In 2011, Transport for London worked with Taylor Woodrow and BAM Nuttall Ltd. to upgrade London’s Tottenham Court Road underground station. The estimated £500 million project resulted in a much larger Crossrail ticket hall, new station entrances, additional escalators and elevators, and more access points to the Northern and Central Line platforms to reduce congestion.
Powering project applications
In building projects that require shaped concrete such as tunnels, building and swimming pools, concrete is pushed through a hose and then projected at high velocity onto the steel rebar framework using compressed air. In the creation of swimming pools, this process is normally referred to as shooting gunite; however, in other building applications it’s referred to as shotcrete.
There are 2 different methods of applying shotcrete – dry and wet. In a dry mix application, the dry cement is conveyed down the hose using an air compressor and then mixed with the water at the gun. In a wet mix application, the premixed concrete is pumped down using compressed air, and the operator sprays it from the gun.
In either method, the air compressor is a critical part of the process because the compressor’s air flow and pressure must be correctly sized to spray the shotcrete at the proper velocity (65 to 100 ft./s). Too much flow and rebound results in concrete reflecting off the wall and back towards the operator, and with too little flow, the shotcrete won’t adhere and cure properly. Furthermore, the compressor’s reliability is critical. In a wet mix application, like the one used in the Tottenham Court Road underground station, the compressor must be able to run continuously without stopping for the entire duration of the job. If it shuts down or overheats, the spraying process will stop and the cement will begin to harden in the hoses. Clearing blockages is very costly, time consuming and also potentially dangerous to the operator when spraying is resumed.
To complete the shotcrete applications, Taylor Woodrow and BAM Nuttall Ltd. chose the Atlas Copco GA 132FF due to its excellent performance and reliability. The rotary screw compressors were positioned on the site’s surface to supply underground applications with compressed air. The compressors were fully weather-proofed and winterized for reliability and use 24/7.