Lifting the Lid on Mixshield Performance

Part two of a two-part series, this article discusses the development of the Mixshield tunnel boring machine (TBM) and the subsequent increase in tunnel diameter enabled by the Mixshield TBM. The construction of two and three lane road tunnels led way to combined-use tunnels such as road/subway and road/water storage tunnels, developments that can be attributed to increased performance demands and past experience. Use of a closed slurry circuit as the mucking system allows for success with higher face pressures as well as control of pressure drops. A list of attributes of this kind of mucking system is given, and technical solutions to reduce the need for human access to the excavation chamber are also included. The article also gives examples of projects where the Mixhshield TBM is being used, including a twin tube road tunnel in Chongming, China, and closing the gap in an orbital motorway Paris. The article concludes with a list of innovative qualities of the Mixshield TBM that were developed in response to numerous projects around the world.