Electrical Manipulation of the Clogging Properties of Ypresian and Boom Clays

Abstract

The decision on which tunneling method to use is essentially based on the lithological characteristics of the crossed soil. Earth pressure balanced (EPB) shields are now the most widely used technology because they can operate in a much broader spectrum of lithological conditions and do not require expensive additional equipment. The soil permeability for EPB drives can reach either values of up to k = 10−3 m/s for the most porous soils (BPNL Lyon-Turin) and/or it can come down to practically impermeable clay (Heathrow T5) (Langmaack and Feng, 2005). With EPB shields, the cohesive soil loosened by the cutting wheel serves to support the tunnel face, unlike other shields, which are dependent on a secondary support medium. The area of the shield in which the cutting wheel rotates is known as the excavation chamber and is separated from the section of the shield under atmospheric pressure by the pressure bulkhead. The soil is loosened by the cutters on the cutting wheel and falls through the openings of the cutting wheel into the excavation chamber, where it mixes with previously excavated plastic soil. Uncontrolled penetration of the soil from the tunnel face into the excavation chamber is prevented because the force of the thrust cylinders is transmitted from the pressure bulkhead onto the soil. A state of equilibrium is reached when the soil in the excavation chamber cannot be compacted any further by the native earth and water pressure. The excavated material is removed from the excavation chamber by an auger conveyor. Since the EBP technique is used in homogeneous as well as in heterogeneous ground conditions, a tunnel boring machine (TBM) cannot be designed for …