Ground improvement in Alaska
By Andy Brown11 June 2021
Bauer has completed ground improvements at Red Dog mine in Alaska, US, one of the world’s largest zinc mines where – below a certain depth – the ground is permanently frozen.
The mine is around 170km north of the Arctic Circle and approximately 10% of the world’s zinc is extracted here in open-cast mining. There is an active zone near the surface that thaws during the summer and refreezes during winter.
Based on an evaluation of the permafrost and soil on the site, ground improvements were identified as a prudent measure to counteract the effects of potential melting permafrost. To this end, Bauer Foundation Corp. was tasked with carrying out field tests using the jet grouting and Cutter Soil Mixing (CSM) methods.
“The trials included detailed data capture and strict quality controls in close collaboration with Teck, the project owner, and other geotechnical consulting engineers,” said Alejandro de la Rosa Knecht, project manager with Bauer Foundation.
“Trials were carried out from August to December of 2019, which ultimately identified the CSM method as the most suitable choice.”
The CSM method combines features of the diaphragm wall technique and the mixed-in-place ground improvement method (MIP). The soil is broken up using a cutter, then rearranged and mixed with an aggregate. The trials for the Red Dog Mine also determined the extent to which existing subsoil were to be replaced with suitable filler material to facilitate later mixing.
From July to November 2000, 50% of the pre-drilling was completed as well as 30% of the CSM. In addition, Bauer was tasked with the construction of a secant pile wall as an extension to an existing slurry wall. To achieve this, the required pile wall was integrated into the existing slurry wall and the underlying rock using primary and secondary piles.
A multi-purpose Bauer BG 30 drilling rig with special Arctic equipment along with various drilling tool and mixer sets were used for the execution of all the works.
One of the main challenges was said to be the mobilisation of equipment in the limited time provided by the schedule to such a remote location. However, Bauer and client teams successfully concluded the first phase of production activities between July and November 2020. The final production phase which includes CSM and demobilisation is due to be completed by June 2021.