GSSL were presented with a basic drawing (mood board) of an underground cave system, and a verbal briefing / instruction during a pre-contract meeting to “think like a Badger”
Fortunately GSSL had been previously been involved in the construction of caving systems for the UK military at Aldershot, and for the caving system at Hertfordshire Young Mariners in Cheshunt, so had a head start in the construction of underground environments, and all the issues they can offer.
Construction issues are the water ingress problems typically associated with underground construction, access and egress for operatives during construction phase, and maintenance of the structure following completion. Modern sprayed concrete materials include for the waterproofing issues, risk assessments and method statements for the actual safe execution of the works, and operational manuals for the maintenance of the the lighting and ventilations systems. But what about if actual real badgers or foxes want to move in? Fortunately this did not happen (as yet anyway) but mosquitos and midges did take up residence.
GSSL crews are trained in confined space working to City & Guilds Level 2 with BA standard, and are well versed in restricted access and confined space working environments. Gas monitoring and escape procedures for working within confined spaces are the highest priority at planning stage and throughout the works to final completion. The tunnel structure was constructed on a 200mm steel reinforced concrete slab, using 20mm diameter steel bar in two layers, together with Expanded Metal Lath (Expamet), and a sprayed concrete lining internally and externally.
The sprayed concrete lining was done in two ways, both using water proofing additives. Shotcrete (wet spray) was used for the outside of the structure due to ease of access. The dry spray method (Gunite) was utilised for the inside of the tunnels, with restricted access, which had to be carved, and then coloured using proprietary concrete dye to achieve the required natural appearance of a Badger sett. On completion the whole structure was buried under 500.00 tonnes of soil to blend into the environment.