Grydale designed an extract ventilation system for K-Road in which air is drawn through the tunnel using negative pressure from the outside and exhausted via ducting to a dust collector, delivering clean air to the atmosphere.
The K-Road ventilation design is separated into 15 construction stages and has been designed around the last stage, where the maximum air flow is required. Each stage represents changes to the tunnel area as construction advances. The required capacity of the ventilation system is determined by air flow, diesel plant and number of workers to ensure there is sufficient clean air within the tunnel to meet health and safety regulations.
Ventilation modelling confirmed that a 450kW, 60m³/s dust collector would meet the requirements for the entire excavation of K-Road station. Grydale provided a JMS-60-MES mobile dust collector named “Jonah”. The unit features a Variable Speed Drive (VSD) which allows air flow to be reduced during the early stages of construction and turned up as construction advances.
Construction began in August 2020 with the Mercury Lane temporary shaft, which is 15m wide and 27m deep. The shaft serves as an access point to the mined tunnels for all excavation equipment.
Ventilation requirements for the excavation of the temporary shaft were met by a 90kW axial fan with an open circuit capacity of 46m³/s. The axial fan continued to be used throughout the construction of K-Road to increase air flow into the tunnel to balance the extraction rate.
The fan is mounted alongside the dust collector on the mezzanine of the acoustic shed on the surface, and connected via 1600mm steel ducting to the excavation area via the shaft. The use of rigid steel ducting helps to reduce the pressure loss within the ventilation design.
Following completion of the shaft, a combination of forced and exhausted ventilation systems have been implemented to ventilate the mined tunnels and adits being excavated by Mitsu S200 and S300 roadheaders.