ABSTRACT
Earth Pressure Balance (EPB) Tunnel Boring Machines (TBMs) have a difficult time excavating through “mixed transitional ground”. Soil conditioning plays a critical role in achieving the desired qualities of the excavated muck within the excavation chamber and the delicate balance between clogging and maintaining face support. Soil conditioning laboratory tests are often completed during the planning phase prior to TBM excavation in an effort to develop a baseline for soil conditioning, reduce risks, costs and improve EPB performance. Often these tests show considerable promise in the lab but don’t deliver even where the excavated materials are relatively homogeneous and with even less success in so-called mixed transitional ground. Very slow advance rates, high torque and thrust and clogging of the cutterhead openings have been experienced on a number of recent projects as a result of varying amounts of clay in the face. This paper will present the observations made during the excavation of the Ohio Canal Interceptor Tunnel in Akron, Ohio, USA particularly with regards to very slow advanced rates, rapid tool wear and clogging of the cutterhead. It also discusses the limits of desktop versus empirical clogging evaluations with respect to actual clogging experienced during tunneling and mitigation measures that have been introduced during the excavation which helped decrease wear and increase advance rates.
