Boubly Mine Man Shaft
Boulby Mine is operated by Cleveland Potash Limited, a subsidiary of Israel Chemicals Ltd (ICL) and is “the world’s first and only Polyhalite mine”. Polyhalite is a natural multi-nutrient fertiliser and a source of potassium, calcium, magnesium, and sulphur.
A recent survey identified that significant areas of repair were required to both the outside and internal faces of the 300mm thick concrete wall of the man shaft. There were significant areas of cracking and spalling to an average depth of 80-100mm, as a result of corrosion to the reinforcing bars. The effect of this was large volumes of concrete delaminating from the structure and falling to the ground below, which, if left unchecked, would pose a significant safety hazard.
From the Client’s perspective, one of the key obstacles to overcome was to facilitate the requirement to keep the shaft operational during the internal works. In this respect, refurbishment was a much better option than demolition and renewal.
The site itself is situated on the North-East coast, in close proximity to the North Sea. Coastal areas are known to provide an environment which is high in chlorides and therefore potentially damaging to steel reinforcement within structures. In addition to this, the aggressive nature of the sulphides from the mined material on site helped to create an environment which had a hugely detrimental effect on the steel reinforcement in the structure.
Internally, high levels of humidity compounded the effect and accelerated the corrosion process further.
Significant hydro-demolition works were carried out to remove 31m3 of defective concrete. Structural steelwork was then installed with the existing steelwork cleaned and fully prepared to remove rust and laitance.
On the external surface, more than 1500 sacrificial anodes were then incorporated with the concrete repairs to slow down the corrosion of reinforcement and prolong its life, thus enhancing the service life of the structure. The whole structure was thoroughly cleaned to remove all surface contaminants prior to two layers of anti-carbonation coatings to help protect from future corrosion problems.
Internally, over 1200 Galvashield XP sacrificial anodes were installed, and the concrete was sprayed back in with two coats of anti-carbonation coatings applied. all while keeping the man shaft operational at all times.
The project is an example of the benefits of repair/refurbishment over replacement. The cost savings to the Client, the ability to maintain operations and the environmental benefits make this an excellent example of a sustainable construction project.
With over 57m3 of concrete broken out and replaced, several tonnes of structural steelwork installation, over 2700 anodes installed, and over 3500m2 of anti-carbonation coatings applied, whilst also strengthening key elements using Carbon Fibre, this project has seen a significant refurbishment utilizing numerous structural rehabilitation techniques.
Our partner, CRL, have demonstrated a can-do approach to overcoming the challenging aspects of the scheme and developed numerous solutions along the way.
These innovative products and technologies were used on this project.