimizing environmental impacts in rehabilitating small remote abandoned mine sites in Manitoba’, British Columbia Mine Reclamation Symposium,

© Copyright 2024, Australian Centre for Geomechanics (ACG), The University of Western Australia. All rights reserved.
View copyright/legal information
Please direct any queries or error reports to